Biology subjects

Narayan, P. S.

Publications and source records attributed to Narayan, P. S..

3 recordsLinked to original sources

bioRxiv2026

APOE4 and INPP5D converge on membrane mechanics to regulate endocytosis in human astrocytes

Disrupted endocytosis is an early feature of Alzheimers disease (AD), but how genetic risk factors functionally impact this pathway remains unclear. Using isogenic human iPSC-derived astrocytes, we show that the AD risk variant, APOE4, impairs clathrin-mediated membrane curvature, clathrin-mediated endocytosis, and alters plasma membrane lipid saturation and tension. Compared to APOE3 astrocytes, APOE4 cells display an accumulation of flat clathrin structures, reduced maturation of clathrin-coated pits, decreased early endosomes, and reduced endocytic uptake. We then identify the AD risk gene INPP5D as a modifier that restores early endocytosis in APOE4 astrocytes by promoting clathrin curvature and maturation through a mechanism distinct from membrane tension regulation. Beyond effects on trafficking, INPP5D overexpression also reduces lipid droplet accumulation and attenuates inflammatory signaling, linking membrane dynamics to disease-associated astrocytic phenotypes. Together, these findings establish altered membrane mechanics as a proximal consequence of the APOE4 variant and identify endocytosis as a common node linking AD risk genes.

cell biology↗

bioRxiv2025

APOE genotypes differentially remodel the astrocytic lipiddroplet-associated proteome to shape lipid droplet dynamics

The lipids and proteins that comprise lipid droplets regulate several cellular functions including lipid storage, stress responses, and inflammation. Glial lipid droplets have been implicated in the pathogenesis and progression of Alzheimers disease (AD), yet the mechanisms linking genetic risk to lipid droplet biology remain unclear. Here we examined how APOE, the strongest genetic modulator of late-onset AD, impacts lipid droplet composition and dynamics. We defined the lipid droplet-associated proteome and lipidome in human induced pluripotent stem cell-derived astrocytes harboring the three common APOE genotypes: APOE2 (protective), APOE3 (neutral), and APOE4 (risk). Each APOE variant displays distinct lipid droplet-associated proteins and lipids. These molecular changes yield differences in lipophagy; lipid droplets in APOE2 astrocytes undergo autophagic turnover, whereas those in APOE4 astrocytes are resistant to degradation. These findings suggest that impaired lipid droplet clearance, rather than accumulation, distinguishes APOE4-associated AD risk, and may present a new metabolic node for modulating risk.

cell biology↗

bioRxiv2024

Triglyceride metabolism controls inflammation and APOE4-associated disease states in microglia

Microglia modulate their cell state in response to various stimuli. Changes to cellular lipids often accompany shifts in microglial cell state, but the functional significance of these metabolic changes remains poorly understood. In human induced pluripotent stem cell-derived microglia, we observed that both extrinsic activation (by lipopolysaccharide treatment) and intrinsic triggers (the Alzheimers disease-associated APOE4 genotype) result in accumulation of triglyceride-rich lipid droplets. We demonstrate that lipid droplet accumulation is not simply concomitant with changes in cell state but rather necessary for microglial activation. We discovered that both triglyceride biosynthesis and catabolism are needed for the transcription and secretion of proinflammatory cytokines and chemokines in response to extrinsic stimuli. Additionally, we reveal that triglyceride biosynthesis and catabolism are necessary for the activation-associated phagocytosis of multiple substrates including the disease-associated amyloid-beta peptide. In microglia harboring the Alzheimers disease risk APOE4 genotype, triglyceride-rich lipid droplets accumulate even in the absence of any external stimuli. Inhibiting triglyceride biosynthesis in APOE4 microglia not only modifies the transcription of immune response genes but also attenuates disease-associated transcriptional states. This work establishes that triglyceride metabolism is necessary for microglia to respond to extrinsic activation. In APOE4 microglia, this metabolic process modulates both immune signaling and a disease-associated transcriptional state. Importantly, our work identifies metabolic pathways that can be used to tune microglial immunometabolism in APOE4-associated disease.

cell biology↗