Parathyroid hormone‐related peptide and Indian hedgehog expression patterns in naturally acquired equine osteochondrosis

Abstract

Early changes in parathyroid hormone-related peptide (PTH-rP) and Indian hedgehog (Ihh) expression were examined in equine articular osteochondrosis (OC) as a inodel of a naturally acquired dyschondroplasia. Cartilage was harvested from OC-affected femoropatellar or scapulohumeral joints from immature horses and normal control horses of similar age. PTH-rP expression levels were assessed by semi-quantitative PCR, in situ hybridization, and immunohistochemistry. Ihh protein expression levels were assessed by immunohistochemistry. Elevated PTH-rP protein and mRNA expression were identified in the deeper layers of affected articular cartilage and the fibrous tissue of interposing clefts. These changes were confined to the chondrocytes in the OC-affected cartilage, which had significantly increased PTH-rP protein and mRNA expression when compared to control cartilages. Ihh protein expression showed similar distribution as PTH-rP in the deeper layers of articular cartilage; however, only a trend for increased Ihh immunostainiiig was evident in the OC cartilage when compared to the normal cartilage. Increased PTH-rP expression in prehypertrophic chondrocytes of diseased OC cartilage suggests a possible link between this peptide and the delayed ossification, which is a consistent histologic alteration in OC. More evidence is necessary to determine the role of Ihh in articular cartilage and if a similar feedback cycle exists as previously described for the growth plate.

Expression patterns of hedgehog signaling peptides in naturally acquired equine osteochondrosis

“…This data supports results from our previous study, which indicated elevated Ihh protein expression in OC samples [25]. This increased Ihh expression in OC suggests a role for Ihh in diseased cartilage.…”

“…The proposed pathogenesis for osteochondrosis includes ischemia and trauma, as well as biochemical and molecular signaling derangements at the level of cartilage differentiation and ossification [ 12,231. Molecular characterization of osteochondrotic cartilage has revealed alterations in matrix collagen and growth factor expression, as well as potential involvement of hedgehog signaling molecules [25,26]. Increased expression of PTH-rP was found in the deeper layers of osteochondrotic cartilage when compared to normal cartilage, leading to inferences that PTH-rP may be inhibiting chondrocyte differentiation in OC [25].…”

“…Molecular characterization of osteochondrotic cartilage has revealed alterations in matrix collagen and growth factor expression, as well as potential involvement of hedgehog signaling molecules [25,26]. Increased expression of PTH-rP was found in the deeper layers of osteochondrotic cartilage when compared to normal cartilage, leading to inferences that PTH-rP may be inhibiting chondrocyte differentiation in OC [25]. Further characterization of osteochondrosis is necessary to delineate the underlying mechanisms leading to aberrant cartilage differentiation and delayed endochondral ossification.…”

Age‐related expression of molecular regulators of hypertrophy and maturation in articular cartilage

“…These riboprobes were previously determined to perform well on equine cartilage samples. 5,6 The probe was added to hybridization buffer containing 25% deionized formamide, 10% dextran sulfate, 300 mM NaCl, 10 mM TRIS, 1 mM EDTA, 1 Â Denhardt's solution (0.02% BSA, 0.02% Ficoll, and 0.02% polyvinylpyrrolidone), 0.5 mg yeast tRNA/mL, and 10 mM dithiothreitol. The probe (0.12 pmoles, specific activity 1.0-1.2 Â 10 7 cpm/pmol) in 40 mL of hybridization buffer was applied to a section on each slide, the slides coverslipped, and then incubated overnight in humid chambers at 438C.…”

“…In addition, alterations in the expression of PTHrP and Ihh have been shown to occur in osteochondrosis, a disease of articular cartilage development. 5,6 Previous studies have shown that the expression of regulatory molecules in articular cartilage may change during the postnatal period. [7][8][9][10][11][12][13][14][15] Qualitative assessment of PTHrP mRNA and protein expression in postnatal rats showed decreased expression in articular cartilage from youth to maturity.…”