Distribution of myofibroblasts, smooth muscle-like cells, macrophages, and mast cells in mitral valve leaflets of dogs with myxomatous mitral valve disease.
OBJECTIVE
To map the cellular distribution and phenotypic alteration of the predominant stromal cell population throughout the entire valve length of dogs with myxomatous mitral valve disease (MMVD).


METHODS
31 mitral valve complexes (ie, mitral valve leaflets) collected from 4 clinically normal dogs and 27 dogs with MMVD of varying severity.


METHODS
A combination of standard histologic and immunohistochemical techniques was used to identify pathologic changes, the presence of mast cells, and the density and distribution of cells expressing vimentin, desmin, alpha-smooth muscle actin (alpha-SMA), smooth muscle myosin, and the macrophage marker MAC387.


RESULTS
Vimentin-positive cells predominated in the mitral valve leaflets from clinically normal dogs and were located throughout the leaflet, but cell density was appreciably decreased with disease progression, and minimal cell numbers were found in distinct myxomatous areas. Cells that were positive for alpha-SMA were uncommon in the mitral valve leaflets from clinically normal dogs and only seen in appreciable numbers in mitral valves of dogs with severe late-stage disease, in which cells were typically located close to the ventricularis valve surface. A slight increase in mast cell numbers was observed in the distal zone of affected leaflets.


CONCLUSIONS
Activated-myofibroblasts (alpha-SMA-positive cells) were increased and inactive-myofibroblasts (vimentin-positive cells) were reduced in mitral valve leaflets of dogs with MMVD, compared with that of clinically normal dogs. Impact on Human Medicine-This is the first description of spatial and temporal alterations in mitral valve cells of any species with MMVD and has clinical importance in the understanding of disease development in dogs and humans.
Hospital for Small Animals, Division of Veterinary Clinical Sciences, the Royal (Dick) School of Veterinary Studies, University of Edinburgh, Roslin, Midlothian EH25 9RG, Scotland.
Richard I
RI
Han
Alexander
A
Black
Geoff J
GJ
Culshaw
Anne T
AT
French
Roderick W
RW
Else
Brendan M
BM
Corcoran
D000818:Animals; D004283:Dog Diseases / Q000473:pathology*; D004285:Dogs; D005347:Fibroblasts / Q000473:pathology; D006349:Heart Valve Diseases / Q000473:pathology / Q000662:veterinary*; D007150:Immunohistochemistry / Q000662:veterinary; D008264:Macrophages / Q000473:pathology; D008407:Mast Cells / Q000473:pathology; D008943:Mitral Valve / Q000166:cytology / Q000473:pathology*; D010641:Phenotype