Kusumika Gharami

Parkinson′s disease (PD) is characterized by a progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta and degeneration of their projections in the striatum (STR) of the brain. Astrocytes are recognized as active contributors to PD pathogenesis, yet the role of calcineurin (CN), a Ca/calmodulin-dependent phosphatase which is well characterized in neurons, remains unexplored in astrocytes in the context of PD. Here, we show that CN protein expression is upregulated in the STR of MPTP-treated mice, coinciding with DA neurodegeneration and astrogliosis. In human astrocytoma cells and primary rat astrocytes, the neurotoxin Rotenone induced rapid intracellular Calcium elevation and CN activation. Unexpectedly, this was accompanied by a decrease in intracellular levels of miR-23a, an astrocyte-enriched microRNA previously linked to CN signalling in cardiomyocytes. We found that this decrease reflected active exosomal export: Rotenone increased both exosomal miR-23a levels and total exosome number, while blocking exosome biogenesis with GW4869 restored intracellular miR-23a levels. Functionally, both astrocyte-derived exosomes and miR-23a overexpression protected neuronal cells (SH-SY5Y, PC12) against Rotenone-, 6-OHDA-, and MPP+-induced toxicity. Mechanistically, miR-23a showed direct binding to the 3′UTR of the pro-apoptotic BH3-only protein NOXA, thereby suppressing its expression, subsequently attenuating caspase-3 activation. Finally, exosomal miR-23a levels were significantly elevated in plasma from PD patients compared with age-matched controls, supporting clinical relevance. Together, these findings identify a previously unrecognized astrocyte-to-neuron communication axis during PD pathogenesis, in which astrocytic CN activation accompanied by exosomal miR-23a release represents a neuroprotective stress-responsive pathway with potential biomarker and therapeutic relevance in PD.

Dysfunctional autophagy is a primary characteristic of Alzheimer’s disease (AD) pathogenesis. How autophagic impairment leads to cellular changes that contributes to AD pathogenesis remains unclear. To study this further, we assessed levels of autophagy related proteins in 5xFAD mice brain at different ages and found their robust upregulation in cortex and hippocampus suggesting increased induction of autophagy with disease progression but failed clearance. We have identified a transcriptional coregulator Sertad1, as a key mediator of dysfunctional autophagy in AD mice. We found a progressive elevation in Sertad1 levels in 5xFAD mice with age compared to wild-type (WT) mice. Sertad1 knockdown in 5xFAD mice brain lowered levels of autophagy related proteins and lysosome marker, LAMP1 suggesting its role in autophagy flux modulation. FoxO3a is an important transcriptional regulator of the autophagy network and lies at the nexus of autophagy-apoptosis cross-talk. We found that Sertad1 knockdown blocked nuclear translocation of FoxO3a along with a restoration in Akt activity. Further, we showed that knockdown of Sertad1 in 5xFAD mice brain improved cognitive functions along with a remarkable restoration in synaptic health and dendritic spine density. Taken together, our results demonstrated that autophagy is robustly induced with disease progression but it is impaired; Sertad1 knockdown restored autophagy defects, synaptic loss and improved learning and memory in AD models. Thus, we propose that Sertad1 acts in a multimodal manner regulating crucial cell death pathways including apoptosis and autophagy and could be an excellent target for therapeutic intervention to combat a multifactorial disorder such as AD.