Intracapillary LPL levels in brown adipose tissue, visualized with an antibody-based approach, are regulated by ANGPTL4 at thermoneutral temperatures.

Lipoprotein lipase (LPL) is secreted into the interstitial spaces by parenchymal cells and then transported into capillaries by GPIHBP1. LPL carries out the lipolytic processing of triglyceride (TG)-rich lipoproteins (TRLs), but the tissue-specific regulation of LPL is incompletely understood. Plasma levels of TG hydrolase activity after heparin injection are often used to draw inferences about intravascular LPL levels, but the validity of these inferences is unclear. Moreover, plasma TG hydrolase activity levels are not helpful for understanding LPL regulation in specific tissues. Here, we sought to elucidate LPL regulation under thermoneutral conditions (30 °C). To pursue this objective, we developed an antibody-based method to quantify (in a direct fashion) LPL levels inside capillaries. At 30 °C, intracapillary LPL levels fell sharply in brown adipose tissue (BAT) but not heart. The reduced intracapillary LPL levels were accompanied by reduced margination of TRLs along capillaries. ANGPTL4 expression in BAT increased fourfold at 30 °C, suggesting a potential explanation for the lower intracapillary LPL levels. Consistent with that idea, Angptl4 deficiency normalized both LPL levels and TRL margination in BAT at 30 °C. In Gpihbp1-/- mice housed at 30 °C, we observed an ANGPTL4-dependent decrease in LPL levels within the interstitial spaces of BAT, providing in vivo proof that ANGPTL4 regulates LPL levels before LPL transport into capillaries. In conclusion, our studies have illuminated intracapillary LPL regulation under thermoneutral conditions. Our approaches will be useful for defining the impact of genetic variation and metabolic disease on intracapillary LPL levels and TRL processing.

Correlation between chylomicronemia diagnosis scores and post-heparin lipoprotein lipase activity.

INTRODUCTION: Sustained chylomicronemia is a defect in post-prandial triglyceride management characterized by severe hypertriglyceridemia (triglyceride > 10 mmol/L) due to functional or genetic defects in lipoprotein lipase (LPL)-mediated triglyceride-rich lipoprotein lipolysis. Familial chylomicronemia syndrome (FCS) is a rare mendelian form of chylomicronemia caused by loss-of-function variants in LPL or LPL-related genes. Most individuals with chylomicronemia however present multifactorial chylomicronemia (MCS), in which LPL bio-availability and activity are variable. FCS and MCS differ in terms of clinical characteristics and risk of disease, and diagnosis scoring systems have been proposed to accurately distinguish FCS from MCS. OBJECTIVE: The aim of this study was to assess the strength of the relationship between plasma post-heparin LPL activity and two published chylomicronemia diagnosis scoring systems. DESIGN AND METHODS: Post-heparin plasma LPL activity was measured using colorimetric assays in a sample of 29 subjects with sustained chylomicronemia (20 FCS and 9 MCS). Chylomicronemia diagnosis scores were obtained for all subjects using the scoring system A (model A), which integrates apolipoprotein B and free glycerol, a surrogate marker of triglyceride hydrolysis, and the scoring system B (model B). Correlation analyses were conducted to estimate the linear relationship between LPL activity and the two diagnosis scoring systems. RESULTS: There was a significant (p < 0.001) difference in post-heparin LPL activity between FCS and MCS. Both scoring systems significantly correlated with post-heparin LPL activity (model A: rs = -0.64, p < 0.001; model B: rs = -0.54, p = 0.002). CONCLUSIONS: These result suggest that chylomicronemia diagnosis scoring systems correlate with LPL activity and adequately contribute to distinguish FCS from MCS.

Promotion effect of salt on intramuscular neutral lipid hydrolysis during dry-salting process of porcine (biceps femoris) muscles by inducing phosphorylation of ATGL, HSL and their regulatory proteins of Perilipin1, ABHD5 and G0S2.

Towards a better understanding of the formation mechanism of salt on intramuscular triglyceride (TG) hydrolysis occurring in biceps femoris (BF) muscles during dry-salting process, the changes of TG hydrolysis, TG hydrolysis activity and phosphorylation of adipose triglyceride lipase (ATGL) and hormone sensitive lipase (HSL) as well as their regulatory proteins (Perilipin1, ABHD5, G0S2) with different salt content (0%, 1%, 3%, 5%) and salting time (the first and third day) were analyzed. The results showed that dry-salting significantly increased the TG hydrolase activity and hydrolysis extent with salting process proceed (P < 0.05), especially upon the treatment with 3% amount of salt. The SDS-PAGE and Western-blot results further demonstrated that the promotion of salt on TG hydrolysis in intramuscular adipocytes was mainly attributed to the activation of protein kinase activity and protein phosphorylation process. Accordingly, the ATGL and HSL were activated, and meanwhile, the TG hydrolysis pivotal switch perilipin1 was also turned on by phosphorylation modification.

Effect of salt promote the muscle triglyceride hydrolysis during dry-salting by inducing the phosphorylation of adipose tissue triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) and lipid droplets splitting.

This study mainly investigated the effect of different salt concentrations (1, 3, or 5%) on triglycerides (TG) hydrolysis in muscle during salting by analyzing moisture distribution, TG hydrolysis, TG hydrolase activity, native and phosphorylated adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) protein content, lipid droplets morphology, and muscle microstructure. The results showed that increasing salt concentration could significantly decrease T21 moisture proportion and relaxation time (p < 0.05), which was more beneficial to the lipase activity. The TG hydrolase activity increased first and then decreased with the salt concentration increasing during dry-salting process, and 3% salt concentration was the point of inflection. Western blot (WB) analysis detected both ATGL, HSL and their phosphorylated proteins, which were increased with the salt content increase. The microstructure analysis showed that the lipid droplets were split into small lipid droplets with the increase of salt content, which was more conducive to the triglycerides hydrolysis.

Role of hepatic neuropeptide Y-Y1 receptors in a methionine-choline-deficient model of non-alcoholic steatohepatitis.

AIMS: NPY-Y1R plays an important role in dietary regulation. Although germline knockdown of NPY-Y1R in mice alleviates high-fat-diet-induced obesity and increases CPT1α levels in the liver, the role of the Y1 receptor in specific tissues has not been studied. MAIN METHODS: MCD diet is the most widely used method to establish a model of lean NASH in a short time. We therefore evaluated the role of liver NPY-Y1R in NASH progression. KEY FINDINGS: In mice with liver-specific knockout of NPY-Y1R (LivKO) and wild-type control littermates fed MCD diet for 4 weeks, NPY-Y1R deficiency significantly decreased body and liver weight. Moreover, NPY-Y1R deletion protected mice against hepatic steatosis and injury. LivKO decreased TG, TC, and FFA levels in the liver and alanine aminotransferase activity in plasma. To clarify the mechanism, we evaluated the key enzymes involved in triglyceride hydrolase and fatty-acid oxidase. Expression of ATGL, CPT1α, and ACO was significantly increased in LivKO mice, whereas expression of fatty-acid synthase was significantly decreased. mRNA expression analysis revealed a marked reduction of genes involved in de-novo lipogenesis and monosaturated fatty-acid synthesis, including sterol-regulatory element-binding protein 1c and fatty-acid synthase. Moreover, liver injury-related factors were significantly decreased in LivKO mice, such as TNF-α, inducible nitric oxide synthase, and MCP-1. Thus, NPY-Y1R deficiency in the liver alleviates lipid deposition and injury. However, NPY-Y1R did not affect inflammation and fibrosis. SIGNIFICANCE: NPY-Y1R deficiency in the liver directly suppresses not only hepatic steatosis, but also liver injury, and thus provides a treatment option for NASH.

Deficiency of liver Comparative Gene Identification-58 causes steatohepatitis and fibrosis in mice.

Triglyceride (TG) accumulation in hepatocytes (hepatic steatosis) preludes the development of advanced nonalcoholic fatty liver diseases (NAFLDs) such as steatohepatitis, fibrosis, and cirrhosis. Mutations in human Comparative Gene Identification-58 (CGI-58) cause cytosolic TG-rich lipid droplets to accumulate in almost all cell types including hepatocytes. However, it is unclear if CGI-58 mutation causes hepatic steatosis locally or via altering lipid metabolism in other tissues. To directly address this question, we created liver-specific CGI-58 knockout (LivKO) mice. LivKO mice on standard chow diet displayed microvesicular and macrovesicular panlobular steatosis, and progressed to advanced NAFLD stages over time, including lobular inflammation and centrilobular fibrosis. Compared with CGI-58 floxed control littermates, LivKO mice showed 8-fold and 52-fold increases in hepatic TG content, which was associated with 40% and 58% decreases in hepatic TG hydrolase activity at 16 and 42 weeks, respectively. Hepatic cholesterol also increased significantly in LivKO mice. At 42 weeks, LivKO mice showed increased hepatic oxidative stress, plasma aminotransferases, and hepatic mRNAs for genes involved in fibrosis and inflammation, such as α-smooth muscle actin, collagen type 1 α1, tumor necrosis factor α, and interleukin-1ß. In conclusion, CGI-58 deficiency in the liver directly causes not only hepatic steatosis but also steatohepatitis and fibrosis.