Protein Kinase D1 Improves Insulin Resistance In Adipocytes Through NF-κB-Mediated Inflammatory Response

Background:Adipose tissue is not only the main organ for energy storage but also an important endocrine organ.It is also one of the key target organs of insulin.It can regulate the homeostasis of lipid and glucose through various physiological and pathological pathways.Insulin resistance in adipose tissue is closely associated with metabolic syndrome and other systemic metabolic disorders,including obesity,type 2 diabetes,and nonalcoholic fatty liver disease.Therefore,improving insulin resistance in adipose tissue is an effective strategy for the treatment of systemic metabolic disorders including type 2 diabetes and nonalcoholic fatty liver disease.Protein kinase D(PKD)is a new serine/threonine kinase family.The three subtypes of PKD1,PKD2,and PKD3 are known as diacylglycerol(DAG)and protein(PKC)effectors,which integrate multiple nutritional and hormonal inputs and are implicated in the regulation of various fundamental biological processes.As a new nutritional sensor,recent studies have shown that PKD1 is involved in the regulation of insulin signal transduction in muscle cells,as well as the regulation of glucose uptake in insulin-resistant cardiomyocytes.Latest studies implicated PKD1 in the regulation of mitochondrial fragmentation and energy consumption in adipocytes.However,the physiological function of PKD1 in adipocytes is not fully understood.Objectives:To investigate the role of PKD1 in regulating insulin signaling.Methods:Lentiviral vector was used to construct 3T3-L1 adipocytes stably overexpressing or knocking out PKD1,and the insulin resistance model of adipocytes was established by inducing differentiation.The mechanism of adipocyte PKD1 in insulin signal transduction was investigated by real-time fluorescent quantitative PCR(RT-qPCR),western blotting analysis,immunoprecipitation(Co-IP),and enzyme-linked immunosorbent assay(ELISA).Results:(1)Insulin resistance induced by long-term insulin stimulation was attenuated by PKD1 deletion in differentiated adipocytes,manifested by inhibition of insulin receptor substrate 1(IRS1)phosphorylation at Ser307.(2)PKD inhibition by CRT0066101 attenuates long-term insulin exposure-induced insulin resistance in differentiated adipocytes,manifested by inhibition of insulin receptor substrate 1(IRS1)phosphorylation at Serine 307 site.(3)Overexpression of PKD 1 enhances long-term insulin exposure-induced insulin resistance in differentiated adipocytes.(4)PKD1 interacted with IKK β in differentiated 3T3-L1 cells.(5)CRT0066101 decreased the expression of pro-inflammatory cytokines in insulin-resistant adipocytes via inhibiting the NF-κB signaling pathway.Conclusion:Taken together,our results demonstrated that PKD1 contributes to the insulin-resistance in differentiated adipocytes,which may provide potential therapeutic target for the treatment of adipose tissue insulin resistance-associated disorders.