👤 Clay F Semenkovich

Genetic variants near LYPLAL1 are associated with Metabolic dysfunction-Associated Steatotic Liver Disease (MASLD) in humans, but their impact on LYPLAL1 function is unknown. We identified LYPLAL1 loss-of-function variants from UK BioBank (UKBB) whole-exome sequencing data that had AlphaMissense or GPN-MSA scores in the top 20% of LYPLAL1 variants for being disruptive. We aggregated these variants and carried out burden analysis for effects on MRI Proton Density-Fat Fraction (MRI-PDFF) and ICD-based MASLD in UKBB. Rare loss-of-function LYPLAL1 variants were associated with reduced MRI-PDFF and ICD diagnosed MASLD across sexes. We used CRISPR to knockout and overexpress LYPLAL1 in human hepatoma cells (HuH-7), measuring lipid content, lipid uptake/export, and changes in de novo lipogenesis and mitochondrial β-oxidation. LYPLAL1 subcellular localization was determined by overexpressing LYPLAL1-HA tagged protein. We purified GST tagged human LYPLAL1 protein and conducted in vitro tests for esterase and depalmitoylase activity. Knocking out LYPLAL1 reduced triglycerides biochemically as well as lipid intensity after oleic (18:1, n-9) acid treatment. LYPLAL1 KO cells had increased expression of PPARα and MLXIPL, increased mitochondrial β-oxidation, and reduced capacity to both import fatty acids (FAs) and export lipoproteins. Overexpression of LYPLAL1 increased lipid droplet accumulation and decreased PPARα and MLXIPL. LYPLAL1-HA is partly localized to mitochondria when treated with oleic acid. Biochemical analyses showed that LYPLAL1 has strong esterase activity but lacks depalmitoylase activity. Reduction of LYPLAL1 esterase function likely increases β-oxidation of FAs in mitochondria through PPARα and MLXIPL and decreases FA import to protect against lipid accumulation in human liver cancer cells. Together, our results indicate that LYPLAL1 loss-of-function protects against MASLD in Europeans and in vitro, LYPLAL1 is an esterase for short-chain substrates which is involved in the regulation of mitochondrial β-oxidation and uptake of fatty acids, influencing lipid accumulation in the liver. Show less

Adipose tissue mass is maintained by a balance between lipolysis and lipid storage. The contribution of adipose tissue lipogenesis to fat mass, especially in the setting of high-fat feeding, is considered minor. Here we investigated the effect of adipose-specific inactivation of the peroxisomal lipid synthetic protein PexRAP on fatty acid synthase (FASN)-mediated lipogenesis and its impact on adiposity and metabolic homeostasis. To explore the role of PexRAP in adipose tissue, we metabolically phenotyped mice with adipose-specific knockout of PexRAP. Bulk RNA sequencing was used to determine transcriptomic responses to PexRAP deletion and Adipose-specific PexRAP deletion promoted diet-induced obesity and insulin resistance through activation of de novo lipogenesis. Mechanistically, PexRAP inactivation inhibited the flux of carbons to ethanolamine plasmalogens. This increased the nuclear PC/PE ratio and promoted cholesterol mislocalization, resulting in activation of liver X receptor (LXR), a nuclear receptor known to be activated by increased intracellular cholesterol. LXR activation led to increased expression of the phospholipid remodeling enzyme LPCAT3 and induced FASN-mediated lipogenesis, which promoted diet-induced obesity and insulin resistance. These studies reveal an unexpected role for peroxisome-derived lipids in regulating LXR-dependent lipogenesis and suggest that activation of lipogenesis, combined with dietary lipid overload, exacerbates obesity and metabolic dysregulation. Show less

Fatty acid metabolism is perturbed in atherosclerotic lesions, but whether it affects lesion formation is unknown. To determine whether fatty acid synthesis affects atherosclerosis, we inactivated fatty-acid synthase (FAS) in macrophages of apoE-deficient mice. Serum lipids, body weight, and glucose metabolism were the same in FAS knock-out in macrophages (FASKOM) and control mice, but blood pressure was lower in FASKOM animals. Atherosclerotic extent was decreased 20-40% in different aortic regions of FASKOM as compared with control mice on Western diets. Foam cell formation was diminished in FASKOM as compared with wild type macrophages due to increased apoAI-specific cholesterol efflux and decreased uptake of oxidized low density lipoprotein. Expression of the anti-atherogenic nuclear receptor liver X receptor alpha (LXRalpha; Nr1h3) and its downstream targets, including Abca1, were increased in FASKOM macrophages, whereas expression of the potentially pro-atherogenic type B scavenger receptor CD36 was decreased. Peroxisome proliferator-activated receptor alpha (PPARalpha) target gene expression was decreased in FASKOM macrophages. PPARalpha agonist treatment of FASKOM and wild type macrophages normalized PPARalpha target gene expression as well as Nr1h3 (LXRalpha). Atherosclerotic lesions were more extensive when apoE null mice were transplanted with LXRalpha-deficient/FAS-deficient bone marrow as compared with LXRalpha-replete/FAS-deficient marrow, consistent with anti-atherogenic effects of LXRalpha in the context of FAS deficiency. These results show that macrophage FAS deficiency decreases atherosclerosis through induction of LXRalpha and suggest that FAS, which is induced by LXRalpha, may generate regulatory lipids that cause feedback inhibition of LXRalpha in macrophages. Show less