Interactions Between Nuclear Receptor SHP and FOXA1 Maintain Oscillatory Homocysteine Homeostasis in Mice

Background & Aims Hyperhomocysteinemia is often associated with liver and metabolic diseases. We studied nuclear receptors that mediate oscillatory control of homocysteine homeostasis in mice. Methods We studied mice with disruptions in Nr0b2 (called small heterodimer partner [SHP]-null mice), betaine-homocysteine S-methyltransferase (Bhmt), or both genes (BHMT-null/SHP-null mice), along with mice with wild-type copies of these genes (controls). Hyperhomocysteinemia was induced by feeding mice alcohol (National Institute on Alcohol Abuse and Alcoholism binge model) or chow diets along with water containing 0.18% DL-homocysteine. Some mice were placed on diets containing cholic acid (1%) or cholestyramine (2%) or high-fat diets (60%). Serum and livers were collected during a 24-hour light-dark cycle and analyzed by RNA-seq, metabolomic, and quantitative polymerase chain reaction, immunoblot, and chromatin immunoprecipitation assays. Results SHP-null mice had altered timing in expression of genes that regulate homocysteine metabolism compared with control mice. Oscillatory production of S-adenosylmethionine, betaine, choline, phosphocholine, glyceophosphocholine, cystathionine, cysteine, hydrogen sulfide, glutathione disulfide, and glutathione, differed between SHP-null mice and control mice. SHP inhibited transcriptional activation of Bhmt and cystathionine γ-lyase by FOXA1. Expression of Bhmt and cystathionine γ-lyase was decreased when mice were fed cholic acid but increased when they were placed on diets containing cholestyramine or high-fat content. Diets containing ethanol or homocysteine induced hyperhomocysteinemia and glucose intolerance in control, but not SHP-null, mice. In BHMT-null and BHMT-null/SHP-null mice fed a control liquid, lipid vacuoles were observed in livers. Ethanol feeding induced accumulation of macrovesicular lipid vacuoles to the greatest extent in BHMT-null and BHMT-null/SHP-null mice. Conclusions Disruption of Shp in mice alters timing of expression of genes that regulate homocysteine metabolism and the liver responses to ethanol and homocysteine. SHP inhibits the transcriptional activation of Bhmt and cystathionine γ-lyase by FOXA1.