Biology subjects

Abumrad, N. A.

Publications and source records attributed to Abumrad, N. A..

7 recordsLinked to original sources

bioRxiv2025

Secretion and transfer of adipose lipoprotein lipase utilizes neutral sphingomyelinase 2 generated exosomes

Lipoprotein lipase (LPL) is critical for clearance of circulating triglycerides and for tissue fatty acid supply. LPL is primarily synthesized and secreted by adipocytes into the interstitium and must traffic from there to the abluminal/basolateral side of capillary endothelial cells. There, LPL binds glycosylphosphatidylinositol-anchored protein 1, GPIHBP1, which stabilizes the protein and facilitates its movement across the endothelial cells to the luminal side where it functions in hydrolysis of lipoprotein triglycerides. Importance of LPL traffic is supported by findings that rare mutations in GPIHBP1 cause hypertriglyceridemia. However our understanding of how LPL is secreted by adipocytes and traffics to endothelial cells is incomplete. Here we examined the possibility that secretion and traffic of adipocyte LPL might involve generation of small extracellular vesicles (sEVs/exosomes) which often mediate cell-cell communication. Proteomic analysis of sEVs secreted by adipocytes showed them enriched in LPL. To study LPL secretion and transfer we generated human derived pre-adipocytes (HPA) that stably express tagged LPL (FLAG and His epitopes). LPL pulldown and sEV isolation from HPA conditioned media documented that greater than 70% of secreted LPL is present in sEVs. The mechanism for LPL secretion in sEVs was found to involve the ESCRT-independent neutral sphingomyelinase 2 (nSMase2) pathway, as treatment with the nSMase2 inhibitor GW4869 reduced secretion by 80%. The above observations were reproduced using highly sensitive nanoparticle flow cytometry. The sEV associated LPL has lipolytic activity and it is released by heparin addition indicating it is on the sEV surface. In addition, using human derived microvascular endothelial cells with stable lentiviral expression of GPIHBP1 we show that LPL positive sEVs transfer LPL to these cells, but not to control cells without GPIHBP1. Our findings suggest that sEV formation by nSMase2 controls adipocyte LPL secretion and traffic, that sEVs protect LPL activity and facilitate LPL transfer to GPIHBP1 on endothelial cells.

cell biology↗

bioRxiv2025

Immune cells regulate circulating adipocyte extracellular vesicle levels in response to metabolic shifts

Extracellular vesicles (EVs) are now recognized as potent mediators of intercellular and inter-organ signaling and implicated in the pathogenesis of obesity and its associated comorbidities such as diabetes, cancer, cardiovascular disease, and neurodegeneration. Despite a surge of new functional information about EVs, we still lack a basic understanding of how endogenous EV levels are controlled to regulate inter-organ signaling. New flow cytometry technology has allowed us to study the regulation of circulating, endogenous EVs from metabolically relevant cell types like adipocytes. From this, we provide evidence for a paradigm of EV regulation where tissue resident immune cells, predominantly macrophages, clear EVs released by local tissue cells or EVs entering the tissue from circulation, an activity that determines circulating EV levels. In obesity, EV uptake by adipose tissue immune cells is reduced, concomitant with increased circulating adipocyte-specific EVs (adipoEVs) and reduced EV clearance rates. AdipoEVs are significantly elevated in mouse circulation from one day to 20 weeks of high-fat feeding. In humans we found that adipocyte EV levels negatively correlate with whole-body and liver insulin sensitivity and are not associated with adipose mass. This work suggests that tissue resident immune cells act as a gatekeeper for tissue EV entry into circulation and are thereby a major regulator of inter-organ EV signaling.

physiology↗

bioRxiv2025

Extracellular vesicles from chylomicron-treated endothelial cells drive macrophage inflammation

BackgroundMovement of circulating lipids into tissues and arteries requires transfer across the endothelial cell barrier. This process allows the heart to obtain fatty acids (FAs), its chief source of energy and apolipoprotein B (apoB)-containing lipoproteins to cross the arterial endothelial barrier leading to cholesterol accumulation in the subendothelial space. Multiple studies have established elevated postprandial triglyceride-rich lipoproteins (TRLs) as an independent risk factor for cardiovascular disease (CVD). We explored how chylomicrons affect ECs and transfer their FAs across the EC barrier. MethodsWe had reported that media from chylomicron-treated ECs leads to lipid droplet (LD) formation in macrophages. To determine the responsible component of this media, we assessed whether removing the extracellular vesicles (EVs) would obviate this effect. EVs from control and treated cells were then characterized by protein, lipid and microRNA (miR) content. We also studied the EV-induced transcription changes in macrophages and ECs and whether knockdown of scavenger receptor-BI (SR-BI) altered these responses. In addition, using chylomicrons labeled with [13C]oleate, we studied the uptake and release of this labed by ECs. ResultsChylomicron treatment of ECs led to an inflammatory response that included production of EVs that drove macrophage LD accumulation. The EVs contained little free fatty acids and triglyceride, but abundant phospholipids and diacylglycerols. In concert with this, [13]C labeled chylomicron triglycerides exited ECs primarily in phospholipids. EVs from chylomicron treated versus untreated ECs were larger, more abundant, and contained specific miRs. Treatment of macrophages and naive ECs with media from chylomicron-treated ECs increased expression of inflammatory genes. ConclusionsEC chylomicron metabolism produces EVs that increase macrophage inflammation and create LDs. Media containing these EVs also increases EC inflammation, illustrating an autocrine inflammatory process. FAs within chylomicron triglycerides are converted to phospholipids within EVs. Thus, EC uptake of chylomicrons constitutes an important pathway for vascular inflammation and tissue lipid acquisition.

cell biology↗

bioRxiv2024

Insulin regulates lymphatic endothelial function via palmitoylation

Lipid metabolism plays a critical role in lymphatic endothelial cell (LEC) development and maintenance. Altered lipid metabolism is associated with loss of lymphatic vessel integrity, which compromises organ function, protective immunity, and metabolic health. However, the role of lipid metabolism in LEC function is not well understood. Insulin is a key regulator of lipid metabolism and protein palmitoylation, the reversible post-translational protein modification by palmitate that affects protein stability, trafficking, protein-protein, and protein-membrane interactions. Human LECs are highly sensitive to insulin and can develop insulin resistance in vitro, but whether insulin regulates LEC protein palmitoylation and function is unknown. To examine the role of palmitoylation in LEC function, we generated the first palmitoylation proteomics profile in human LECs, validated insulin regulated targets and profiled differences in palmitoylation between lymphatic and blood endothelial cells. Palmitoylation occurred primarily in proteins involved in LEC vesicular or membrane trafficking, translation initiation, and in those found in membrane rafts. Insulin enriched palmitoylation of LEC proteins involved in GTPase signaling, ubiquitination, and junctional anchoring. We also determined that the long-chain fatty acid receptor CD36 mediates optimal lymphatic palmitoylation. CD36 silencing in LECs doubled palmitoylation targets involving proteins related to inflammation and neutrophil degranulation contributing to an activated inflamed endothelium. These results suggest that the coordination of the process of palmitoylation is critical for normal lymphatic endothelial function.

physiology↗

bioRxiv2024

MXRA8 promotes adipose tissue whitening to drive obesity

Matrix-remodeling associated 8 (MXRA8), also known as Dual immunoglobulin domain cell adhesion molecule (DICAM), is a type 1 transmembrane protein that reportedly binds the V{beta}3 integrin1 and regulates the differentiation of osteoclasts2 and chondrocytes3, tumor growth4, T cell trafficking5, and angiogenesis6. MXRA8 is also an essential entry receptor for chikungunya virus and other related arthritogenic alphaviruses.7-9 We compared MXRA8 expression in 51 tissues in the Human Protein Atlas and found it is most highly expressed in white adipose tissue (WAT), however the function of MXRA8 in WAT is unknown. Here, we found that MXRA8 expression in WAT is increased in people with obesity and that this response is also observed in a mouse model of high fat-diet (HFD)-induced obesity. Single-nucleus RNA sequencing and high-dimensional spectral flow cytometry analyses revealed that MXRA8 is expressed predominantly by adipocyte progenitor (AP) cells and mature adipocytes. MXRA8 mutant primary adipocytes from inguinal (i)WAT exhibited increased expression of Uncoupling protein 1 (UCP1), a thermogenic protein expressed by beige and brown adipocytes that limits obesity pathogenesis.10-12 Indeed, MXRA8 mutant mice fed a HFD had preserved UCP1+ beige and brown adipocytes and were protected from HFD-induced obesity in a UCP1-dependent manner. Collectively, these findings indicate that MXRA8 promotes whitening of beige and brown adipose tissues to drive obesity pathogenesis and identify MXRA8 as a possible therapeutic target to treat obesity and associated metabolic diseases.

physiology↗

bioRxiv2021

Monoacylglycerol disrupts Golgi structure and perilipin 2 association with lipid droplets

The two major products of intestinal triacylglycerol digestion and lipoprotein lipolysis are monoacylglycerols (MAG) and fatty acids. In the gut, these products are taken up by enterocytes and packaged into perilipin-coated cytosolic lipid droplets and then secreted as chylomicrons. We observed that fat feeding or intragastric administration of triacylglycerol oil caused the enterocyte Golgi to fragment into submicron puncta dispersed throughout the cytosol. Further, this apparent Golgi dispersion was also observed in cultured fibroblasts after treatment with fat (cream) and pancreatic lipase, but not when treated with deactivated lipase. We therefore hypothesized that a hydrolytic fat product, specifically monoacylglycerols, fatty acids or a combination of these molecules can trigger Golgi fragmentation. Disruption of coatomer function is known to cause Golgi to fuse with the ER, and blocks perilipin 2 delivery to lipid droplets. Thus, we assessed the effects of MAG on coatomer distribution, Golgi structure and perilipin 2 localization. We found that MAG, but not fatty acids, dispersed coatomer from the Golgi, fragmented the Golgi and caused perilipin 2 to accumulate on cellular membranes. Thus, our findings suggest that monoacylglycerol production during digestion disperses the Golgi, possibly by altering coatomer function, which may regulate metabolite transport between the ER and Golgi.

cell biology↗

bioRxiv2020

Oxidized Lipids and CD36-Mediated Lipid Peroxidation in CD8 T Cells Suppress Anti-Tumor Immune Responses

T cell metabolic fitness plays a pivotal role in anti-tumor immunity and metabolic deregulation causes T cell dysfunction (i.e., exhaustion) in cancer. We identify that the scavenger receptor CD36 limits anti-tumor CD8+ T cell effector functions through lipid peroxidation. In murine tumors, oxidized phospholipids (OxPLs) were highly abundant and CD8+ TILs increased uptake and accumulation of lipids and lipid peroxidation. Functionally exhausted CD8+ TILs substantially increased CD36 expression and CD36-deficient CD8+ TILs had more robust anti-tumor activity and cytokine production than wild-type cells. We further show that CD36 promotes uptake of oxidized low-density lipoproteins (OxLDL) and induces lipid peroxidation in CD8+ TILs, and OxLDL inhibits CD8+ T cell functions in a CD36-dependent manner. Moreover, glutathione peroxidase 4 (GPX4) over-expression lowers lipid peroxidation and restores functionalities in CD8+ TILs. These results define a key role for an oxidized lipid-CD36 axis in promoting intratumoral CD8+ T cell dysfunction.

immunology↗