Growing evidence has shown that the p75 neurotrophin receptor (p75NTR) may play important roles in controlling neuronal survival or cell apoptosis within the central nervous system in development, and in pathological or neural injury. Recent studies have further revealed that p75NTR acts as a “molecular signal switch” that determines cell death or survival by three processes. First, pro-nerve growth factor (proNGF) triggers cell apoptosis by its high affinity binding to p75NTR, while NGF induces neuronal survival with lowaffinity binding. Second, p75NTR mediates cell death by combining with co-receptor sortilin, whereas it promotes neuronal survival through combination with proNGF. Third, release of the intracellular domain chopper or cleavaged “short p75NTR” can independently initiate neuronal apoptosis. We have identified the cell self-destructive proNGF-p75NTR-sortilin signalling apparatus assembled in ventral tier dopamine neurons of the substantia nigra pars compacta, suggesting that p75NTR signalling might be involved in selective cell death mechanisms of substantia nigra neurons or disease progression of Parkinsons disease (PD). In addition, experimental manipulation of p75NTR benefited cell survival of cholinergic or motor neurons and improved disease progression of the neurodegenerative diseases Alzheimers disease and Amyotrophic lateral sclerosis. The proNGF-p75NTR-sortilin signalling complex may thus provide new target for neuroprotection of substantia nigra neurons and the therapeutic treatment of PD.

Reactive astrogliosis is a remarkable pathogenetic hallmark of the brains of Parkinson’s disease (PD) patients, but its progressive fate and regulation mechanisms are poorly understood. In this study, growth arrest specific 1 (Gas1), a tumor growth suppressor oncogene, was identified as a novel modulator of the cell apoptosis of reactive astrocytes in primary culture and the injured substantia nigra. Animal models and cell cultures were utilized in the present study. Lipopolysaccharide (LPS)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated animal models were used to detect Gas1 expression in the brain via immunohistochemistry and western blot. Cell cultures were performed to analyze Gas1 functions in the viability and apoptosis of reactive astrocytes and SH-SY5Y cells by double labeling, CCK-8, LDH, TUNEL, flow cytometry, and siRNA knockdown methods. Gas1 expressions were significantly elevated in the majority of the reactive astrocytes of the brains with LPS or MPTP insults. In the injured substantia nigras, GFAP-positive astrocytes exhibited higher levels of cleaved caspase-3. In cell culture, the up-regulated Gas1 expression induced apoptosis of reactive astrocytes that were insulted by LPS in combination with interferon-γ and tumor necrosis factor-a. This effect was confirmed through siRNA knockdown of Gas1 gene expression. Finally and interestingly, the potential underlying signaling pathways were evidently related to an increase in the Bax/Bcl-2 ratio, the abundant generation of reactive oxygen species and the activation of cleaved caspase-3. This study demonstrated that the up-regulation of inducible Gas1 contributed to the apoptosis of reactive astrocytes in the injured nigra. Gas1 signaling may function as a novel regulator of astrogliosis and is thus a potential intervention target for inflammatory events in PD conditions.

Neuroimmunology and Neuroinflammation is an open access journal, with focuses on neuroimmunology and neuroinflammation research, and coverage extending to other basic and clinical studies related to neuroscience.

While aberrant activation of microglial cells was evidently involved in neuroinflammation and neurotoxicity in the neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease, objective of study was to address if activated microglias deliver their effect by releasing pro-neurotrophins. By in vitro culture of N9 and BV2 cell lines and lipopolysaccharide (LPS) stimulation model, generation and release of proNGF, proBDNF and MMP-9 was studied in the activated microglial cells by immunocytochemistry, western blotting and bioassay methods. Activation of microglial cells was observed with obvious increasing iba1-immunoreactivity following LPS stimulation in cell culture. Synthesis and up-regulation of proNGF protein significantly occurred in N9 and BV2 cells 12h-48h after LPS exposure, whereas no significant changes of proBDNF and MMP9 were observed in these microglial cell lines with LPS insult. More interestingly, extracellular release or secretion of proNGF molecule was also detected in culture medium of N9 cells after LPS stimulation. Finally, bioassay using MTT, Hoechst/PI and TUNEL staining in SH-SY5Y cells further confirmed that proNGF treatment could result in apoptotic cell death but it did not significantly influence cell viability of SH-SY5Y cells. This in vitro study revealed LPS-stimulated proNGF synthesis and release in activated N9/BV2 microglial cell lines, also suggesting that proNGF may appeal a new pathway or possible mechanism underlying microglial toxicity in the neuroinflammation and a potential target for therapeutic manipulation of the neurodegenerative diseases.