Variability in cognitive impairment in Huntington’s disease: the effect of environment on cognitive reserve
Although CAG repeat length is a strong predictor of when HD symptoms will begin, environmental and lifestyle factors can contribute to variability in the age of onset. Individuals with similar repeat length and pathology, even with identical genetic makeup, can show differences in disease severity, including cognitive impairment. The variability in cognitive performance that cannot be explained by neuropathy or genetic factors is attributed to cognitive reserve. Cognitive reserve builds up across one’s lifespan as a result of a cognitively stimulating lifestyle. Research on animal models of HD has shown that exposing animals to an enriched environment during development slows disease progression. In addition, research on HD patients has provided promising results that lifestyle has an effect on disease progression. However, this work has been limited and there is a need for more research. The aim of the proposed project is to characterize the variability in cognitive ability in HD that is not explained by pathology, and understand the contribution of environmental factors to the build-up of cognitive reserve across the lifespan. We will analyze data already available in Track-HD, a longitudinal, observational study, which acquired detailed cognitive, motor and neuroimaging measures in addition to detailed environmental information from both symptomatic and presymptomatic HD patients. Our analyses will quantify cognitive reserve in HD, examine its effect on disease progression and, most importantly, identify the contribution of environmental factors to cognitive reserve. Our findings will have important implications for the design of lifestyle interventions and inform guidelines on neuroprotective lifestyle choices for HD patients.
The protective role of NAD salvage pathway proteins against mutant huntingtin toxicity
Previously, our lab worked with a yeast model of Huntington’s disease to discover that several proteins that form the NAD+ salvage pathway can protect against the adverse effects usually caused by mutant huntingtin. We further found that overexpression of NAD+ salvage pathway proteins helped to degrade 103Q oligomers in these cells, independent of NAD+ levels. Our preliminary studies have further demonstrated that these NAD+ salvage pathway proteins have an innate chaperone function in vitro and that catalytically inactive forms of these salvage pathway proteins can also protect against 103Q toxicity in vivo. We therefore propose that these NAD+ salvage pathway proteins have a previously undiscovered, dual function in the cell, and can moonlight as chaperone proteins. We propose to continue our investigations, with the help of this funding, to elucidate more specifically how these proteins are acting as chaperones, and how these findings translate to human patient-derived cells. This research will give us a greater understanding of the complexities of Huntington’s disease, as well as other diseases of protein misfolding, and will potentially open the door to new therapeutic protein and pathway targets.
Exploring intestinal dysbiosis and developing GI-based therapeutics for Huntington’s disease
Disruptions to the gastrointestinal (GI) tract and the homeostasis of intestinal microbiota are implicated in several brain disorders. HD patients display GI symptoms and metabolic abnormalities like extreme weight loss. However, the cause and contribution of GI dysfunction to the progression of neurological symptoms has not been investigated. We hypothesize that HD patients have altered intestinal microbiota (dysbiosis), which may contribute to GI dysfunction, systemic inflammation, mutant huntingtin (mHTT) aggregation, and brain pathology. In support of this hypothesis, we find that inflammatory bacterial products promote the oligomerization of mHTT in neurons, immune cells derived from HD patients, and epithelial cells. Moreover, in Drosophila models of HD, inflammation-inducing bacteria promote the aggregation of mutant HTT and exacerbate motor behavior. This project will explore whether the homeostasis of intestinal bacteria is altered in HD patients. We plan to profile the microbiome of pre-symptomatic and symptomatic HD patients by 16S RNA sequencing and identify bacterial species that could be overpopulated or eliminated. We also plan to develop qPCR protocols to quantify selected bacteria, which might be linked to different stages of clinical symptoms in HD. Finally, we propose to examine whether intestinal microbiota regulates the oligomerization of mutant HTT in the enteric nervous system and contributes to the development of CNS symptoms in a preclinical mouse model of HD. Studies on the microbiota of HD patients may ultimately identify novel pathogenic mechanisms, easy to access biomarkers, and GI-based therapeutics.
CircRNAs, non-coding, stable RNA circles as potential new bio-markers for Huntington’s Disease
Although there are currently no available treatments that modify the onset or progression of HD, a number of therapeutic strategies are under investigation or even in clinical trials to reduce or block transcription from the mutant HTT allele. This includes antisense oligonucleotides, gene correction through CRISPR/Cas9, and other genetic techniques. Therefore, there is an increasing need to develop and validate biomarkers in accessible biofluids (such as blood) to either follow disease progression (prognostic biomarkers) and/or to predict treatment outcomes (predictive biomarkers). Since a valuable biomarker must be objectively measured and easily evaluated during the pathogenic process or therapeutic intervention, a variety of molecules such as small RNAs, proteins or metabolites can be taken into consideration. Here, for the first time in HD, we aim to focus, detect and characterize circRNAs in peripheral blood. CircRNAs are highly abundant and stable non-coding circular transcripts, enriched in brain districts and permeable to the blood brain barrier. We will investigate these molecules in a cohort of gender and age matched healthy and HD individuals in premanifest, in the first stages (stage I and II) and in the advanced stages (stage III and over) of disease. We aim to characterize the expression pattern of circRNAs in blood samples from HD patients, to correlate specific circRNAs with disease progression (prodromic vs early and late stages), and to develop a sensitive RT-qPCR assay for the detection and quantification of specific CAG-sensitive circRNAs to be used as reliable disease biomarkers in HD.