Early Deficits in Glycolysis Are Specific to Striatal Neurons from a Rat Model of Huntington Disease

Abstract

In Huntington disease (HD), there is increasing evidence for a link between mutant huntingtin expression, mitochondrial dysfunction, energetic deficits and neurodegeneration but the precise nature, causes and order of these events remain to be determined. In this work, our objective was to evaluate mitochondrial respiratory function in intact, non-permeabilized, neurons derived from a transgenic rat model for HD compared to their wild type littermates by measuring oxygen consumption rates and extracellular acidification rates. Although HD striatal neurons had similar respiratory capacity as those from their wild-type littermates when they were incubated in rich medium containing a supra-physiological glucose concentration (25 mM), pyruvate and amino acids, respiratory defects emerged when cells were incubated in media containing only a physiological cerebral level of glucose (2.5 mM). According to the concept that glucose is not the sole substrate used by the brain for neuronal energy production, we provide evidence that primary neurons can use lactate as well as pyruvate to fuel the mitochondrial respiratory chain. In contrast to glucose, we found no major deficits in HD striatal neurons’ capacity to use pyruvate as a respiratory substrate compared to wild type littermates. Additionally, we used extracellular acidification rates to confirm a reduction in anaerobic glycolysis in the same cells. Interestingly, the metabolic disturbances observed in striatal neurons were not seen in primary cortical neurons, a brain region affected in later stages of HD. In conclusion, our results argue for a dysfunction in glycolysis, which might precede any defects in the respiratory chain itself, and these are early events in the onset of disease.

The Association of VDAC with Cell Viability of PC12 Model of Huntington’s Disease

“…However, it has also been shown that some mitochondria deficits in HD pathomechanism may only be detected in intact cells [e.g., Gouarné et al (30)]. Our data confirm the assumption as distinct differences in cell respiration and the status of mitochondrial coupling are observed for PC12 HD-Q23 and PC12 HD-Q74 cells when compared to the proper control cells (Figure 2).…”

“…However, the role of mitochondria dysfunction is randomly studied in intact cells although the available data highlight the importance of the cellular environment (30). …”

“…The rate of oxygen uptake by cells (2 × 10 6 ) was measured at 37°C in 0.4 ml of high glucose DMEM without antibiotic and antimycotic compounds, in a water-thermostated incubation chamber with a computer-controlled Clark-type O 2 electrode (Oxygraph, Hansatech, UK) (27–30). State 4 (oligomycin-resistant respiration) was enforced by addition of 2 μg/ml oligomycin (an inhibitor of mitochondrial ATPase), whereas state U (uncoupled state) was induced by FCCP (carbonyl cyanide p-trifluoromethoxyphenylhydrazone; an uncoupler) added in portions of 0.1 μM each to avoid respiration inhibition (Figure 2A).…”

Oxidative metabolism and Ca 2+ handling in striatal mitochondria from YAC128 mice, a model of Huntington's disease

“…Olah et al found that the activities of Complexes I–IV in brain mitochondria from 20-week-old transgenic N171-82Q mice were not diminished compared to mitochondria from wild-type animals (Olah et al, 2008). Gouarne et al did not find a difference in respiration of cultured striatal neurons from heterozygous transgenic BACHD rats compared to wild-type neurons, when cells were incubated in the presence of 25 mM glucose and 1 mM pyruvate (Gouarne et al, 2013). In experiments with STHdh Q111/Q111 cells, mitochondrial pathways were not significantly altered and the obtained data uniformly refuted a view of direct deleterious mHtt effect on mitochondria (Lee et al, 2007).…”

The chicken or the egg: mitochondrial dysfunction as a cause or consequence of toxicity in Huntington’s disease

“…In fact, most of the indications are that parallel metabolic processes also are not optimal. The activity of aconitase, an essential enzyme in the TCA cycle, is significantly decreased in the striatum and cerebral cortex (Tabrizi et al, 1999), GADPH is impaired by faulty autophagy (Hwang et al, 2015), loss of the pyruvate dehydrogenase complex is detected even in asymptomatic patients with caudate/putamen atrophy (Butterworth et al, 1985; Sorbi et al, 1983), glucose uptake is low in HD patients (Pagano et al, 2016), and it is also widely reported that glycolytic rate is reduced in rodent models of HD (Gouarne et al, 2013). …”