Universität zu Köln

Moschandrea, Chrysanthi ORCID: 0000-0003-0770-5786 (2023). The role of mitochondria in dietary lipid processing by enterocytes. PhD thesis, Universität zu Köln.

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Abstract

The intestinal epithelium consists of a single layer of columnar epithelial cells, which perform important functions in nutrient absorption and metabolic regulation, and form a structural barrier between the luminal microbiota and mucosal immune cells. Mitochondria are best known for their function in energy production, but they are also involved in the regulation of multiple cellular processes including metabolic, immune and stress responses. Mitochondrial dysfunction is associated with ageing and a steadily increasing number of human diseases. Patients with mutations affecting mitochondrial function often present with a multitude of gastrointestinal symptoms including dramatic weight loss, gut dysmotility and pseudo-obstruction and severe abdominal pain that are associated with malnutrition. However, the function of mitochondria in the intestine and specifically in intestinal lipid trafficking and secretion remains poorly understood. To study the role of mitochondria in the intestine, we generated mice with intestinal epithelial cell (IEC)-specific ablation of DARS2, referred to as DARS2IEC-KO mice. DARS2 is a mitochondrial specific aspartyl - tRNA synthetase, essential for facilitating mitochondrial translation of the 13 mtDNA - encoded OXPHOS subunits. Deficiency in DARS2 ultimately leads to a very prominent respiratory chain dysfunction. DARS2IEC-KO mice were born in the expected Mendelian ratios, but developed a spontaneous postnatal phenotype, manifested by severe weight loss, hypoglycemia and failure to thrive. Histological examination of intestinal tissues from these mice revealed perturbed tissue architecture accompanied by impaired epithelial stemness, proliferation and differentiation and a massive accumulation of lipids within large lipid droplets (LDs). Tamoxifen administration on five consecutive days induced DARS2 ablation in IECs of adult Dars2fl/fl Villin-CreERT2mice (DARS2tamIECKO mice). Histologically, only the enterocytes of the proximal small intestine that are capable of facilitating efficient uptake, mobilization and transport of dietary nutrients, including fats were engorged with large LDs in DARS2tamIEC-KO mice. Moreover, mice with IEC specific ablation of succinate dehydrogenase (SDHA), which is part of CII of the electron transport chain and additionally serves as enzyme of the TCA cycle, as well as mice lacking the cytochrome c oxidase assembly factor heme A: farnesyltransferase (COX10) that is an assembly factor of CIV in the IECs, were studied. Both SDHAIEC-KO and COX10IEC-KO mice demonstrated a similar phenotype to mice with DARS2 deficiency in IECs. These mice exhibited markedly reduced body weight, did not survive beyond the age of four weeks and displayed massive LD accumulation in enterocytes. Together, these findings showed that mitochondrial deficiency caused LD accumulation in enterocytes, suggesting that loss of mitochondrial function causes impaired transport of dietary lipids. Digested lipids taken up by enterocytes are re-esterified and assembled into triglyceriderich lipoproteins primarily in the form of chylomicrons (CMs), which are then released in the circulation to supply peripheral organs with lipids. Interestingly, feeding with a fat-free diet prevented fat accumulation in LDs in enterocytes of DARS2tamIEC-KO mice, showing that the lipid overload observed in DARS2-deficient enterocytes derives primarily from dietary fat. In addition, postprandial studies revealed that DARS2 deficiency in IECs significantly impaired dietary lipid transport to the plasma and peripheral organs. Furthermore, transmission electron microscopy revealed a distinct lack of mature chylomicrons in DARS2-deficient enterocytes concomitant with a total disorganization of the Golgi apparatus, suggesting that defective ER to Golgi trafficking underlies impaired chylomicron production and secretion. Taken together, our results revealed an essential function of mitochondria, in regulating chylomicron production and dietary lipid transport IV in enterocytes, a mechanism that could potentially explain the intestinal and nutritional defects observed in patients with mitochondrial diseases.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Moschandrea, Chrysanthi cmoschan@uni-koeln.de orcid.org/0000-0003-0770-5786 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-722592
DOI:	10.1038/s41586-023-06857-0
Date:	20 December 2023
Publisher:	Nature
Place of Publication:	University of Cologne
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	CECAD - Cluster of Excellence Cellular Stress Responses in Aging-Associated Diseases
Subjects:	Natural sciences and mathematics
Uncontrolled Keywords:	Keywords Language mitochondrial OXPHOS, DARS2, small intestine, proximal enterocytes, dietary lipids, ER to Golgi trafficking, chylomicron production English
Date of oral exam:	3 June 2022
Referee:	Name Academic Title Moschandrea, Chrysanthi UNSPECIFIED
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/72259