Compromised IGF signaling causes caspase-6 activation in Huntington disease.

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by an expansion of a polyglutamine repeat in the huntingtin (HTT) protein. Aberrant activation of caspase-6 and cleavage of mutant HTT generating the toxic N-terminal 586 HTT fragment are important steps in the pathogenesis of HD. Similarly, alterations in the insulin-like growth factor 1 (IGF-1) signaling pathway have been implicated in the disease as a result of decreased plasma IGF-1 levels in HD patients. In addition, two recent studies have demonstrated therapeutic benefit of IGF-1 treatment in mouse models of HD. Since IGF-1 promotes pro-survival pathways, we examined the relationship between IGF-1 signaling and aberrant caspase-6 activation in HD. Using immortalized mouse striatal cells expressing wild-type (STHdhQ7) or mutant HTT (STHdhQ111), we show that reduced levels of IGF-1 are associated with enhanced activation of caspase-6, increased cell death, and mutant HTT cleavage in a cellular stress paradigm. We demonstrate that IGF-1 supplementation reverses these effects and lowers the level of the toxic 586 HTT fragment. In addition, transcriptional analysis in the R6/2 HD transgenic mouse model demonstrated that the IGF-1 signaling system is dysregulated at multiple levels in several tissues including liver, muscle, and brain. Among these changes, we found increased expression of IGF-1 binding protein 3 (IGFBP-3), which may further reduce the bioavailability of IGF-1 as a consequence of increased IGF-1 binding. Our findings thus suggest that the therapeutic benefit of IGF-1 supplementation in HD may be significantly improved if other defects in the IGF-1 signaling pathway are corrected concurrently.

Liver function in Huntington's disease assessed by blood biochemical analyses in a clinical setting.

Huntington's disease (HD) is a dominantly inherited, progressive neurological disorder caused by a CAG repeat elongation in the huntingtin gene. In addition to motor-, psychiatric- and cognitive dysfunction, peripheral disease manifestations in the form of metabolic changes and cellular dysfunction are seen. Blood levels of a wide range of hormones, metabolites and proteins have been analyzed in HD patients, identifying several changes associated with the disease. However, a comprehensive panel of liver function tests (LFT) has not been performed. We investigated a cohort of manifest and premanifest HD gene-expansion carriers and controls, using a clinically applied panel of LFTs. Here, we demonstrate that the level of alkaline phosphatase is increased in manifest HD gene-expansion carriers compared to premanifest HD gene-expansion carriers and correlate with increased disease severity indicated by the Unified Huntington's disease rating scale-Total Functional Capacity Score (UHDRS-TFC). For gamma-glutamyl transferase, elevated levels were more frequent in the manifest groups than in both the HD gene-expansion negative controls and premanifest HD gene-expansion carriers. Finally, the manifest HD gene-expansion carriers displayed moderate increases in total cholesterol and blood glucose relative to the premanifest HD gene-expansion carriers, as well as increased C-reactive protein relative to HD gene-expansion negative controls. Our results show that LFT values are elevated more frequently in manifest compared to premanifest HD gene-expansion carriers and controls. The majority of the manifest HD gene-expansion carriers receive medication, and it is possible that this can influence the liver function tests performed in this study.

Progressive Impairment of Lactate-based Gluconeogenesis in the Huntington's Disease Mouse Model R6/2.

Huntington's disease (HD) is a neurodegenerative illness, where selective neuronal loss in the brain caused by expression of mutant huntingtin protein leads to motor dysfunction and cognitive decline in addition to peripheral metabolic changes. In this study we confirm our previous observation of impairment of lactate-based hepatic gluconeogenesis in the transgenic HD mouse model R6/2 and determine that the defect manifests very early and progresses in severity with disease development, indicating a potential to explore this defect in a biomarker context. Moreover, R6/2 animals displayed lower blood glucose levels during prolonged fasting compared to wild type animals.

Effect of dietary gluten on dendritic cells and innate immune subsets in BALB/c and NOD mice.

The innate immune system is known to play an important role in oral tolerance to dietary antigens. This is important in development of celiac disease (CD) but may also be important in type 1 diabetes (T1D), and could potentially explain the reduced incidence of T1D in mice receiving a gluten-free (GF) diet. The direct in vivo effect of gluten on innate cells, and particularly dendritic cells (DC) is not sufficiently clarified. Therefore, we wished to investigate the innate cell populations of spontaneous diabetic NOD mice and healthy BALB/c mice kept on a GF or a standard (STD) gluten containing diet. We studied, by flow cytometry and reverse transcription-quantitative polymerase chain reaction (qRT-PCR), if dietary gluten induces changes in the activation of DCs and distribution of selected innate cells in lymphoid, pancreatic and intestinal tissues in BALB/c and NOD mice. We found that a GF diet increased the percentage of macrophages in BALB/c spleen and of CD11c+ DCs in BALB/c and NOD spleen. Strictly gluten-free (SGF) diet increased the percentage of CD103+ DCs in BALB/c mice and decreased percentages of CD11b+ DCs in mesenteric and pancreatic lymph nodes in BALB/c mice. SGF diet in BALB/c mice also decreased DC expression of CD40, CCR7 and MHC-II in pancreatic lymph nodes. In conclusion, GF diet changes the composition of the innate immune system in BALB/c and NOD mice and increases expression of DC activation markers in NOD mice. These results contribute to the explanation of the low diabetes incidence in GF NOD mice. This mechanism may be important in development of type 1 diabetes, celiac disease and non-celiac gluten sensitivity.

Reduction in mitochondrial DNA copy number in peripheral leukocytes after onset of Huntington's disease.

Huntington's disease (HD) is an inherited neurodegenerative disorder characterised by movement disorder, cognitive symptoms and psychiatric symptoms with predominantly adult-onset. The mutant huntingtin protein leads to mitochondrial dysfunction in blood leukocytes. This discovery led to the investigation of the mitochondrial DNA (mtDNA) copy number relative to nuclear DNA (nDNA) in leukocytes from carriers of the HD mutation compared to healthy individuals. We found significantly reduced mtDNA/nDNA in HD mutation carriers compared to controls. A longitudinal study of archive DNA sample pairs from HD patients revealed a biphasic pattern of increasing mtDNA/nDNA before onset of motor symptoms and decreasing mtDNA/nDNA after.

Dysfunctional mitochondrial respiration in the striatum of the Huntington's disease transgenic R6/2 mouse model.

Metabolic dysfunction and mitochondrial involvement are recognised as part of the pathology in Huntington's Disease (HD). Post-mortem examinations of the striatum from end-stage HD patients have shown a decrease in the in vitro activity of complexes II, III and IV of the electron transport system (ETS). In different models of HD, evidence of enzyme defects have been reported in complex II and complex IV using enzyme assays. However, such assays are highly variable and results have been inconsistent. We investigated the integrated ETS function ex vivo using a sensitive high-resolution respirometric (HRR) method. The O2 flux in a whole-cell sample combined with the addition of mitochondrial substrates, uncouplers and inhibitors enabled us to accurately quantitate the function of individual mitochondrial complexes in intact mitochondria, while retaining mitochondrial regulation and compensatory mechanisms. We used HRR to examine the mitochondrial function in striata from 12-week old R6/2 mice expressing exon 1 of human HTT with 130 CAG repeats. A significant reduction in complex II and complex IV flux control ratios was found in the R6/2 mouse striatum at 12 weeks of age compared to controls, confirming previous findings obtained with spectrophotometric enzyme assays.