Short-term Succinic Acid Treatment Mitigates Cerebellar Mitochondrial OXPHOS Dysfunction, Neurodegeneration and Ataxia in a Purkinje-specific Spinocerebellar Ataxia Type 1 (SCA1) Mouse Model

Mitochondrial dysfunction plays a significant role in neurodegenerative disease including ataxias and other movement disorders, particularly those marked by progressive degeneration in the cerebellum. In this study, we investigate the role of mitochondrial oxidative phosphorylation (OXPHOS) deficits in cerebellar tissue of a Purkinje cell-driven spinocerebellar ataxia type 1 (SCA1) mouse. Using RNA sequencing transcriptomics, OXPHOS complex assembly analysis and oxygen consumption assays, we report that in the presence of mutant polyglutamine-expanded ataxin-1, SCA1 mice display deficits in cerebellar OXPHOS complex I (NADH-coenzyme Q oxidoreductase). Complex I genes are upregulated at the time of symptom onset and upregulation persists into late stage disease; yet, functional assembly of complex I macromolecules are diminished and oxygen respiration through complex I is reduced. Acute treatment of postsymptomatic SCA1 mice with succinic acid, a complex II (succinate dehydrogenase) electron donor to bypass complex I dysfunction, ameliorated cerebellar OXPHOS dysfunction, reduced cerebellar pathology and improved motor behavior. Thus, exploration of mitochondrial dysfunction and its role in neurodegenerative ataxias, and warrants further investigation

Natural Variation in Decision-Making Behavior in Drosophila melanogaster

There has been considerable recent interest in using Drosophila melanogaster to investigate the molecular basis of decision-making behavior. Deciding where to place eggs is likely one of the most important decisions for a female fly, as eggs are vulnerable and larvae have limited motility. Here, we show that many natural genotypes of D. melanogaster prefer to lay eggs near nutritious substrate, rather than in nutritious substrate. These preferences are highly polymorphic in both degree and direction, with considerable heritability (0.488) and evolvability

Long term rebaudioside A treatment does not alter circadian activity rhythms, adiposity, or insulin action in male mice

<div><p>Obesity is a major public health problem that is highly associated with insulin resistance and type 2 diabetes, two conditions associated with circadian disruption. To date, dieting is one of the only interventions that result in substantial weight loss, but restricting caloric intake is difficult to maintain long-term. The use of artificial sweeteners, particularly in individuals that consume sugar sweetened beverages (energy drinks, soda), can reduce caloric intake and possibly facilitate weight loss. The purpose of the present study was to examine the effects of the artificial sweetener, rebaudioside A (Reb-A), on circadian rhythms, in vivo insulin action, and the susceptibility to diet-induced obesity. Six month old male C57BL/6 mice were assigned to a control or Reb-A (0.1% Reb-A supplemented drinking water) group for six months. Circadian wheel running rhythms, body weight, caloric intake, insulin action, and susceptibility to diet-induced obesity were assessed. Time of peak physical activity under a 12:12 light-dark (LD) cycle, mean activity levels, and circadian period in constant dark were not significantly different in mice that consumed Reb-A supplemented water compared to normal drinking water, indicating that circadian rhythms and biological clock function were unaltered. Although wheel running significantly reduced body weight in both Reb-A and control mice (P = 0.0001), consuming Reb-A supplemented water did not alter the changes in body weight following wheel running (P = 0.916). <i>In vivo</i> insulin action, as assessed by glucose, insulin, and pyruvate tolerance tests, was not different between mice that consumed Reb-A treated water compared to normal drinking water. Finally, Reb-A does not appear to change the susceptibility to diet-induced obesity as both groups of mice gained similar amounts of body weight when placed on a high fat diet. Our results indicate that consuming Reb-A supplemented water does not promote circadian disruption, insulin resistance, or obesity.</p></div

Reb-A does not alter the caloric intake response to a HFD.

<p>Caloric intake was assessed before and following 18 weeks of a HFD in mice treated with Reb-A or vehicle. One way ANOVA revealed no significant main effects for Reb-A treatment (P = 0.325) or diet (P = 0.095). N = 8 mice per group.</p

Reb-A does not alter the body weight response to a HFD.

<p>Body weight was assessed before and following 18 weeks of a HFD in mice treated with Reb-A or vehicle. *, Denotes statistically significant difference from respective vehicle group by LSD post-hoc analysis (P = 0.0001) conduct after a significant ANOVA main effect for diet (P = 0.0001). N = 8 mice per group.</p

Rebaudioside A treatment does not alter weight loss following circadian wheel running activity.

<p>Mice were fed a standard rodent diet for and given free access to a running wheel. Body weight was measured before and after 32 days of wheel running. *, Denotes statistically significant changes in body weight following the wheel running intervention within respective groups of mice. N = 10 mice per group.</p

SA as a treatment strategy for B05 mice.

<p><b>(A)</b> Schematic (drawn in ChemDraw) showing mitochondrial inner membrane (IMM) OXPHOS complexes, flow of protons (H⁺), redox and phosphorylation reactions, and the flow of electrons (thick black lines). OMM = outer mitochondrial membrane. <b>(B)</b> Volume of water measured daily in untreated and succinic acid treated mice. <b>(C)</b> Average water intake over a two-week period in treated (SA) (mean = 5.415 ± 1.069 mL) and untreated (6.463 ± 1.058 mL) mice. Error bars represent means ± SEM. T-test, **** P < 0.0001. <b>(D)</b> Standard curve of succinic acid by HPLC. Slope = 0.01939 ± 0.0007448, R² = 0.9956. <b>(E)</b> succinic acid concentrations in cerebellar tissue detected in untreated and 4-week treated wild type mice. Error bars represent means ± SEM. T-test, P < 0.0001. <b>(F)</b> Schema of treatment plan. Symptom onset begins approximately 5 weeks after birth. We began treatment of 0.75 mg/mL succinic acid beginning at 4 months of age and continued for four weeks. Subjects were behaviorally tested during weeks 2 (footprint analysis), 3 (beam analysis) and 4 (accelerating rotarod). Following treatment, 5 month-old mice were sacrificed and cerebellar tissue was harvested for oxygen respiration analysis and neuropathology.</p

OXPHOS complex I dysfunction in adult B05 cerebellum.

<p><b>(A)</b> OXPHOS complex assembly in B05 (lanes 1–3) and wild type (lanes 4–6) cerebellum by Western blot using an assembly-specific OXPHOS antibody cocktail. <b>(B)</b> Quantification of western blot data in (B). CI, CII, CIII and CV bands are each normalized to CIV. Data is in triplicate. Error bars show means ± SEM. T-test, * P < 0.05. <b>(C)</b> Mitochondrial respiration analysis of B05 and wild type cerebellum in the presence of ADP or rotenone. Data is shown as the percent maximal respiration which was calculated in the presence of TMPD/Ascorbate. Samples were run in triplicate. Error bars show means ± SEM. T-test, * P< 0.05.</p

SA as a treatment strategy for B05 mice.

<p><b>(A)</b> Schematic (drawn in ChemDraw) showing mitochondrial inner membrane (IMM) OXPHOS complexes, flow of protons (H⁺), redox and phosphorylation reactions, and the flow of electrons (thick black lines). OMM = outer mitochondrial membrane. <b>(B)</b> Volume of water measured daily in untreated and succinic acid treated mice. <b>(C)</b> Average water intake over a two-week period in treated (SA) (mean = 5.415 ± 1.069 mL) and untreated (6.463 ± 1.058 mL) mice. Error bars represent means ± SEM. T-test, **** P < 0.0001. <b>(D)</b> Standard curve of succinic acid by HPLC. Slope = 0.01939 ± 0.0007448, R² = 0.9956. <b>(E)</b> succinic acid concentrations in cerebellar tissue detected in untreated and 4-week treated wild type mice. Error bars represent means ± SEM. T-test, P < 0.0001. <b>(F)</b> Schema of treatment plan. Symptom onset begins approximately 5 weeks after birth. We began treatment of 0.75 mg/mL succinic acid beginning at 4 months of age and continued for four weeks. Subjects were behaviorally tested during weeks 2 (footprint analysis), 3 (beam analysis) and 4 (accelerating rotarod). Following treatment, 5 month-old mice were sacrificed and cerebellar tissue was harvested for oxygen respiration analysis and neuropathology.</p