Steatosis inhibits liver cell store-operated Ca2+ entry and reduces ER Ca2+ through a protein kinase C-dependent mechanism

Abstract

Lipid accumulation in hepatocytes can lead to non-alcoholic fatty liver disease (NAFLD), which can progress to non-alcoholic steatohepatitis (NASH) and Type 2 diabetes (T2D). Hormone-initiated release of Ca²⁺ from the endoplasmic reticulum (ER) stores and subsequent replenishment of these stores by Ca²⁺ entry through SOCs (store-operated Ca²⁺ channels; SOCE) plays a critical role in the regulation of liver metabolism. ER Ca²⁺ homoeostasis is known to be altered in steatotic hepatocytes. Whether store-operated Ca²⁺ entry is altered in steatotic hepatocytes and the mechanisms involved were investigated. Lipid accumulation in vitro was induced in cultured liver cells by amiodarone or palmitate and in vivo in hepatocytes isolated from obese Zucker rats. Rates of Ca²⁺ entry and release were substantially reduced in lipid-loaded cells. Inhibition of Ca²⁺ entry was associated with reduced hormone-initiated intracellular Ca²⁺ signalling and enhanced lipid accumulation. Impaired Ca²⁺ entry was not associated with altered expression of stromal interaction molecule 1 (STIM1) or Orai1. Inhibition of protein kinase C (PKC) reversed the impairment of Ca²⁺ entry in lipid-loaded cells. It is concluded that steatosis leads to a substantial inhibition of SOCE through a PKC-dependent mechanism. This enhances lipid accumulation by positive feedback and may contribute to the development of NASH and insulin resistance.

Exploring the impact of a naturally occurring sapogenin diosgenin on underlying mechanisms of Ca2+ movement and cytotoxicity in human prostate cancer cells

“…The interaction of PKC and store‐operated Ca 2+ entry has been reported. Steatosis was shown to inhibit liver cell store‐operated Ca 2+ entry and reduce the endoplasmic reticulum Ca 2+ content through a PKC‐dependent mechanism . The results show that diosgenin‐evoked [Ca 2+ ] i increases were inhibited by enhancing or inhibiting PKC activity by 30%.…”

Live Imaging and Quantitation of Lipid Droplets and Mitochondrial Membrane Potential Changes with Aggregation‐Induced Emission Luminogens in an in Vitro Model of Liver Steatosis

“…The induction of steatosis is often with palmitate or a drug such as amiodarone, followed in various studies performed to understand the mechanism and/or to test potential therapeutics . Amiodarone (Scheme ), a commonly used antiarrhythmic drug, is one of the compounds used to induce steatosis in HepG2 cells . In order to study intracellular lipid droplets, various fluorescent probes have been developed for imaging .…”

“…It has been shown that amiodarone directly inhibits fatty acid oxidation enzymes and results in intracellular lipid accumulation. Amiodarone is used to induce lipid accumulation in cells . We first evaluated the cytotoxicity of amiodarone on HepG2 cells since there is evidence suggesting amiodarone may have significant cytotoxicity on HepG2 cells .…”

“…Quantitation of lipid droplet numbers showed that the number increased more than twice (132(±29) per cell) in HepG2 treated with amiodarone at 24 h compared to that at 0 h (50(±17) per cell; Figure D). This finding is in line with other studies that used 24 h amiodarone treatment to induce lipid accumulation in cell models . At 48 h the lipid droplet number reached 144(±35) per cell.…”

Rice black-streaked dwarf virus P10 suppresses protein kinase C in insect vector through changing the subcellular localization of LsRACK1

“…PKC is a multimember protein kinase family involved in regulating functions of many other proteins through phosphorylating the hydroxyl groups on serine and threonine amino acid residues. PKC itself can be activated by signalling molecules, such as increased concentrations of diacylglycerol or calcium ions (Ca 2þ ) [25]. PKC enzymes are known to play important roles in several signal transduction cascades [26].…”