Analysis of the expression of chondroadherin in mouse ocular and non-ocular tissues

Chondroadherin (Chad) is a unique member of the small leucine rich repeat proteoglycan gene family. It is expressed at high levels in certain zones of cartilage and also has been detected in bone, tendon, bone marrow, and chondrosarcoma cells. Recently, we demonstrated that Chad is expressed in human and mouse lens and that its expression is decreased in the absence of mimecan/osteoglycin. This finding prompted us to explore the expression of Chad in other ocular and non-ocular tissues.

Reverse transcription-polymerase chain reaction amplification (RT-PCR), in situ hybridization (ISH), and immunohistochemistry (IHC) were used to determine the expression of Chad in human and mouse tissues.

RT-PCR analysis showed strong expression of Chad in mouse brain, heart, lung, and embryo. Moderate expression was detected in mouse thymus, spleen, testis, and ovary, and very low expression in kidney and liver. Chad was highly expressed in human cornea, brain, and skeletal muscle, and moderately in human retina and lens. By ISH, Chad mRNA was detected in cornea, lens, and retina of postnatal day 21 mouse eyes. By IHC, immunostaining for Chad was seen in epithelial and endothelial layers of the cornea, as well as in lens, ciliary body, and retina of the adult mouse eye. Strong immunostaining was noted in retinal rod, cone, and plexiform layers. IHC analysis of tissue microarray demonstrated presence of Chad in brain (cerebellum), skeletal and cardiac muscles, lung, gastrointestinal tract, ovary, and cartilage. In most tissues, Chad expression was associated with either peripheral nerves and/or blood vessels. In the stomach and intestines, positive immunostaining was observed in Meissner's plexus and enteroendocrine cells. Intriguingly, positive immunostaining also was observed in Purkinje cells of the cerebellum and pancreatic islets.

The present work establishes the expression and localization of Chad in several new locations including cornea, lens, ciliary body, retina, cerebellum, pancreatic islet, blood vessels, and peripheral nerves. The surprisingly broad expression pattern of Chad suggests potential roles for this protein in cell specific and/or tissues specific function(s). The results reported here are an essential prerequisite for future studies aimed at understanding the biological roles of Chad in health and disease.