ABSTRACT
We investigated the role of LMNA in adipose tissue by developing a novel mouse model of lipodystrophy. Transgenic mice were generated that express the LMNA mutation that causes familial partial lipodystrophy of the Dunnigan type (FPLD2). The phenotype observed in FPLD-transgenic mice resembles many of the features of human FPLD2, including lack of fat accumulation, insulin resistance, and enlarged, fatty liver. Similar to the human disease, FPLD-transgenic mice appear to develop normally, but after several weeks they are unable to accumulate fat to the same extent as their wild-type littermates. One poorly understood aspect of lipodystrophies is the mechanism of fat loss. To this end, we have examined the effects of the FPLD2 mutation on fat cell function. Contrary to the current literature, which suggests FPLD2 results in a loss of fat, we found that the key mechanism contributing to the lack of fat accumulation involves not a loss, but an apparent inability of the adipose tissue to renew itself. Specifically, preadipocytes are unable to differentiate into mature and fully functional adipocytes. These findings provide insights not only for the treatment of lipodystrophies, but also for the study of adipogenesis, obesity, and insulin resistance.
Subject(s)
Adipose Tissue/metabolism , Lamin Type A/genetics , Lamin Type A/metabolism , Lipodystrophy, Familial Partial/genetics , Lipodystrophy, Familial Partial/metabolism , Mutation , Adipocytes/metabolism , Adipocytes/pathology , Adipose Tissue/pathology , Adipose Tissue, Brown/metabolism , Adipose Tissue, Brown/pathology , Animals , Base Sequence , Cell Differentiation , DNA Primers/genetics , Disease Models, Animal , Fatty Liver/genetics , Fatty Liver/metabolism , Fatty Liver/pathology , Humans , Insulin Resistance/genetics , Insulin Resistance/physiology , Lipodystrophy, Familial Partial/pathology , Lipolysis/genetics , Lipolysis/physiology , Male , Mice , Mice, Transgenic , Phenotype , Thermogenesis/genetics , Thermogenesis/physiologyABSTRACT
Germline mutations that inactivate the tumor suppressor gene BRCA1 are associated with an increased risk of cancers of the breast and other tissues, but the functional consequence of many missense variants found in the human population is uncertain. Several predictive methods have been proposed to distinguish cancer-predisposing missense mutations from harmless polymorphisms, including a small colony phenotype (SCP) assay performed in the model organism, yeast (Saccharomyces cerevisiae). The goal of this study was to further evaluate this colony size assay. We constructed 28 missense mutations throughout the C-terminal 305 amino acid residues of BRCA1. Mutated proteins were expressed in yeast and evaluated using the SCP assay. We conclude there is as yet no evidence the assay can identify inactivating mutations upstream of the BRCT repeats. However, within and between the BRCT repeats, results of the assay are in general agreement with predictions based on structural modeling, other in vitro and in vivo assays, and cross-species sequence conservation. Thus, the yeast assay appears to provide confirmatory in vivo evidence to aid in characterizing some BRCA1 missense variants.
