Biology subjects

Larrea, D.

Publications and source records attributed to Larrea, D..

9 recordsLinked to original sources

bioRxiv2026

Cholesterol availability drives the assembly of mitochondria-associated ER membranes

Mitochondria-associated endoplasmic reticulum (ER) membranes (MAM domains, or MAMs) are transient lipid raft domains of the ER that coordinate multiple cellular metabolic pathways and the ER-mitochondria communication. However, the mechanisms that drive their formation remain poorly understood. Here, we reveal that MAM assembly is dynamically regulated by the availability of plasma membrane (PM) cholesterol. We show that cholesterol delivered through high-density lipoproteins (HDLs) via the scavenger receptor class B type 1 (SR-B1) pathway is rapidly redistributed from the PM to the ER, where increased cholesterol availability promotes the assembly of MAM domains. In turn, MAM formation promotes the communication between the ER and mitochondria, the esterification of excess cholesterol and the suppression of cholesterol biosynthesis. Disruption of MAMs uncouples these responses, altering cholesterol trafficking and metabolic adaptation to extracellular cholesterol. Our findings identify MAM as a dynamic metabolic regulator that translates changes in extracellular lipoprotein availability into coordinated intracellular metabolic responses and cellular adaptation.

cell 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↗

bioRxiv2024

The contribution of mitochondria-associated ER membranes to cholesterol homeostasis

Cellular demands for cholesterol are met by a balance between its biosynthesis in the endoplasmic reticulum (ER) and its uptake from lipoproteins. Cholesterol levels in intracellular membranes form a gradient maintained by a complex network of mechanisms including the control of the expression, compartmentalization and allosteric modulation of the enzymes that balance endogenous and exogenous sources of cholesterol. Low-density lipoproteins (LDLs) are internalized and delivered to lysosomal compartments to release their cholesterol content, which is then distributed within cellular membranes. High-density lipoproteins (HDLs), on the other hand, can transfer their cholesterol content directly into cellular membranes through the action of receptors such as the scavenger receptor B type 1 (SR-B1; gene SCARB1). We show here that SR-B1-mediated exogenous cholesterol internalization from HDL stimulates the formation of lipid-raft subdomains in the ER known as mitochondria-associated ER membranes (MAM), that, in turn, suppress de novo cholesterol biosynthesis machinery. We propose that MAM is a regulatory hub for cholesterol homeostasis that offers a novel dimension for understanding the intracellular regulation of this important lipid.

cell biology↗

bioRxiv2023

MFN2-dependent recruitment of ATAT1 coordinates mitochondria motility with alpha-tubulin acetylation and is disrupted in CMT2A

Acetylated microtubules play key roles in the regulation of mitochondria dynamics. It has however remained unknown if the machinery controlling mitochondria dynamics functionally interacts with the -tubulin acetylation cycle. Mitofusin-2 (MFN2), a large GTPase residing in the mitochondrial outer membrane and mutated in Charcot-Marie-Tooth type 2 disease (CMT2A), is a regulator of mitochondrial fusion, transport and tethering with the endoplasmic reticulum. The role of MFN2 in regulating mitochondrial transport has however remained elusive. Here we show that mitochondrial contacts with microtubules are sites of -tubulin acetylation, which occurs through the MFN2-mediated recruitment of -tubulin acetyltransferase 1 (ATAT1). We discover that this activity is critical for MFN2-dependent regulation of mitochondria transport, and that axonal degeneration caused by CMT2A MFN2 associated mutations, R94W and T105M, may depend on the inability to release ATAT1 at sites of mitochondrial contacts with microtubules. Our findings reveal a function for mitochondria in regulating acetylated -tubulin and suggest that disruption of the tubulin acetylation cycle play a pathogenic role in the onset of MFN2-dependent CMT2A. O_FIG O_LINKSMALLFIG WIDTH=193 HEIGHT=200 SRC="FIGDIR/small/532838v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@3db8eorg.highwire.dtl.DTLVardef@143821corg.highwire.dtl.DTLVardef@1132b13org.highwire.dtl.DTLVardef@1710383_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIMitochondria contacts with MTs are hotspots of -tubulin acetylation through the recruitment of ATAT1 by MFN2 C_LIO_LIMutations in MFN2 associated with CMT2A disease lose this activity by sequestering ATAT1 C_LIO_LIDistal axonal degeneration caused by loss of MFN2 depends on acetylated tubulin-mediated mitochondria transport C_LI eTOCRecruitment of ATAT1 to mitochondria by MFN2 is critical for axonal viability through the regulation of mitochondria transport, and is disrupted in CMT2A

cell biology↗

bioRxiv2022

Altered MAM function shifts mitochondrial metabolism in SOD1-mutant models of ALS

Mitochondrial defects are a common hallmark of familial and sporadic forms of amyotrophic lateral sclerosis (ALS). However, the origin of these defects, including reduced pyruvate metabolism and reduced oxygen consumption, is poorly understood. These metabolic functions are regulated in specialized endoplasmic reticulum (ER) domains in close contact with mitochondria, called mitochondrial-associated ER membranes (MAM). Recently it has been shown that MAM domains are disrupted in ALS, but the connection between MAM dysregulation and mitochondrial defects in ALS cells remains unclear. Using human embryonic stem cell (ESC)-derived motor neurons (hMNs) and mouse models with ALS-pathogenic mutations in superoxide dismutase 1 (SOD1), we found that the glycolytic deficiency in ALS is a direct consequence of the progressive disruption of MAM structure and function that hinders the use of glucose-derived pyruvate as a mitochondrial fuel and triggers a shift in mitochondrial substrates from pyruvate to fatty acids. This glycolytic deficiency, over time, induces significant alterations in mitochondrial electron flow and in the active/dormant (A/D) status of complex I in spinal cord, but not in brain. These data agree with a role for MAM in the maintenance and regulation of cellular glucose metabolism and suggest that MAM disruption in ALS could be the underlying cause of the bioenergetic deficits observed in the disease.

molecular biology↗

bioRxiv2020

Upregulated functionality of mitochondria-associated ER membranes in a mouse model of traumatic brain injury

Traumatic brain injury (TBI) can lead to neurodegenerative diseases such as Alzheimers disease (AD) through mechanisms that remain incompletely characterized. Similar to AD, TBI models present with cellular metabolic alterations and modulated cleavage of amyloid precursor protein (APP). Specifically, AD and TBI tissues display increases in amyloid-{beta} as well as its precursor, APP C-terminal fragment of 99 a.a. (C99). Our recent data in cell models of AD indicate that C99, due to its affinity for cholesterol, induces the formation of transient lipid raft domains in the ER known as mitochondria-associated ER membranes ("MAM" domains). The formation of these domains recruits and activates specific lipid metabolic enzymes that regulate cellular cholesterol trafficking and sphingolipid turnover. Increased C99 levels in AD cell models promote MAM formation and significantly modulate cellular lipid homeostasis. Here, these phenotypes were recapitulated in the controlled cortical impact (CCI) model of TBI in adult mice. Specifically, the injured cortex and hippocampus displayed significant increases in C99 and MAM activity, as measured by phospholipid synthesis, sphingomyelinase activity and cholesterol turnover. In addition, our cell type-specific lipidomics analyses revealed significant changes in microglial lipid composition that are consistent with the observed alterations in MAM-resident enzymes. Altogether, we propose that alterations in the regulation of MAM and relevant lipid metabolic pathways could contribute to the epidemiological connection between TBI and AD. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=128 SRC="FIGDIR/small/381756v2_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@12d0989org.highwire.dtl.DTLVardef@1cd1eb2org.highwire.dtl.DTLVardef@19a56caorg.highwire.dtl.DTLVardef@1b7f3e1_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2019

Cyb5r3 links FoxO1-dependent mitochondrial dysfunction with β-cell failure

ObjectiveDiabetes is characterized by pancreatic {beta}-cell dedifferentiation. Dedifferentiating {beta}-cells inappropriately metabolize lipids over carbohydrates and exhibit impaired mitochondrial oxidative phosphorylation. However, the mechanism linking the {beta}-cells response to an adverse metabolic environment with impaired mitochondrial function remains unclear.\n\nMethodsHere we report that the oxidoreductase cytochrome b5 reductase 3 (Cyb5r3) links FoxO1 signaling to {beta}-cell stimulus/secretion coupling by regulating mitochondrial function, reactive oxygen species generation, and NAD/NADH ratios.\n\nResultsExpression of Cyb5r3 is decreased in FoxO1-deficient {beta}-cells. Mice with {beta}-cell-specific deletion of Cyb5r3 have impaired insulin secretion resulting in glucose intolerance and diet-induced hyperglycemia. Cyb5r3-deficient {beta}-cells have a blunted respiratory response to glucose and display extensive mitochondrial and secretory granule abnormalities, consistent with altered differentiation. Moreover, FoxO1 is unable to maintain expression of key differentiation markers in Cyb5r3-deficient {beta}-cells, suggesting that Cyb5r3 is required for FoxO1-dependent lineage stability.\n\nConclusionsThe findings highlight a pathway linking FoxO1 to mitochondrial dysfunction that can mediate {beta}-cell failure.

molecular biology↗

bioRxiv2019

THE C99 FRAGMENT OF APP REGULATES CHOLESTEROL TRAFFICKING

The link between cholesterol homeostasis and the cleavage of the amyloid precursor protein (APP), and their relationship to the pathogenesis of Alzheimers disease (AD) is still unknown. Cellular cholesterol levels are regulated by a crosstalk between the plasma membrane (PM), where most of the cholesterol resides, and the endoplasmic reticulum (ER), where the protein machinery that regulates cholesterol resides. This crosstalk between PM and ER is believed to be regulated by lipid-sensing peptide(s) that can modulate the internalization of extracellular cholesterol and/or its de novo synthesis in the ER. Our data here indicates that the 99-aa C-terminal fragment of APP (C99), a cholesterol-binding peptide, regulates cholesterol trafficking between the PM and the ER. In AD models, increases in C99 provoke the upregulation of cholesterol internalization and its delivery to the ER, which in turn result into the loss of lipid homeostasis and the appearance of AD signatures, such as higher production of longer forms of amyloid {beta}. Our data suggest a novel role of C99 as mediator of cholesterol disturbances in AD, and as a potential early hallmark of the disease.

molecular biology↗

bioRxiv2018

APOE4 is Associated with Differential Regional Vulnerability to Bioenergetic Deficits in Aged APOE Mice

The {varepsilon}4 allele of apolipoprotein E (APOE) is the dominant genetic risk factor for late-onset Alzheimers disease (AD). However, the reason for the association between APOE4 and AD remains unclear. While much of the research has focused on the ability of the apoE4 protein to increase the aggregation and decrease the clearance of A{beta}, there is also an abundance of data showing that APOE4 negatively impacts many additional processes in the brain, including bioenergetics. In order to gain a more comprehensive understanding of the APOE4s role in AD pathogenesis, we performed a multi-omic analysis of APOE4 vs. APOE3 expression in the entorhinal cortex (EC) and primary visual cortex (PVC) of aged APOE mice. These studies revealed region-specific alterations in several bioenergetic pathways, including oxidative phosphorylation (OxPhos), the TCA-cycle and fatty acid metabolism. Follow-up analysis utilizing the Seahorse platform revealed decreased mitochondrial respiration in the hippocampus and cortex of aged APOE4 vs. APOE3 mice, but not in the EC of these mice. Additional studies, as well as the original multi-omic data suggest that bioernergetic pathways in the EC of aged APOE mice may be differentially regulated by APOE4 expression. Given the importance of the EC as one of the first regions to be affected by AD pathology in humans, this differential bionenergetic regulation observed in the EC vs. other brain regions of aged APOE4 mice may play an important role in the pathogenesis of AD, particularly among APOE4 carriers.

neuroscience↗