C. elegans Aging: Proteolysis Cuts Both Ways

Ablation of placental REST deregulates fetal brain metabolism and impacts gene expression of the offspring brain at the postnatal and adult stages

In this study, the transcriptional repressor REST (Repressor Element 1 Silencing Transcription factor) was ablated in the mouse placenta to investigate molecular and cellular impacts on the offspring brain at different life stages. Ablation of placental REST deregulated several brain metabolites, including glucose and lactate that fuel brain energy, vitamin C (ascorbic acid) that functions in the epigenetic programming of the brain during postnatal development, and glutamate and creatine that help the brain to respond to stress conditions during adult life. Bulk RNA-seq analysis showed that a lack of placental REST persistently altered multiple transport genes, including those related to oxygen transportation in the offspring brain. While metabolic genes were impacted in the postnatal brain, different stress response genes were activated in the adult brain. DNA methylation was also impacted in the adult brain due to the loss of placental REST, but in a sex-biased manner. Single-nuclei RNA-seq analysis showed that specific cell types of the brain, particularly those of the choroid plexus and ependyma, which play critical roles in producing cerebrospinal fluid and maintaining metabolic homeostasis, were significantly impacted due to the loss of placental REST. These cells showed significant differential expression of genes associated with the metabotropic (G coupled protein) and ionotropic (ligand-gated ion channel) glutamate receptors, suggesting an impact of ablation of placental REST on the glutamatergic signaling of the offspring brain. The study expands our understanding of placental influences on the offspring brain.

Post-translational modification of cellular proteins by ubiquitin and ubiquitin-like molecules: role in cellular senescence and aging

Ubiquitination ofendogenous proteins is one of the key regulatory steps that guides protein degradation through regulation of proteasome activity. During the last years evidence has accumulated that proteasome activity is decreased during the aging process in various model systems and that these changes might be causally related to aging and age-associated diseases. Since in most instances ubiquitination is the primary event in target selection, the system ofubiquitination and deubiquitination might be of similar importance. Furthermore, ubiquitination and proteasomal degradation are not completely congruent, since ubiquitination confers also functions different from targeting proteins for degradation. Depending on mono- and polyubiquitination and on how ubiquitin chains are linked together, post-translational modifications of cellular proteins by covalent attachment of ubiquitin and ubiquitin-like proteins are involved in transcriptional regulation, receptor internalization, DNA repair, stabilization of protein complexes and autophagy. Here, we summarize the current knowledge regarding the ubiquitinome and the underlying ubiquitin ligases and deubiquitinating enzymes in replicative senescence, tissue aging as well as in segmental progeroid syndromes and discuss potential causes and consequences for aging.

Error-protein metabolism and ageing

Ageing and many associated pathologies are accompanied by accumulation of altered proteins. It is suggested that erroneous polypeptide biosynthesis, cytosolic and mitochondrial, is not an insignificant source of aberrant protein in growing and non-mitotic cells. It is proposed that (i) synthesis of sufficient proteases and chaperone proteins necessary for rapid elimination of altered proteins, from cytoplasmic and mitochondrial compartments, is related to cellular protein biosynthetic potential, and (ii) cells growing slowly, or not at all, automatically generate lower levels of protease/chaperone molecules than cells growing rapidly, due to decreased general rate of protein synthesis and lowered amount of error-protein produced per cell. Hence the increased vulnerability of mature organisms may be explained, at least in part, by the decline in constitutive protease/chaperone protein biosynthesis. Upregulation of mitochondria biogenesis, induced by dietary restriction or aerobic exercise, may also increase protease/chaperone protein synthesis, which would improve cellular ability to degrade both error-proteins and proteins damaged post-synthetically by reactive oxygen species etc. These proposals may help explain, in part, the latency of those age-related pathologies where altered proteins accumulate only late in life, and the beneficial effects of aerobic exercise and dietary restriction.