MSH3 polymorphisms and protein levels affect CAG repeat instability in huntington's disease mice

Expansions of trinucleotide CAG/CTG repeats in somatic tissues are thought to contribute to ongoing disease progression through an affected individual's life with Huntington's disease or myotonic dystrophy. Broad ranges of repeat instability arise between individuals with expanded repeats, suggesting the existence of modifiers of repeat instability. Mice with expanded CAG/CTG repeats show variable levels of instability depending upon mouse strain. However, to date the genetic modifiers underlying these differences have not been identified. We show that in liver and striatum the R6/1 Huntington's disease (HD) (CAG)~100 transgene, when present in a congenic C57BL/6J (B6) background, incurred expansion-biased repeat mutations, whereas the repeat was stable in a congenic BALB/cByJ (CBy) background. Reciprocal congenic mice revealed the Msh3 gene as the determinant for the differences in repeat instability. Expansion bias was observed in congenic mice homozygous for the B6 Msh3 gene on a CBy background, while the CAG tract was stabilized in congenics homozygous for the CBy Msh3 gene on a B6 background. The CAG stabilization was as dramatic as genetic deficiency of Msh2. The B6 and CBy Msh3 genes had identical promoters but differed in coding regions and showed strikingly different protein levels. B6 MSH3 variant protein is highly expressed and associated with CAG expansions, while the CBy MSH3 variant protein is expressed at barely detectable levels, associating with CAG stability. The DHFR protein, which is divergently transcribed from a promoter shared by the Msh3 gene, did not show varied levels between mouse strains. Thus, naturally occurring MSH3 protein polymorphisms are modifiers of CAG repeat instability, likely through variable MSH3 protein stability. Since evidence supports that somatic CAG instability is a modifier and predictor of disease, our data are consistent with the hypothesis that variable levels of CAG instability associated with polymorphisms of DNA repair genes may have prognostic implications for various repeat-associated diseases

Diabetes Ther

INTRODUCTION: Type 2 diabetes represents a significant public health issue, with increasing prevalence in developing countries while adherence to insulin treatment remains a challenge. No studies have evaluated the relationship between adherence to insulin, diabetes-related distress, and trust in physician among persons with diabetes. Our objectives were to evaluate treatment adherence to insulin, emotional distress (using the Problem Areas in Diabetes Questionnaire, PAID), trust in physician, and to examine associations between them among Lebanese patients with diabetes. METHODS: This cross-sectional study, conducted in all districts of Lebanon between August 2016 and April 2017, enrolled 135 adult patients. RESULTS: The mean percentage score of adherence to insulin was 79.7 +/- 19.94. A significantly higher mean adherence score was found in non-sedentary (81.96) compared to sedentary patients (67.41) (p = 0.017), with no difference between gender, employment, rural vs non-rural residence, or familial history of diabetes. In addition, no significant relationship was seen between adherence score and education level, smoking, or alcohol intake. A significant positive association was found between trust in physician and adherence scores, whereas a significant but negative one was found between PAID and adherence scores. The results of linear regressions showed that a secondary level of education (beta = - 13.48) significantly decreased the trust in physician score, whereas the total number of oral antidiabetics (beta = 0.93) increased it. Having a sedentary lifestyle (beta = - 12.73) and smoking < 3 waterpipes/week compared to no smoking (beta = - 16.82) significantly decreased the adherence score. Female gender (beta = 10.46), smoking < 3 waterpipes (beta = 27.42) and 3 + waterpipes/week (beta = 17.95) significantly increased the PAID score. CONCLUSION: Trust in physician is associated with an increased adherence and with decreased diabetes-related distress. This distress was also associated with poor adherence in our study

New insights into the mechanism of DNA mismatch repair

The genome of all organisms is constantly being challenged by endogenous and exogenous sources of DNA damage. Errors like base:base mismatches or small insertions and deletions, primarily introduced by DNA polymerases during DNA replication are repaired by an evolutionary conserved DNA mismatch repair (MMR) system. The MMR system, together with the DNA replication machinery, promote repair by an excision and resynthesis mechanism during or after DNA replication, increasing replication fidelity by upto-three orders of magnitude. Consequently, inactivation of MMR genes results in elevated mutation rates that can lead to increased cancer susceptibility in humans. In this review, we summarize our current understanding of MMR with a focus on the different MMR protein complexes, their function and structure. We also discuss how recent findings have provided new insights in the spatio-temporal regulation and mechanism of MMR