gms | German Medical Science

Objectives: Mechanical loading plays an important role in regulating the development and maintenance of cartilage. Permanent improper loading supports the pathogenesis of osteoarthritis (OA) whereas moderate loading supports the preservation of cartilage. As post-transcriptional regulators of gene expression, microRNAs (miRs) represent promising molecules to quickly adjust the cellular transcriptome in a stimulus-dependent manner. Some miR clusters are associated with mechanosensitivity and mechanotransduction in cardiovascular biology and mechanical airway ventilation. Other miRs are related to regulation of skeletal development, joint homeostasis and OA pathophysiology. Surprisingly little is known about the role of mechanosensitive miRs in cartilage function and pathology of OA. We here aimed to investigate the influence of mechanical load on miR expression and to identify mechanosensitive miRs clusters characteric for anabolic and catabolic loading regimes which may serve as future tools for improved diagnosis or treatment of OA.

Methods: Human chondrocyte-seeded collagen scaffolds consisting of 5x10⁵ cells were connected to ß-tricalcium-phosphate and pre-cultivated under chondrogenic conditions before exposed to cyclic unconfined compression. Anabolic or catabolic loading regimes were established based on radiolabel incorporation for proteoglycan synthesis within 24h after loading. miR microarray profiling was performed immediately after exposure to 1-4 loading episodes. Selected miRs were re-evaluated in independently generated samples via qRT-PCR.

Results and conclusion: According to miR microarray analysis 7 miRs were significantly regulated by an anabolic loading protocol. To determine whether the response of engineered cartilage to loading was consistent, hierarchical clustering of miR expression data was performed. miR expression values allowed no clear separation between control and compressed samples demonstrating low concordance of miR regulation under anabolic conditions. Regulation of 2/3 miR was confirmed via qRT-PCR. Catabolic stimulation of engineered cartilage resulted in significant regulation of 80 miRs, 20 of which were upregulated, 10 of them > 2-fold. Hierarchical clustering revealed a clear separation of control and compressed samples indicating a consistent response to catabolic loading. Regulation of 6/11 miR was confirmed by qRT-PCR. Cross-testing of the 8 confirmed mechanosensitive miRs by qRT-PCR revealed that 3 miRs were upregulated by both loading conditions and 5 were specifically elevated by catabolic loading.

We found 2 mechanosensitive miR clusters. One cluster consisting of 3 miRs might serve as useful marker for mechanical stimulation independently of the loading regime. Another cluster containing 5 miRs is specificially regulated under non-physiologic mechanical conditions.