Abstract
It is becoming increasingly apparent that mitochondria dysfunction plays an important role in the pathogenesis of Huntington’s disease (HD), but the underlying mechanism is still elusive. Thus, there is a still need for further studies concerning the upstream events in the mitochondria dysfunction that could contribute to cell death observed in HD. Taking into account the fundamental role of the voltage-dependent anion-selective channel (VDAC) in mitochondria functioning, it is reasonable to consider the channel as a crucial element in HD etiology. Therefore, we applied inducible PC12 cell model of HD to determine the relationship between the effect of expression of wild type and mutant huntingtin (Htt and mHtt, respectively) on cell survival and mitochondria functioning in intact cells under conditions of undergoing cell divisions. Because after 48 h of Htt and mHtt expression differences in mitochondria functioning co-occurred with differences in the cell viability, we decided to estimate the effect of Htt and mHtt expression lasted for 48 h on VDAC functioning. Therefore, we isolated VDAC from the cells and tested the preparations by black lipid membrane system. We observed that the expression of mHtt, but not Htt, resulted in changes of the open state conductance and voltage-dependence when compared to control cells cultured in the absence of the expression. Importantly, for all the VDAC preparations, we observed a dominant quantitative content of VDAC1, and the quantitative relationships between VDAC isoforms were not changed by Htt and mHtt expression. Thus, Htt and mHtt-mediated functional changes of VDAC, being predominantly VDAC1, which occur shortly after these protein appearances in cells, may result in differences concerning mitochondria functioning and viability of cells expressing Htt and mHtt. The assumption is important for better understanding of cytotoxicity as well as cytoprotection mechanisms of potential clinical application.
Highlights
Huntington’s disease (HD) is a fatal neurodegenerative disease, which is characterized by progressive cognitive deterioration, psychiatric disturbances, and movement disorder with maximum degeneration occurring in striatum and deep layers of the cerebral cortex [e.g., Bonelli and Hofmann [1]; Gövert and Schneider [2]; Glajch and Sadri-Vakili [3]]
To monitor viability of PC12 cells expressing Htt and mHtt (PC12 HD-Q23 and PC12 HD-Q74, respectively) for the studied periods of time (4, 12, 24, and 48 h), the number of cells that adhere to the bottom of the applied plates was calculated [e.g., Rantzsch et al [37]], and the data were verified by the application of MTT assay based on metabolic activity of living cells [e.g., Kupcsik [38]]
The obtained results indicated that a clear difference in viability of PC12 HD-Q23 and PC12 HD-Q74 cells occurred when Htt and mHtt expression lasted for 48 h
Summary
Huntington’s disease (HD) is a fatal neurodegenerative disease, which is characterized by progressive cognitive deterioration, psychiatric disturbances, and movement disorder with maximum degeneration occurring in striatum and deep layers of the cerebral cortex [e.g., Bonelli and Hofmann [1]; Gövert and Schneider [2]; Glajch and Sadri-Vakili [3]]. The disease is caused by the VDAC and Huntington’s Disease expansion of the unstable trinucleotide CAG (glutamine codon) repeat region within the first exon of the gene encoding the protein huntingtin (Htt) that results in synthesis of its mutant form (mHtt) containing a sequence of 36 or more glutamines at N-terminus [4]. Over 130 review papers on the role of mitochondria in HD pathogenesis have been published till now. Over 130 review papers on the role of mitochondria in HD pathogenesis have been published till They address mHtt effects on mitochondrial bioenergetics and biogenesis, protein import complex assembly, fission and fusion, mitochondrial transport including Ca2+ and metal homeostasis, and the degradation of damaged mitochondria via autophagy (mitophagy). It is evident that voltage-dependent anionselective channel (VDAC), regarded as a dynamic regulator, or even governor, of mitochondrial functions, contributes to affected phenomena directly or by interacting with the involved proteins [e.g., Colombini [11]; Mannella and Kinnally [12]; Shoshan-Barmatz et al [13]; Maldonado and Lemasters [14]; Martel et al [15]; Karachitos et al [16]]
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