Fasting Inhibits the Recruitment of Kinesin-1 to Lipid Droplets and Stalls Hepatic Triglyceride Secretion

Sex-specific responses in glucose-insulin homeostasis and lipoprotein-lipid components after high-dose supplementation with marine n-3 PUFAs in abdominal obesity: a randomized double-blind crossover study

Background

Clinical studies on effects of marine-derived omega-3 (n-3) polyunsaturated fatty acids (PUFAs), mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and the plant-derived omega-6 (n-6) PUFA linoleic acid (LA) on lipoprotein-lipid components and glucose-insulin homeostasis have shown conflicting results, which may partly be explained by differential responses in females and males. However, we have lacked data on sexual dimorphism in the response of cardiometabolic risk markers following increased consumption of n-3 or n-6 PUFAs.

Objective

To explore sex-specific responses after n-3 (EPA + DHA) or n-6 (LA) PUFA supplementation on circulating lipoprotein subfractions, standard lipids, apolipoproteins, fatty acids in red blood cell membranes, and markers of glycemic control/insulin sensitivity among people with abdominal obesity.

Methods

This was a randomized double-blind crossover study with two 7-week intervention periods separated by a 9-week washout phase. Females (n = 16) were supplemented with 3 g/d of EPA + DHA (fish oil) or 15 g/d of LA (safflower oil), while males (n = 23) received a dose of 4 g/d of EPA + DHA or 20 g/d of LA. In fasting blood samples, we measured lipoprotein particle subclasses, standard lipids, apolipoproteins, fatty acid profiles, and markers of glycemic control/insulin sensitivity.

Results

The between-sex difference in relative change scores was significant after n-3 for total high-density lipoproteins (females/males: -11%*/-3.3%, p = 0.036; *: significant within-sex change), high-density lipoprotein particle size (+2.1%*/-0.1%, p = 0.045), and arachidonic acid (-8.3%*/-12%*, p = 0.012), and after n-6 for total (+37%*/+2.1%, p = 0.041) and small very-low-density lipoproteins (+97%*/+14%, p = 0.021), and lipoprotein (a) (-16%*/+0.1%, p = 0.028). Circulating markers of glucose-insulin homeostasis differed significantly after n-3 for glucose (females/males: -2.1%/+3.9%*, p = 0.029), insulin (-31%*/+16%, p < 0.001), insulin C-peptide (-12%*/+13%*, p = 0.001), homeostasis model assessment of insulin resistance index 2 (-12%*/+14%*, p = 0.001) and insulin sensitivity index 2 (+14%*/-12%*, p = 0.001), and quantitative insulin sensitivity check index (+4.9%*/-3.4%*, p < 0.001).

Conclusion

We found sex-specific responses after high-dose n-3 (but not n-6) supplementation in circulating markers of glycemic control/insulin sensitivity, which improved in females but worsened in males. This may partly be related to the sex differences we observed in several components of the lipoprotein-lipid profile following the n-3 intervention.

Clinical trial registration

https://clinicaltrials.gov/, identifier [NCT02647333].

miR-122-5p/KIF5B/AMPK/AKT regulatory network regulates the progression of NAFLD

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a progressive liver disease, which may develop into end-stage liver disease and endanger human life. miR-122-5p may be related to the progression of NAFLD disease, but the specific regulation mechanism is still unknown. It is helpful for us to optimize the prevention or treatment strategy of NAFLD.

METHODS

Real-time PCR was applied to test miR-122-5p and KIF5B in serum, rat liver tissue induced by high fat diet (HFD), and primary hepatocytes exposed to oleic acid ester and palmitate (FFA) of NAFLD patients. The role of miR-122-5p on inflammatory factors (MCP-1, TNF-α, IL-10) and liver injury markers (AST, ALT) in vivo and in vitro was analyzed.

RESULTS

miR-122-5p and KIF5B were both highly expressed in NAFLD patients' serum, rat liver tissue and primary hepatocytes, while KIF5B was low expressed. miR-122-5p expression enhanced with the increase of HFD feeding time. The dual luciferase reporter gene assay system confirmed that there was a targeting relationship between miR-122-5p and KIF5B, indicating that KIF5B and protein level were evidently up-regulated in primary hepatocytes. Down-regulation of miR-122-5p was helpful to improve the liver weight/body weight ratio (liver index) level of rats, as well as the levels of triglyceride (TG), inflammatory factors and liver injury markers in liver tissues in vivo and in vitro. Phosphorylation of AMPK/AKT pathway-related proteins and fat metabolism-related factors in rat liver tissues and cells in primary hepatocytes were notably reduced, while down-regulation of miR-122-5p was helpful to restore activation of the pathway and increase the level of fat metabolism-related factors.

CONCLUSION

Decrease of miR-122-5p can target and enhance KIF5B, which can be applied for treating NAFLD.

Insulin activates intracellular transport of lipid droplets to release triglycerides from the liver

Kumar et al. describe a detailed pathway for channeling fat from the liver into blood across fed/fasted cycles. Insulin, phosphatidic acid, and kinesin collaborate in hepatocytes to deliver lipid droplets to the smooth ER, where they are catabolized to supply fat for lipoprotein production and secretion.

Triglyceride-rich lipid droplets (LDs) are catabolized with high efficiency in hepatocytes to supply fatty acids for producing lipoprotein particles. Fasting causes a massive influx of adipose-derived fatty acids into the liver. The liver in the fasted state is therefore bloated with LDs but, remarkably, still continues to secrete triglycerides at a constant rate. Here we show that insulin signaling elevates phosphatidic acid (PA) dramatically on LDs in the fed state. PA then signals to recruit kinesin-1 motors, which transport LDs to the peripherally located smooth ER inside hepatocytes, where LDs are catabolized to produce lipoproteins. This pathway is down-regulated homeostatically when fasting causes insulin levels to drop, thus preventing dangerous elevation of triglycerides in the blood. Further, we show that a specific peptide against kinesin-1 blocks triglyceride secretion without any apparent deleterious effects on cells. Our work therefore reveals fundamental mechanisms that maintain lipid homeostasis across metabolic states and leverages this knowledge to propose a molecular target against hyperlipidemia.