• Altering Mechanisms of Frailty in Persons Living with HIV

      Nelson, Amy; Klinedinst, N. Jennifer (2021)
      Background: People with HIV experience frailty more often and earlier than others. Little is known about mechanisms driving early frailty in HIV. There are a lack of effective interventions for frailty in HIV. This study explored the mechanisms of musculoskeletal frailty in people living with HIV and the influence of baseline activity after a six-week aerobic exercise intervention. Methods: A literature review developed an adapted conceptual model for musculoskeletal frailty in HIV for the first manuscript. Due to COVID-19 restrictions, a secondary data analysis utilized the baseline activity measure (Yale Physical Activity Survey) from 11 healthy participants who completed a six-week moderate paced walking program, aged 50 to 65. Cellular energy production and inflammation markers were available pre- and post-intervention. Correlation with baseline activity was assessed using Kendall’s tau-b. Results: Mechanisms of musculoskeletal frailty in people living with HIV include increased inflammation, dysregulated energy metabolism, immune activation, and endocrine alterations. Aerobic exercise has the potential to moderate each of these. The relationship between baseline activity and changes in cellular energy metabolism was not statistically significant. However, strong positive associations were noted between body mass index and change in platelet spare respiratory capacity, the ability of mitochondria to produce more energy upon demand. In examining the effect of baseline activity on inflammatory markers, no significant relationships were found, and no markers showed significant change. Conclusion: Moderate walking did not make significant changes in inflammation after a six-week moderate paced walking intervention. Baseline activity levels did not play a significant role in the change of either inflammation or cellular energy production. This may be because healthy participants did not have impaired levels of inflammation or cellular energy metabolism at baseline. This study should be repeated in people living with HIV who have altered inflammation or cellular energy metabolism.
    • Mitochondrial Dysfunction is Linked to Pathogenesis in the P497S UBQLN2 Mouse Model of ALS/FTD

      Lin, Brian; Monteiro, Mervyn J.; 0000-0003-2944-3051 (2021)
      Ubiquilin-2 (UBQLN2) mutations cause amyotrophic lateral sclerosis (ALS) with frontotemporal dementia (FTD), but the mechanisms that drive disease pathogenesis remain unclear. Neurons have especially high energy requirements and consume copious amounts of ATP to support synaptic transmission and other complex processes. As such, mitochondrial dysfunction has been thought to play a pathogenic role in ALS. Recently, UBQLNs have been implicated in mitochondrial protein quality control whereby their inactivation in cells leads to the accumulation of cytostatic mitochondrial precursors. However, it is unclear what specific role UBQLN2 plays in maintaining mitochondrial proteostasis and how UBQLN2 mutations impact mitochondria physiology. In this thesis, I tested my hypothesis that the ALS-linked UBQLN2 P497S mutation causes mitochondrial dysfunction through loss of UBQLN2 chaperone function and impaired mitochondrial import. Our lab previously generated proteomic profiles of early-stage (8 weeks) hippocampal and spinal cord (SC) tissues isolated from non-transgenic (Non-Tg), wild-type (WT356), and P497S UBQLN2 mutant mice, whereby the mutant animal closely models human ALS/FTD. Gene ontology analysis revealed “mitochondrial proteins” as a major category altered in P497S animals. I immunoblotted SC lysates of Non-Tg, WT356 and P497S UBQLN2 animals for various mitochondrial proteins, and found decreased levels of many mitochondrial proteins, including those involved in oxidative phosphorylation (OXPHOS), network dynamics and import. I discovered through Seahorse respiration assays that mitochondria purified from the SC of P497S mice have age-dependent respiration deficits unlike those of age-matched Non-Tg and WT356 animals. Electron microscopy of spinal motor neurons in the P497S animals revealed distortions to mitochondria cristae. I demonstrated that mitochondrial alterations found in P497S mutant animals are recapitulated in UBQLN2 knock-out cells, suggesting loss of UBQLN2 function may underlie the mutation’s effects. Additionally, inactivation of UBQLN2 compromised proper targeting and processing of the mitochondrial import factor, TIMM44, which subsequently could be rescued by reexpression of WT UBQLN2, but not by mutant UBQLN2 proteins. ALS/FTD UBQLN2 mutants bind weaker to TIMM44 compared to WT UBQLN2, providing a possible mechanism for the mitochondrial import defects. Overall, these studies highlight a potential key role of UBQLN2 in maintaining mitochondrial health, and how its function is impaired by mutations in UBQLN2.
    • Sex dependent Mitochondrial Mechanisms of Neonatal Cerebral Hypoxic-ischemic Encephalopathy

      Demarest, Tyler G.; Fiskum, Gary (2016)
      Many neurodevelopmental disorders are sex-biased, with males being particularly susceptible to central nervous system (CNS) abnormalities, but mechanisms underlying the sex-biased susceptibility are unclear. Neonatal hypoxic-ischemic encephalopathy (HIE) is one such disorder affecting 1.5-2/1000 live term births that contributes to lifelong cognitive and motor impairments, with males being at a greater risk for these adverse outcomes. Moreover, sex differences in neurobehavioral outcome are observed following the Rice-Vannucci (1981) rodent model of neonatal hypoxic-ischemia (HI). The unilateral carotid artery ligation in this model of HI results in an ipsilateral infarct, and a contralateral "hypoxia-only" hemisphere. Mitochondrial dysfunction is a common feature of CNS injury with increasing evidence suggesting marked sex differences in mitochondrial metabolism of humans and rodents. Following HI, mitochondrial bioenergetic dysfunction contributes to an extended secondary energy failure lasting days or weeks, making it a prime neuroprotective target. Acetyl-L-Carnitine (ALCAR) is neuroprotective following neurotrauma in juvenile and adult animal models; ALCAR is hypothesized to function as an alternative biofuel, antioxidant or by promoting mitochondrial biogenesis but the exact mechanism of neuroprotection is unclear. Emerging evidence suggests that mechanisms implicated in the pathophysiology of CNS injury are also sex dependent including oxidative phosphorylation, oxidative stress, antioxidant defense systems, mitochondrial biogenesis, autophagy and cell death signaling pathways. Therefore, these studies tested the hypotheses that following HIE: mitochondrial function, oxidative stress, antioxidant responses, mitochondrial quality control and cell death are sex dependent, and that ALCAR administration protects against these pathophysiological mechanisms. We observed that complex I mitochondrial respiration is impaired significantly more in males than females, which is associated with increased protein oxidation, impairment of mitochondrial glutathione peroxidase (GPx) activity, and decreased GPx4 immunoreactivity in male, but not female brain. Females have a higher level of reduced glutathione (GSH) than males in shams, decreased GSH, and increased non-mitochondrial GPx activity following HI in both cerebral hemispheres. There is no increase in protein oxidation in the female brain after HI. Furthermore, we find that ALCAR reduces protein oxidation in males following HI. Moreover, we determined mitochondrial fragmentation occurs, to different extents, in both sexes 24 hours after HI. Female mitochondria in the contralateral hemisphere are degraded by mitophagy while male mitochondrial proteins are tagged for removal but the mitophagy machinery is impaired, resulting in an accumulation of damaged mitochondria in the male brain following injury. Finally, we determined that there is significant neuronal cell death in both hemispheres in the male brain following HI, while neuronal death occurs exclusively in the ipsilateral hemisphere of the female brain. These sex-dependent mitochondrial mechanisms further the understanding of a sexually dimorphic neonatal brain injury and will aid in the advancement of sex-specific therapeutic development.