Susmita Sil, PhD
Durham Research Center 8024
985880 Nebraska Medical Center
Omaha, NE 68198-5880
Keywords: HIV, drugs of abuse, neurodegeneration, Alzheimer’s Disease, autophagy, long non-coding RNA, exosomes
Long non-coding RNAs (lncRNAs) have gained huge attention in recent years as a potentially new and crucial player in non-canonical functions including wide range of developmental processes and diseases, but knowledge of the mechanisms by which they act is still surprisingly limited. My research interests include investigating the roles of long non-coding RNAs (lncRNAs) and extracellular vesicles (EVs) in different neurodegenerative diseases, including HIV associated neurological disorders and Alzheimer’s Disease as well as dementia in drug addicts. Specifically I would like to see the regulatory roles of these lncRNAs in expression of specific neurotoxic proteins by RNA-protein interaction and further to evaluate the role of these lncRNAs in biogenesis and release of EVs carrying these proteins, which may have a role in disease pathogenesis and progression. For my long-term research career, I would like to investigate the different molecular mechanisms leading to glia mediated neuronal injury and dementia in drug addicts, HIV patients, as well as in different neurodegenerative diseases. Using herbal nanoformulations and lncRNA based therapies, I would like to target the upstream components involved in the disease conditions.
Alzheimer’s Disease as a co-morbidity of HIV: Role of astrocytes
Increased life expectancy of HIV+ patients in the current era of effective treatment is unfortunately accompanied with the continued prevalence of HIV-associated neurological disorders and risk of age-associated comorbidities such as Alzheimer’s Disease (AD). Interestingly, there are reports implicating HIV-1 Tat-mediated production of the toxic neuronal amyloid protein and the interaction of the two, further resulting in enhanced neurotoxicity. In the current project, I sought to assess the contribution of other non-neuronal cells such as the astrocytes in Tat-mediated amyloidosis. Preliminary findings showed that astrocytes can produce amyloids in presence of HIV protein Tat, HIV/ SIV, and HIF-1α-lncRNA BACE1-AS complex is associated with this process of astrocytic amyloidosis and can be targeted to develop adjunctive therapies for HAND-associated comorbidity of AD.
Role of astrocyte derived-extracellular vesicles in disease pathogenesis
Extracellular vesicles (EVs) have become the focus of rising interest because of their numerous functions in physiology and pathology. Cells release heterogeneous vesicles of different sizes and intracellular origins, including small EVs formed inside endosomal compartments (i.e., exosomes) and EVs of various sizes budding from the plasma membrane. Based on the existing literature on the role of brain and serum-derived extracellular vesicles (EVs) in seeding of the toxic amyloid forms to various sites in the CNS and the periphery, we hypothesized that Tat exposed astrocytes could also mediate amyloidosis that could be propagated via EVs, leading, in turn, to further potentiation of pathogenesis of HAND. We are screening for various amyloid forms in the brains of HIV/ SIV+ subjects. We are isolating and characterizing the neuron/astrocyte-derived brain and serum-derived EVs invivo via differential ultracentrifugation, zetaview, atomic force microscopy, electron microscopy, and immunoblot analysis. We will assess for the presence and enrichment of L1CAM+ neuronal- & GLAST+ astrocyte-derived EVs in the brain and serum of HIV rat model, and for content of amyloids. These findings will give us information about the role of specific EVs in disease progression and as biomarkers.
Morphine-mediated brain region-specific astrocytosis involves the ER stress-autophagy axis
Morphine is the most potent painkiller among all the opiates and is used extensively in the clinical settings, because of its comfort giving properties including drowsiness, relief from anxiety, and euphoric effects. However, it has been reported that almost half of all the accidental drug-overdose related deaths can be attributed to morphine or heroin overdose. Chronic exposure to morphine leads to increased complications such as addiction, tolerance, cognitive impairment, withdrawal, and severely compromised immune system with increased risk of opportunistic infections. In addition, morphine also exerts its adverse effects on various cells of the central nervous system. Astrocytes are the most abundant glial cells of the brain that are critical for neuroprotection. In response to injury, these cells undergo activation/astrogliosis, which is a key feature underlying various neurodegenerative disorders. Based on the premise that morphine is a potent painkiller and since astrogliosis has been implicated in the pain potentiating synapses, we hypothesized that chronic morphine exposure could lead to astrogliosis. A recent study from our lab has shown that morphine exposure of hippocampal neurons resulted in synaptodendritic injury involving the ER stress-autophagy axis. We hypothesized that morphine abuse may lead to astrogliosis and neuroinflammation. Although morphine is a highly effective painkiller, its long-term use results in tolerance, addiction, and cognitive impairments. The current study was aimed at investigating whether morphine-mediated activation of astrocytes involved the endoplasmic reticulum (ER) stress/autophagy axis. Our in vitro findings demonstrated a dose- and time-dependent upregulation of the GFAP (glial fibrillary acidic protein) indicating astrocyte activation with a concomitant increase of neuroinflammation in morphine-exposed human A172 astrocytoma cell lines and human primary astrocytes. Morphine significantly increased autophagosome formation as demonstrated by a time-dependent increase of autophagy markers (BECN1, MAP1LC3B-II, and SQSTM1) and a concomitant defect in the autophagic flux. Pharmacological blocking of the OPRM1 underscored the role of the opioid receptor in this process. Using both pharmacological and gene-silencing approaches, it was demonstrated that morphine-mediated dysregulation of autophagy involved upstream activation of ER stress with subsequent downstream activation of GFAP and production of proinflammatory cytokines. These results were also validated in the morphine-dependent rhesus macaques. Our findings showed preferential activation of ER stress/autophagy axis along that correlated with astrocyte activation and inflammation in the basal ganglia, frontal cortex, occipital cortex and cerebellum of morphine-dependent rhesus macaques. Intriguingly, areas of the brain not associated with pain were found to be more susceptible to morphine-mediated astrocytosis and neuroinflammation. Interventions aimed at blocking either the μ-opioid receptor or ER stress could thus provide promising therapeutic targets for abrogating morphine-mediated astrocytosis.
Cocaine-mediated neuroinflammation: Role of dysregulated autophagy in pericytes
Cocaine, one of the most commonly used street drugs, is a powerful addictive psychostimulant that activates the brain reward pathway. According to a Drug Abuse Warning Network (DAWN) report in 2011, cocaine abuse accounted for 40% of drug misuse or abuse-related emergency department visits. Both cocaine and HIV can affect the central nervous system (CNS). Cocaine, that can cross the blood-brain barrier (BBB), has also been shown to result in BBB dysfunction while also exerting its effects on multiple cells of the CNS. In the setting of HIV-1 infection, cocaine-mediated neuroinflammation and increased transmigration of infected/activated leukocytes from the periphery into the brain can ultimately lead to exacerbated neurodegeneration. Pericytes are vascular mural cells that play a vital role in the functioning of the neurovascular unit. More recently, these cells have gained attention based on their proximity and contact with other cells of the neurovascular unit such as the endothelial cells, the astrocyte end feet, perivascular microglia, and neurons. Pericytes play critical roles in the maintenance of BBB integrity, regulation of angiogenesis, control of cerebral blood flow, neuroinflammation as well as stem cell activity Additionally, pericytes also play a vital role in regulating the immunological response via modulation of the peripheral immune cell transmigration across the BBB. The present study was undertaken to assess the role of non-glial cells such as pericytes as contributors of cocaine-mediated neuroinflammation, with the involvement of ER stress-autophagy pathway. In this report, we demonstrated for the first time that exposure of primary human brain vascular pericytes to cocaine-induced ER stress-mediated formation of autophagosomes, with a concomitant block in the fusion of autophagosomes with the lysosomes, resulting, in turn, to increased activation of pericytes with upregulated expression of TNF-α, IL-1β and IL-6. These findings were further validated in an in vivo model of cocaine addiction. Taken together these findings underpin the role of pericytes in cocaine-mediated neuroinflammation. Interventions aimed at targeting the upstream components of the ER-stress-autophagy pathway could thus be developed as therapeutic strategies to dampen cocaine-mediated neuroinflammation in cocaine addicts and/or in HIV-infected cocaine abusers.
- Sil S, Hu G, Liao K, Niu F, Callen S, Periyasamy P, Fox H, Buch S. 2020. HIV-1 Tat-mediated astrocytic amyloidosis involves the HIF-1α/lncRNA BACE1-AS axis. PlosBiol. https://doi.org/10.1371/journal.pbio.3000660.
- Sil S, Niu F, Tom E, Liao K, Periyasamy P. 2018. Cocaine mediated neuroinflammation: Role of dysregulated autophagy in pericytes, Mol. Neurobiol. org/10.1007/s12035-018-1325-0.
- Sil S, Periyasamy P, Guo M, Callen S, Buch S. 2018. Morphine-mediated brain region specific astrocytosis involves the ER stress-autophagy axis. Mol. Neurobiol. 55, 6713-6733.
- Sil S, Periyasamy P, Thangaraj A, Chivero E, Buch S. 2018. PDGF/PDGFR axis in the neural systems – review article, Molecular Aspects of Medicine. 62, 63-74.
- Sil, S., Ghosh, A., Ghosh, T. 2016. Impairment of blood brain barrier is related with the neuroinflammation induced peripheral immune status in intracerebroventricular colchicine injected rats: An experimental study with mannitol. Brain Res.1646, 278-86.
- Sil S, Ghosh T, Ghosh R, Gupta P. Nitric oxide synthase inhibitor, aminoguanidine reduces intracerebroventricular colchicine induced neurodegeneration, memory impairments and changes of systemic immune responses in rats. J Neuroimmunol. 303, 51 – 61.
- Sil S, Ghosh T, Gupta P, Ghosh R, Kabir SN, Roy A. 2016. Dual Role of Vitamin C on the Neuroinflammation Mediated Neurodegeneration and Memory Impairments in Colchicine Induced Rat Model of Alzheimer Disease. J Mol Neurosci. 60, 421- 435.
- Sil, S., Ghosh, T. 2016. Role of cox-2 mediated neuroinflammation on the neurodegeneration and cognitive impairments in colchicine induced rat model of Alzheimer's Disease. J Neuroimmunol. 291, 115-124.
- Sil, S., Ghosh, R., Sanyal, M., Guha, D., Ghosh, T.K. 2016. A comparison of neurodegeneration linked with neuroinflammation in brain areas of rats after intracerebroventricular colchicine injection. J Immunotoxicol. 13: 182-190.
- Sil, S., Goswami, A.R., Dutta, G., Ghosh, T. 2014. Effects of naproxen on some immune responses in colchicine induced rat model of Alzheimer’s Disease. Neuroimmunomodulat. 21, 304-321.