Hormones and catecholamines acting through G-protein coupled receptors (GPCRs) linked to phospholipase C (PLC) and increases in intracellular Ca 2+ concentration (Ca 2+ i) regulate many metabolic functions of the liver. In the liver hormones such as glucagon, and catecholamines such as norepinephrine integrate and synergize to regulate the frequency and extent to which Ca 2+ i waves propagate across hepatic lobules to control carbohydrate and lipid metabolism. Caloric excess leads to hepatic steatosis, the development of metabolic-associated fatty liver disease (MAFLD) and comorbidities such as diabetes and cardiovascular disease. Previously we demonstrated that hepatic catecholamine resistance develops with short-term exposure to high fat diet (HFD), resulting in attenuated norepinephrine-dependent Ca 2+ signals in isolated hepatocytes and intact perfused liver preparations.The aim of this current study is to determine the molecular mechanisms that lead to catecholamine resistance induced by HFD in a mouse model. C57Bl6 mice expressing GCaMP6f (a Ca 2+ i indicator) were fed chow or high fat diet (HFD) (45% w/v) from 6 weeks of age for up to 8 weeks. Hepatocytes were isolated by collagenase perfusion and changes in Ca 2+ i measured using an epifluorescent microscope coupled to a digital camera. We corroborated our previous findings that one week of HFD exposure results in suppressed catecholamine signaling and demonstrate this attenuation is observed in hepatocytes from both male and female mice. Moreover, norepinephrine-dependent Ca 2+ i responses were attenuated in both sexes after 8 weeks of feeding, demonstrating this is not a transient effect of HFD. Norepinephrine acts on both α1B-adrenergic and β-adrenergic GPCRs in hepatocytes which increase Ca 2+ i and cAMP, respectively. As cAMP can potentiate Ca 2+ release we determined whether HFD suppresses norepinephrine-dependent Ca 2+ i due to a change in β-adrenergic receptor activity. The β-adrenergic inverse agonist, acebutolol ICI 118,551 Hydrochloride (500 nM), was without effect on the norepinephrine dose response in hepatocytes from both chow and HFD fed mice, negating a role of β-adrenergic receptors. Stimulation of hepatocytes with the purinergic receptor P2Y1 ligand ADP, revealed HFD (1 and 8 weeks of feeding) also suppresses P2Y1-dependent Ca 2+ i responses. Therefore, we hypothesize HFD suppresses GPCRs via a common mechanism. qPCR analysis of key components of the Ca 2+ signaling pathway revealed no changes in mRNA expression of the GPCRs, Gαq or 11 or PLC enzymes. Hepatic steatosis is associated with elevated flux through the triacylglycerol pathway, which increases diacylglycerol and protein kinase C activity (PKC). Previously we have shown PKC enzymes suppress GPCR mediated Ca 2+ i responses, leading us to hypothesize HFD suppresses GPCR signaling due to a tonic elevation in PKC activity. Our preliminary data demonstrates that PKC inhibition by bisindolylmaleimide II (5 µM) rescues ADP dependent Ca 2+ i responses in HFD fed hepatocytes. In conclusion, HFD feeding of mice attenuates GPCR-dependent Ca 2+ regulation of metabolism and preliminary findings indicate a role of PKC. This work was supported by NIH grant 1R01DK139244 (PJB, APT) and the Thomas P. Infusino Endowment (APT). This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Bartlett et al. (Fri,) studied this question.