PARM-1 Is an Endoplasmic Reticulum Molecule Involved in Endoplasmic Reticulum Stress-Induced Apoptosis in Rat Cardiac Myocytes

To identify novel transmembrane and secretory molecules expressed in cardiac myocytes, signal sequence trap screening was performed in rat neonatal cardiac myocytes. One of the molecules identified was a transmembrane protein, prostatic androgen repressed message-1 (PARM-1). While PARM-1 has been identified as a gene induced in prostate in response to castration, its function is largely unknown. Our expression analysis revealed that PARM-1 was specifically expressed in hearts and skeletal muscles, and in the heart, cardiac myocytes, but not non-myocytes expressed PARM-1. Immunofluorescent staining showed that PARM-1 was predominantly localized in endoplasmic reticulum (ER). In Dahl salt-sensitive rats, high-salt diet resulted in hypertension, cardiac hypertrophy and subsequent heart failure, and significantly stimulated PARM-1 expression in the hearts, with a concomitant increase in ER stress markers such as GRP78 and CHOP. In cultured cardiac myocytes, PARM-1 expression was stimulated by proinflammatory cytokines, but not by hypertrophic stimuli. A marked increase in PARM-1 expression was observed in response to ER stress inducers such as thapsigargin and tunicamycin, which also induced apoptotic cell death. Silencing PARM-1 expression by siRNAs enhanced apoptotic response in cardiac myocytes to ER stresses. PARM-1 silencing also repressed expression of PERK and ATF6, and augmented expression of CHOP without affecting IRE-1 expression and JNK and Caspase-12 activation. Thus, PARM-1 expression is induced by ER stress, which plays a protective role in cardiac myocytes through regulating PERK, ATF6 and CHOP expression. These results suggested that PARM-1 is a novel ER transmembrane molecule involved in cardiac remodeling in hypertensive heart disease

C9orf72-derived arginine-rich poly-dipeptides impede phase modifiers

Nuclear import receptors (NIRs) not only transport RNA-binding proteins (RBPs) but also modify phase transitions of RBPs by recognizing nuclear localization signals (NLSs). Toxic arginine-rich poly-dipeptides from C9orf72 interact with NIRs and cause nucleocytoplasmic transport deficit. However, the molecular basis for the toxicity of arginine-rich poly-dipeptides toward NIRs function as phase modifiers of RBPs remains unidentified. Here we show that arginine-rich poly-dipeptides impede the ability of NIRs to modify phase transitions of RBPs. Isothermal titration calorimetry and size-exclusion chromatography revealed that proline:arginine (PR) poly-dipeptides tightly bind karyopherin-β2 (Kapβ2) at 1:1 ratio. The nuclear magnetic resonances of Kapβ2 perturbed by PR poly-dipeptides partially overlapped with those perturbed by the designed NLS peptide, suggesting that PR poly-dipeptides target the NLS binding site of Kapβ2. The findings offer mechanistic insights into how phase transitions of RBPs are disabled in C9orf72-related neurodegeneration

Cavin‐2 promotes fibroblast‐to‐myofibroblast trans‐differentiation and aggravates cardiac fibrosis

Abstract Aims Transforming growth factor β (TGF‐β) signalling is one of the critical pathways in fibroblast activation, and several drugs targeting the TGF‐β/Smad signalling pathway in heart failure with cardiac fibrosis are being tested in clinical trials. Some caveolins and cavins, which are components of caveolae on the plasma membrane, are known for their association with the regulation of TGF‐β signalling. Cavin‐2 is particularly abundant in fibroblasts; however, the detailed association between Cavin‐2 and cardiac fibrosis is still unclear. We tried to clarify the involvement and role of Cavin‐2 in fibroblasts and cardiac fibrosis. Methods and results To clarify the role of Cavin‐2 in cardiac fibrosis, we performed transverse aortic constriction (TAC) operations on four types of mice: wild‐type (WT), Cavin‐2 null (Cavin‐2 KO), Cavin‐2flox/flox, and activated fibroblast‐specific Cavin‐2 conditional knockout (Postn‐Cre/Cavin‐2flox/flox, Cavin‐2 cKO) mice. We collected mouse embryonic fibroblasts (MEFs) from WT and Cavin‐2 KO mice and investigated the effect of Cavin‐2 in fibroblast trans‐differentiation into myofibroblasts and associated TGF‐β signalling. Four weeks after TAC, cardiac fibrotic areas in both the Cavin‐2 KO and the Cavin‐2 cKO mice were significantly decreased compared with each control group (WT 8.04 ± 1.58% vs. Cavin‐2 KO 0.40 ± 0.03%, P < 0.01; Cavin‐2flox/flox, 7.19 ± 0.50% vs. Cavin‐2 cKO 0.88 ± 0.44%, P < 0.01). Fibrosis‐associated mRNA expression (Col1a1, Ctgf, and Col3) was significantly attenuated in the Cavin‐2 KO mice after TAC. α1 type I collagen deposition and non‐vascular αSMA‐positive cells (WT 43.5 ± 2.4% vs. Cavin‐2 KO 25.4 ± 3.2%, P < 0.01) were reduced in the heart of the Cavin‐2 cKO mice after TAC operation. The levels of αSMA protein (0.36‐fold, P < 0.05) and fibrosis‐associated mRNA expression (Col1a1, 0.69‐fold, P < 0.01; Ctgf, 0.27‐fold, P < 0.01; Col3, 0.60‐fold, P < 0.01) were decreased in the Cavin‐2 KO MEFs compared with the WT MEFs. On the other hand, αSMA protein levels were higher in the Cavin‐2 overexpressed MEFs compared with the control MEFs (2.40‐fold, P < 0.01). TGF‐β1‐induced Smad2 phosphorylation was attenuated in the Cavin‐2 KO MEFs compared with WT MEFs (0.60‐fold, P < 0.01). Heat shock protein 90 protein levels were significantly reduced in the Cavin‐2 KO MEFs compared with the WT MEFs (0.69‐fold, P < 0.01). Conclusions Cavin‐2 loss suppressed fibroblast trans‐differentiation into myofibroblasts through the TGF‐β/Smad signalling. The loss of Cavin‐2 in cardiac fibroblasts suppresses cardiac fibrosis and may maintain cardiac function