Kallstatin/Serpina3c improves hyperlipidemia induced by high-fat diet via regulating glycolipid metabolism in adipose tissue

Abstract

Abstract Background Hyperlipidemia is an independent risk factor for cardiovascular diseases. Studies showed that the plasma Kallstatin (KS) in obese patients was reduced, and the decreased KS in obese patients with type 2 diabetes was increased after weight loss. The mouse homologous gene of human KS is Serpina3c, and the relationship between KS/Serpina3c and hyperlipidemia and its regulatory mechanism are unclear. Purpose To explore whether KS/Serpina3c improves hyperlipidemia and specific mechanisms. Methods The serum KS level of Chinese hyperlipidemia population was detected by ELISA. Serpina3c knockout mice (Serpina3c KO) were constructed based on the strategy of Cre/loxP recombination system. The adipocyte-specific Serpina3c knockout adeno-associated virus (AAV8-shSerpina3c) and control (AAV8-shNC) were constructed, and the adipocyte-specific Serpina3c overexpression adeno-associated virus (AAV8-Serpina3c) were constructed. The 8-week-old C57BL/6J mice were injected with AAV8-shSerpina3c or AAV8-shNC in situ into the inguinal adipose tissue (iWAT). Serpina3c KO mice were injected with AAV8-Serpina3c or AAV8-shNC in situ into the iWAT. The mice model of hyperlipidemia was established by feeding high-fat diet (HFD) for 16 weeks. The fat content of mice was observed with 7.0T magnetic resonance imaging (MRI)system. The serum triglyceride, total cholesterol, LDL and HDL were detected with the kit. Serpina3c KD, Serpina3c OV or control 3T3-L1 adipocytes were stimulated by PA for RNA-seq. Results (1) The serum KS decreased in hyperlipidemic people in China. (2) The 7.0T MRI system displayed bigger fat in the Serpina3c KO mice and AAV8-shSerpina3c mice. (4) The serum results showed higher lipids in Serpina3c KO and AAV8-shSerpina3c mice. (5) Oil red O staining showed increased lipid deposition in liver, muscle and heart. (6) The RNA-seq results revealed that the HIF1α and glycolysis pathways of Serpina3c KD adipocyte increased, while the fatty acid metabolic pathway decreased. The results of primary adipocytes verified the increase of glycolysis and decreased β oxidation. (7) And the fatty acid uptake in liver, heart and muscle tissue of Serpina3c KO mice and AAV8-shSerpina3c mice increased, and the β oxidation decreased. Conclusions The expression and secretion of KS/Serpina3c decreased in HFD adipose, which promotes glycolysis and inhibits fatty acids β oxidation of adipocytes. On the one hand, the decrease of Serpina3c activates glycolysis and increases the production of glycerol 3-phosphate by activating HIF1α. On the other hand, CPT1 was inhibited by increased HIF1α, impeding the activated fatty acid (Fatty-acyl-CoA) in the cytoplasm entering the mitochondria through CPT1. Glycerol 3-phosphate and fatty acyl CoA accumulated in the cytoplasm of adipocyte synthesize triglycerides through the diglyceride pathway, aggravating hyperlipidemia induced by HFD.Schematic diagram