Professor Mato has been working in the field of methionine adenosyltransferases (MAT) genes and proteins for over 30 years. MAT catalyzes the synthesis of S-adenosylmethionine (SAMe, the principal biological methyl donor) from methionine, an essential amino acid, and ATP. This is the only reaction that metabolizes methionine in mammals. Two genes encode for MAT: MAT1A, which is expressed in normal differentiated liver, and MAT2A, which is expressed in all extrahepatic tissues as well as in fetal liver. A third gene, MAT2B, encodes a MAT2β subunit that regulates MAT2A-encoded enzyme.

In the middle 80s his laboratory discovered that hepatic MAT activity was markedly reduced in patients with chronic liver disease independently of its etiology. Subsequently, the laboratory of Mato cloned MAT1A gene and promoter and discovered the differential expression of MAT1A and MAT2A genes in developing rat liver. In collaboration with the laboratory of Shelly Lu, at the Cedars-Sinai Medical Center in Los Angeles (US), described their transcriptional and post-transcriptional regulation and how changes in MAT expression affect liver health, growth, death, and malignant degeneration. Together, they developed the Mat1a knockout (KO) mouse model, which exhibits hypermethioninemia, chronic SAMe deficiency, increased oxidative stress, spontaneously develop steatohepatitis, fibrosis and hepatocellular carcinoma (HCC). Patients with liver injury often show reduced expression of MAT1A, indicating that the Mat1a KO mouse model is relevant to study human NASH.

The laboratory of Mato also developed the Gnmt KO mouse model, where hepatic SAMe accumulates to supraphysiological level and the mice also develop steatohepatitis and HCC but by different mechanisms than Mat1a KO mice. The Gnmt KO model is relevant to human disease as children with GNMT mutations were identified to have liver injury. These models have been instrumental in teaching us about the various functions of SAMe and pathways that it regulates. This work stimulated pharmaceutical companies to study the effect of SAMe therapy on liver disease and in 1999 the laboratory of Mato demonstrated that SAMe treatment increased survival in human alcoholic liver cirrhosis.

Recent studies from this laboratory have revealed that SAMe, through regulation of mitochondrial function, red-ox processes, and CYP450, causes major changes in cellular metabolism that are vital for maintaining lipid homeostasis. Ongoing studies, merging epigenetics, transcriptomics, proteomics and metabolomics, are defining how changes in SAMe concentration alter the flux of metabolites such as fatty acids and bile acids and how these changes lead to fat accumulation and liver injury.

Another major focus of this laboratory is to develop non-invasive tests to diagnose liver diseases. Using mass spectrometry metabolomics, in collaboration with the biotech company OWL (co-founded by Dr. Mato) the laboratory of Mato developed the first non-invasive serum test to diagnose nonalcoholic steatohepatitis. Dr. Mato is considered one of the world’s leading authorities on SAMe and MAT. The Plan Nacional of R&D of the Spanish Ministry of Economy and Competitiveness (MINECO) has uninterruptedly funded his laboratory since the early 1980s, been his laboratory also funded uninterruptedly by the NIH during the last 15-years.