Hepatic Tmem30a Deficiency Causes Intrahepatic Cholestasis by Impairing Expression and Localization of Bile Salt Transporters

Abstract

Mutations in ATP8B1 or ATP11C (members of P4-type ATPases) cause progressive familial intrahepatic cholestasis type 1 in human or intrahepatic cholestasis in mice. Transmembrane protein 30A (TMEM30A), a β-subunit, is essential for the function of ATP8B1 and ATP11C. However, its role in the etiology of cholestasis remains poorly understood. To investigate the function of TMEM30A in bile salt (BS) homeostasis, we developed Tmem30a liver-specific knockout (LKO) mice. Tmem30a LKO mice experienced hyperbilirubinemia, hypercholanemia, inflammatory infiltration, ductular proliferation, and liver fibrosis. The expression and membrane localization of ATP8B1 and ATP11C were significantly reduced in Tmem30a LKO mice, which correlated with the impaired expression and localization of BS transporters, such as OATP1A4, OATP1B2, NTCP, BSEP, and MRP2. The proteasome inhibitor bortezomib partially restored total protein levels of BS transporters but not the localization of BS transporters in the membrane. Furthermore, the expression of nuclear receptors, including FXRα, RXRα, HNF4α, LRH-1, and SHP, was also down-regulated. A cholic acid-supplemented diet exacerbated the liver damage in Tmem30a LKO mice. TMEM30A deficiency led to intrahepatic cholestasis in mice by impairing the expression and localization of BS transporters and the expression of related nuclear receptors. Therefore, TMEM30A may be a novel genetic determinant of intrahepatic cholestasis.

Evidence that decreased expression of sinusoidal bile acid transporters accounts for the inhibition by rapamycin of bile flow recovery following liver ischemia

“…Quantitative PCR was employed as the principle technique for measurement of the expression of bile acid transporters because it can offer more precise quantitation than measurement of protein expression by western blot and can more readily be applied to the assay of multiple samples generated in dose-response experiments. Other studies of bile acid transporter expression have shown a good correlation between results obtained using qPCR and those obtained using western blot (Liu et al, 2017;Weerachayaphorn et al, 2009;Weerachayaphorn et al, 2012).…”

Tmem30a Plays Critical Roles in Ensuring the Survival of Hematopoietic Cells and Leukemia Cells in Mice

“…16 Two studies about the functions of Tmem30a have been performed in the retina and liver, respectively, by using Tmem30a tissue-specific deletion mouse models. 16,20 Deletion of Tmem30a resulted in a loss of PS flippase activity and exposure of PS on cell outer surface. 16,20 Tmem30a deficiency in mouse cone cells results in loss of cone cells and impaired photopic electroretinogram responses in the retina.…”

“…16,20 Deletion of Tmem30a resulted in a loss of PS flippase activity and exposure of PS on cell outer surface. 16,20 Tmem30a deficiency in mouse cone cells results in loss of cone cells and impaired photopic electroretinogram responses in the retina. 16 Currently, the physiologic roles of Tmem30a in hematopoietic cells are unknown.…”

TMEM30A deficiency in endothelial cells impairs cell proliferation and angiogenesis

“…P4-ATPases are members of a family of proteins that transport aminophospholipids from the exoplasmic to the cytoplasmic leaflet of cell membranes by utilizing ATP, thereby maintaining the aminophospholipid asymmetry in the cellular membrane (Halleck et al, 1999;Holthuis and Levine, 2005). Several P4-ATPases have been reported to have important functions in physiological and pathological conditions (Bull et al, 1998;Cacciagli et al, 2010;Darland-Ransom et al, 2008;Wang et al, 2004;Liu et al, 2017;Zhang et al, 2017). By using RT-PCR, we demonstrated that eight of 14 P4-ATPases are expressed in HRECs (Fig.…”

“…These genes encode N-glycosylated proteins with two transmembrane domains and play critical roles in the folding and function of P4-ATPases (Katoh and Katoh, 2004;van der Velden et al, 2010). Our previous studies have demonstrated the essential roles of the TMEM30A gene in retinal development, bile salt transportation and the survival of hematopoietic cells (Li et al, 2018;Liu et al, 2017;Zhang et al, 2017).…”