Abstract
ObjectiveHorses afflicted with degenerative suspensory ligament desmitis (DSLD) suffer from progressive leg pain and lameness without history of trauma. DSLD is a systemic disorder caused by abnormal accumulation of proteoglycans in many connective tissues. One proteoglycan found in higher quantities in DSLD is decorin. The accumulated decorin has an abnormally glycosylated glycosaminoglycan chain in DSLD. In addition to acellular accumulations of proteoglycans foci of active fibroblasts/tenoblasts were observed in some tendons and suspensory ligaments (SLs) from DSLD cases We have hypothesized that this represents an early event in DSLD and that production of chondrogenic growth factors, such as BMP2, and/or enzyme participating in glycosylation of glycosaminoglycans is a major factor in initiation and progression of DSLD.ResultsUsing immunohistochemistry we have identified BMP2 in these cellular foci, indicating association with proteoglycan production, but not in other cells in the tendon and SLs. In contrast, very little staining for TGFβ and dermatan sulfate epimerase, an enzyme involved in glycosylation of glycosaminoglycan chains, was observed in these foci and other cells in both control and DSLD-affected tendons and SLs. Our data support our hypothesis that chondrogenic growth factors may be responsible, at least in part for progression of DSLD in horses.
Highlights
Equine Degenerative Suspensory Ligament Desmitis (DSLD) was identified first in Peruvian Paso horses [1]
Very little staining for transforming growth factor β (TGFβ) and dermatan sulfate epimerase, an enzyme involved in glycosylation of glycosaminoglycan chains, was observed in these foci and other cells in both control and DSLD-affected tendons and suspensory ligament (SL)
The DSLD group was divided in two sub-groups, one consisting of 14 subjects (H1-H14) with prominent hypercellular foci in their tendons and SLs, whereas tendons and SLs from 7 horses with prevalence of large proteoglycan collections were in included in the second sub-group
Summary
Subjects Tendons and SLs were obtained from 21 horses from DSLD and from 5 control horses without DSLD (Table 1). The hallmark of DSLD are inappropriate acellular foci or accumulations of proteoglycans in tendons and other connective tissues, especially SLs without any evidence of inflammation Such deposits are clearly recognizable even with hematoxylin-eosin staining as blue to purple acellular material (Fig. 1b) and likely represent a more advanced stage of DSLD, when cartilage metaplasia and occasional foci of calcification are present. The first type forms distinct foci in affected tendons and SLs, consisting of spindly, plump active fibroblasts/tenoblasts, sometimes arranged in whorls and containing small amounts of cytoplasmic proteoglycans (Fig. 1c). TGFβ-1 was present in fibroblasts and tenocytes, but not in collagen fibers of both normal and DSLDaffected tissues or in the proteoglycan masses Immunohistochemistry identified both TGFβ-1 and BMP2 in tendon sheath and coverings like peritenon and epitenon in all examined samples in moderate amounts regardless of the presence of DSLD. Immunohistochemistry revealed only mild staining in tenoblasts of both normal and DSLD-affected tendons and SLs
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