Age-related proteostasis and metabolic alterations in Caspase-2-deficient mice.

Ageing is a complex biological process for which underlying biochemical changes are still largely unknown. We performed comparative profiling of the cellular proteome and metabolome to understand the molecular basis of ageing in Caspase-2-deficient (Casp2(-/-)) mice that are a model of premature ageing in the absence of overt disease. Age-related changes were determined in the liver and serum of young (6-9 week) and aged (18-24 month) wild-type and Casp2(-/-) mice. We identified perturbed metabolic pathways, decreased levels of ribosomal and respiratory complex proteins and altered mitochondrial function that contribute to premature ageing in the Casp2(-/-) mice. We show that the metabolic profile changes in the young Casp2(-/-) mice resemble those found in aged wild-type mice. Intriguingly, aged Casp2(-/-) mice were found to have reduced blood glucose and improved glucose tolerance. These results demonstrate an important role for caspase-2 in regulating proteome and metabolome remodelling during ageing.

Promoter polymorphisms in two overlapping 6p25 genes implicate mitochondrial proteins in cognitive deficit in schizophrenia.

In a previous study, we detected a 6p25-p24 region linked to schizophrenia in families with high composite cognitive deficit (CD) scores, a quantitative trait integrating multiple cognitive measures. Association mapping of a 10 Mb interval identified a 260 kb region with a cluster of single-nucleotide polymorphisms (SNPs) significantly associated with CD scores and memory performance. The region contains two colocalising genes, LYRM4 and FARS2, both encoding mitochondrial proteins. The two tagging SNPs with strongest evidence of association were located around the overlapping putative promoters, with rs2224391 predicted to alter a transcription factor binding site (TFBS). Sequencing the promoter region identified 22 SNPs, many predicted to affect TFBSs, in a tight linkage disequilibrium block. Luciferase reporter assays confirmed promoter activity in the predicted promoter region, and demonstrated marked downregulation of expression in the LYRM4 direction under the haplotype comprising the minor alleles of promoter SNPs, which however is not driven by rs2224391. Experimental evidence from LYRM4 expression in lymphoblasts, gel-shift assays and modelling of DNA breathing dynamics pointed to two adjacent promoter SNPs, rs7752203-rs4141761, as the functional variants affecting expression. Their C-G alleles were associated with higher transcriptional activity and preferential binding of nuclear proteins, whereas the G-A combination had opposite effects and was associated with poor memory and high CD scores. LYRM4 is a eukaryote-specific component of the mitochondrial biogenesis of Fe-S clusters, essential cofactors in multiple processes, including oxidative phosphorylation. LYRM4 downregulation may be one of the mechanisms involved in inefficient oxidative phosphorylation and oxidative stress, increasingly recognised as contributors to schizophrenia pathogenesis.

Disulphide formation on mitochondrial protein thiols.

A large number of proteins contain free thiols that can be modified by the formation of internal disulphides or by mixed disulphides with low-molecular-mass thiols. The majority of these latter modifications result from the interaction of protein thiols with the endogenous glutathione pool. Protein glutathionylation and disulphide formation are of significance both for defence against oxidative damage and in redox signalling. As mitochondria are central to both oxidative damage and redox signalling within the cell, these modifications of mitochondrial proteins are of particular importance. In the present study, we review the mechanisms and physiological significance of these processes.

Lipophilic triphenylphosphonium cations as tools in mitochondrial bioenergetics and free radical biology.

Lipophilic phosphonium cations were first used to investigate mitochondrial biology by Vladimir Skulachev and colleagues in the late 1960s. Since then, these molecules have become important tools for exploring mitochondrial bioenergetics and free radical biology. Here we review why these molecules are useful in mitochondrial research and outline some of the ways in which they are now being utilized.

Using mitochondria-targeted molecules to study mitochondrial radical production and its consequences.

The production of ROS (reactive oxygen species) by the mitochondrial respiratory chain contributes to a range of pathologies, including neurodegenerative diseases, ischaemia/reperfusion injury and aging. There are also indications that mitochondrial ROS production plays a role in damage response and signal transduction pathways. To unravel the role of mitochondrial ROS production in these processes, we have developed a range of mitochondria-targeted probe molecules. Covalent attachment of a lipophilic cation leads to their accumulation into mitochondria, driven by the membrane potential. Molecules developed so far include antioxidants designed to intercept mitochondrial ROS and reagents that specifically label mitochondrial thiol proteins. Here we outline how mitochondrial ROS formation and its consequences can be investigated using these probes.