Mechanosensitive MiRs regulated by anabolic and catabolic loading of human cartilage

Elucidation of whether miRs are involved in mechanotransduction pathways by which cartilage is maintained or disturbed has a particular importance in our understanding of osteoarthritis (OA) pathophysiology. The aim was to investigate whether mechanical loading influences global miR-expression in human chondrocytes and to identify mechanosensitive miRs responding to beneficial and non-beneficial loading regimes as potential to obtain valuable diagnostic or therapeutic targets to advance OA-treatment.

Mature tissue-engineered human cartilage was subjected to two distinct loading regimes either stimulating or suppressing proteoglycan-synthesis, before global miR microarray analysis. Promising candidate miRs were selected, re-evaluated by qRT-PCR and tested for expression in human healthy vs OA cartilage samples.

After anabolic loading, miR microarray profiling revealed minor changes in miR-expression while catabolic stimulation produced a significant regulation of 80 miRs with a clear separation of control and compressed samples by hierarchical clustering. Cross-testing of selected miRs revealed that miR-221, miR-6872-3p, miR-6723-5p were upregulated by both loading conditions while others (miR-199b-5p, miR-1229-5p, miR-1275, miR-4459, miR-6891-5p, miR-7150) responded specifically after catabolic loading. Mechanosensitivity of miR-221 correlated with pERK1/2-activation induced by both loading conditions. The miR-response to loading was transient and a constitutive deregulation of mechano-miRs in OA vs healthy articular cartilage was not observed.

MiRs with broader vs narrower mechanosensitivity were discovered and the first group of mechanosensitive miRs characteristic for non-beneficial loading was defined that may shape the proteome differentially when cartilage tissue is disturbed. The findings prompt future investigations into miR-relevance for mechano-responsive pathways and the corresponding miR-target molecules.