Function of hTim8a in complex IV assembly in neuronal cells provides insight into pathomechanism underlying Mohr-Tranebjærg syndrome

Abstract

Human Tim8a and Tim8b are members of an intermembrane space chaperone network, known as the small TIM family. Mutations in TIMM8A cause a neurodegenerative disease, Mohr-Tranebjærg syndrome (MTS), which is characterised by sensorineural hearing loss, dystonia and blindness. Nothing is known about the function of hTim8a in neuronal cells or how mutation of this protein leads to a neurodegenerative disease. We show that hTim8a is required for the assembly of Complex IV in neurons, which is mediated through a transient interaction with Complex IV assembly factors, in particular the copper chaperone COX17. Complex IV assembly defects resulting from loss of hTim8a leads to oxidative stress and changes to key apoptotic regulators, including cytochrome c, which primes cells for death. Alleviation of oxidative stress with Vitamin E treatment rescues cells from apoptotic vulnerability. We hypothesise that enhanced sensitivity of neuronal cells to apoptosis is the underlying mechanism of MTS.

The TIM22 complex regulates mitochondrial one-carbon metabolism by mediating the import of Sideroflexins

“…Firstly, we excluded changes in the abundance of SFXN proteins due to alterations in gene expression by measuring mRNA abundance for SFXN1, SFXN2, SFXN3 and MTHFD2. Expression of SFXN1, SFXN2 and SFXN3 was unchanged in AGKKO HEK293 cells and Tim9MUT HEK293 cells (Kang et al, 2019) (Figure 2A). Tim9 also functions in the TIM22 pathway (Kang et al, 2019), suggesting the observed changes to the SFXN proteins were indeed posttranslational.…”

“…Expression of SFXN1, SFXN2 and SFXN3 was unchanged in AGKKO HEK293 cells and Tim9MUT HEK293 cells (Kang et al, 2019) (Figure 2A). Tim9 also functions in the TIM22 pathway (Kang et al, 2019), suggesting the observed changes to the SFXN proteins were indeed posttranslational. Protein levels of SFXN1 and SFXN4 were reduced in AGKKO HEK293 and Tim9MUT HEK293 mitochondria, as confirmed by western blot (Figure 2B).…”

“…In summary, the levels of SFXN proteins are reduced as a result of TIM22 complex dysfunction. This dependency is specific to the TIM22 complex rather than a non-specific response to stress, as Tim8aKO and Tim8bKO HEK293 mitochondria, which exhibit general mitochondrial dysfunction, but no TIM22 complex impairment (Kang et al, 2019), show no changes in abundance of SFXN proteins ( Figure 2G).…”

Proteomic identification ofCoxiella burnetiieffector proteins targeted to the host cell mitochondria during infection

“…For label free quantitative LC-MS/MS experiments of mitochondria, statistical analysis of data was consistent with published analyses from our and other groups employing similar instrumentation and methods (46,62,63). All experiments were performed in at least 3 independent biological replicates.…”

“…Tris-tricine SDS-PAGE was performed as previously described (44)(45)(46)(47). Samples for electrophoresis were combined with SDS-PAGE loading dye (50 mM Tris-Cl (pH 8.…”