Authors:	Dietsche, Felicia
Title:	The effect of knockout and mutation of the Transmembrane BAX Inhibitor Motif containing Protein 5 (TMBIM5) on cellular and mitochondrial function in cells and mice
Online publication date:	8-Mar-2022
Year of first publication:	2022
Language:	english
Abstract:	Mitochondria are dynamic organelles with a central role in many vital processes. Besides ATP generation and other functions, they are crucial for cellular Ca2+ buffering. In close cooperation with the endoplasmic reticulum, mitochondria can shape cytosolic Ca2+ signals by taking in Ca2+. Free Ca2+ in the mitochondrial matrix enhances ATP production which links mitochondrial metabolism to the cellular energy demand. Only a decade ago, the mitochondrial Ca2+ uptake pore was identified as the Mitochondrial Calcium Uniporter (MCU). However, MCU knockout (KO) mice are viable and lack a drastic phenotype. This created doubts about the singularity of MCU. We propose the Transmembrane BAX Inhibitor Motif containing protein (TMBIM) 5 as a novel mitochondrial Ca2+ channel. TMBIM5 is ubiquitously expressed, localises to the inner mitochondrial membrane and shares conserved sequence homologies with TMBIM6 and the bacterial homologue BsYetJ. Both are pH-dependent Ca2+ channels. Loss of TMBIM5 leads to a disruption in the cristae structure. Using TMBIM5 KO cell lines (HAP1/HEK293), I demonstrated that it does not interact with the mitochondrial contact site and cristae organizing system. The KO impairs mitochondrial Ca2+ uptake and affects the expression of MCU and its regulator Mitochondrial Calcium Uptake 1. In addition, I detected changes in the abundance and processing of Optical Atrophy 1 (OPA1), a protein involved in cristae stabilisation. Its dysregulation may cause the observed abnormal cristae structure. To study the effect of TMBIM5 in vivo, we obtained a mouse line containing an amino acid exchange (D326R) in the putative pore domain. The analogue mutation induces a loss-of-function in TMBIM6. Similar to MCU KO, the mice did not show any gross phenotype. Yet, they were born at a reduced Mendelian rate and the mutated protein was downregulated in the adult animals. Screening for functional abnormalities revealed a striking cell-type dependence. The skeletal muscle is most severely affected by myopathy and dysregulation in mitochondrial Ca2+ uptake and buffering. My results indicate that TMBIM5 is involved in mitochondrial Ca2+ handling and presumably only indirectly affects mitochondrial cristae structure. The tissue-specificity in the mouse suggests that additional regulatory elements may exist that affect TMBIM5 function.
DDC:	500 Naturwissenschaften 500 Natural sciences and mathematics 570 Biowissenschaften 570 Life sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 10 Biologie
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-6798
URN:	urn:nbn:de:hebis:77-openscience-c32a476e-dfcc-4d8c-ad71-64b6145a5d565
Version:	Original work
Publication type:	Dissertation
License:	CC BY-ND
Information on rights of use:	https://creativecommons.org/licenses/by-nd/4.0/
Appears in collections:	JGU-Publikationen