Biology subjects

Gandasi, N. R.

Publications and source records attributed to Gandasi, N. R..

4 recordsLinked to original sources

bioRxiv2025

p21-activated kinase regulates Rab3a vesicles to repair plasma membrane damage caused by Amyloid-β oligomers

The interaction of amyloid-{beta} (A{beta}) peptides with the plasma membrane (PM) is a potential trigger that initiates the formation of higher-order aggregates, membrane alterations/damage, and progressive neurotoxicity in Alzheimers disease (AD). In a previous study, we showed that oligomers of A{beta}1-42 (oA{beta}1-42) induced PM damage, resulting in PM repair cascade via lysosomal exocytosis coupled with endocytosis, and facilitation of tunneling nanotubes (TNTs)-like membrane protrusions to promote direct cell-to-cell transfer of aggregates. In this study, we demonstrated that PM damage induced by oligomers of the aggregation-prone peptide A{beta}1-42 significantly facilitates PM repair by enhancing phosphorylated p21-activated kinase 1 (pPAK1)-dependent endocytosis and Rab3a-dependent exocytosis in SH-SY5Y and SK-N-SH neuronal cells compared to control and oA{beta}1-40 treated cells. We studied the kinetics of pPAK1-dependent endocytosis and the fusion of EGFP-Rab3a vesicles near the PM using total internal reflection fluorescence (TIRF) microscopy. IPA-3, a selective non-ATP competitive inhibitor of PAK1, inhibits endocytosis of oA{beta} peptides and Rab3a-dependent PM repair. Further, shRNA-mediated knockdown of the Rab3a gene inhibits pPAK1 and disrupts PM repair. Repair of damaged PM is a vital protective mechanism for non-proliferative cells like neurons, as disruption in PM repair leads to gradual neuronal cell death. However, there was no explicit understanding of PM repair in response to A{beta} oligomers. This study revealed the interconnected action of Rab3a and pPAK1 in PM repair in response to oA{beta}-mediated damage, and its potential correlation in AD pathogenesis.

cell biology↗

bioRxiv2023

Localization and function of multivesicular-bodies that release exosomes in islet cells: dysregulation during type-2 diabetes

Type-2 diabetes (T2D) is characterized by high blood glucose due to compromised insulin secretion from pancreatic {beta}-cells. {beta}-cells primarily comprise insulin-secreting large-dense-core-vesicles/insulin-secretory-granules (ISGs) and also multivesicular-bodies (MVBs). MVBs are vesicles of endosomal origin containing intraluminal vesicles, which upon fusion with the plasma membrane, secrete exosomes. These play a significant role in the physiology and pathology of T2D via intercellular communication. The role of MVBs and their influence on ISGs of {beta}-cells or their characterization is yet to be uncovered. In our study, we characterized the role of MVBs by comparing them to largely well-characterized ISGs in {beta}-cells. We compared the density, localization, and exocytosis of MVBs with ISGs in {beta}-cells. For this, we developed a novel probe where we exploit the efficiency of tetraspanins CD63 and CD151 to label the MVBs in {beta}-cells. We showed that the {beta}-cells have a significantly higher density of ISGs than MVBs. MVBs and ISGs are spatially localized apart within {beta}-cells. The proteins that localize with MVBs are different from the ones that localize with ISGs. Exocytosis of ISGs occurs at the periphery of the {beta}-cells and takes significantly lesser time when compared to exosome release, which is non-peripheral and takes a longer duration. Further, we also observed a significant reduction in the density of ISGs and MVBs in T2D patients islets compared to healthy controls. Studying the effect of MVBs on insulin secretion in physiological and T2D conditions has huge potential. This study provides a strong basis to open new avenues for such future studies.

cell biology↗

bioRxiv2022

Global loss of cellular m6A RNA methylation following infection with different SARS-CoV-2 variants

Host-viral interactions during SARS-CoV-2 infection are needed to understand COVID-19 pathogenesis and may help to guide the design of novel antiviral therapeutics. N6-methyladenosine modification (m6A), one of the most abundant cellular RNA modifications, regulates key processes in RNA metabolism during a stress response. Gene expression profiles observed post-infection with different SARS-CoV-2 variants show changes in the expression of genes related to RNA catabolism, including m6A readers and erasers. We found that infection with SARS-CoV-2 variants caused a loss of m6A in cellular RNAs, whereas m6A was detected abundantly in viral RNA. METTL3, the m6A methyltransferase, showed an unusual cytoplasmic localization post-infection. The B.1.351 variant had a less pronounced effect on METTL3 localization and loss of m6A than the B.1 and B.1.1.7 variants. We also observed a loss of m6A upon SARS-CoV-2 infection in air/liquid interface cultures of human airway epithelia, confirming that m6A loss is characteristic of SARS-CoV-2 infected cells. Further, transcripts with m6A modification were preferentially down-regulated post-infection. Inhibition of the export protein XPO1 resulted in the restoration of METTL3 localization, recovery of m6A on cellular RNA, and increased mRNA expression. Stress granule formation, which was compromised by SARS-CoV-2 infection, was restored by XPO1 inhibition and accompanied by a reduced viral infection in vitro. Together, our study elucidates how SARS-CoV-2 inhibits the stress response and perturbs cellular gene expression in an m6A-dependent manner.

molecular biology↗

bioRxiv2018

Fusion pore regulation by Epac2/cAMP controls cargo release during insulin exocytosis

Regulated exocytosis establishes a narrow fusion pore as the initial aqueous connection to the extracellular space, through which small transmitter molecules such as ATP can exit. Co-release of larger peptides and hormones like insulin requires further expansion of the pore. There is evidence that pore expansion is regulated and can fail in type-2 diabetes and neurodegenerative disease. Here we report that the cAMP-sensor Epac2 (Rap-GEF4) controls fusion pore behavior by acutely recruiting two pore-restricting proteins, amisyn and dynamin-1, to the exocytosis site in insulin-secreting beta-cells. cAMP elevation leads to pore expansion and peptide release, but not when Epac2 is inactivated pharmacologically or in Epac2-/- mice. Conversely, overexpression of Epac2 impedes pore expansion. Widely used antidiabetic drugs (GLP-1 agonists and sulfonylureas) activate this pathway and thereby paradoxically restrict hormone release. We conclude that Epac2/cAMP controls fusion pore expansion and thus the balance of hormone and transmitter release during insulin granule exocytosis.

cell biology↗