High susceptibility to fatty liver disease in two-pore channel 2-deficient mice

Abstract

Endolysosomal organelles play a key role in trafficking, breakdown and receptor-mediated recycling of different macromolecules such as low-density lipoprotein (LDL)-cholesterol, epithelial growth factor (EGF) or transferrin. Here we examine the role of two-pore channel (TPC) 2, an endolysosomal cation channel, in these processes. Embryonic mouse fibroblasts and hepatocytes lacking TPC2 display a profound impairment of LDL-cholesterol and EGF/EGF-receptor trafficking. Mechanistically, both defects can be attributed to a dysfunction of the endolysosomal degradation pathway most likely on the level of late endosome to lysosome fusion. Importantly, endolysosomal acidification or lysosomal enzyme function are normal in TPC2-deficient cells. TPC2-deficient mice are highly susceptible to hepatic cholesterol overload and liver damage consistent with non-alcoholic fatty liver hepatitis. These findings indicate reduced metabolic reserve of hepatic cholesterol handling. Our results suggest that TPC2 plays a crucial role in trafficking in the endolysosomal degradation pathway and, thus, is potentially involved in the homoeostatic control of many macromolecules and cell metabolites.

Calcium signals regulated by NAADP and two-pore channels - their role in development, differentiation and cancer

“…In human cytotoxic Tcells, endogenous TPCs have been shown in immunofluorescence studies to localise to the cytolytic granules, secretory vesicles that are exocytosed during the cell-killing response; moreover, TPCs play important functional roles in this response (Davis et al, 2012). In line with their localization to the endolysosomal compartment, TPCs have recently been shown to be involved in receptor trafficking and endolysosomal function (Grimm et al, 2014;Ruas et al, 2014). Deficiencies in endolysosomal trafficking in vivo have metabolic consequences.…”

Differential effects of two-pore channel protein 1 and 2 silencing in MDA-MB-468 breast cancer cells

“…The ability of TPC2 but not TPC1 to attenuate EGF-induced vimentin expression could have arisen from effects on EGF receptor trafficking given results of studies in TPC2 null mice [28]. However, this is unlikely given that EGF-mediated STAT3 activation was unaffected by TPC2 silencing in MDA-MB-468 breast cancer cells.…”

Two-pore channels (TPCs): Novel voltage-gated ion channels with pleiotropic functions

“…4 RT-PCR showed TPC2 mRNA expression in pancreas in mice, 21 in liver and heart in rats, 40,68 and in the human heart. 40,67 Protein expression of TPC2 was detectable by protein gel blot in liver in mice, 44 and in human and rat hearts, 40,67 and by immunofluorescence in human pancreatic b-cells. 21 …”

“…77,78 In fact, Grimm et al 44 have demonstrated in primary fibroblasts and hepatocytes cultures from TPC2 KO mice that, in the absence of this channel, there is a damage in cholesterol trafficking and in the epidermal growth factor receptor (EGFR), that could be attributed to a dysfunction in endolysosomal degradation due to the absence of fusion between the lysosome and the endosome. 44 To note, mice deficient in TPC2 had liver damage, compatible with a non alcoholic esteohepatitis. 44 Recently, it has been shown that TPC1/2 KO mice have a respiratory quotient higher than the wild-type (WT) mice and that develop obesity between 6 and 9 months of age.…”

“…44 To note, mice deficient in TPC2 had liver damage, compatible with a non alcoholic esteohepatitis. 44 Recently, it has been shown that TPC1/2 KO mice have a respiratory quotient higher than the wild-type (WT) mice and that develop obesity between 6 and 9 months of age. 23 Expression levels of hormone-sensitive lipase (HSL) and lipid availability are reduced in brown adipose tissue in TPC1/2 KO mice, in which also exist a defect in b-adrenergic receptor signaling that leads to all these metabolic alterations.…”