mARC1 in MASLD: Modulation of lipid accumulation in human hepatocytes and adipocytes.

BACKGROUND: Mutations in the gene MTARC1 (mitochondrial amidoxime-reducing component 1) protect carriers from metabolic dysfunction-associated steatohepatitis (MASH) and cirrhosis. MTARC1 encodes the mARC1 enzyme, which is localized to the mitochondria and has no known MASH-relevant molecular function. Our studies aimed to expand on the published human genetic mARC1 data and to observe the molecular effects of mARC1 modulation in preclinical MASH models. METHODS AND RESULTS: We identified a novel human structural variant deletion in MTARC1, which is associated with various biomarkers of liver health, including alanine aminotransferase levels. Phenome-wide Mendelian Randomization analyses additionally identified novel putatively causal associations between MTARC1 expression, and esophageal varices and cardiorespiratory traits. We observed that protective MTARC1 variants decreased protein accumulation in in vitro overexpression systems and used genetic tools to study mARC1 depletion in relevant human and mouse systems. Hepatocyte mARC1 knockdown in murine MASH models reduced body weight, liver steatosis, oxidative stress, cell death, and fibrogenesis markers. mARC1 siRNA treatment and overexpression modulated lipid accumulation and cell death consistently in primary human hepatocytes, hepatocyte cell lines, and primary human adipocytes. mARC1 depletion affected the accumulation of distinct lipid species and the expression of inflammatory and mitochondrial pathway genes/proteins in both in vitro and in vivo models. CONCLUSIONS: Depleting hepatocyte mARC1 improved metabolic dysfunction-associated steatotic liver disease-related outcomes. Given the functional role of mARC1 in human adipocyte lipid accumulation, systemic targeting of mARC1 should be considered when designing mARC1 therapies. Our data point to plasma lipid biomarkers predictive of mARC1 abundance, such as Ceramide 22:1. We propose future areas of study to describe the precise molecular function of mARC1, including lipid trafficking and subcellular location within or around the mitochondria and endoplasmic reticulum.

Soluble Guanylyl Cyclase Activator BI 685509 Reduces Portal Hypertension and Portosystemic Shunting in a Rat Thioacetamide-Induced Cirrhosis Model.

Portal hypertension (PT) commonly occurs in cirrhosis. Nitric oxide (NO) imbalance contributes to PT via reduced soluble guanylyl cyclase (sGC) activation and cGMP production, resulting in vasoconstriction, endothelial cell dysfunction, and fibrosis. We assessed the effects of BI 685509, an NO-independent sGC activator, on fibrosis and extrahepatic complications in a thioacetamide (TAA)-induced cirrhosis and PT model. Male Sprague-Dawley rats received TAA twice-weekly for 15 weeks (300-150 mg/kg i.p.). BI 685509 was administered daily for the last 12 weeks (0.3, 1, and 3 mg/kg p.o.; n = 8-11 per group) or the final week only (Acute, 3 mg/kg p.o.; n = 6). Rats were anesthetized to measure portal venous pressure. Pharmacokinetics and hepatic cGMP (target engagement) were measured by mass spectrometry. Hepatic Sirius Red morphometry (SRM) and alpha-smooth muscle actin (αSMA) were measured by immunohistochemistry; portosystemic shunting was measured using colored microspheres. BI 685509 dose-dependently increased hepatic cGMP at 1 and 3 mg/kg (3.92 ± 0.34 and 5.14 ± 0.44 versus 2.50 ± 0.19 nM in TAA alone; P < 0.05). TAA increased hepatic SRM, αSMA, PT, and portosystemic shunting. Compared with TAA, 3 mg/kg BI 685509 reduced SRM by 38%, αSMA area by 55%, portal venous pressure by 26%, and portosystemic shunting by 10% (P < 0.05). Acute BI 685509 reduced SRM and PT by 45% and 21%, respectively (P < 0.05). BI 685509 improved hepatic and extrahepatic cirrhosis pathophysiology in TAA-induced cirrhosis. These data support the clinical investigation of BI 685509 for PT in patients with cirrhosis. SIGNIFICANCE STATEMENT: BI 685509 is an NO-independent sGC activator that was tested in a preclinical rat model of TAA-induced nodular, liver fibrosis, portal hypertension, and portal systemic shunting. BI 685509 reduced liver fibrosis, portal hypertension, and portal-systemic shunting in a dose-dependent manner, supporting its clinical assessment to treat portal hypertension in patients with cirrhosis.

Deep learning-based quantification of NAFLD/NASH progression in human liver biopsies.

Non-alcoholic fatty liver disease (NAFLD) affects about 24% of the world's population. Progression of early stages of NAFLD can lead to the more advanced form non-alcoholic steatohepatitis (NASH), and ultimately to cirrhosis or liver cancer. The current gold standard for diagnosis and assessment of NAFLD/NASH is liver biopsy followed by microscopic analysis by a pathologist. The Kleiner score is frequently used for a semi-quantitative assessment of disease progression. In this scoring system the features of active injury (steatosis, inflammation, and ballooning) and a separated fibrosis score are quantified. The procedure is time consuming for pathologists, scores have limited resolution and are subject to variation. We developed an automated deep learning method that provides full reproducibility and higher resolution. The system was established with 296 human liver biopsies and tested on 171 human liver biopsies with pathologist ground truth scores. The method is inspired by the way pathologist's analyze liver biopsies. First, the biopsies are analyzed microscopically for the relevant histopathological features. Subsequently, histopathological features are aggregated to a per-biopsy score. Scores are in the identical numeric range as the pathologist's ballooning, inflammation, steatosis, and fibrosis scores, but on a continuous scale. Resulting scores followed a pathologist's ground truth (quadratic weighted Cohen's κ on the test set: for steatosis 0.66, for inflammation 0.24, for ballooning 0.43, for fibrosis 0.62, and for the NAFLD activity score (NAS) 0.52. Mean absolute errors on a test set: for steatosis 0.29, for inflammation 0.53, for ballooning 0.61, for fibrosis 0.78, and for the NAS 0.77).

In vivo selective inhibition of TRPC6 by antagonist BI 749327 ameliorates fibrosis and dysfunction in cardiac and renal disease.

Transient receptor potential canonical type 6 (TRPC6) is a nonselective receptor-operated cation channel that regulates reactive fibrosis and growth signaling. Increased TRPC6 activity from enhanced gene expression or gain-of-function mutations contribute to cardiac and/or renal disease. Despite evidence supporting a pathophysiological role, no orally bioavailable selective TRPC6 inhibitor has yet been developed and tested in vivo in disease models. Here, we report an orally bioavailable TRPC6 antagonist (BI 749327; IC50 13 nM against mouse TRPC6, t1/2 8.5-13.5 hours) with 85- and 42-fold selectivity over the most closely related channels, TRPC3 and TRPC7. TRPC6 calcium conductance results in the stimulation of nuclear factor of activated T cells (NFAT) that triggers pathological cardiac and renal fibrosis and disease. BI 749327 suppresses NFAT activation in HEK293T cells expressing wild-type or gain-of-function TRPC6 mutants (P112Q, M132T, R175Q, R895C, and R895L) and blocks associated signaling and expression of prohypertrophic genes in isolated myocytes. In vivo, BI 749327 (30 mg/kg/day, yielding unbound trough plasma concentration ∼180 nM) improves left heart function, reduces volume/mass ratio, and blunts expression of profibrotic genes and interstitial fibrosis in mice subjected to sustained pressure overload. Additionally, BI 749327 dose dependently reduces renal fibrosis and associated gene expression in mice with unilateral ureteral obstruction. These results provide in vivo evidence of therapeutic efficacy for a selective pharmacological TRPC6 inhibitor with oral bioavailability and suitable pharmacokinetics to ameliorate cardiac and renal stress-induced disease with fibrosis.