Collagen II is the major fibril-forming
collagen in cartilage. Complete absence of
collagen II in mice is not compatible with life and in humans mutations in the COL2A1 gene lead to
osteochondrodysplasias with diverse phenotypes. However, mechanistic studies on how chondrocytes respond to a lack of
collagen II in their extracellular matrix are limited. Primary mouse chondrocytes were isolated from knee joints of newborn mice and transfected with
siRNA targeting Col2α1 to suppress
collagen II expression. The expression of
integrin receptors and matrix
proteins was investigated by RT-PCR and immunoblots. The localization of matrix components was evaluated by immunostaining. Signaling pathways and the differentiation state of chondrocytes was monitored by RT-PCR and flow cytometry. We demonstrate that in the absence of
collagen II chondrocytes start to produce
collagen I. Some binding partners of
collagen II are partially lost from the matrix while other
proteins, e.g. COMP, were still found associated with the newly formed
collagen network. The lack of
collagen II induced changes in the expression profile of
integrins. Further, we detected alterations in the Indian hedgehog/
parathyroid hormone-related protein (Ihh/
PTHrP) pathway that were accompanied by changes in the differentiation state of chondrocytes.
Collagen II seems not to be essential for chondrocyte survival in culture but it plays an important role in maintaining chondrocyte differentiation. We suggest that a crosstalk between extracellular matrix and cells via
integrins and the Ihh/
PTHrP pathway is involved in regulating the differentiation state of chondrocytes.