RNAi reduces expression and intracellular retention of mutant cartilage oligomeric matrix protein.

Mutations in cartilage oligomeric matrix protein (COMP), a large extracellular glycoprotein expressed in musculoskeletal tissues, cause two skeletal dysplasias, pseudoachondroplasia and multiple epiphyseal dysplasia. These mutations lead to massive intracellular retention of COMP, chondrocyte death and loss of growth plate chondrocytes that are necessary for linear growth. In contrast, COMP null mice have only minor growth plate abnormalities, normal growth and longevity. This suggests that reducing mutant and wild-type COMP expression in chondrocytes may prevent the toxic cellular phenotype causing the skeletal dysplasias. We tested this hypothesis using RNA interference to reduce steady state levels of COMP mRNA. A panel of shRNAs directed against COMP was tested. One shRNA (3B) reduced endogenous and recombinant COMP mRNA dramatically, regardless of expression levels. The activity of the shRNA against COMP mRNA was maintained for up to 10 weeks. We also demonstrate that this treatment reduced ER stress. Moreover, we show that reducing steady state levels of COMP mRNA alleviates intracellular retention of other extracellular matrix proteins associated with the pseudoachondroplasia cellular pathology. These findings are a proof of principle and the foundation for the development of a therapeutic intervention based on reduction of COMP expression.

Nonpurging binge eaters versus nonbinge eaters and treatment retention for adult obesity

Dropout from obesity treatment has been a major factor associated with weight control failure, with few reliable predictors of dropouts or completers. Previous studies have tended to treat obese people as a homogeneous group with standard behavior modification-based interventions. Current research indicates there may be subgroups within the obese population, binge eaters and nonbinge eaters, who have different dropout rates. Current studies also recommend focusing on the subset of this subgroup that does not engage in purging (vomiting, laxative abuse, or excessive exercise) to compensate for binge eating. This research uses a secondary dataset (N = 156) from a prospective study in which participants were randomized to a Food Dependency (FD) and a Behavioral Self-Management (BSM) group for weight reduction. Criteria for subjects in the original study included (1) scoring higher on the existing Binge Eating Scale (BES) in order to ensure enrollment of more binge eaters and (2) no compensatory purging behavior for binge eating. Subjects were then reclassified in this study as binge eaters or nonbinge eaters using the more stringent proposed 1994 DSM-IV criteria for Binge Eating Disorder (BED). Subjects were followed for dropout. Variables studied were binge status, age at obesity onset, age at study baseline, class instructor, number of previous weight loss attempts, race, marital status, body mass index (BMI kg/m$\sp2$), type of intervention, work status, educational level, and social support. Stepwise backward regression Cox survival analysis indicated binge status had a consistent, statistically significant protective effect on dropout in which binge eaters were half as likely to dropout versus nonbinge eaters (p = 0.04). Cox proportional hazards analysis indicated no statistical difference in dropout by type of intervention (FD, p = 0.13; BSM, p = 0.80) when controlling for binge status. All other variables did not reach significance, which is consistent with the literature. Implications of these findings suggest that (1) the proposed 1994 DSM-IV criteria for BED is a more useful classification that the existing DSM-III-R criteria, and (2) the identification of subgroups among obese subjects is an important step in dropout and weight loss intervention research. Future research can confirm this finding. ^