The ketogenic diet (KD) has been utilized as a dietary therapeutic for nearly a century. One experimental model particularly responsive to the KD is the BTBR^T+tf/j (BTBR) mouse, which displays phenotypic characteristics of autism spectrum disorder (ASD) and insulin resistance. Recently, the study of impaired mitochondrial function has become a focal point of research investigating the pathophysiology of ASD. As highly dynamic organelles, mitochondria undergo constant fluctuations in morphology, biogenesis, and quality control in order to maintain cellular homeostasis. An important modifier of mitochondrial dynamics is energy availability. Therefore, the aim of this study was to examine the impact of a KD on mitochondrial dynamics in the liver and brain (prefrontal cortex) of the BTBR mouse model of ASD. Juvenile male C57Bl/6 (B6) and BTBR mice were age-matched to 5 weeks of age before being fed standard chow (CD, 13% kcal fat) or a KD (75% kcal fat) for 10-14 days. Analysis of brain tissue identified differences in mitochondrial gene expression but no correlation with protein levels. Unlike in the brain, KD led to decreased levels of mitochondrial proteins in the liver, despite increased gene expression. Consistent with decreased mitochondrial proteins, we also observed decreased mtDNA for all mice on the KD, demonstrating that the KD reduces the total amount of mitochondria in the liver. In order to explain the discrepancy between protein levels and gene expression, we investigated whether mitochondrial turnover via mitophagy was increased. To this end, we examined expression levels of the mitophagy regulator BNIP3 (BCL2/adenovirus E1B 19 kd-interacting protein 3). BNIP3 gene and protein expression were significantly elevated in liver of KD animals (p < 0.05), indicating the potential activation of mitophagy. Therefore, consumption of a KD exerts highly tissue-specific effects, ultimately increasing mitochondrial turnover in the liver, while gene and protein expression in the brain remaining tightly regulated.

Background

Protein O-linked-β-N-acetyl glucosamine (O-GlcNAc) is a post-translational modification to Ser/Thr residues that integrates energy supply with demand. Abnormal O-GlcNAc patterning is evident in several neurological disease states including epilepsy, Alzheimer's disease and autism spectrum disorder (ASD). A potential treatment option for these disorders includes the high-fat, low-carbohydrate, ketogenic diet (KD). The goal of this study was to determine whether the KD induces changes in O-GlcNAc in the BTBR^T+tf/j (BTBR) mouse model of ASD.

Methods

Juvenile male (5weeks), age-matched C57 or BTBR mice consumed a chow diet (13% kcal fat) or KD (75% kcal fat) for 10-14days. Following these diets, brain (prefrontal cortex) and liver were examined for gene expression levels of key O-GlcNAc mediators, global and protein specific O-GlcNAc as well as indicators of energy status.

Results

The KD reduced global O-GlcNAc in the livers of all animals (p<0.05). Reductions were likely mediated by lower protein levels of O-GlcNAc transferase (OGT) and increased O-GlcNAcase (OGA) (p<0.05). In contrast, no differences in global O-GlcNAc were noted in the brain (p>0.05), yet OGT and OGA expression (mRNA) were elevated in both C57 and BTBR animals (p<0.05).

Conclusions

The KD has tissue specific impacts on O-GlcNAc. Although levels of O-GlcNAc play an important role in neurodevelopment, levels of this modification in the juvenile mouse brain were stable with the KD despite large fluctuations in energy status. This suggests that it is unlikely that the KD exerts it therapeutic benefit in the BTBR model of ASD by O-GlcNAc related pathways.