Excessive lipolysis and inflammatory response in adipose tissue are associated with elevated serum growth hormone in dairy cows with clinical ketosis

Excessive lipolysis and inflammatory response are critically involved in the pathogenesis of ketosis in periparturient dairy cows. Evidence has been growing for participation of the growth hormone (GH) in the metabolic regulation of adipose tissue. However, the potential role of GH in promoting lipolysis and proinflammatory signaling activation in bovine adipocytes remains to be elucidated. The objective of this study was to investigate the regulatory effects of GH on the lipolysis and inflammatory response of bovine adipocytes. Subcutaneous adipose tissue and blood samples were collected from 10 healthy cows (blood BHB concentration <1.2 mM) and 10 cows with clinical ketosis (CK; blood BHB concentration >3.0 mM). For in vitro experiments, adipocytes were isolated from healthy Holstein cows. Differentiated adipocytes were used for (1) treatment with 0, 5, 10, or 15 ng/mL of GH for 8 h, or 15 ng/mL of GH for 0, 4, 8 or 12 h; (2) co-treatment with 15 ng/mL GH and 0.1 ng/mL tumor necrosis factor α (TNF-α); (3) pretreatment with 10 μM BAY 11-7082, a nuclear factor kappa B (NF-κB) inhibitor, and then treatment with 15 ng/mL GH. The CK cows displayed higher serum GH concentration. The protein abundance of phosphorylated lipolysis-limiting enzyme hormone sensitive lipase (HSL) was higher and mRNA abundance of lipid droplet coating proteins cell death-inducing DFFA-like effector c and perilipin 1 was lower in adipose tissue of CK cows versus healthy cows. The protein abundance of phosphorylated inhibitor of kappa B α (IκBα) and NF-κB, mRNA abundance of proinflammatory cytokines TNFA, NLR family pyrin domain containing 3 (NLRP3), IL-18 (IL18), caspase 1 (CASP1) and IL-1B (IL1B), and the activity of caspase 1 were greater in adipose tissue of CK cows, but protein abundance of IκBα was lower. In bovine adipocytes, GH induced lipolysis and inflammatory response, as evidenced by increased glycerol content in the supernatant and decreased cellular triglyceride content, as well as elevated phosphorylation levels of IκBα and NF-κB, decreased protein abundance of IκBα, upregulated mRNA abundance of TNFA, NLRP3, IL18, CASP1, and IL1B, and enhanced caspase 1 activity. Furthermore, TNF-α exacerbated GH-induced lipolysis and inflammation, whereas inhibition of NF-κB signaling pathway partially reverses these metabolic alterations of GH-treated adipocytes. These findings suggested that GH promote lipolysis in bovine adipocytes by activating inflammatory pathways.