Project description:Mitochondrial energy metabolism and function are key processes underlying the pathophysiology of insulin resistance and predisposition to type 2 diabetes. This is because mitochondria produce most of the energy required by the cell. Impaired energy production, use of energy stores and mitochondrial dysfunction are major features in metabolic diseases. Nevertheless, it remains uncertain how mitochondrial dysfunction can cause, contribute to, or result in insulin resistance and metabolic diseases. Furthermore there is growing evidence from genetic and genome wide-association studies that genetic variation in mtDNA contributes to these common metabolic diseases (Wallace, 2005), however there has been essentially no in vivo functional validation for these findings. Therefore we generated a mouse model homozygous for a polymorphism in the Mrpp3 gene identified in the French Canadian population responsible for 22% of mitochondrial epitranscriptome variation, with likely consequences on metabolism. We investigated the in vivo effects of the polymorphism on mitochondrial function and metabolism in mice fed normal and high fat diet. We identify that the polymorphism reduces the efficiency of mitochondrial RNA processing and this is most pronounced in the pancreas that results in insulin resistance. The MRPP3 protein containing the Asn434Ser polymorphism associates specifically with the calcium antiporter LETM1 preventing effective release of calcium from mitochondria and consequently impairs insulin release from the pancreatic islet cells of these mice. Reduction in insulin secretion and enlarged pancreatic islet size results in lower circulating levels of insulin that causes insulin resistance and liver steatosis. Our findings reveal for the first time the link between mitochondrial gene regulation and insulin resistance via calcium signaling.
Project description:BACKGROUND: A common missense variant of the CDKN2A gene (A148T) predisposes to malignant melanoma in Poland. An association between malignant melanoma and breast cancer has been reported in several families with CDKN2A mutations, OBJECTIVE: To determine whether this variant also predisposes to breast cancer. METHODS: Genotyping was undertaken in 4209 cases of breast cancer, unselected for family history, from 18 hospitals throughout Poland and in 3000 controls. RESULTS: The odds ratio (OR) associated with the CDKN2A allele for women diagnosed with breast cancer before the age of 50 was 1.5 (p = 0.002) and after age 50 it was 1.3 (p = 0.2). The effect was particularly strong for patients diagnosed at or before the age of 30 (OR = 3.8; p = 0.0002). CONCLUSIONS: CDKN2A appears to be a low penetrance breast cancer susceptibility gene in Poland. The association should be confirmed in other populations.
Project description:Insulin resistance in muscle, adipocytes and liver is a gateway to a number of metabolic diseases. Here, we show a selective deficiency in mitochondrial coenzyme Q (CoQ) in insulin-resistant adipose and muscle tissue. This defect was observed in a range of in vitro insulin resistance models and adipose tissue from insulin-resistant humans and was concomitant with lower expression of mevalonate/CoQ biosynthesis pathway proteins in most models. Pharmacologic or genetic manipulations that decreased mitochondrial CoQ triggered mitochondrial oxidants and insulin resistance while CoQ supplementation in either insulin-resistant cell models or mice restored normal insulin sensitivity. Specifically, lowering of mitochondrial CoQ caused insulin resistance in adipocytes as a result of increased superoxide/hydrogen peroxide production via complex II. These data suggest that mitochondrial CoQ is a proximal driver of mitochondrial oxidants and insulin resistance, and that mechanisms that restore mitochondrial CoQ may be effective therapeutic targets for treating insulin resistance.
Project description:Mitochondrial energy metabolism and function are key processes underlying the pathophysiology of insulin resistance and predisposition to type 2 diabetes. This is because mitochondria produce most of the energy required by the cell. Impaired energy production, use of energy stores and mitochondrial dysfunction are major features in metabolic diseases. Nevertheless, it remains uncertain how mitochondrial dysfunction can cause, contribute to, or result in insulin resistance and metabolic diseases. Furthermore there is growing evidence from genetic and genome wide-association studies that genetic variation in mtDNA contributes to these common metabolic diseases (Wallace, 2005), however there has been essentially no in vivo functional validation for these findings. Therefore we generated a mouse model homozygous for a polymorphism in the Mrpp3 gene identified in the French Canadian population responsible for 22% of mitochondrial epitranscriptome variation, with likely consequences on metabolism. We investigated the in vivo effects of the polymorphism on mitochondrial function and metabolism in mice fed normal and high fat diet. We identify that the polymorphism reduces the efficiency of mitochondrial RNA processing and this is most pronounced in the pancreas that results in insulin resistance. The MRPP3 protein containing the Asn434Ser polymorphism associates specifically with the calcium antiporter LETM1 preventing effective release of calcium from mitochondria and consequently impairs insulin release from the pancreatic islet cells of these mice. Reduction in insulin secretion and enlarged pancreatic islet size results in lower circulating levels of insulin that causes insulin resistance and liver steatosis. Our findings reveal for the first time the link between mitochondrial gene regulation and insulin resistance via calcium signaling.
Project description:INTRODUCTION: Mutations in the BRCA2 gene are one of the two major causes of hereditary breast cancer. Protein-truncating mutations of BRCA2 are usually deleterious and increase the risk of breast cancer up to 80% over a lifetime. A few missense mutations in BRCA2 are believed to have a similarly high penetrance, apart from more common neutral polymorphisms. It is often difficult to classify a particular sequence variant as a mutation or a polymorphism. For a deleterious variant, one would expect a greater allele frequency in breast cancer cases than in ethnic-matched controls. In contrast, neutral polymorphic variants should be equally frequent in the two groups. METHODS: We genotyped 3,241 cases of breast cancer diagnosed at under 51 years of age, unselected for family history, from 18 hospitals throughout Poland and 2,791 ethnic-matched controls for a single BRCA2 C5972T variant. RESULTS: The variant was present in approximately 6% of the Polish population. In the study, 13 women (11 cases and two controls (OR = 4.7; p = 0.02)) were homozygous for the variant allele. The overall odds ratio for breast cancer in women with a single copy of the BRCA2 C5972T variant was 1.1 (p = 0.7); however, the effect was significant for patients diagnosed at or before age 40 (OR = 1.4; p = 0.04). We reviewed the association between the BRCA2 variant in different histologic subgroups and found the effect most pronounced in women who had ductal carcinoma in situ (DCIS) with micro-invasion (OR = 2.8; p < 0.0001). CONCLUSION: The BRCA2 C5972T allele is a common variant in Poland that increases the risk of DCIS with micro-invasion. The homozygous state is rare but increases the risk of breast cancer five-fold.
Project description:Chemical inhibition and genetic knockdown of enzymes are not equivalent in cells, but network-level mechanisms that cause discrepancies between knockdown and inhibitor perturbations are not understood. Here we report that enzymes regulated by negative feedback are robust to knockdown but susceptible to inhibition. Using the Raf-MEK-ERK kinase cascade as a model system, we find that ERK activation is resistant to genetic knockdown of MEK but susceptible to a comparable degree of chemical MEK inhibition. We demonstrate that negative feedback from ERK to Raf causes this knockdown-versus-inhibitor discrepancy in vivo. Exhaustive mathematical modeling of three-tiered enzyme cascades suggests that this result is general: negative autoregulation or feedback favors inhibitor potency, whereas positive autoregulation or feedback favors knockdown potency. Our findings provide a rationale for selecting pharmacologic versus genetic perturbations in vivo and point out the dangers of using knockdown approaches in search of drug targets.
Project description:Autopsy studies suggest that most aging men will develop lesions that, if detected clinically, would be diagnosed as prostate cancer (PCa). Most of these cancers are indolent and remain localized; however, a subset of PCa is aggressive and accounts for more than 27,000 deaths in the United States annually. Identification of factors specifically associated with risk for more aggressive PCa is urgently needed to reduce overdiagnosis and overtreatment of this common disease. To search for such factors, we compared the frequencies of SNPs among PCa patients who were defined as having either more aggressive or less aggressive disease in four populations examined in the Genetic Markers of Susceptibility (CGEMS) study performed by the National Cancer Institute. SNPs showing possible associations with disease severity were further evaluated in an additional three independent study populations from the United States and Sweden. In total, we studied 4,829 and 12,205 patients with more and less aggressive disease, respectively. We found that the frequency of the TT genotype of SNP rs4054823 at 17p12 was consistently higher among patients with more aggressive compared with less aggressive disease in each of the seven populations studied, with an overall P value of 2.1 x 10(-8) under a recessive model, exceeding the conservative genome-wide significance level. The difference in frequency was largest between patients with high-grade, non-organ-confined disease compared with those with low-grade, organ-confined disease. This study demonstrates that inherited variants predisposing to aggressive but not indolent PCa exist in the genome, and suggests that the clinical potential of such variants as potential early markers for risk of aggressive PCa should be evaluated.