Profiling microRNA expression in bovine articular cartilage and implications for mechanotransduction.

Objective: Articular cartilage is an avascular tissue with precise polarity and organization comprising 3 distinct functional zones: the surface, middle, and deep zones. Each zone has a different gene expression pattern that plays a specific role in articular cartilage development and maintenance. MicroRNA (miRNA) are small noncoding gene products that play an important regulatory role in determining cell differentiation and function. The purpose of this study was to test our hypothesis that miRNA expression profiles in the different articular cartilage zones as well as between regions subjected to different levels of weight-bearing stresses are unique.

Methods: Using an miRNA microarray approach in conjunction with quantitative reverse transcription-polymerase chain reaction, we identified miRNA in bovine articular cartilage that were differentially expressed in the different functional zones and in the anterior weight-bearing and posterior non-weight-bearing regions of the medial femoral condyle (M1 and M4, respectively).

Results: We identified miRNA-221 and miR-222 as part of a subset of differentially expressed miRNA that were up-regulated in articular cartilage in the anterior, M1, greater weight-bearing location. Additionally, miR-126, miR-145, and miR-335 were down-regulated in monolayers of tissue-cultured chondrocytes as compared with levels determined directly from intact native cartilage.

Conclusion: In conclusion, miR-222 expression patterns in articular cartilage are higher in the weight-bearing anterior medial condyle as compared with the posterior non-weight-bearing medial condyle. Thus, miR-222 might be a potential regulator of an articular cartilage mechanotransduction pathway. These data implicate miRNA in the maintenance of articular cartilage homeostasis and are therefore targets for articular cartilage tissue engineering and regenerative medicine.