FERMT2 expression in human articular chondrocytes is regulated by hypoxia-associated transcriptional programs
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Objective
Kindlin-2, encoded by FERMT2 , is a focal adhesion protein essential for cartilage homeostasis and mechanotransduction. While loss of Kindlin-2 in mice induces osteoarthritis (OA)–like pathology, the upstream mechanisms regulating its expression in human cartilage remain unknown.
Methods
A bioinformatics pipeline was applied to the FERMT2 promoter to predict transcriptional regulators, followed by network and enrichment analyses. Predicted candidates were validated by siRNA knockdown in the human C28/I2 chondrocyte cell line and in primary OA chondrocytes. Pathway enrichment highlighted hypoxia-related regulators, which were further tested by hypoxia mimetic treatment (IOX2) and culture under low oxygen (1% O₂). Gene expression changes were quantified by qPCR, and effects on extracellular matrix (ECM) markers were assessed.
Results
In silico analysis identified 21 candidate transcription factors, of which GATA1 , MEF2A , and RBPJ were validated as regulators of FERMT2 . Silencing of GATA1 and MEF2A reduced FERMT2 expression, whereas RBPJ knockdown increased FERMT2 in both C28/I2 cells and primary OA chondrocytes. However, RBPJ silencing also reduced ACAN and increased COL1A1 , suggesting detrimental effects on ECM homeostasis. Enrichment analysis revealed a strong association between FERMT2 regulation and hypoxia pathways, supported by conserved hypoxia response elements in the promoter. Experimentally, both IOX2 and 1% O₂ significantly upregulated FERMT2 expression in primary chondrocytes. Hypoxia also increased anabolic ECM genes and reduced catabolic enzymes, but these effects occurred independently of Kindlin-2.
Conclusions
This study identifies hypoxia as a novel regulator of kindlin-2 expression in human cartilage, providing new insight into the upstream control of this molecule in osteoarthritis. While additional transcription factors such as GATA1 , MEF2A , and RBPJ contribute to FERMT2 regulation, only hypoxia consistently enhanced FERMT2 expression without adverse ECM effects.
