Loss of Mitochondrial AAA Proteases AFG3L2 and YME1L Impairs Mitochondrial Structure and Respiratory Chain Biogenesis

Abstract

Mitochondrial protein quality control is crucial for the maintenance of correct mitochondrial homeostasis. It is ensured by several specific mitochondrial proteases located across the various mitochondrial subcompartments. Here, we focused on characterization of functional overlap and cooperativity of proteolytic subunits AFG3L2 (AFG3 Like Matrix AAA Peptidase Subunit 2) and YME1L (YME1 like ATPase) of mitochondrial inner membrane AAA (ATPases Associated with diverse cellular Activities) complexes in the maintenance of mitochondrial structure and respiratory chain integrity. We demonstrate that loss of AFG3L2 and YME1L, both alone and in combination, results in diminished cell proliferation, fragmentation of mitochondrial reticulum, altered cristae morphogenesis, and defective respiratory chain biogenesis. The double AFG3L2/YME1L knockdown cells showed marked upregulation of OPA1 protein forms, with the most prominent increase in short OPA1 (optic atrophy 1). Loss of either protease led to marked elevation in OMA1 (OMA1 zinc metallopeptidase) (60 kDa) and severe reduction in the SPG7 (paraplegin) subunit of the m-AAA complex. Loss of the YME1L subunit led to an increased Drp1 level in mitochondrial fractions. While loss of YME1L impaired biogenesis and function of complex I, knockdown of AFG3L2 mainly affected the assembly and function of complex IV. Our results suggest cooperative and partly redundant functions of AFG3L2 and YME1L in the maintenance of mitochondrial structure and respiratory chain biogenesis and stress the importance of correct proteostasis for mitochondrial integrity.

Down‐regulation of the mitochondrial i‐AAA protease Yme1L induces muscle atrophy via FoxO3a and myostatin activation

“…In contrast, reduction in Yme1L seems directly to induce protein breakdown in muscle cells via an imbalance in mitochondrial dynamics. Indeed, Yme1L participates in various processes to maintain healthy mitochondria, including the regulation of mitophagy by controlling Oma1 and s‐Opa1 . Yme1L is involved in the assembly of mitochondrial respiratory chain subunits, including F1F0‐ATPase, Cox4 and ND1, and it removes damaged or misfolded mitochondrial inner membrane proteins .…”

Investigating the influence of mtDNA and nuclear encoded mitochondrial variants on high intensity interval training outcomes

“…An intronic variant within AFG3L2 was also shown to be associated with the composite exercise response phenotype (rs7231304), but this gene has not previously been associated with exercise response. However, mutations in AFG3L2 have been shown to cause spinocerebellar ataxia through the development of mitochondrial proteotoxicity 27,28 . As such, the intronic variation within this gene might inhibit exercise response through dysregulation of mitochondrial structure and function.…”

Identification of novel mitochondrial and mitochondrial related genetic loci associated with exercise response in the Gene SMART study

“…An intronic variant within AFG3L2 was also shown to be associated with the composite exercise response phenotype (rs7231304), but this gene has not previously been associated with exercise response. However, mutations in AFG3L2 have been shown to cause spinocerebellar ataxia through the development of mitochondrial proteotoxicity (25, 26). As such, the intronic variation within this gene might inhibit exercise response through dysregulation of mitochondrial structure and function.…”

“…FASTA files were generated for all samples and then merged VCF and FASTA files were produced for the entire data set. The merged FASTA files were annexed using MITOMASTER, a mitochondrial sequence database, to call haplogroups and obtain variant annotation information for all samples (39)(25). The merged VCF file was converted to PLINK (v1.90p) format using the function ‘ --make-bed’ for further association analysis.…”