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Changes in molecular expression of aggrecan and collagen types I, II, and X, insulin-like growth factor-I, and transforming growth factor-β1 in articular cartilage obtained from horses with naturally acquired osteochondrosis

Stacy A. SemevolosComparative Orthopaedics Laboratory, Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.

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 DVM, MS
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Alan J. NixonComparative Orthopaedics Laboratory, Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.

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 BVSc, MS
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Brent D. Brower-TolandComparative Orthopaedics Laboratory, Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.

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 MA

Abstract

Objective—To determine molecular changes in the expression of insulin-like growth factor-I (IGF-I) and transforming growth factor-β1 (TGF-β1) in horses with osteochondrosis, and to characterize expression of matrix aggrecan and collagen types I, II, and X in articular cartilage of affected joints.

Sample Population—Articular cartilage from affected stifle or shoulder joints of 11 horses with naturally acquired osteochondrosis and corresponding joints of 11 clinically normal horses.

Procedure—Harvested specimens were snap frozen in liquid nitrogen, and total RNA was isolated. Specimens were fixed in 4% paraformaldehyde for histologic examinations. Expression of matrix molecules was assessed by analysis of northern blots and in situ hybridization, using equine-specific cDNA probes and riboprobes, respectively. Expression of IGF-I and TGF-β1 was assessed by use of noncompetitive quantitative polymerase chain reaction, in situ hybridization, and immunohistochemical analysis.

Results—Cartilage obtained from osteochondrosis lesions had significantly greater expression of IGF-I, compared with normal cartilage. Expression of TGF- β1 and collagen type I were higher, but not significantly so, in affected tissues. Expression of aggrecan or collagen types II and X did not differ between affected and clinically normal cartilage.

Conclusions and Clinical Relevance—Increased expression of growth factors and collagen type I was found in cartilage from osteochondrosis lesions. However, this probably reflects a healing response to injured tissue rather than a primary alteration. Therefore, methods aimed at altering concentrations of growth factors in cartilage of growing horses would be unlikely to alter the incidence or progress of the disease. (Am J Vet Res 2001;62:1088–1094)

Abstract

Objective—To determine molecular changes in the expression of insulin-like growth factor-I (IGF-I) and transforming growth factor-β1 (TGF-β1) in horses with osteochondrosis, and to characterize expression of matrix aggrecan and collagen types I, II, and X in articular cartilage of affected joints.

Sample Population—Articular cartilage from affected stifle or shoulder joints of 11 horses with naturally acquired osteochondrosis and corresponding joints of 11 clinically normal horses.

Procedure—Harvested specimens were snap frozen in liquid nitrogen, and total RNA was isolated. Specimens were fixed in 4% paraformaldehyde for histologic examinations. Expression of matrix molecules was assessed by analysis of northern blots and in situ hybridization, using equine-specific cDNA probes and riboprobes, respectively. Expression of IGF-I and TGF-β1 was assessed by use of noncompetitive quantitative polymerase chain reaction, in situ hybridization, and immunohistochemical analysis.

Results—Cartilage obtained from osteochondrosis lesions had significantly greater expression of IGF-I, compared with normal cartilage. Expression of TGF- β1 and collagen type I were higher, but not significantly so, in affected tissues. Expression of aggrecan or collagen types II and X did not differ between affected and clinically normal cartilage.

Conclusions and Clinical Relevance—Increased expression of growth factors and collagen type I was found in cartilage from osteochondrosis lesions. However, this probably reflects a healing response to injured tissue rather than a primary alteration. Therefore, methods aimed at altering concentrations of growth factors in cartilage of growing horses would be unlikely to alter the incidence or progress of the disease. (Am J Vet Res 2001;62:1088–1094)