Human <scp>ALPI</scp> deficiency causes inflammatory bowel disease and highlights a key mechanism of gut homeostasis

Abstract

Herein, we report the first identification of biallelic-inherited mutations in <i>ALPI</i> as a Mendelian cause of inflammatory bowel disease in two unrelated patients. <i>ALPI</i> encodes for intestinal phosphatase alkaline, a brush border metalloenzyme that hydrolyses phosphate from the lipid A moiety of lipopolysaccharides and thereby drastically reduces Toll-like receptor 4 agonist activity. Prediction tools and structural modelling indicate that all mutations affect critical residues or inter-subunit interactions, and heterologous expression in HEK293T cells demonstrated that all <i>ALPI</i> mutations were loss of function. <i>ALPI</i> mutations impaired either stability or catalytic activity of ALPI and rendered it unable to detoxify lipopolysaccharide-dependent signalling. Furthermore, ALPI expression was reduced in patients' biopsies, and ALPI activity was undetectable in ALPI-deficient patient's stool. Our findings highlight the crucial role of ALPI in regulating host-microbiota interactions and restraining host inflammatory responses. These results indicate that <i>ALPI</i> mutations should be included in screening for monogenic causes of inflammatory bowel diseases and lay the groundwork for ALPI-based treatments in intestinal inflammatory disorders.