Biology subjects

RATNAPARKHI, G. S.

Publications and source records attributed to RATNAPARKHI, G. S..

5 recordsLinked to original sources

bioRxiv2026

Neuro-glial lipid imbalance in a Drosophila model of Amyotrophic Lateral Sclerosis 8

Membrane Contact sites (MCS) have emerged as physiologically relevant zones that coordinate inter-organelle communication and cellular function. VAPB, an ER-resident MCS tethering protein, plays a central role in regulating MCSs through its numerous protein interactors, thereby influencing cellular homeostasis. A pathogenic missense VAPBP56S mutation causes familial Amyotrophic Lateral Sclerosis 8 (ALS8) in humans, with progressive degeneration of motor neurons. The precise mechanisms underlying the motor neurodegeneration remain poorly understood. In this study, we examine lipid imbalance in the brain of a Drosophila model of ALS8 (VAPBP58S). Specifically, we find that lipid homeostasis is disrupted in an age-dependent manner. Strikingly, cholesterol esters and sphingolipids show an age-dependent increase, while cholesterol shows a decrease. Intriguingly, from a cellular perspective, despite the accumulation of triacylglycerols (TAGs) in the brains of VAPBP58S animals, the increased neutral lipid species do not correlate with lipid droplets (LDs), which are fewer in density and smaller in size. Lipid imbalance and progressive motor dysfunction in VAPBP58S animals can be reversed by expressing VAPBWT, suggesting a relationship between VAPB activity and lipid flux. To uncover VAPBs role in lipid homeostasis, we modulate VAPB activity in neurons and glia to dissect out tissue-specific roles. We find that both cell types contribute to lipid homeostasis in differential ways. In glia, LD flux is strongly dependent on VAPB activity, a dependence further recapitulated in cultured human cell lines, suggesting evolutionary conservation of the regulatory mechanism. Thus, we hypothesise that lipid dysregulation constitutes a critical pathogenic feature of ALS8, with the VAPBP56S allele disrupting lipid homeostasis in the neuro-glial axis. Summary StatementThe ER-membrane tethering protein VAPB regulates lipid homeostasis

neuroscience↗

bioRxiv2026

Fos regulates age-dependent neuroinflammation in VAPBALS

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive loss of motor function. We have developed a Drosophila model of ALS8 (VAPBP58S) using CRISPR/Cas9 genome editing. VAPB is an ER-based adapter protein associated with and regulating intracellular membrane:membrane contact sites. VAPBP58S flies show progressive age-dependent motor deficits and a shortened lifespan, paralleling features of the human disease. VAPBP58S brains exhibit age-dependent neuroinflammation, as measured by whole-transcriptome quantitative mRNA sequencing, suggesting a broad, low-grade enhancement in signalling in multiple (Toll, IMD, Jak-STAT and Jun-kinase) immune pathways. We implicate glial cells in the brain as the site of brain inflammation and identify Drosophila Fos (Kayak) as a key modulator of age-dependent inflammation. In accordance, we find that overexpression of wild-type kayak or its dominant-active variant kayakK357R in glia reduces inflammation and, concomitantly, improves motor function. In contrast, knockdown of glial kayak accelerates age-dependent deterioration of motor function and enhances neuroinflammation. Our study underscores the roles of glial-modulated brain inflammation in dictating ALS8 progression and identifies kayak as a central negative regulator of neuroinflammation in disease. Summary StatementWe uncover definitive evidence for age-dependent neuroinflammation, originating from glial cells and regulated by Fos, as a key mechanism underlying Amyotrophic Lateral Sclerosis 8.

neuroscience↗

bioRxiv2026

Glial ceramide orchestrates Lipid Droplet homeostasis and age-dependent motor function in Drosophila

Glia cells have emerged as equal partners to neurons in the development and maintenance of the nervous system. In this study, we examine the roles of ceramide metabolism and intracellular transfer in glia, contrasting these with those of neurons. We find that glia are more sensitive to the cessation of ceramide synthesis than neurons. Knockdown of ER-localised ceramide synthesis enzymes in glia, but not in neurons, leads to age-dependent motor defects. Intriguingly, Lipid Droplet (LD) size and density are lowered when either glial ceramide is reduced or its transfer to the Golgi, by Ceramide Transfer protein (CERT), is disturbed. Glial CERT knockdown or disruption of its interaction with the ER tethering protein VAPB also affects both motor function and LD dynamics, highlighting the importance of targeted, efficient non-vesicular ceramide transfer at membrane contact sites. Our research implicates reduced flux through the sphingolipid pathway in glial cells as a critical determinant of adult motor function, with LDs serving as a sensitive diagnostic readout. As such, our study has implications for a host of human motor neuron diseases that show late-onset motor deficits. Summary StatementWe find that the production and transfer of ceramides in glial cells are required for both Lipid Droplet formation and maintenance of adult motor function.

neuroscience↗

bioRxiv2025

Mon1-Rab7 axis is essential for transport, localization and anchoring of oskar mRNA

Asymmetric localization of oskar mRNA to the posterior of the oocyte is a complex process driven by autonomous and non-cell autonomous mechanisms. The former includes Oskar protein that reinforces localization and anchoring of its mRNA through activation of endocytosis and regulation of actin cytoskeleton; the latter includes signals from the posterior follicle cells (PFCs) that regulates microtubule orientation for polarized transport. Here we identify Monensin Sensitivity 1 (Mon1), as a novel factor regulating anterior-posterior (A-P) patterning. Mon1 is an evolutionarily conserved activator of Rab7-a key regulator of the endo-lysosomal pathway. Embryos lacking maternal mon1 (mon1m) show mislocalized oskar and bicoid mRNAs leading to loss of patterning and lethality. In the mutant oocyte Staufen appears clumpy and the levels of Oskar protein and Par-1 is significantly reduced. Abnormal actin rings are seen in the ooplasm. Driving expression of mon1 in the germline rescues these phenotypes and restores viability. In contrast, expression in the PFC predominantly rescues the Par-1 phenotype with a modest effect on viability. We demonstrate that oskar mRNA interacts with Rab7 suggesting possible role for the Mon1-Rab7 axis in the transport of oskar. We show that Mon1 in the PFCs, regulates PIP2 levels to influence accumulation of Par-1 in the oocyte. We propose that Mon1 regulates oskar localization in two distinct ways: cell autonomously in the germline by regulating Rab7, and non-cell autonomously through the PFCs by regulating accumulation of Par-1. Summary statementMon1, an established Rab converter, has roles in embryonic axial patterning, modulating transport, localisation and anchoring of posteriorly localised mRNA during oocyte maturation. Mon1 influence is both cell autonomous, from within the oocyte and non-cell autonomous, through posterior follicle cells.

developmental biology↗

bioRxiv2025

Bioinformatics analysis identifies sequence determinants of enzymatic activity for the PHARC associated lipase ABHD12

In humans, PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract) is an early onset autosomal recessive neurological disorder caused by deleterious mutations to ABHD12 (/{beta}-hydrolase domain protein # 12). Biochemically, ABHD12 functions as a lipase, and catalyzes the hydrolysis of lysophosphatidylserine (lyso-PS) (lyso-PS lipase). By doing so, it controls the concentrations and signaling pathways regulated by this potent signaling lysophospholipid in the mammalian brain. While genetic mapping efforts have identified over 30 mutations in ABHD12 from human PHARC subjects, the biochemical activity of these pathogenic mutants remains unknown. To understand this, here, we performed an exhaustive bioinformatics survey, and collated ABHD12 protein sequences from various organisms across evolution. Next, based on sequence alignments and structural modeling, we identified functionally relevant conserved residues in the ABHD12 protein sequence that are potentially important for its enzymatic activity. To validate these in silico findings, we generated numerous mutants of murine ABHD12, including those associated with human PHARC subjects, and assayed them for their enzymatic activity. Taken together, these complementary in silico and biochemical studies provide the first thorough sequence-function relationship for mammalian ABHD12, especially relevant in the context of PHARC. Finally, our evolutionary analysis identified CG15111 as an ABHD12 ortholog in the fruit fly (Drosophila melanogaster), and enzymatic assays indeed confirmed that recombinant CG15111 has robust lyso-PS lipase activity. Flies serve as an excellent animal system to model various human neurological diseases, and the identification of CG15111 as a Drosophila melanogaster ABHD12 ortholog opens new avenues to study PHARC in fly models.

biochemistry↗