RSS 1.0SUNY Downstate Health Sciences University
For more information about SOAR and how to submit your work, check out our libguide or contact Gregg Headrick in the Library.
Collections in this community
Recent Submissions
-
Powered-hand tools and vibration-related disorders in US-railway maintenance-of-way workersMaintenance-of-way workers in North America who construct railroad tracks utilize specialized powered-hand tools, which lead to hand-transmitted vibration exposure. In this study, the maintenance-of-way workers were surveyed about neuro-musculoskeletal disorders, powered-hand tools and work practices. Information about vibration emission data of trade specific powered-hand tools for the North American and European Union markets was searched online to obtain respective user information of manufacturer and compared to non-commercial international data banks. The survey showed that maintenance-of-way workers frequently reported typical hand-transmitted vibration-related symptoms, and appear to be at a risk for neuro-musculoskeletal disorders of the upper extremity. Of all of the powered-hand tools used by this trade, 88% of the selected tools exceeded a=5 m/s2 and were above vibration magnitudes of common tools of other comparable industries. This may create a risk if these tools are used throughout an 8-h work day and management of vibration exposure may be needed. In the North-American market, limited or no vibration emission data is available from manufacturers or distributors. Vibration emission information for powered-hand tools, including vibration emission levels (in m/s2), uncertainty factor K, and the applied testing standard/norm may assist employers, users and occupational health providers to better assess, compare and manage risk.
-
Current work hours and coronary artery calcification (CAC): The Multi‐Ethnic Study of Atherosclerosis (MESA)Background: Long work hours may be associated with adverse outcomes, including cardiovascular disease. We investigated cross-sectional associations of current work hours with coronary artery calcification (CAC). Methods: Participants (n = 3046; 54.6% men) were from the Multi-Ethnic Study of Atherosclerosis. The number of hours worked in all jobs was obtained by questionnaire and CAC from computed tomography. The probability of a positive CAC score was modeled using log-binomial regression. Positive scores were modeled using analysis of covariance and linear regression. Results: Sixteen percent of the sample worked over 50 hours per week. The overall geometric mean CAC score was 5.2 ± 10.0; 40% had positive scores. In fully-adjusted models, prevalence ratios were less than 40 hours: 1.00 (confidence interval [CI]: 0.88-1.12), 40:(ref), 41 to 49:1.13 (CI: 0.99-1.30), and ≥50:1.07 (CI: 0.94-1.23) and longer current work hours were not associated with higher mean CAC scores (<40:56.0 [CI: 47.3-66.3], 40:57.8 [CI: 45.6-73.3], 41 to 49:59.2 [CI: 45.2-77.6], ≥50:51.2 [CI: 40.5-64.8]; P = .686). Conclusions: Current work hours were not independently associated with CAC scores.
-
Introduction to the Special Issue: Opioids and the Workplace - Risk Factors and SolutionsThe workplace has been a neglected element in the national response to the opioid crisis. This ignores that workplace safety and health and drug policies have become important factors in opioid use disorder among workers. This results from physical or emotional pain related to workplace injuries, illnesses, and stress, and through punitive workplace drug policies, failure to address stigma, and inadequate access to treatment and recovery resources. This comprehensive New Solutions special issue encompasses timely cutting-edge research, commentaries, activism, and calls for action on primary prevention in the workplace and intervention research. It also addresses the convergence of the COVID-19 and the opioid crises, high-risk occupations and industries, health inequalities, employer and union programs, peer advocacy and member assistance programs, worker training, health parity for addiction treatment and recovery services, protection of first responders and site clean-up workers, working conditions of substance use treatment workers, and calls for necessary funding.
-
Expanding the Conceptualization of Support in Low-Wage Carework: The Case of Home Care Aides and Client DeathHome care aides are a rapidly growing, non-standard workforce who face numerous health risks and stressors on the job. While research shows that aides receive limited support from their agency employers, few studies have explored the wider range of support that aides use when navigating work stress and considered the implications of these arrangements. To investigate this question, we conducted 47 in-depth interviews with 29 home care aides in New York City, focused specifically on aides' use of support after client death. Theories of work stress, the social ecological framework, and feminist theories of care informed our research. Our analysis demonstrates aides' extensive reliance on personal sources of support and explores the challenges this can create in their lives and work, and, potentially, for their communities. We also document aides' efforts to cultivate support stemming from their home-based work environments. Home care aides' work stress thus emerges as both an occupational health and a community health issue. While employers should carry responsibility for preventing and mitigating work stress, moving toward health equity for marginalized careworkers requires investing in policy-level and community-level supports to bolster employer efforts, particularly as the home care industry becomes increasingly fragmented and non-standard.
-
Investigation of Hand-Arm Vibration (HAV) in Railroad Track Workers: Addressing Stakeholder Conflict of Interestfirst_pagesettingsOrder Article Reprints Open AccessProceeding Paper Investigation of Hand-Arm Vibration (HAV) in Railroad Track Workers: Addressing Stakeholder Conflict of Interest † by Eckardt Johanning 1,*ORCID andPaul Landsbergis 2 1 Center for Family and Community Medicine, Columbia University and Johanning MD PC, New York, NY 10032, USA 2 School of Public Health, State University of New York (SUNY)-Downstate Health Sciences University, Brooklyn, NY 11203, USA * Author to whom correspondence should be addressed. † Presented at the 15th International Conference on Hand-Arm Vibration, Nancy, France, 6–9 June 2023. Proceedings 2023, 86(1), 16; https://doi.org/10.3390/proceedings2023086016 Published: 11 April 2023 (This article belongs to the Proceedings of The 15th International Conference on Hand-Arm Vibration) Downloadkeyboard_arrow_down Versions Notes Abstract The use of powered hand tools and equipment that exposes track workers to HAV vibration and other biomechanical hazards in the USA was investigated by a research team, following scientific principles and guidelines including protecting confidentiality of study participants. Musculoskeletal symptoms and neuro-musculoskeletal disorders were linked to workplace physical factors, such as HAV, and were reported in peer-reviewed journals. The methodology and results were subsequently challenged by a team of consultants hired by the Association of American Railroads (AAR), which represents major North American railroad corporations. Such an influence appears to challenge the integrity of occupational health research and impede the conduct of such research.
-
Mental health outcomes among urban public transport workers: A systematic literature reviewBackground Although abundant evidence suggests that Urban Public Transport (UPT) workers are at high risk of poor mental health, there is no consensus on the exposures that explain these outcomes, nor on the effectiveness of mental health interventions in this occupational group. Objective This study aims to systematically review the literature on the mental health of UPT workers to assess the effects of occupational exposures and interventions. Method A systematic review was conducted following the PRISMA guidelines. The literature search was performed from 1990 to December 2021 in three databases (PubMed, Scopus, and the Web of Science). The included observational, experimental, intervention and qualitative studies were critically appraised and assessed for risk of bias. A narrative evidence synthesis was conducted by mental health outcomes, occupational exposures, and intervention categories. Results The database search yielded 1383 records. A total of 83 studies (49 cross-sectional, 8 longitudinal, 8 experiments, 7 interventions, and 11 qualitative) met the inclusion criteria. Bus drivers were the most studied population, followed by metro and train drivers. The included studies covered eleven mental health outcomes: sleep problems, fatigue and recovery needs, alcohol and substance use, PTSD, panic disorders, depression, anxiety, psychopathology symptoms, psychosomatic symptoms, and psychological stress. Work organization-related stressors (work content, workload and pace, working hours, participation and control, career development, status and salary, role in the organization, and interpersonal relationships) and occupational safety risks are the main predictors of negative mental health outcomes. Most intervention studies focus on the management of PTSD symptoms of UPT workers exposed to safety hazards. Conclusion The results of this review contribute to the consensus on the antecedents of negative mental health outcomes among UPT workers, as well as to the identification of intervention targets and promising research lines for the development of this study field.
-
Role of laminins containing beta2 and gamma3 chains in regulating retinal angiogenesisRetinal vasculature related pathologies account for much of the global blinding disease. Proliferative diabetic retinopathy (PDR) is the main cause of acquired blindness in working adults and retinopathy of prematurity (ROP) is the leader cause of acquired blindness in children. A thorough understanding of the cell intrinsic and extrinsic regulation of vascular development in the retina is required to address such vasculature related pathologies. Unlike other organs, specialized glial cells called astrocytes guide vascular development in the retina. The astrocytes invade the retina around birth and form a template in the retina for endothelial cells to migrate on. It is well known that an astrocyte-derived template is crucial for vascular development in the retina; however, the factors that guide astrocytes into the retina remain unknown. It is important to know the mechanism by which astrocytes are guided, because models for ROP and diabetic retinopathy (DR) show degeneration of astrocytes. Maintaining astrocytes under such conditions reduces neovascularization events. In this study, we show that astrocyte migration into the retina is dependent upon laminins deposited at the inner limiting membrane (ILM). Deletion of Lamc3 gene reduced astrocyte migration rate at early stages and recovers at later stages. Deletion of Lamb2 and Lamb2:c3 genes severely affect astrocyte migration and spatial patterning. Astrocytes in these null retinas clump together and appear like a honeycomb. Interestingly, these Lamb2 and Lamb2:c3- also show a loss of integrin beta1 expression specifically in astrocytes. Using both in vitro and ex vivo techniques we show that laminins induce astrocyte migration in an isoform specific manner. Exogenous treatment of Lamb2:c3- null retinas with EHS-laminin rescues both migration and spatial patterning of astrocytes. Moreover, we show that exogenous laminin restores integrin-beta1 in Lamb2:c3- null astrocytes in culture. Functional blocking of integrin-beta1 receptor affects astrocyte migration in the presence of laminin, suggesting that laminin- integrin-beta1 interaction is critical for astrocyte migration. In addition, functional blocking of integrin-beta1 affects the recruitment of both ILK and FAK, which are downstream kinases that are important for cell migration. siRNA knockdown of FAK affects astrocyte filopodial extension and alpha-actinin organization during migration. This suggests that laminin likely orchestrates astrocyte migration through integrin-beta1- FAK mediated signaling mechanism. As mentioned above, an astrocyte template is critical for vascular development in the retina. As astrocyte migratory pattern were affected in laminin nulls, we analyzed vascular growth in these nulls. Lamc3- null retinas show a delay in vascular growth progression at early stages with increased vascular branches at the leading edges. At later stages vascular growth was complete and appeared as similar to WT. Deletion of Lamb2 and Lamb2:c3- genes however, severely affected vascular growth with persistent hyaloid vessels (commonly observed in ROP). These nulls also show abnormal astrocyte-endothelial interactions, which resulted in leaky vasculature, analyzed by fluorescein angiography. In summary, our study clearly suggests that laminin mediated signaling mechanism is critical for astrocyte migration and spatial organization and subsequent vascular growth.
-
The Effects of Early Life Stress on the Kynurenic Pathway Contributing to the Development of Affective Disorders.By the year 2030, major depressive disorder is projected to become the top cause of disease and disability worldwide (Won and Kim 2016). Early life stress (ELS) varies greatly in type and severity but has a significant impact on the brain both structurally and functionally (Carpenter et al. 2003; Nemeroff 2004). ELS and the development of treatment-resistant depression (TRD) have been strongly correlated in the clinical setting (Coplan et al. 2014). While several mechanisms have been proposed to account for the link between inflammation and depression, the kynurenic acid pathway has become prominent due to an abundance of evidence (Dantzer et al 2011). An example of the importance of the kynurenic pathway in the development of MDD is that kynurenine has been found at higher concentrations in CSF suicide attempters than in depressed non-attempters and healthy controls (Sublette et al. 2011). The inflammatory model of depression with its basis in the kynurenic system has yet to be investigated with ELS as a contributing factor even though ELS has been linked to increased inflammation (Simons 2019). By using the variable foraging demand animal model of ELS in macaque monkeys, separation stress, and fluoxetine treatment coupled with LC-MS/MS quantitation of kynurenine pathway the relationship between ELS and the inflammatory model of depression was investigated with a focus on the characteristic of treatment resistance. Kynurenine was unchanged between the VFD and non-VFD groups. VFD animals were shown to be biased away from kynurenic acid metabolism and towards increased anthralinic acid production possibly as a protective mechanism against neurotoxicity. Kynurenic acid, a known neuroprotectant (Won and Kin 2011), was found to be decreased in VFD regardless of separation stress or fluoxetine treatment. This biological “switch” of kynurenic acid is vital in the development of understanding the characteristic of treatment resistance in the clinical setting and its link to ELS.
-
Molecular Changes in the Sensorimotor Cortex During Learning and Recall: Tracking and Manipulating PKMζProcedural learning and memories, such as those associated with learning how to ride a bike, are believed to be supported by plasticity and reorganization of the sensorimotor cortex. Several studies utilizing a rodent reaching task, as that used in the current work, have shown that procedural learning is accompanied by enhanced synaptic strength and structural modification in the sensorimotor cortex at distinct layers (e.g. layers II/III and V). However, an investigation that causally links these changes with synaptic molecular machinery and behavior has been elusive. This study aims to fill this gap in our current understanding by tracking changes in task performance as well as layer specific modifications in key molecules, atypical protein kinase M zeta (PKMζ) and postsynaptic density protein 95 (PSD-95), that have been shown necessary for the maintenance of long-term potentiation (LTP) and activity-dependent synapse stabilization respectively. Our results demonstrate that PKMζ levels decrease in S1 during an early pause in learning on day 3, and both PKMζ and PSD-95 peak in S1 and M1 once the performance has reached an asymptote on day 9. Continued daily practice after day 9 is accompanied by sustained higher levels of PKMζ, but not PSD-95. Past this correlation, we utilized genetic and pharmacological methods to causally perturb PKMζ during and after learning. We found results indicating the importance of PKMζ both during learning and in maintaining the procedural memory engram. Taken together, we propose a model integrating PKMζ-dependent LTP and PSD-95-assisted synaptogenesis as the molecular mechanisms to encode and store motor memory traces in sensorimotor cortex.
-
Cardiac Lineage Protein 1 (Clp-1), An Inhibitor of Positive Transcription Elongation Factor B (P-Tefb), Plays A Regulatory Role In Skeletal Muscle Cell DifferentiationEmerging evidence suggests that one level of transcriptional regulation in eukaryotic cells is at the stage of transcription elongation in part by the Positive-Transcription Elongation Factor b (P-TEFb) complex. The P-TEFb complex consists of cyclin dependent kinase 9 (cdk9) and its cyclin partner, cyclin T and is dynamically partitioned between the active versus inactive states. The kinase activity is inactivated when P-TEFb associates with Cardiac Lineage Protein-1 (CLP-1), the mouse ortholog of human Hexamethylene bis-acetamide inducible protein 1 (HEXIM1). Recent reports implicate a link between P-TEFb and skeletal muscle in which P-TEFb associates with the skeletal muscle specific transcription factor MyoD. In this study, I present evidence that CLP-1 protein is critical for the regulation of skeletal muscle cell differentiation. I examined the expression of CLP-1 in the mouse myoblast cell line, C2C12, and found that there was a marked increase in CLP-1 association to P-TEFb at the onset of differentiation. I also observed that CLP-1 associates with MyoD, as well as with histone-deacetylases (HDACs), and that this association was maximal in the early stage of C2C12 differentiation. To further investigate the role of CLP-1 in skeletal muscle cell differentiation, I generated CLP-1 +/- knock-down C2C12 cells through homologous recombination. The deficiency in CLP-1 resulted in an inability of C2C12 heterozygote cells to transition into myotubes. I next examined the possibility that the inhibitory complex consisting of CLP-1, MyoD and HDACs targets the promoter of proliferative genes, such as cyclin D1. Chromatin immunoprecipitation (ChIP) analysis confirmed CLP-1/MyoD/HDAC binding to the cyclin D1 gene promoter during differentiation. These data suggest that CLP-1 plays a synergistic role in conjunction with MyoD and HDAC to control the genetic program that ensues in the transition of skeletal myoblasts from proliferative to terminally differentiated cells.
-
Simultaneous functional diffuse optical tomography and EEG in freely moving rats.Diffuse Optical Tomography (DOT) is a non-invasive technology that uses near-infrared light to measure oxyhemoglobin (oxyHb) and deoxyhemoglobin (deoxyHb) levels and spatial distributions in the entire brain of anesthetized and freely moving rats. To spatially calibrate DOT imaging, local anesthetic was stereotactically injected into known brain regions. Rats (n=3) were anesthetized with urethane and 20% procaine was injected into the left hippocampus or left striatum (1uL over 2min). Shortly after procaine injection near the hippocampus, oxyHb decreased and deoxyHb increased in the left side of the brain in a posterior position (presumably the hippocampus). Likewise, following injection aimed at the striatum the same pattern of oxyHb decrease and deoxyHb increase was observed in an anterior position (presumably the striatum). OxyHb returned to baseline after ~60 min, in good agreement with the expected duration of procaine action. Results from anesthetized rats demonstrate the utility and reliability of DOT imaging and allow for the investigation of natural brain hemodynamics in awake, freely moving rats. To show that DOT can detect and localize oxyHb and deoxyHb in the brains of freely moving rats, DOT and hippocampal EEG recordings were made as rats (n=6) foraged for food pellets and slept in a bucket (n=3). When the EEG switched from large irregular activity (LIA, seen when the rat is not walking or is in slow-wave sleep) to theta (5-12 Hz rhythm seen when the rat walks or enters REM sleep) whole brain oxyHb decreased for ~1 sec and then increased over ~4 sec in a way that resembled the Blood Oxygenation Level Dependent (BOLD)-response observed with fMRI. EEG shifts from theta to LIA, however, were accompanied by decreases in oxyHb levels. Since oxyHb dynamics after transitions into theta mimic BOLD responses, and are oppositely directed to the oxyHb changes seen in LIA, it is suggested that the theta is a higher energy state than LIA. When the oxyHb shifts that accompanied LIA to theta switches were analyzed for their spatial distribution, major increases were found in regions that co-localize with the hippocampal procaine injections in anesthetized rats, implying that DOT can correctly detect sources of signals in the brain of freely moving rats. These results demonstrate that DOT imaging is a reliable tool for measuring hemodynamic changes linked to physiological changes in the brain. These studies serve as the basis for future experiments utilizing DOT that have the potential to provide useful information on hemodynamic changes related to learning and memory, as well as acute and chronic pathologies that affect blood flow, such as traumatic brain injury, cancer, and others.
-
Circuit Breakers: α4βδ GABA-A Receptors Drive Adolescent Refinement of Neural Circuits in Prefrontal Cortex.Adolescence is a time when synaptic connections are sculpted to prepare for the cognitive challenges of adulthood, a process known as synaptic pruning. Although this process was first reported over 30 years ago, the initial trigger and functional reason for pruning remain unknown. This thesis provides a multifaceted investigation of α4βδ GABA-A receptor regulation of dendritic spine pruning within pyramidal neurons of the prelimbic prefrontal cortex across adolescent development in mice. The prelimbic cortex projects to the amygdala and drives anxiety states, making precise pruning of juvenile connections critical for proper maturation. Using high-resolution microscopic analysis of Golgi-stained samples, I report a dramatic developmental decrease in basilar dendritic spine density on layer 5 pyramidal neurons between early puberty (16.39 ± 1.55 spines/10μm) and young adulthood (6.10 ± 0.58 spines/10μm), reflecting a 63% reduction (p < 0.0001). This remodeling coincides with a transient 10-fold increase in α4 subunit expression precisely at puberty onset (p < 0.00001) within layer 5 pyramidal neuron dendrites, revealed by immunohistochemistry and amplified electrophysiological responses to a δ subunit-selective agonist (p = 0.00125). Convergent pharmacological, local knockdown (using viral shRNA knockdown and Cre-loxP deletion), and global knockout of α4βδ GABAARs prevented adolescent pruning, while augmenting α4βδ signaling via the selective agonist gaboxadol during early puberty significantly enhanced spine elimination (p<0.05). This demonstrates the causal role of this signaling pathway in mediating the extensive remodeling. The mechanism likely involves α4βδ receptor-mediated suppression of NMDA receptor activation of Kalirin-7 pathways which maintain the dendritic cytoskeleton. α4 knockout prevents the typical 50% decrease in Kalirin-7 levels at puberty (p<0.0001), suggesting dependence on α4βδ signaling. In contrast, increasing NMDAR expression prevents pruning. Critically, preventing pubertal pruning through localized α4βδ knockdown in the prelimbic cortex using AAV-Cre administration increases anxiety-like avoidance behaviors on the elevated plus maze test after an aversive stimulus by 60% in late adolescence (p<0.0001) and 40% in adulthood (p<0.05). This causally links excess prelimbic connectivity from disrupted juvenile synapse elimination to anxiety-related behavioral phenotypes. Furthermore, a similar developmental decrease in spine density occurs in layer 2/3 pyramidal neurons in female mice, aligned with a key role for α4-containing receptors as evidenced by a lack of pruning in α4 knockout mice. Taken together, these results suggest a role for the extrasynaptic α4βδ GABAARs in triggering synaptic pruning and further demonstrate one pathological outcome which can result from dysregulated pruning.
-
Gap junctions in hippocampal principal neurons.Gap junctions in principal neurons of the mammalian brain have been postulated to exist based on experimental and computer simulation studies. The subcellular location of these gap junctions have been suggested to be intersomatic, interdendritic and most recently between the axons of cortical principal neurons. However, definitive ultrastructural evidence for gap junctions in cortical principal neurons has been lacking. The development of methods such as confocal laser scanning microscopy (CLSM) and digital reconstruction of fluorescent dye-filled neurons in lightly perfusion-fixed brain tissue allow for the delineation of neuronal fine structure at near the limits of light microscopic resolution. We applied such methods to the study of CA3 pyramidal neurons in the adult rats. Using CLSM, in 4 out of 500 dye-loaded CA3 neurons (~1%), we found nonspiny processes contacting the proximal segment of CA3 principal neuron apical dendrites. These processes were not part of the injected neuron, but nevertheless filled with dye. Based on these dye coupling studies and the similarity of nonspiny processes to mossy fiber axons, we hypothesized that the mossy fiber synapses onto proximal dendrites of CA3 pyramidal neurons may support structures such as gap junctions, allowing the passage of low-molecular weight dyes from the CA3 pyramidal neurons to the mossy fiber axon. Using thin-section transmission electron microscopy (TEM) we found two classes of putative axodendritic gap junctions onto CA3 pyramidal dendrites. The first class was found between mossy fiber boutons and the thorny excrescences of CA3 pyramidal neurons, as was originally hypothesized based on our dye-coupling experiments. The second class of putative gap junctions was found between an inhibitory terminal and a positively identified CA3 pyramidal dendrite. We also found one example of a putative gap junction between a dendritic spine and another spiny dendrite in the CA3 region. While scanning hippocampal stratum lucidum under high magnification (20,000-30,000 ×) TEM, we found six close membrane appositions resembling gap junctions (~30-70 nm in diameter) between pairs of hippocampal mossy fiber axons (~100-200 nm in diameter) in the CA3b field of the adult rat ventral hippocampus. Using freeze-fracture replica immunogold labeling (FRIL) TEM, one axonal gap junction (~100 connexons) was found on a mossy fiber axon in the CA3c field of the adult rat dorsal hippocampus. Immunogold labeling with two sizes of gold beads revealed that connexin36 was present in that axonal gap junction. These ultrastructural data suggest that axodendritic synapses from both excitatory and inhibitory terminals onto CA3 pyramidal neurons are mixed (chemical and electrical) at least in some instances. They also support computer modeling and in vitro electrophysiological studies suggesting that axoaxonic gap junctions may play an important role in the generation of very fast (≻70 Hz) network oscillations and in the hypersynchronous electrical activity of epilepsy.
-
Pivotal role of Cardiac Lineage Protein-1 (CLP-1) in Positive Transcriptional Elongation Factor b complex activity in cardiac hypertrophy.Emerging evidence illustrates the importance of the Positive Transcription Elongation Factor b (P-TEFb) in control of global RNA synthesis which constitutes a major feature of the compensatory response to diverse hypertrophic stimuli in cardiomyocytes. P-TEFb, a complex composed of cyclin T and Cdk9, is critical for elongation of nascent RNA chains via phosphorylation of the carboxyl terminal domain of RNA polymerase II (CTD RNA Pol II). HEXIM1, the human homolog of mouse cardiac lineage protein 1 (CLP-1), was shown to be associated with P-TEFb and inhibit Cdk9 kinase activity. Therefore, I hypothesize that CLP-1/HEXIM1 dissociation from the P-TEFb complex is required for triggering the increased synthesis of RNA, the hallmark of cardiac hypertrophy. To determine, if the expression pattern of CLP-1 in the heart is consistent with its role in controlling P-TEFb activity, I performed immunoprecipitation and immunofluorescence analysis of CLP-1 and the components of P-TEFb in the fetal mouse heart and in 2 day post-natal mouse cardiomyocytes. I observed that CLP-1 is colocalized with Cdk9 and Cyclin T1 and is associated with the P-TEFb complex. I subjected cardiomyocytes to hypertrophic stimuli, such as mechanical stretch or treatment with hypertrophic agents (endothelin-1 and phenylephrine), which results in dissociation of CLP-1 from P-TEFb. Association and dissociation of CLP-1 with the P-TEFb is regulated by the Jak/STAT signaling pathway as inhibition of Jak2 signaling by AG490 prevented release of CLP-1 from P-TEFb despite the ongoing presence of hypertrophic stimulation by mechanical stretch. To extend these studies to the animal models, I used a transgenic mouse model of hypertrophy obtained by cardiac-specific over-expression of calcineurin. I observed that the level of CLP-1 associated with the P-TEFb complex was reduced in transgenic hypertrophic hearts. I also generated bigenic mice (MHC-cyclin T1/CLP-1+/-) by crossing MHC-cyclin T1 transgenic mice with CLP-1 heterozygote. The bigenic mice exhibit enhanced susceptibility to hypertrophy which is accompanied with an increase in Cdk9 activity via an increase in serine-2 phosphorylation of CTD and an increase in GLUT1/GLUT4 ratio. These mice exhibit compensated systolic function without evidence of fibrosis or reduced life span. Taken together, these data suggest that the reduced level of CLP-1 introduced in the background of elevated level of cyclin T1 de-represses of P-TEFb activity and emphasizes the importance of CLP-1’s role in the mechanism governing compensatory hypertrophy in cardiomyocytes. Therefore, the decrease in CLP-1 binding to the P-TEFb complex is critical to the regulation of the hypertrophic response in cardiomyocytes.
-
Minocycline plus N-acetylcysteine repairs the injured brain by modulating neuroinflammation and inducing remyelination.Mild traumatic brain injury (mTBI) occurs to 1.3 million people every year. While symptoms of mTBI can be treated, little can be done for the underlying injury. The FDA-approved drugs Minocycline plus N-acetylcysteine (MINO plus NAC) synergistically improved cognition and memory in an animal model of traumatic brain injury, moderate controlled cortical impact. Mechanisms underlying the synergistic action of MINO plus NAC are unknown nor is it known whether the drug combination improves mild controlled cortical impact (mCCI). This thesis addresses these issues via 3 specific aims: 1) Does MINO plus NAC improve cognition and memory after mCCI?, 2) Does MINO plus NAC promote remyelination following mCCI?, and 3) How are microglia modulated by MINO plus NAC? The effect of the drug combination on white matter damage and neuroinflammation were examined during time points when behavioral deficits arise after mCCI. MINO plus NAC synergistically improved memory and cognition following mCCI. Additional synergies of MINO plus NAC were seen in protecting resident oligodendrocytes and modulating microglial activation. Synergistic drug effects are uncommon suggesting that modulation of inflammation protects oligodendrocytes leading to remyelination and improved cognition and memory. These findings provide new and important insights into how drug treatments can repair the brain after traumatic brain injury.
-
Sphingosine kinase 1 in septic brain injurySepsis is the number one killer in hospital critical care units, and the 10th leading cause of death in the United States. Despite such staggering statistics, the pathogenesis of the central nervous system (CNS) dysfunction during sepsis is poorly understood. CNS dysfunction usually results in neuroinflammation and encephalopathy. During sepsis blocking of ceramide (Cer), tumor necrosis factor (TNFα), platelet-activating factor (PAF) and prostaglandins have not proven to be effective in clinical trials. This suggests that several parallel and interacting molecular mechanisms are involved. Regulation of sphingolipid metabolism is a likely mechanism in maintaining the cellular processes, such as cell differentiation, proliferation, migration, cell survival and cell death, in the CNS. Sphingosine kinase (SPHK) is the enzyme in the sphingolipid pathway that converts sphingosine (Sph) into sphingosine-1-phosphate (S-1-P). At least two sphingosine kinase isoforms have been cloned and characterized - sphingosine kinase 1 (SPHK1) and sphingosine kinase 2 (SPHK2). We hypothesized that SPHK1 induction and/or SPHK2 inhibition may represent novel treatment targets for sepsis and septic encephalopathy (SE). Bacterial endotoxin - lipopolysaccharide (LPS) was used to establish a septic brain injury model in vivo and study neuroinflammatory parameters. Neuroinflammation was induced by intracerebral injection of LPS 1mg/kg into the lateral ventricles of wild type (WT) and SphK1-/- mice; control animals received sterile saline. Neuroinflammatory parameters were assayed such as white matter rarefactions, development of cytotoxic edema, astrogliosis, oligodendrocytes precursors loss, and cytokines levels. The data showed significant upregulation of the neuroinflammatory response in SphK1-/- mice. We tested intraperitoneal injection of LPS at two doses 5mg/kg and 10 mg/kg. Heart rates were measured, white blood cells were counted, antigenic markers of microglial and astrocytic activation and oligodendrocytes progenitors were assayed by immunohistochemistry and Western Blot. Levels of TNFα and IL-6 were assayed by reverse transcriptase PCR (rt-PCR) and level of pro-apoptotic protein - caspase-8 was assayed by Western Blot. These data showed that LPS at a dose of 10mg/kg is more sufficient to induce severe septic brain injury. In addition, SphK1-/- mice had persistent upregulation of neuroinflammatory parameters in the absence of exogenous induction of neuroinflammation. These data proved that SPHK1-/- mice are more susceptible to LPS induced brain injury and revealed a protective role of SphK1 in the regulation of neuroinflammation. These data also strongly suggest that SphK1 regulates basal levels of neuroinflammatory proteins as well.
-
Regulation of Mouse Intestinal L Cell Progenitors Proliferation by the Glucagon Family of Peptides.Glucagon like peptide-1 (GLP-1) and glucagon like peptide-2 (GLP-2) are hormones secreted by intestinal L cells that stimulate glucose-dependent insulin secretion and regulate intestinal growth, respectively. Mice with deletion of the glucagon receptor (Gcgr) have high levels of circulating GLP-1 and GLP-2. In the first part of my study, I sought to determine whether the increased level of the glucagon-like peptides in Gcgr-/- mice is due to L cell hyperplasia. I found, first, that high circulating levels of the glucagon-like peptides increase L cell number but do not affect the numbers of other intestinal epithelial cell types. Second, a large proportion of ileal L cells of Gcgr-/- mice co-expressed glucose-dependent insulinotropic peptide (GIP), a hormone that induces an increase in insulin secretion following a meal. Cells co-expressing GIP and GLP-1 are termed LK cells. Third, the increase in L cell number was due to a higher rate of proliferation of L cell progenitors rather than of mature L cells. Fourth, high circulating levels of the glucagon-like peptides were associated with increased mRNA levels of transcription factors expressed by late but not early enteroendocrine progenitors. Fifth, administration of exendin 9-39, a GLP-1 receptor antagonist, to Gcgr-/- mice decreased the rate of L cell precursor proliferation, indicating that the rate of cell division is regulated by GLP-1. Finally, we determined that L cells do not express the GLP-1 receptor, suggesting that the effect of GLP-1 is mediated by paracrine and/or neuronal signals. These results indicate that GLP-1 plays an important role in the regulation of L cell number via activation of its precursor population. In the second part of my study, I sought to characterize L and K cells during embryonic development. I found that GLP-1+ cells first appear at embryonic (e) day 15 of development and that their number is increased at e-17. Most GLP-1+ cells of ileum of e-17 embryos co-express GIP and, therefore, are LK cells. In addition, a subset of GLP-1+ cells of embryos but not of neonates, co-express glucagon, indicating that the expression of Glu in GLP-1+ cells disappears after birth. Taken together, these observations indicate that the phenotype of L cells changes after birth, presumably, reflecting the initiation of intestinal functional activity. Analogs of the hormones secreted by L cells are currently used in the clinic. My studies suggest a mechanism that will allow to increase the endogenous source of the glucagon-like peptides. This strategy will help to circumvent harmful side effects of pharmacological doses of the drugs. Therefore, the identification of the signals controlling the number of this important cell type will provide crucial information for the regulation of endogenous levels of GLP-1 and the control of glucose homeostasis.
