KNOCKOUT (KO) OF NEUROKININ RECEPTOR 1 (NK1R) AMELIORATES LIVER PHENOTYPES IN AN ACUTE MODEL OF ALCOHOL-INDUCED LIVER DISEASE (ALD)

Background: Alcoholic hepatitis (AH) is a life-threatening form of alcohol-associated liver disease (ALD), with no effective therapy. Liver neutrophil infiltration is a hallmark of AH, yet the mechanisms by which alcohol promotes neutrophil recruitment and disrupts neutrophil functions remain elusive. Identifying new therapeutic targets to reduce neutrophil-mediated liver damage is essential. Bruton’s tyrosine kinase (BTK), a non-receptor tyrosine kinase, plays an important role in neutrophil development and function, however, the mechanism by which BTK regulates neutrophil-mediated liver damage, specifically in AH, is not yet studied.
Methods: Female, C57BL6 mice aged 10-12 weeks received Lieber-deCarli diet with alcohol for 10 days followed by one binge (alcoholic hepatitis-AH-model) or calorie-matched control diet. Some mice received oral gavage of Evobrutinib, a BTK inhibitor (BTKi) or DMSO from day7 to day10. Liver damage was assessed by measuring serum ALT. Serum levels of proinflammatory cytokines were measured by ELISA. BTK phosphorylation (pBTK) was assessed in human or mouse livers by western blotting, and in bone marrow (BM) progenitors or liver neutrophils by flow cytometry. Circulating neutrophils from healthy controls (HC) and AH patients were analyzed for BTK expression by RNA-seq. Tandem mass spectrometry (LC-MS/MS) was performed in mouse liver lysates to identify BTK substrates.
Results: Our results from unbiased RNA-seq in circulating neutrophils showed a significant increase in BTK in AH patients compared to HC. Consistently, pBTK was significantly increased in neutrophils from AH patients compared to HC. We found that pBTK (Y223 and Y551) was upregulated in humans as well as in mouse livers with ALD. We further dissected that acute alcohol binge rather than chronic moderate alcohol use triggers pBTK in mice. In vitro, physiologically relevant doses of alcohol induced rapid pBTK induction in neutrophils that was partially TLR4-mediated. In a preclinical model of AH, administration of Evobrutinib, a small molecule BTK inhibitor, significantly decreased pro-inflammatory cytokines levels, and attenuated liver damage. Importantly, we discovered that alcohol-induced liver neutrophil infiltration correlated with the expansion of BM granulopoiesis, and that pBTK in BM progenitors was essential for alcohol-induced granulopoiesis. In vivo, BTK inhibition significantly reduced granulopoiesis, circulating neutrophils, and liver infiltration in the presence of alcohol administration. Mechanistically, using LC-MS/MS we discovered CD84 as a novel kinase target of BTK which is involved in granulopoiesis.
Conclusion: Our findings define a novel role of BTK in regulating CD84 phosphorylation and granulopoiesis that could be harnessed to address pressing therapeutic needs in AH.

Background: ALD ranges from simple steatosis to alcohol-induced steatohepatitis (ASH), alcoholic hepatitis and liver cirrhosis. Liver steatosis, inflammation, fibrosis, and ductular reaction (DR) and biliary senescence are hallmarks of ALD. Substance P (SP, encoded by Tac1 and degraded by membrane metalloendopeptidase, MME) modulates biliary functions by interaction with NK1R. While activation of the SP/NK1R axis increases DR and liver fibrosis via the release of biliary SASPs, KO of NK1R ameliorates liver phenotypes in cholestatic mice. Women are more susceptible to ALD than men and there is no data regarding the role of NK1R in the progression of ALD in females. We evaluated the role of NK1R on liver damage in an acute model of ALD in female mice. Methods: Wild-type (WT, n=8) and NK1R KO female mice (n=5) were subjected to the chronic-plus-binge ethanol (EtOH) feeding model of ALD (NIAAA model). Mice were fed EtOH diet for 10 days with a single gavage (5 g/kg EtOH) to induce ASH. Control mice were pair-feed an isocaloric control diet for 10 days, followed by a single gavage of isocaloric maltodextrin. On day 10, we collected liver, serum, cholangiocytes and hepatocytes. In mice we measured the levels of ALT in serum, and SP in serum and biliary supernatant. Steatosis was examined by H&E and Oil Red O staining. Fatty acid oxidation in hepatocytes was evaluated by qPCR for PPARa and Acetyl CoA synthetase 1 (ACS1). We evaluated DR by IHC for CK-19 and biliary senescence by IF for p16 in liver sections. Human specimens from male (n=5) and female (n=4) healthy controls (n=9), and patients with alcoholic cirrhosis male (n=15) and female (n=6) were evaluated for serum SP levels and NK1R immunoreactivity of cholangiocytes, hepatocytes and hepatic stellate cells. NK1R and MME protein levels were evaluated in human total liver (n=4) by immunoblots. Results: NK1R was mainly expressed by human cholangiocytes. There were enhanced SP serum levels and increased NK1R biliary immunoreactivity in female/male patients with alcoholic cirrhosis compared to controls. MME protein expression decreased in total liver from female patients with alcoholic cirrhosis compared to controls. There were increased levels of ALT in serum, and SP levels in serum and biliary supernatant from WT EtOH-fed mice compared to controls. There was a moderate (not significant) increase in DR in EtOH-fed mice compared to controls. There was increased hepatic steatosis, lipid accumulation and enhanced p16 immunoreactivity in mouse liver sections from EtOH-fed WT mice (compared to CD-fed WT mice), phenotypes that returned to normal values in EtOH-fed NK1R KO mice. All EtOH-fed mice showed a significant decrease in the expression of PPARa and ACS1 in hepatocytes compared to CD-fed WT mice. Conclusion: Downregulation of NK1R signaling may be important in the management of ALD phenotypes.