Dynamic metabolism of endothelial triglycerides protects against atherosclerosis in mice

Apolipoprotein B-containing lipoproteins in atherogenesis

Apolipoprotein B (apoB) is the main structural protein of LDLs, triglyceride-rich lipoproteins and lipoprotein(a), and is crucial for their formation, metabolism and atherogenic properties. In this Review, we present insights into the role of apoB-containing lipoproteins in atherogenesis, with an emphasis on the mechanisms leading to plaque initiation and growth. LDL, the most abundant cholesterol-rich lipoprotein in plasma, is causally linked to atherosclerosis. LDL enters the artery wall by transcytosis and, in vulnerable regions, is retained in the subendothelial space by binding to proteoglycans via specific sites on apoB. A maladaptive response ensues. This response involves modification of LDL particles, which promotes LDL retention and the release of bioactive lipid products that trigger inflammatory responses in vascular cells, as well as adaptive immune responses. Resident and recruited macrophages take up modified LDL, leading to foam cell formation and ultimately cell death due to inadequate cellular lipid handling. Accumulation of dead cells and cholesterol crystallization are hallmarks of the necrotic core of atherosclerotic plaques. Other apoB-containing lipoproteins, although less abundant, have substantially greater atherogenicity per particle than LDL. These lipoproteins probably contribute to atherogenesis in a similar way to LDL but might also induce additional pathogenic mechanisms. Several targets for intervention to reduce the rate of atherosclerotic lesion initiation and progression have now been identified, including lowering plasma lipoprotein levels and modulating the maladaptive responses in the artery wall.

Drugs for dyslipidaemia: the legacy effect of the Scandinavian Simvastatin Survival Study (4S)

Since the discovery of statins and the Scandinavian Simvastatin Survival Study (4S) results three decades ago, remarkable advances have been made in the treatment of dyslipidaemia, a major risk factor for atherosclerotic cardiovascular disease. Safe and effective statins remain the cornerstone of therapeutic approach for this indication, including for children with genetic dyslipidaemia, and are one of the most widely prescribed drugs in the world. However, despite the affordability of generic statins, they remain underutilised worldwide. The use of ezetimibe to further decrease plasma LDL cholesterol and the targeting of other atherogenic lipoproteins, such as triglyceride-rich lipoproteins and lipoprotein(a), are likely to be required to further reduce atherosclerotic cardiovascular disease events. Drugs directed at these lipoproteins, including gene silencing and editing methods that durably suppress the production of proteins, such as PCSK9 and ANGPTL3, open novel therapeutic options to further reduce the development of atherosclerotic cardiovascular disease.

Intracellular endothelial cell metabolism in vascular function and dysfunction

Endothelial cells (ECs) form the inner lining of blood vessels that is crucial for vascular function and homeostasis. They regulate vascular tone, oxidative stress, and permeability. Dysfunction leads to increased permeability, leukocyte adhesion, and thrombosis. ECs undergo metabolic changes in conditions such as wound healing, cancer, atherosclerosis, and diabetes, and can influence disease progression. We discuss recent research that has revealed diverse intracellular metabolic pathways in ECs that are tailored to their functional needs, including lipid handling, glycolysis, and fatty acid oxidation (FAO). Understanding EC metabolic signatures in health and disease will be crucial not only for basic biology but can also be exploited when designing new therapies to target EC-related functions in different vascular diseases.

Thrombolysis exacerbates cerebrovascular injury after ischemic stroke via a VEGF-B dependent effect on adipose lipolysis

Cerebrovascular injuries leading to edema and hemorrhage after ischemic stroke are common. The mechanisms underlying these events and how they are connected to known risk factors for poor outcome, like obesity and diabetes, is relatively unknown. Herein we demonstrate that increased adipose tissue lipolysis is a dominating risk factor for the development of a compromised cerebrovasculature in ischemic stroke. Reducing adipose lipolysis by VEGF-B antagonism improved vascular integrity by reducing ectopic cerebrovascular lipid deposition. Thrombolytic therapy in ischemic stroke using tissue plasminogen activator (tPA) leads to increased risk of hemorrhagic complications, substantially limiting the use of thrombolytic therapy. We provide evidence that thrombolysis with tPA promotes adipose tissue lipolysis, leading to a rise in plasma fatty acids and lipid accumulation in the ischemic cerebrovasculature after stroke. VEGF-B blockade improved the efficacy and safety of thrombolysis suggesting the potential use of anti-VEGF-B therapy to extend the therapeutic window for stroke management.

Lipid droplets sequester palmitic acid to disrupt endothelial ciliation and exacerbate atherosclerosis in male mice

Disruption of ciliary homeostasis in vascular endothelial cells has been implicated in the development of atherosclerosis. However, the molecular basis for the regulation of endothelial cilia during atherosclerosis remains poorly understood. Herein, we provide evidence in male mice that the accumulation of lipid droplets in vascular endothelial cells induces ciliary loss and contributes to atherosclerosis. Triglyceride accumulation in vascular endothelial cells differentially affects the abundance of free fatty acid species in the cytosol, leading to stimulated lipid droplet formation and suppressed protein S-palmitoylation. Reduced S-palmitoylation of ciliary proteins, including ADP ribosylation factor like GTPase 13B, results in the loss of cilia. Restoring palmitic acid availability, either through pharmacological inhibition of stearoyl-CoA desaturase 1 or a palmitic acid-enriched diet, significantly restores endothelial cilia and mitigates the progression of atherosclerosis. These findings thus uncover a previously unrecognized role of lipid droplets in regulating ciliary homeostasis and provide a feasible intervention strategy for preventing and treating atherosclerosis.

Neuronal lipid droplets play a conserved and sex-biased role in maintaining whole-body energy homeostasis

Lipids are essential for neuron development and physiology. Yet, the central hubs that coordinate lipid supply and demand in neurons remain unclear. Here, we combine invertebrate and vertebrate models to establish the presence and functional significance of neuronal lipid droplets (LD) in vivo. We find that LD are normally present in neurons in a non-uniform distribution across the brain, and demonstrate triglyceride metabolism enzymes and lipid droplet-associated proteins control neuronal LD formation through both canonical and recently-discovered pathways. Appropriate LD regulation in neurons has conserved and male-biased effects on whole-body energy homeostasis across flies and mice, specifically neurons that couple environmental cues with energy homeostasis. Mechanistically, LD-derived lipids support neuron function by providing phospholipids to sustain mitochondrial and endoplasmic reticulum homeostasis. Together, our work identifies a conserved role for LD as the organelle that coordinates lipid management in neurons, with implications for our understanding of mechanisms that preserve neuronal lipid homeostasis and function in health and disease.

Oxysterol Sensing Through GPR183 Triggers Endothelial Senescence in Hypertension

BACKGROUND

Despite endothelial dysfunction being an initial step in the development of hypertension and associated cardiovascular/renal injuries, effective therapeutic strategies to prevent endothelial dysfunction are still lacking. GPR183 (G protein-coupled receptor 183), a recently identified G protein-coupled receptor for oxysterols and hydroxylated metabolites of cholesterol, has pleiotropic roles in lipid metabolism and immune responses. However, the role of GPR183 in the regulation of endothelial function remains unknown.

METHODS

Endothelial-specific GPR183 knockout mice were generated and used to examine the role of GPR183 in endothelial senescence by establishing 2 independent hypertension models: desoxycorticosterone acetate/salt-induced and Ang II (angiotensin II)-induced hypertensive mice. Echocardiography, transmission electron microscopy, blood pressure measurement, vasorelaxation response experiments, flow cytometry analysis, and chromatin immunoprecipitation analysis were performed in this study.

RESULTS

Endothelial GPR183 was significantly induced in hypertensive mice, which was further confirmed in renal biopsies from subjects with hypertensive nephropathy. Endothelial-specific deficiency of GPR183 markedly alleviated cardiovascular and renal injuries in hypertensive mice. Moreover, we found that GPR183 regulated endothelial senescence in both hypertensive mice and aged mice. Mechanistically, GPR183 disrupted circadian signaling by inhibiting PER1 (period circadian regulator 1) expression, thereby facilitating endothelial senescence and dysfunction through the cAMP (cyclic adenosine monophosphate)/PKA (protein kinase A)/CREB (cAMP-response element binding protein) signaling pathway. Importantly, pharmacological inhibition of the oxysterol-GPR183 axis by NIBR189 or clotrimazole ameliorated endothelial senescence and cardiovascular/renal injuries in hypertensive mice.

CONCLUSIONS

This study discovers a previously unrecognized role of GPR183 in promoting endothelial senescence. Pharmacological targeting of GPR183 may be an innovative therapeutic strategy for hypertension and its associated complications.

Endothelial-adipocyte Cx43 Mediated Gap Junctions Can Regulate Adiposity

Obesity is a multifactorial metabolic disorder associated with endothelial dysfunction and increased risk of cardiovascular disease. Adipose capillary adipose endothelial cells (CaECs) plays a crucial role in lipid transport and storage. Here, we investigated the mechanisms underlying CaEC-adipocyte interaction and its impact on metabolic function. Single-cell RNA sequencing (scRNAseq) revealed an enrichment of fatty acid handling machinery in CaECs from high fat diet (HFD) mice, suggesting their specialized role in lipid metabolism. Transmission electron microscopy (TEM) confirmed direct heterocellular contact between CaECs and adipocytes. To model this, we created an in vitro co-culture transwell system to model the heterocellular contact observed with TEM. Contact between ECs and adipocytes in vitro led to upregulation of fatty acid binding protein 4 in response to lipid stimulation, hinting intercellular signaling may be important between ECs and adipocytes. We mined our and others scRNAseq datasets to examine which connexins may be present in adipose capillaries and adipocytes and consistently identified connexin 43 (Cx43) in mouse and humans. Genetic deletion of endothelial Cx43 resulted in increased epididymal fat pad (eWAT) adiposity and dyslipidemia in HFD mice. Consistent with this observation, phosphorylation of Cx43 at serine 368, which closes gap junctions, was increased in HFD mice and lipid-treated ECs. Mice resistant to this post-translational modification, Cx43S368A, were placed on an HFD and were found to have reduced eWAT adiposity and improved lipid profiles. These findings suggest Cx43-mediated heterocellular communication as a possible regulatory mechanism of adipose tissue function.

Endothelial lipid droplets drive atherosclerosis and arterial hypertension

Lipid droplets (LDs) are essential for cellular pathophysiology. In two recent reports, Kim et al. and Boutagy et al. show that accumulation of LDs in endothelial cells (ECs) elevates blood pressure and accelerates progression of atherosclerosis. These findings identify a novel mechanism of EC lipid metabolism which drives cardiometabolic diseases.

In the Beginning, Lipoproteins Cross the Endothelial Barrier

Atherosclerosis begins with the infiltration of cholesterol-containing lipoproteins into the arterial wall. White blood cell (WBC)-associated inflammation follows. Despite decades of research using genetic and pharmacologic methods to alter WBC function, in humans, the most effective method to prevent the initiation and progression of disease remains low-density lipoprotein (LDL) reduction. However, additional approaches to reducing cardiovascular disease would be useful as residual risk of events continues even with currently effective LDL-reducing treatments. Some of this residual risk may be due to vascular toxicity of triglyceride-rich lipoproteins (TRLs). Another option is that LDL transcytosis continues, albeit at reduced rates due to lower circulating levels of this lipoprotein. This review will address these two topics. The evidence that TRLs promote atherosclerosis and the processes that allow LDL and TRLs to be taken up by endothelial cells leading to their accumulation with the subendothelial space.

Lipid droplets in the endothelium: The missing link between metabolic syndrome and cardiovascular disease?

The physiology of lipid droplets (LDs) has been most extensively characterized in adipocytes, but LDs also accumulate in endothelial cells lining blood vessels in response to changing levels of triglycerides. In recent issues of the JCI, two independent papers highlight a direct role of endothelial LDs in the genesis of hypertension and atherosclerosis in rodent models. Kim et al. demonstrated that accumulation of LDs in the endothelium leads to hypertension, impairs endothelial function, and accelerates atherosclerosis. Boutagy, Gamez-Mendez, et al. knocked out Atgl in the endothelium and confirmed triglyceride accumulation in endothelial cells that was associated with reduced NO synthesis and impaired endothelial-dependent vasodilation. These data suggest that enhancing triglyceride breakdown in the endothelium could provide a treatment target for patients with metabolic syndrome.