Xinya Mi

Skeletal muscle atrophy underlies sarcopenia, frailty, and muscular dystrophies, but the molecular mechanisms linking oxidative stress to muscle degeneration remain incompletely understood. We previously identified protein complex formation between transient receptor potential canonical 3 (TRPC3) and NADPH oxidase 2 (Nox2) as a key driver of anthracycline-induced myocardial atrophy. Here, we investigated whether this complex also contributes to skeletal muscle wasting. In skeletal muscle from sciatic nerve transection model mice and Duchenne muscular dystrophy (mdx) mice, TRPC3-Nox2 complex formation was enhanced. TRPC3 deletion significantly attenuated denervation-induced soleus atrophy and reduced reactive oxygen species (ROS) production. TRPC3-Nox2 complex formation was upregulated in the soleus muscle (SM) of mdx mice. Pharmacological disruption of the TRPC3-Nox2 interaction improved muscle size and strength and reduced plasma creatine kinase in mdx mice. A recombinant adeno-associated virus (AAV) encoding a TRPC3 C-terminal peptide was used to suppress TRPC3-Nox2 complex formation in vivo. AAV-mediated expression of TRPC3 C-terminal peptide mitigated muscle wasting (CSA) in mdx mice, while muscle strength and plasma CK were not significantly improved. Thus, TRPC3-Nox2 complex formation may be a pivotal driver of oxidative stress-mediated skeletal muscle atrophy. Targeting this protein–protein interaction represents a promising therapeutic strategy for Duchenne muscular dystrophy (DMD) and other intractable muscle-wasting disorders.

Vascular smooth muscle cells (VSMCs) can dynamically change their phenotype between contractile and synthetic forms in response to environmental stress, which is pivotal in maintaining vascular homeostasis and mediating pathological remodeling of blood vessels. We previously reported that suppression of canonical transient receptor potential 6 (TRPC6) channel-mediated cation entry sustains VSMCs contractile phenotype and promotes the blood flow recovery after hindlimb ischemia in mice. We also reported that Zn²⁺, a metal biomolecule mobilized by TRPC6 channel activation, exerts potential beneficial effects on cardiac contractility and remodeling. Therefore, we hypothesized that TRPC6-mediated Zn²⁺ influx participates in phenotype switching of VSMCs and vascular remodeling. We established rat aortic smooth muscle cells (RAoSMCs) stably expressing wild type (WT) and Zn²⁺ only impermeable TRPC6 (KYD) mutant. Although the resting phenotypes were similar in both RAoSMCs, pharmacological TRPC6 activation by PPZ2 prevented the transforming growth factor (TGF) β-induced reduction in the intracellular Zn²⁺ amount and contractile differentiation in RAoSMCs (WT), but failed to prevent them in RAoSMCs (KYD). There were no significant differences in TRPC6-dependent cation currents among all RAoSMCs pretreated with or without TGFβ and/or PPZ2, suggesting that TRPC6 channels are functionally expressed in RAoSMCs regardless of their phenotype. Treatment of mice with PPZ2 attenuated the progression of vascular remodeling caused by chronic angiotensin II infusion. These results suggest that Zn²⁺ influx through TRPC6 channels negatively regulates the TGFβ-induced contractile differentiation of VSMCs and the progression of vascular remodeling in rodents.

G protein-coupled receptors (GPCRs) exist in the conformational equilibrium between inactive state and active state, where the proportion of active state in the absence of a ligand determines the basal activity of GPCRs. Although many GPCRs have different basal activity, it is still unclear whether physiological stresses such as substrate stiffness affect the basal activity of GPCRs. In this study, we identified that purinergic P2Y₆ receptor (P2Y₆R) induced spontaneous Ca²⁺ oscillation without a nucleotide ligand when cells were cultured in a silicon chamber. This P2Y₆R-dependent Ca²⁺ oscillation was absent in cells cultured in glass dishes. Coating substrates, including collagen, laminin, and fibronectin, did not affect the P2Y₆R spontaneous activity. Mutation of the extracellular Arg-Gly-Asp (RGD) motif of P2Y₆R inhibited spontaneous activity. Additionally, extracellular Ca²⁺ was required for P2Y₆R-dependent spontaneous Ca²⁺ oscillation. The GPCR screening assay identified cells expressing 10 GPCRs, including purinergic P2Y₁R, P2Y₂R, and P2Y₆R, that exhibited spontaneous Ca²⁺ oscillation under cell culture soft substrate. Our results suggest that stiffness of the cell adhesion surface modulates spontaneous activities of several GPCRs, including P2Y₆R, through a ligand-independent mechanism.

Vascular smooth muscle cells (VSMCs) can dynamically change their phenotype between con-tractile and synthetic forms in response to environmental stress, which is pivotal in maintaining vascular homeostasis and mediating pathological remodeling of blood vessels. We previously reported that suppression of canonical transient receptor potential 6 (TRPC6) activation by Ca2+ entry sustains VSMCs contractile phenotype and promotes the blood flow recovery after hindlimb ischemia. In contrast, a metal biomolecule, Zn2+ mobilized by TRPC6 channel activation, is revealed to exert a potential beneficial effect on cardiac contractility. However, the role of TRPC6-mediated Zn²⁺ influx in VSMCs phenotypic switching is still unknown. Here we found the involvement of Zn²⁺ influx through TRPC6 channels in TGFβ-induced contractile differentiation of rat aorta-origin smooth muscle cells (RAoSMCs). Using wild type (WT)- and Zn2+ permeation-dead TRPC6 (KYD) mutant-expressing RAoSMCs, we revealed that pharmacological TRPC6 activation by PPZ2 enhanced the intracellular Zn2+ amounts which overcame TGFβ-induced intracellular Zn2+ depletion and contractile differentiation in RAoSMCs (WT), but failed in RAoSMCs (KYD). There is no significant difference in TRPC6 currents of both RAoSMCs (WT) and (KYD) cells with or without TGFβ stimulation. In addition, PPZ2 attenuated the progression of vascular remodeling caused by chronic angiotensin II treatment in mice. These data suggest that Zn2+ influx through TRPC6 channels will be a therapeutic potential for vascular diseases characterized by maladaptive phenotypic switching.

Lipid droplet (LD) accumulation in hepatocytes is one of the major symptoms associated with fatty liver disease. Mitochondria play a key role in catabolizing fatty acids for energy production through β-oxidation. The interplay between mitochondria and LD assumes a crucial role in lipid metabolism, while it is obscure how mitochondrial morphology affects systemic lipid metabolism in the liver. We previously reported that cilnidipine, an already existing anti-hypertensive drug, can prevent pathological mitochondrial fission by inhibiting protein–protein interaction between dynamin-related protein 1 (Drp1) and filamin, an actin-binding protein. Here, we found that cilnidipine and its new dihydropyridine (DHP) derivative, 1,4-DHP, which lacks Ca²⁺ channel-blocking action of cilnidipine, prevent the palmitic acid-induced Drp1–filamin interaction, LD accumulation and cytotoxicity of human hepatic HepG2 cells. Cilnidipine and 1,4-DHP also suppressed the LD accumulation accompanied by reducing mitochondrial contact with LD in obese model and high-fat diet-fed mouse livers. These results propose that targeting the Drp1–filamin interaction become a new strategy for the prevention or treatment of fatty liver disease.

Lipid droplet (LD) accumulation in hepatocytes is one of the major symptoms associated with fatty liver disease. Mitochondria play a key role in catabolizing fatty acids for energy production through β-oxidation. The interplay between mitochondria and LD assumes a crucial role in lipid metabolism, while it is obscure how mitochondrial morphology affects systemic lipid metabolism in the liver. We previously reported that cilnidipine, an already existing anti-hypertensive drug, has potency to prevent pathological mitochondrial fission by inhibiting protein-protein interaction between dynamin-related protein 1 (Drp1) and filamin, an actin-binding protein. Here, we found that cilnidipine and its new dihydropyridine (DHP) derivative, 1,4-DHP, which lacks Ca2+ channel blocking action of cilnidipine, prevent the palmitic ac-id-induced Drp1-filamin interaction, LD accumulation and cytotoxicity of human hepatic HepG2 cells. Cilnidipine and 1,4-DHP also suppressed the LD accumulation accompanied by reducing mitochondrial contact with LD in obese model and high fat diet-fed mouse livers. These results propose that targeting Drp1-filimin interaction becomes a new strategy for the prevention or treatment of fatty liver disease.

We recently reported that transient receptor potential canonical (TRPC) 6 channel activity contributes to intracellular Zn²⁺ homeostasis in the heart. Zn²⁺ has also been implicated in the regulation of intestinal redox and microbial homeostasis. This study aims to investigate the role of TRPC6-mediated Zn²⁺ influx in the stress resistance of the intestine. The expression profile of TRPC1-C7 mRNAs in the actively inflamed mucosa from inflammatory bowel disease (IBD) patients was analyzed using the GEO database. Systemic TRPC3 knockout (KO) and TRPC6 KO mice were treated with dextran sulfate sodium (DSS) to induce colitis. The Zn²⁺ concentration and the mRNA expression levels of oxidative/inflammatory markers in colon tissues were quantitatively analyzed, and gut microbiota profiles were compared. TRPC6 mRNA expression level was increased in IBD patients and DSS-treated mouse colon tissues. DSS-treated TRPC6 KO mice, but not TRPC3 KO mice, showed severe weight loss and increased disease activity index compared with DSS-treated WT mice. The mRNA abundances of antioxidant proteins were basically increased in the TRPC6 KO colon, with changes in gut microbiota profiles. Treatment with TRPC6 activator prevented the DSS-induced colitis progression accompanied by increasing Zn²⁺ concentration. We suggest that TRPC6-mediated Zn²⁺ influx activity plays a key role in stress resistance against IBD, providing a new strategy for treating colitis.

Zn2+ has been implicated in the regulation of intestinal redox and microbial homeostasis, and we recently reported that transient receptor potential canonical (TRPC) 6 channel activity contributes to intracellular Zn2+ homeostasis in mammalian cells. This study aims to investigate the role of TRPC6-mediated Zn2+ influx in stress resistance of intestine. Expression profile of TRPC1-C7 mRNAs in the actively inflamed mucosa from inflammatory bowel disease (IBD) patients was analyzed using GEO database. Systemic TRPC3-knockout (KO) and TRPC6-KO mice were treated with dextran sulphate sodium (DSS) to induce colitis. The Zn2+ concentration and the mRNA expression levels of oxidative/inflammatory markers in colon tissues were quantitatively analyzed, and gut microbiota profiles were compared. TRPC6 mRNA expression level was increased in IBD patients and DSS-treated mouse colon tissues. DSS-treated TRPC6-KO mice, but not TRPC3-KO mice, showed severe weight loss and increased disease activity index compared with DSS-treated WT mice. The mRNA abundances of antioxidant proteins were basically increased in TRPC6-KO colon, with changes in gut microbiota profiles. Treatment with TRPC6 activator prevented the DSS-induced colitis progression accompanied by increasing Zn2+ concentration. We suggest that TRPC6-mediated Zn2+ influx activity plays a key role in stress resistance against IBD, providing a new strategy for treating colitis.

Nonalcoholic steatohepatitis (NASH) is a disease that progresses from nonalcoholic fatty liver (NAFL) and which is characterized by inflammation and fibrosis. The purinergic P2Y₆ receptor (P2Y₆R) is a pro-inflammatory G_q/G₁₂ family protein-coupled receptor and reportedly contributes to intestinal inflammation and cardiovascular fibrosis, but its role in liver pathogenesis is unknown. Human genomics data analysis revealed that the liver P2Y₆R mRNA expression level is increased during the progression from NAFL to NASH, which positively correlates with inductions of C-C motif chemokine 2 (CCL2) and collagen type I α1 chain (Col1a1) mRNAs. Therefore, we examined the impact of P2Y₆R functional deficiency in mice crossed with a NASH model using a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD). Feeding CDAHFD for 6 weeks markedly increased P2Y₆R expression level in mouse liver, which was positively correlated with CCL2 mRNA induction. Unexpectedly, the CDAHFD treatment for 6 weeks increased liver weights with severe steatosis in both wild-type (WT) and P2Y₆R knockout (KO) mice, while the disease marker levels such as serum AST and liver CCL2 mRNA in CDAHFD-treated P2Y₆R KO mice were rather aggravated compared with those of CDAHFD-treated WT mice. Thus, P2Y₆R may not contribute to the progression of liver injury, despite increased expression in NASH liver.

In the adult mammalian heart, no data have yet shown the existence of cardiomyocyte-differentiable stem cells that can be used to practically repair the injured myocardium. Atypically shaped cardiomyocytes (ACMs) are found in cultures of the cardiomyocyte-removed fraction obtained from cardiac ventricles from neonatal to aged mice. ACMs are thought to be a subpopulation of cardiomyocytes or immature cardiomyocytes, most closely resembling cardiomyocytes due to their spontaneous beating, well-organized sarcomere and the expression of cardiac-specific proteins, including some fetal cardiac gene proteins. In this review, we focus on the characteristics of ACMs compared with ventricular myocytes and discuss whether these cells can be substitutes for damaged cardiomyocytes. ACMs reside in the interstitial spaces among ventricular myocytes and survive under severely hypoxic conditions fatal to ventricular myocytes. ACMs have not been observed to divide or proliferate, similar to cardiomyocytes, but they maintain their ability to fuse with each other. Thus, it is worthwhile to understand the role of ACMs and especially how these cells perform cell fusion or function independently in vivo. It may aid in the development of new approaches to cell therapy to protect the injured heart or the clarification of the pathogenesis underlying arrhythmia in the injured heart.