Mechanisms Of Alpha]-synuclein-induced Neurodegenertaion In Parkinson\u27s Disease And Stroke

Parkinson’s disease (PD) is a debilitating neurodegenerative disorder affecting one million Americans. Despite its social and economic impact, the pathological cascades that lead to neuron dysfunction and degeneration in PD are poorly understood. Endoplasmic reticulum (ER) stress has been implicated as an initiator or contributing factor in neurodegenerative diseases including PD. The ER is an organelle central to protein folding and intracellular Ca2+ homeostasis. Perturbations of these functions result in ER stress and upregulation of ER stress proteins, of which some have been implicated in counteracting ER stress-induced cell death. The mechanisms that lead to ER stress and how ER stress proteins contribute to the degenerative cascades remain unclear but their understanding is critical to devising effective therapies for PD. Both the accumulation of mutant -synuclein (Syn), which causes an inherited form of PD, and the inhibition of mitochondrial complex I function by PDinducing neurotoxin lead to ER stress. The critical involvement of ER stress in experimental models of PD supports its potential relevance to PD pathogenesis and led us to test the hypothesis whether the homocysteine-inducible ER protein (Herp), an ubiquitin-like domain (UBD) containing ER-resident protein, can counteract mutant Syn- and neurotoxin- induced pathological cascades. In the first part of my study I showed that knockdown of Herp aggravates ER stress-mediated cell death induced by PD-linked mutant Syn. Functionally, Herp plays iv a role in maintaining ER homeostasis by facilitating proteasome-mediated degradation of ER-resident Ca2+ release channels in a neuronal-like cell line expressing the mutant A53T-Syn. Deletion of UBD or pharmacological inhibition of the proteasomes abolishes the Herp-mediated stabilization of ER Ca2+ homeostasis. Furthermore, knockdown or pharmacological inhibition of ER Ca2+ release channels ameliorates ER stress suggesting that impaired homeostatic regulation of Ca2+ channels promotes a protracted ER stress with the consequent activation of ER stress-associated cell death pathways. Interestingly, sustained upregulation of ER stress markers and aberrant accumulation of ER Ca2+ release channels were detected in transgenic mutant A53T- Syn mice. These data establish a causative link between impaired ER Ca2+ homeostasis and chronic ER stress in the degenerative cascades induced by mutant A53T-Syn and suggest that Herp is essential for the resolution of ER stress through maintenance of ER Ca2+ homeostasis. Because oxidants and mitochondria-derived free radicals can target ER-based Ca2+ regulatory proteins and cause uncontrolled Ca2+ release that may contribute to protracted ER stress resulting in cell death, I next determined the impact of the PD causing neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), the precursor of 1-methyl-4-phenylpyridinium (MPP+ ) on ER functions. I demonstrated that knockdown of Herp renders dopaminergic cells vulnerable to MPP+ -induced toxicity by a mechanism involving upregulation of CCAAT/enhancer binding protein homologous protein (CHOP) and depletion of the ER Ca2+ store. Conversely, ectopic expression of Herp confers protection by blocking MPP+ -induced CHOP upregulation, ER Ca2+ store depletion and mitochondrial Ca2+ accumulation in a manner dependent on a functional v ubiquitin-proteasomal protein degradation pathway. Deletion of the UBD or treatment with a proteasomal inhibitor abolished the central function of Herp in ER Ca2+ homeostasis. Collectively, our findings suggest that approaches that aim to increase Herp levels or its ER Ca2+ -stabilizing action may prevent or ameliorate neuronal loss in PD. Though abnormal protein aggregates are characteristic features of the slowly progressive neurodegenerative disorders, they are also found in acute pathological states such as cerebral ischemia. The role of protein aggregation in neuronal pathology after brain ischemia is not clear. In the last part of my work, I show that transient focal ischemia induces the continuous accumulation of insoluble Syn and DJ-1, two proteins linked to early-onset PD, in vulnerable neurons from the onset of reperfusion until delayed neuronal death. Double immunocytochemical analysis reveals that Syn and DJ-1 are co-localized in inclusion-like structures in the vulnerable neurons of the lesioned cortices suggesting that DJ-1 is recruited into the Syn-containing inclusions and thereby precludes this neuroprotective protein from exercising its anti-oxidant and chaperone-like activities. Supporting this notion, knockdown of DJ-1 promotes Syn insolubility and renders neurons vulnerable to an ischemic insult whereas ectopic expression of DJ-1 ameliorates Syn -induced degenerative cascades and reverses ischemic neuronal injury. Furthermore, mice deficient in Syn exhibit significantly smaller infarcts and improved behavioral recovery after ischemia compared to nontransgenic mice. Ablation of Syn ameliorates the accumulation of insoluble DJ-1 and the ensuing oxidative damage following an ischemic insult. Taken together, our data show that aberrant accumulation of Syn plays a precipitating role in ischemic neuronal vi injury and suggest that PD-causing mutations in Syn and DJ-1 can worsen ischemic brain damage. In conclusion, these studies provide insights into the molecular cascade of Syninduced degeneration and may uncover novel therapeutic strategies for PD and stroke

The Homocysteine-inducible Endoplasmic Reticulum Stress Protein Counteracts Calcium Store Depletion and Induction of CCAAT Enhancer-binding Protein Homologous Protein in a Neurotoxin Model of Parkinson Disease

The endoplasmic reticulum (ER) is a key organelle regulating intracellular Ca(2+) homeostasis. Oxidants and mitochondria-derived free radicals can target ER-based Ca(2+) regulatory proteins and cause uncontrolled Ca(2+) release that may contribute to protracted ER stress and apoptosis. Several ER stress proteins have been suggested to counteract the deregulation of ER Ca(2+) homeostasis and ER stress. Here we showed that knockdown of Herp, an ubiquitin-like domain containing ER stress protein, renders PC12 and MN9D cells vulnerable to 1-methyl-4-phenylpyridinium-induced cytotoxic cell death by a mechanism involving up-regulation of CHOP expression and ER Ca(2+) depletion. Conversely, Herp overexpression confers protection by blocking 1-methyl-4-phenylpyridinium-induced CHOP upregulation, ER Ca(2+) store depletion, and mitochondrial Ca(2+) accumulation in a manner dependent on a functional ubiquitin-proteasomal protein degradation pathway. Deletion of the ubiquitin-like domain of Herp or treatment with a proteasomal inhibitor abolished the central function of Herp in ER Ca(2+) homeostasis. Thus, elucidating the underlying molecular mechanism(s) whereby Herp counteracts Ca(2+) disturbances will provide insights into the molecular cascade of cell death in dopaminergic neurons and may uncover novel therapeutic strategies to prevent and ameliorate Parkinson disease progression

Chronic Nicotine Administration Impairs Activation Of Cyclic Amp-Response Element Binding Protein And Survival Of Newborn Cells In The Dentate Gyrus

Image analysis in the presence of surface scatter due to residual optical fabrication errors is often perceived to be complicated, nonintuitive, and achieved only by computationally intensive nonsequential ray tracing with commercial optical analysis codes such as ASAP, Zemax, Code V, TracePro, or FRED. However, we show that surface scatter can be treated very similarly to conventional wavefront aberrations. For multielement imaging systems degraded by both surface scatter and aberrations, the composite point spread function is obtained in explicit analytic form in terms of convolutions of the geometrical point spread function and scaled bidirectional scattering distribution functions of the individual surfaces of the imaging system. The approximations and assumptions in this formulation are discussed, and the result is compared to the irradiance distribution obtained using commercial software for the case of a two-mirror telescope operating at an extreme ultraviolet wavelength. The two results are virtually identical. © 2012 Optical Society of America

The Homocysteine-Inducible Endoplasmic Reticulum (Er) Stress Protein Herp Counteracts Mutant Α-Synuclein-Induced Er Stress Via The Homeostatic Regulation Of Er-Resident Calcium Release Channel Proteins

Jail staff are the heart and soul of any jail. Jails rely on staff to complete a myriad of tasks and duties in order to maintain a safe, secure, and humane jail facility. One area of importance is job involvement (i.e., the psychosocial bond between the staff member with his or her job). The current study examined the job characteristics model to explain job involvement among staff at a large county correctional system in Orlando, Florida. The job characteristic variables were formalization, instrumental communication, relations with coworkers, input into decision making, job variety, perceived dangerousness of the job, role strain, and administrative support. It was found that formalization, input into decision making, and administrative support all had positive associations with job involvement. The implications of these findings for correctional researchers and practitioners are discussed. © 2012 International Association for Correctional and Forensic Psychology

MicroRNA-101 Regulates Multiple Developmental Programs to Constrain Excitation in Adult Neural Networks

A critical feature of neural networks is that they balance excitation and inhibition to prevent pathological dysfunction. How this is achieved is largely unknown, although deficits in the balance contribute to many neurological disorders. We show here that a microRNA (miR-101) is a key orchestrator of this essential feature, shaping the developing network to constrain excitation in the adult. Transient early blockade of miR-101 induces long-lasting hyper-excitability and persistent memory deficits. Using target site blockers in vivo, we identify multiple developmental programs regulated in parallel by miR-101 to achieve balanced networks. Repression of one target, NKCC1, initiates the switch in γ-aminobutyric acid (GABA) signaling, limits early spontaneous activity, and constrains dendritic growth. Kif1a and Ank2 are targeted to prevent excessive synapse formation. Simultaneous de-repression of these three targets completely phenocopies major dysfunctions produced by miR-101 blockade. Our results provide new mechanistic insight into brain development and suggest novel candidates for therapeutic intervention

Stress-induced Switch in Numb Isoforms Enhances Notch-dependent Expression of Subtype-specific Transient Receptor Potential Channel*

The Notch signaling pathway plays an essential role in the regulation of cell specification by controlling differentiation, proliferation, and apoptosis. Numb is an intrinsic regulator of the Notch pathway and exists in four alternative splice variants that differ in the length of their phosphotyrosine-binding domain (PTB) and proline-rich region domains. The physiological relevance of the existence of the Numb splice variants and their exact regulation are still poorly understood. We previously reported that Numb switches from isoforms containing the insertion in PTB to isoforms lacking this insertion in neuronal cells subjected to trophic factor withdrawal (TFW). The functional relevance of the TFW-induced switch in Numb isoforms is not known. Here we provide evidence that the TFW-induced switch in Numb isoforms regulates Notch signaling strength and Notch target gene expression. PC12 cells stably overexpressing Numb isoforms lacking the PTB insertion exhibited higher basal Notch activity and Notch-dependent transcription of the transient receptor potential channel 6 (TRPC6) when compared with those overexpressing Numb isoforms with the PTB insertion. The differential regulation of TRPC6 expression is correlated with perturbed calcium signaling and increased neuronal vulnerability to TFW-induced death. Pharmacological inhibition of the Notch pathway or knockdown of TRPC6 function ameliorates the adverse effects caused by the TFW-induced switch in Numb isoforms. Taken together, our results indicate that Notch and Numb interaction may influence the sensitivity of neuronal cells to injurious stimuli by modulating calcium-dependent apoptotic signaling cascades