Increased mitochondrial oxidative stress causes fatigue and metabolic dysfunction in muscle tissue. It is unclear whether the oxidative stress is due to elevated production or impaired consumption of reactive oxygen species (ROS). The purpose of this study is to test whether the capacity of the antioxidant defense system is impaired or the mitochondrial ROS production rate is elevated in response to chronic changes in mitochondrial oxidative stress. To experimentally manipulate mitochondrial oxidative stress, we use an inducible mouse model to knockdown superoxide dismutase 2 (SOD2) in skeletal muscle and heart to increase oxidative stress, and exercise training to decrease oxidative stress. Knockdowns (KD) or littermate controls (CON) performed a six-week voluntary wheel running (EX) or sedentary control intervention (SED). Following completion of the intervention, I isolated heart and skeletal muscle mitochondria using differential centrifugation. I measured mitochondrial hydrogen peroxide (H₂O₂) production rate and tested the antioxidant capacity by treating isolated mitochondria with Auranofin (AFN) or 1-chloro-2,4-dintrobenzene (CDNB), which inhibit the thioredoxin and glutathione S-transferase components of the mitochondrial antioxidant defense system, respectively. KD heart and skeletal muscle had similar absolute H₂O₂ production rates compared to CON, but normalized to oxygen consumption the KD had significantly higher H₂O₂ production. Since absolute H₂O₂ production under vehicle conditions was not different, this suggests that the antioxidant capacity adapts to meet the changes in mitochondrial H₂O₂ production. We will collect data from the exercise-trained cohort next month. I expect to see an increase in H₂O₂ production rate and antioxidant capacity in both groups due to the increased mitochondrial biogenesis from exercise training. These results demonstrate that chronic increases in mitochondrial oxidative stress decrease mitochondrial H₂O₂ production capacity from skeletal muscle.

Stress resilience, the ability of cells and tissues to adapt to stimuli, declines with age. Skeletal muscle contraction is a physiological stressor when repeated through exercise training enhances stress resilience and mitigates age-related comorbidities. However, as the body's capacity to mount adaptive responses diminishes with age, the extent to which this decline affects physiological adaptation to stress remains unclear. This would guide future therapeutic strategies surrounding muscular degeneration over the lifespan. The goal of this study is to assess the magnitude of stress response activation across metabolic, oxidative, proteostatic, and heat shock stress response pathways. We use gene expression analysis to evaluate the transcriptional response to controlled in vivo muscle stimulation, providing insight into age-related differences in stress resilience. Young (6mo) and old (23-24mo) male and female mice (C57Bl/6JNia) underwent an in vivo fatiguing muscle stimulation (Stim) or served as an unstimulated control (Unstim). Three hours following the stimulation both right and left limb muscles were collected and processed for gene expression analysis. Following stimulation and collection, I performed tissue processing, RNA extractions, and RT-qPCR assays on muscle tissue. There was a significant increase in PGC1a, HMOX1, TRIM63, and HSPa1a genes in response to muscle stimulation when compared to the unstimulated limb within the same animal. The magnitude of these changes in response to stimulation were not different across age or sex. Analysis of basal changes in unstimulated groups across age and sex is planned for next month. These preliminary results suggest no significant age or sex differences across multiple pathways of stress resilience in skeletal muscle. A strength of this study design is that we use a combined within- and between-animal analysis of both stimulated and unstimulated conditions to control for any potential variations associated with each age, sex, and stimulation condition, increasing confidence in our results.

The retina possesses an intrinsic circadian clock that synchronizes directly to light without input from the brain or visual photoreceptors. Previous research has shown that removing this clock affects photoreceptor health as an animal ages. Furthermore, disruptions to these circadian rhythms, which are increasingly common in modern lifestyles, may exacerbate retinal degenerative diseases such as Retinitis Pigmentosa (RP), a condition that leads to progressive vision loss and affects millions worldwide. Examples of circadian rhythm disruptions include cross-time-zone travel, the use of backlit devices, and social and work obligations. This study investigates the impact of chronic circadian dysregulation (chronic jet lag) on the progression of retinal degeneration in two murine models of RP. We hypothesize that stably synchronized circadian clocks protect against progressive retinal degeneration, while chronic disruption accelerates disease progression. We used three mouse models: a healthy wildtype, mice heterozygous for mild RP, and mice exhibiting retinal white deposits and degeneration. These mice were subjected to either a control lighting schedule or chronic jet lag beginning at one month of age. We assessed retinal health at multiple time points using fundus imaging to quantify white deposit area, immunohistochemistry staining to measure the thickness and depth of the outer nuclear layer (ONL) of the retina, and qRT-PCR to quantify the abundance of Rhodopsin and Opsin transcripts. We used ANOVA and Tukey post-hoc analyses to compare measured values among groups. The results of this experiment provide preliminary data that can inform research into RP models in other organisms and contribute to understanding the implications of chronic circadian desynchronization in the progression of RP in humans.