CeMM: Rare disease reveals crucial factor for fat digestion

Patients with congenital diarrheal disorders, a group of rare inherited diseases with largely unknown mechanisms, suffer from severe to life-threatening diarrhea and nutrient malabsorption from birth. Using state-of-the-art genetic and molecular biology analysis methods involving the revolutionary gut organoid technology, researchers from the LBI-RUD and CeMM, together with the Medical University of Innsbruck and University Medical Center Utrecht identified the largest cohort of DGAT1-deficient patients to date. The scientists also unveiled the molecular mechanisms of the affected protein and discovered its crucial role in fat digestion.

For our body to absorb fat from our diet, a series of complex biochemical reactions take place. First, the fat molecules consisting of a glycerol bound to three fatty acids (therefore also known as triglycerides) have to be digested by various enzymes into its components prior to being absorbed by cells of the small intestine, the enterocytes. Here, they are restored into triglycerides and packed into small particles which are released into the blood stream and transported into the rest of the body. If this process of dietary fat is disturbed, it can lead to devastating conditions.

This was the case with ten children from six families, all of whom suffered since birth from extreme diarrhea and/or vomiting. After a number of conventional therapies failed, the case of the young children was reported to the team of Kaan Boztug, Director of the Ludwig Boltzmann Institute for Rare and Undiagnosed Diseases (LBI-RUD) and Adjunct Principal Investigator of the CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences. In collaboration with the Medical University of Innsbruck and University Medical Center Utrecht, the scientists performed DNA sequencing on the patients and identified mutations in the gene for a protein called diacylglycerol-acyltransferase 1 or DGAT1. The study was published in Gastroenterology (DOI:10.1053/j.gastro.2018.03.040).

DGAT1 is an enzyme crucial for the terminal step of triglyceride formation in enterocytes representing cells lining the intestinal tract. The scientists showed that the mutations resulted in a reduced or total lack of DGAT1 protein in cells of the patients. In an in vitro experiment, those cells were not able to metabolize lipids properly. Above that, the researchers were able to establish gut organoids - miniaturized and simplified structures with organ-like properties - out of patient-derived biopsies and recapitulated the effects of the genetic defect. Excitingly, repairing the function of DGAT1 in patient-derived fibroblast cells or inducing another enzyme called DGAT2  restored the lipid metabolism.

The study highlights the importance of genetic diagnosis of patients with early onset diseases as a crucial step for developing a proper care and therapy. At the same time, this work once again shows the general relevance of research on rare diseases, which in many cases not only helps affected patients, but also provides new insights into human biology.

Publication:

Jorik M van Rijn#, Rico Chandra Ardy#, Zarife Kuloğlu#, Bettina Härter#, Désirée Y. Van Haaften-Visser#, Hubert van der Doef, Marliek van Hoesel, Aydan Kansu, Anke H.M. van Vugt, Marini Thian, Freddy T.M. Kokke, Ana Krolo, Meryem Keçeli Başaran, Neslihan Gürcan Kaya, Aysel Ünlüsoy Aksu, Buket Dalgıç, Figen Ozcay, Zeren Baris, Renate Kain, Edwin C.A Stigter, Klaske D. Lichtenbelt, Maarten P.G. Massink, Karen J Duran, Joke B.G.M Verheij, Dorien Lugtenberg, Peter G.J Nikkels, Henricus G.F. Brouwer, Henkjan Verkade, Rene Scheenstra, Bart Spee, Edward E.S. Nieuwenhuis, Paul J. Coffer, Andreas R Janecke, Gijs van Haaften, Roderick H.J. Houwen, Thomas Müller*, Sabine Middendorp* and Kaan Boztug* (#shared first authors, *shared senior authors). Intestinal failure and aberrant lipid metabolism in patients with DGAT1 deficiency. Gastroenterology, July, 2018. DOI:10.1053/j.gastro.2018.03.040

Funding:

The study was funded by the Austrian Academy of Sciences, the OeNB Jubiläumsfonds, the Netherlands Organisation for Scientific Research and the European Research Council (ERC).