Effects of a Mutation in the HSPE1 Gene Encoding the Mitochondrial Co-chaperonin HSP10 and Its Potential Association with a Neurological and Developmental Disorder

Abstract

We here report molecular investigations of a missense mutation in the HSPE1 gene encoding the HSP10 subunit of the HSP60/ HSP10 chaperonin complex that assists protein folding in the mitochondrial matrix. The mutation was identified in an infant who came to clinical attention due to infantile spasms at 3 months of age. Clinical exome sequencing revealed heterozygosity for a HSPE1 NM_002157.2:c.217C>T de novo mutation causing replacement of leucine with phenylalanine at position 73 of the HSP10 protein. This variation has never been observed in public exome sequencing databases or the literature. To evaluate whether the mutation may be disease-associated we investigated its effects by in vitro and ex vivo studies. Our in vitro studies indicated that the purified mutant protein was functional, yet its thermal stability, spontaneous refolding propensity, and resistance to proteolytic treatment were profoundly impaired. Mass spectrometric analysis of patient fibroblasts revealed barely detectable levels of HSP10-p.Leu73Phe protein resulting in an almost 2-fold decrease of the ratio of HSP10 to HSP60 subunits. Amounts of the mitochondrial superoxide dismutase SOD2, a protein whose folding is known to strongly depend on the HSP60/HSP10 complex, were decreased to approximately 20% in patient fibroblasts in spite of unchanged SOD2 transcript levels. As a likely consequence, mitochondrial superoxide levels were increased about 2-fold. Although, we cannot exclude other causative or contributing factors, our experimental data support the notion that the HSP10-p.Leu73Phe mutation could be the cause or a strong contributing factor for the disorder in the described patient.

Cytosolic Trapping of a Mitochondrial Heat Shock Protein Is an Early Pathological Event in Synucleinopathies

“…Therefore, even subtle changes in its concentration may affect the functionality of several proteins and cellular functions. The regulation of HSP10 levels in neurological diseases is not well understood (Hickey et al, 2000;Bross et al, 2007;Kim and Lee, 2007;Bie et al, 2016;Bross and Fernandez-Guerra, 2016;Fan et al, 2017), and to our knowledge, this has not been investigated in the context of synucleinopathies. To assess whether the level of HSP10 is altered in human brain tissue, we fractionated putamen samples of patients with PD and controls (Figures 1A and 1B).…”

“…Interestingly, the levels of HSP10 limit the formation of the symmetric complexes, and the asymmetric complex has reduced folding capacity (Nisemblat et al, 2015). Because the HSP10/HSP60 complex is one of the most important players in mitochondrial quality control (Horwich et al, 2007;Campos et al, 2016), reduced function of the complex results in embryonic lethality (Christensen et al, 2010), and a heterozygous mutation in the HSPE1 gene associates with severe, early-onset neurological disorder in humans (Bie et al, 2016). Although the mutant protein is functional, its resistance to proteases is substantially reduced, resulting in an almost 2-fold reduction in the HSP10/HSP60 ratio.…”

Chaperonin of Group I: Oligomeric Spectrum and Biochemical and Biological Implications

“…Noteworthy is that the ability of the mutant chaperonin to form oligomers was affected (Parnas et al, 2009 ). In addition, a missense mutation, Leu73Phe, of HSP10, the co-chaperone of HSP60, was recently reported to be associated to a severe neurological and developmental disorder (Bie et al, 2016 ). The detailed molecular mechanism involving the mutant HSP10 that causes the lesions observed has not yet been fully elucidated.…”

Mitochondrial Chaperones in the Brain: Safeguarding Brain Health and Metabolism?

“…But besides the impairment of protein degradation machineries by mutations, e.g., of LonP and ClpP ( 172 ), also the chaperone system can be compromised, as mutations of Hsp60 are implicated in hereditary spastic paraplegia ( 34 ). Furthermore, a discovered missense mutation of the Hspe1 gene (coding for Hsp10) has been associated with neurodegeneration ( 79 ) and thus likely to metabolic complications as well. Interestingly, reduction of these proteins also alter metabolism.…”