Studies of pseudoachondroplasia chondrocytes and knockdown of the cartilage oligomeric matrix protein

Cartilage oligomeric matrix protein (COMP) is a large, homopentameric, extracellular matrix glycoprotein. Mutations in COMP cause two skeletal dysplasias: pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (EMD1). These dwarfing conditions are caused by retention of misfolded mutant COMP with type IX collagen and matrilin-3 (MATN3) in the rough endoplasmic reticulum (rER) of the chondrocyte. These proteins form a matrix in the rER that continues to expand until it fills the entire cell, eventually causing cell death. Interestingly, loss of COMP in COMP null mice does not affect normal bone development or growth, suggesting that elimination of COMP (wildtype and mutant) expression may prevent PSACH. The hypothesis of these studies was that a hammerhead ribozyme could eliminate or knockdown COMP mRNA expression in PSACH chondrocytes . To test this hypothesis, a human chondrocyte model system that recapitulates the PSACH chondrocyte phenotype was developed by over-expressing mutant (mt-) COMP in normal chondrocytes using a recombinant adenovirus. Chondrocytes over-expressing mt-COMP developed giant rER cisternae containing COMP, type IX collagen and MATN3. Deconvolution microscopy and computer modeling showed that these proteins formed an ordered matrix surrounding a type II pro-collagen core. Additionally, the results show that a hammerhead ribozyme, ribozyme 56 (Ribo56) reduced over-expressed mt-COMP in COS cells and endogenous COMP in normal chondrocytes and mt-COMP in three PSACH chondrocytes cell line (with different mutations) by 40-70%. Altogether, these studies show that the PSACH cellular phenotype can be created in vitro and that the mt-COMP protein burden can be reduced by the presence of a COMP-specific ribozyme. Future studies will focus on designing ribozymes or short interfering RNA (siRNA) technologies that will result in better knockdown of COMP expression as well as the temporal constraints imposed by the PSACH phenotype. ^

Parent modeling and child food consumption

Obesity, among both children and adults, is a growing public health epidemic. One area of interest relates to how and why obesity is developing at such a rapid pace among children. Despite a broad consensus about how controlling feeding practices relate to child food consumption and obesity prevalence, much less is known about how non-controlling feeding practices, including modeling, relate to child food consumption. This study investigates how different forms of parent modeling (no modeling, simple modeling, and enthusiastic modeling) and parent adiposity relate to child food consumption, food preferences, and behaviors towards foods. Participants in this experimental study were 65 children (25 boys and 40 girls) aged 3-9 and their parents. Each parent was trained on how to perform their assigned modeling behavior towards a food identified as neutral (not liked, nor disliked) by their child during a pre-session food-rating task. Parents performed their assigned modeling behavior when cued during a ten-minute observation period with their child. Child food consumption (pieces eaten, grams eaten, and calories consumed) was measured and food behaviors (positive comments toward food and food requests) were recorded by event-based coding. After the session, parents self-reported on their height and weight, and children completed a post-session food-rating task. Results indicate that parent modeling (both simple and enthusiastic forms) did not significantly relate to child food consumption, food preferences, or food requests. However, enthusiastic modeling significantly increased the number of positive food comments made by children. Children's food consumption in response to parent modeling did not differ based on parent obesity status. The practical implications of this study are discussed, along with its strengths and limitations, and directions for future research.^