Organs whose source is the mesoderm lineage contain a subpopulation of stem cells that are able to differentiate among mesodermal derivatives (chondrocytes, osteocytes, adipocytes). This subpopulation of adult stem cells, called “mesenchymal stem cells” or “mesenchymal stromal cells (MSCs)”, contributes directly to the homeostatic maintenance of their organs; hence, their senescence could be very deleterious for human bodily functions. MSCs are easily isolated and amenable their expansion in vitro because of the research demanding to test them in many diverse clinical indications. All of these works are shown by the rapidly expanding literature that includes many in vivo animal models. We do not have an in-depth understanding of mechanisms that induce cellular senescence, and to further clarify the consequences of the senescence process in MSCs, some hints may be derived from the study of cellular behaviour in vivo and in vitro , autophagy, mitochondrial stress and exosomal activity. In this particular work, we decided to review these biological features in the literature on MSC senescence over the last three years.

IntroductionThis study assessed whether mesenchymal stem cell (MSC)-derived extracellular vesicles influenced ageing and pluripotency markers in cell cultures where they are added.MethodsMSC-derived extracellular vesicles from old and young rat bone marrows were isolated by ultracentrifugation and were characterised by western blotting, nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM). They were added to young and old MSC cultures. Real-time quantitative reverse transcription polymerase chain reactions and western blot analysis were performed to check the markers of ageing (vinculin and lamin A), pluripotency markers (Nanog and Oct4) and components of the mTOR signalling pathway (Rictor, Raptor, AKT and mTOR) in these cell populations. Subsequently, microRNA (miR)-188-3p expression was transiently inhibited in young MSCs to demonstrate the influence of mTOR2 on MSC ageing.ResultsIncubation with young MSC-derived extracellular vesicles decreased the levels of ageing markers and components of the mTOR pathway and increased the pluripotency markers from old MSC populations. By contrast, incubation of young MSCs with old MSC-derived extracellular vesicles generated the reverse effects. Inhibition of miR-188-3p expression in young MSCs produced extracellular vesicles that when incubated with old MSCs produced an increase in the levels of Rictor, as well as a decrease of phosphor-AKT, as indicated by a significant decrease in beta-galactosidase staining.ConclusionsMSC-derived extracellular vesicles affected the behaviour of MSC cultures, based on their composition, which could be modified in vitro. These experiments represented the basis for the development of new therapies against ageing-associated diseases using MSC-derived extracellular vesicles.

Hutchinson-Gilford progeria syndrome (HGPS) is a very rare fatal disease characterized for accelerated aging. Although the causal agent, a point mutation in LMNA gene, was identified more than a decade ago, the molecular mechanisms underlying HGPS are still not fully understood and, currently, there is no cure for the patients, which die at a mean age of thirteen. With the aim of unraveling non-previously altered molecular pathways in the premature aging process, human cell lines from HGPS patients and from healthy parental controls were studied in parallel using Next-Generation Sequencing (RNAseq) and High-Resolution Quantitative Proteomics (iTRAQ) techniques. After selection of significant proteins and transcripts and crosschecking of the results a small set of protein/transcript pairs were chosen for validation. One of those proteins, ribose-phosphate pyrophosphokinase 1 (PRPS1), is essential for nucleotide synthesis. PRPS1 loss-of-function mutants present lower levels of purine. PRPS1 protein and transcript levels are detected as significantly decreased in HGPS cell lines vs. healthy parental controls. This modulation was orthogonally confirmed by targeted techniques in cell lines and also in an animal model of Progeria, the ZMPSTE24 knock-out mouse. In addition, functional experiments through supplementation with S-adenosyl-methionine (SAMe), a metabolite that is an alternative source of purine, were done. Results indicate that SAMe has a positive effect in the proliferative capacity and reduces senescence-associated Beta-galactosidase staining of the HPGS cell lines. Altogether, our data suggests that nucleotide and, specifically, purine-metabolism, are altered in premature aging, opening a new window for the therapeutic treatment of the disease.