title: Role of Peroxiredoxin 2 and microRNAs in mitochondrial adaptations to exercise and ageing
Creators: name: Xia, Qin
Publisher: name: University of Galway
Year: 2024
Subjects: subject: Medicine
subject: Physiology
subject: FOS: Biological sciences
subject: Ageing

description: Exercise-induced increase in reactive oxygen species (ROS) within skeletal muscle triggers changes at both the transcriptional and posttranscriptional levels. Acute changes in the redox environment can influence mitochondrial quality, essential for the beneficial adaptive response. However, the mechanisms that mediate mechanical events into intracellular functional adaptations remain unclear. In Chapter Three, it was demonstrated that Prdx2 is required for the adaptive hormesis response to physiological levels of H2O2 in myoblasts and following an exercise intervention in C. elegans. A short bolus addition of H2O2 increased mitochondrial capacity and improved myogenesis potential; this beneficial adaptive response was suppressed in myoblasts with decreased levels of cytoplasmic Peroxiredoxins (Prdxs). Moreover, a swimming exercise protocol in C. elegans increased ROS generation and was associated with increased mitochondrial content, fitness, survival and longevity in N2 wild type worms. In contrast, prdx-2 mutant worms had decreased fitness, disrupted mitochondria, reduced survival and lifespan following exercise. Global proteomics following exercise identified distinct changes in the proteome of control (N2) and prdx-2 mutants. Furthermore, a redox proteomic approach to quantify reversible oxidation of specific Cysteine (Cys) residues revealed that specific Cys residues from regulatory proteins became more reduced in N2 strains while a more reduced redox state in non-exercised prdx-2 mutants that became oxidised following exercise, suggesting the key regulatory role of PRDX-2 in a redox signalling cascade following endogenous ROS generation. Together, these data demonstrate that conserved cytoplasmic 2-Cys Peroxiredoxins are required for the beneficial adaptive response to a physiological redox stress. The ageing process entails a gradual decline in physiological function and exercise is widely recognised as a nonpharmacological intervention to mitigate its adverse effects. In Chapter Four, it was demonstrated that blunted mitochondrial remodelling with age and loss of PRDX-2 was associated with an altered redox environment. Ageing was accompanied by elevated levels of ROS and coincided with reduced survival ability, impaired mitochondrial dynamics and compromised mitophagy. Employing a cycle of acute exercise and recovery period at various developmental stages in C. elegans, it was observed acute exercise induced mitochondrial dynamics, mitophagy, and MERCS formation, ultimately influencing physical fitness potentially through the activation of DAF-16 (FOXO) pathway. At adult day 4, the prdx2 mutant strain displayed fragmented mitochondrial morphology compared to wild type worms and did not have alterations in mitochondrial membrane potential or dynamics following exercise interventions. The inability to resolve the altered redox environment in the prdx-2 mutant strain resulted in decreased locomotory activity following exercise. PRDX-2 was sensitive to the redox environment and decreased dimer ratio of PRDX-2 during ageing in response to exercise in C. elegans. These results demonstrate the pivotal role of PRDX-2 in regulating mitochondrial morphology and function during exercise and ageing. Exercise significantly influences various biological mechanisms and signalling pathways at post-transcriptional level. microRNAs (miRs) play a pivotal role in modulating post-transcriptional gene expression during exercise in skeletal muscle. In Chapter Five, it was elucidated the role of miRs in modulating mitochondrial capacity in response to acute H2O2 treatment in myoblasts and following exercise in C. elegans. miR-181a-5p (miR-181), miR-199a-5p (miR-199), and miR-378a-3p (miR-378) were upregulated in C2C12 myoblasts following a physiologically-relevant H2O2 treatment. Modulating the levels of these miRs resulted in heightened mitochondrial mass, leading to increased myotube size. In C. elegans, the expression of celmiR-57-5p (miR-57), cel-miR-72-3p (miR-72), cel-miR-77-5p (miR-77) and cel-miR-249-3p (miR-249) were altered following the chronic exercise. Mutant strains of these miRs had altered fertility, survival ability and mitochondrial capacity. Although the C. elegans miRs identified to change with exercise are not conserved in mammals, it was identified that common predicted targets with miRs identified as sensitive to H2O2 in mammals. Using a computational approach, it was predicted that Inositol Polyphosphate-5- Phosphatase A (Inpp5a)/ipp-5 as a shared target of mmu-miR-181a-5p and celmiR-77-5p, associated with Ca2+ homeostasis in skeletal muscle. Additionally, Kinase suppressor of Ras 1 (Ksr1)/ksr-2 was identified as a shared target of mmu-miR-378a-3p and cel-miR-249-3p, linked to the activation of MAPK for the regulation of mitochondrial biogenesis. These data demonstrate the potential roles of miRs in likely conserved regulatory mechanisms associated with mitochondria across species. In summary, my research delved into the intricate interplay between exerciseinduced redox signalling, mitochondrial quality, and post-transcriptional gene regulation in the context of muscle physiology and ageing. Through a series of investigations using both in vitro myoblast models and C. elegans as a model organism, it was uncovered that the indispensable role of cytoplasmic 2-Cys Peroxiredoxins, particularly PRDX-2, in orchestrating the adaptive responses to redox stress and exercise. Furthermore, my studies shed light on the potential involvement of miRs in modulating mitochondrial function in response to endogenous redox stress generated during exercise, underscoring potential conserved regulatory mechanisms across species. The results of this thesis would suggest the key role played by Peroxiredoxin 2 in regulating the adaptive response to physiological stress. Overall, the integration of these findings highlights the intricate network of molecular pathways involved in mediating the physiological adaptations to exercise and ageing.