Biology subjects

Fernandez-Bernal, A.

Publications and source records attributed to Fernandez-Bernal, A..

2 recordsLinked to original sources

bioRxiv2026

A sphingomyelin-cholesterol complex regulates TLR4 activation in microglia

Microglial activation in response to lipopolysaccharide (LPS) requires Toll-like receptor 4 (TLR4) redistribution into cholesterol- and sphingolipid-rich membrane domains, yet the lipid determinants of this process remain unclear. Here, we identify cholesterol accessibility as a key driver of TLR4-dependent microglial activation. We show that LPS increases cholesterol uptake and mobilization, whereas inhibition of intracellular cholesterol trafficking or the plasma membrane-to-ER cholesterol transporter Aster attenuates inflammatory responses. Scavenger receptor class B type 1 (SR-B1) mediates LPS-induced cholesterol uptake, and its inhibition suppresses TLR4 signaling, receptor recruitment to detergent-resistant membrane domains, and TLR4 endocytosis without altering bulk cellular cholesterol. Instead, SR-B1 inhibition remodels the sphingolipidome and expands the sphingomyelin-associated cholesterol pool, as detected by OlyA, while LPS promotes remodeling of this pool and increases accessible cholesterol detected by D4H. Manipulation of sphingomyelin-cholesterol interactions alters membrane properties and TLR4 trafficking, while stabilization of these complexes suppresses inflammatory activation. In vivo, LPS induces remodeling of sphingomyelin-associated cholesterol in microglia, whereas Alzheimer's disease-related ApoE4/Trem2R47H microglia show impaired cholesterol-pool remodeling and enhanced inflammatory responses. Together, these findings establish sphingolipid-dependent cholesterol accessibility as a key regulatory layer controlling TLR4 organization and microglial inflammatory activation, positioning SR-B1 as an upstream regulator of this lipid-signaling axis.

molecular biology↗

bioRxiv2025

Upregulation of MAM by C99 disrupts ACSL4 activity and phospholipid homeostasis in Alzheimer disease.

The structure and function of cellular and intracellular membranes are critically governed by the fatty acid (FA) composition of phospholipids (PLs), which is dynamically regulated by a network of enzymes that fine-tune lipid species according to cellular demands. In this study, we identify a mechanism through which the formation of mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) modulates the activity of the acyl-CoA synthetase long-chain family member 4 (ACSL4), an enzyme that channels polyunsaturated fatty acids (PUFAs) into phosphatidylcholine (PC) via the Lands cycle. Through integrated biochemical, proteomic, and lipidomic analyses in both cellular and animal models, we demonstrate that MAM formation enhances ACSL4 activity, promoting arachidonic acid (AA) activation and its preferential incorporation into PC in concert with the MAM-localized lysophospholipid acyltransferase 4 (LPCAT4). Our findings further uncover an unexpected link between this pathway and the pathogenesis of Alzheimers disease (AD). We show that elevated levels of C99--the {beta}-secretase cleavage product of amyloid precursor protein (APP)--induce MAM remodeling through cholesterol clustering, which in turn activates ACSL4 and alters PC composition. This effect is mirrored in AD models as well as in fibroblasts, neurons, and immune cells derived from both familial and sporadic AD patients, all of which exhibit chronically increased C99 levels, heightened ACSL4 activity, and enrichment of PUFA-containing PC species, leading to lipid imbalance and membrane dysfunction. Together, these results establish MAMs as dynamic lipid-regulatory hubs that coordinate ACSL4-dependent membrane remodeling and highlight the contribution of MAM dysregulation to lipid abnormalities observed in AD.

molecular biology↗