Abstract
Ionic calcium (Ca2+) is a key messenger in signal transduction and its mitochondrial uptake plays an important role in cell physiology. This uptake is mediated by the mitochondrial Ca2+ uniporter (MCU), which is regulated by EMRE (essential MCU regulator) encoded by the SMDT1 (single-pass membrane protein with aspartate rich tail 1) gene. This work presents the genetic, clinical and cellular characterization of two patients harbouring SMDT1 variants and presenting with muscle problems. Analysis of patient fibroblasts and complementation experiments provide evidence that these variants lead to absence of EMRE protein, induce MCU subcomplex formation and impair mitochondrial Ca2+ uptake. However, the activity of the oxidative phosphorylation enzymes, mitochondrial morphology and membrane potential, as well as routine/ATP-linked respiration were not affected. We hypothesize that the muscle-related symptoms in the patients with SMDT1 variants result from aberrant mitochondrial Ca2+ uptake.
Competing Interest Statement
WJHK is a scientific advisor of Khondrion B.V. (Nijmegen, The Netherlands). This company was not involved in the data analysis and interpretation, writing of the manuscript, and in the decision to submit the manuscript for publication.
Footnotes
↵% Shared first authors.
Abbreviations
- ΔΨ
- trans-MIM mitochondrial membrane potential
- [Ca2+]c
- cytosolic free Ca2+ concentration
- [Ca2+]m
- mitochondrial free Ca2+ concentration
- [Ca2+]n
- nuclear free Ca2+ concentration
- BK
- bradykinin
- CK
- creatine kinase
- ECAR
- extracellular acidification rate
- EMRE
- essential MCU Regulator
- FOV
- field of view
- IF
- immunofluorescence
- LGMD
- limb-girdle muscular dystrophy
- MCU
- mitochondrial calcium uniporter
- MICU1/2
- mitochondrial calcium uptake protein 1/2
- MIM
- mitochondrial inner membrane
- MOM
- mitochondrial outer membrane
- MW
- molecular weight
- OCR
- oxygen consumption rate
- OXPHOS
- oxidative phosphorylation
- PHSFs
- primary human skin fibroblasts
- SMDT1
- single-pass membrane protein with aspartate rich tail 1
- TCA
- tricarboxylic acid cycle
- WB
- Western blot
- WES
- whole exome sequencing.