re C-KIT, MMP-9 and Type II Collagen Positive Undifferentiated Cells Involved in Cartilage Growth?

What is it about?

Cartilages growth requires activation of perichondrial cells and chondrocyte multiplication. Activated perichondrial cells produce an outer cartilage matrix and in appositional growth and chondrocytes division produce new chondrogenic cells which participate in interstitial growth of cartilage. This study was performed to identify a third type of cartilage growth in skeletal elements of quail embryos at 6, 7, 8, 9, 10, 13, 16, 17 days of incubation. Paraffin sections of the whole embryos were stained using H&E and Safranin O stains. Immunohistochemical staining for C-KIT, matrix metallpoproteinase-9 (MMP-9) and type II collagen was performed. Other samples were processed for scanning and transmission electron microscopy. We found that cells extended form mesenchymal tissue or perichondrium penetrated the cartilage templates of different skeletal elements. The morphological and immunohistochemical characteristics of these cells were identical to mesenchymal cells; characterized by their small size, having multiple cell processes and staining positive for C-KIT. MMP-9 positive cells were detected in cartilage matrix. The mesenchymal cells further differentiated into chondrocytes which were positive for type II collagen immunostaining and secreted Safranin O positive cartilage matrix. In conclusion, our results suggest that C-KIT positive mesenchymal cells secrete MMP-9 to penetrate growing cartilage, produce type II collagen and proteoglycan and have a role in interstitial growth of embryonic cartilage templates in quail. (Graphical Abstract

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Why is it important?

Degenerative cartilaginous disorders are a major concern in skeletal diseases. Undifferentiated mesenchymal cells have been used in recent research towards the development of therapeutic applications toward replacing damaged cartilage. In the current study, we found that undifferentiated mesenchymal cells invaded the growing cartilage to provide a new population of chondrogenic progenitors and secrete new cartilage matrix.

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