M1 Muscarinic Receptor Deficiency Attenuates Azoxymethane-Induced Chronic Liver Injury in Mice

Abstract

Cholinergic nervous system regulates liver injury. However, the role of M1 muscarinic receptors (M1R) in modulating chronic liver injury is uncertain. To address this gap in knowledge we treated M1R-deficient and WT mice with azoxymethane (AOM) for six weeks and assessed liver injury responses 14 weeks after the last dose of AOM. Compared to AOM-treated WT mice, M1R-deficient mice had attenuated liver nodularity, fibrosis and ductular proliferation, α-SMA staining, and expression of α1 collagen, Tgfβ-R, Pdgf-R, Mmp-2, Timp-1 and Timp-2. In hepatocytes, these findings were associated with reductions of cleaved caspase-3 staining and Tnf-α expression. In response to AOM treatment, M1R-deficient mice mounted a vigorous anti-oxidant response by upregulating Gclc and Nqo1 expression, and attenuating peroxynitrite generation. M1R-deficient mouse livers had increased expression of Trail-R2, a promotor of stellate cell apoptosis; dual staining for TUNNEL and α-SMA revealed increased stellate cells apoptosis in livers from M1R-deficient mice compared to those from WT. Finally, pharmacological inhibition of M1R reduced H2O2-induced hepatocyte apoptosis in vitro. These results indicate that following liver injury, anti-oxidant response in M1R-deficient mice attenuates hepatocyte apoptosis and reduces stellate cell activation, thereby diminishing fibrosis. Therefore, targeting M1R expression and activation in chronic liver injury may provide therapeutic benefit.

Progressive changes in detrusor function and micturition patterns with chroinc bladder ischemia

“…M1 prevail in neuronal tissues and seems to regulate cholinergic neurotransmission discharge in the bladder. The bladder M1 receptors are believed to facilitate acetylcholine release from cholinergic nerves [ 21 22 23 ]. In our study, upregulation of M2 receptors in early-stage ischemia was associated with micturition patterns and cystometrograms consistent with bladder overactivity.…”

“…Inhibition of M1 was shown to protect cells from free radical injury by enhancing antioxidant defense mechanisms [ 21 ]. M1 deficient mice exhibited markedly reduced fibrosis, apoptosis, and oxidative stress when exposed to cytotoxic conditions [ 22 ]. Inhibition of M1 receptor was shown to reduce caspase-3 activation and enhance cell survival signaling [ 22 ].…”

“…M1 deficient mice exhibited markedly reduced fibrosis, apoptosis, and oxidative stress when exposed to cytotoxic conditions [ 22 ]. Inhibition of M1 receptor was shown to reduce caspase-3 activation and enhance cell survival signaling [ 22 ]. M1 deficiency in the mouse model exhibited markedly lower tumor necrosis factorlike weak inducer of apoptosis (TWEAK) and diminished proliferation and fibrosis [ 22 ].…”

“…Inhibition of M1 receptor was shown to reduce caspase-3 activation and enhance cell survival signaling [ 22 ]. M1 deficiency in the mouse model exhibited markedly lower tumor necrosis factorlike weak inducer of apoptosis (TWEAK) and diminished proliferation and fibrosis [ 22 ]. In light of these findings, we speculate that increased M1 expression may contribute to cellular structural damage and neurodegeneration by amplifying oxidative damage in chronic bladder ischemia.…”

Reduction of hepatic fibrosis by overexpression of von Hippel–Lindau protein in experimental models of chronic liver disease

“…Particularly, TGF-β1 induces phenotypic transdifferentiation of HSCs and synthesis of ECM29. PDGF-B is the most potent stimulus for HSCs proliferation and migration and contributes to the perpetuation of liver fibrosis30. It has been reported that VHL is involved in the negative regulation of both TGF-β1 and PDGF-B in wound healing31.…”