Open access publications in the SLU publication database

Abstract

Inhibited differentiation Of the hoof keratinocytes has been proposed as a mechanism underlying the epidermal histopathology of equine laminitis. The aim of this thesis was to carry out morphological studies on the keratinocytes and immunohistochemical and biochemical studies on the cytokeratins of the equine hoof wall and chestnut in order to elucidate the differentiation ofthese cells in an acute attack ofspontaneous laminitis. The investigation comprised four studies. Study I was a histopathological analysis of the hoof wall, skin and chestnut in horses with spontaneous laminitis in the acute phase, i.e. within 48 hours of onset of lameness, and in horses with no symptoms of laminitis, with special emphasis on the epidermal basal cells. In studies II-IV, in the same groups of horses, an analysis was made of the cytokeratin composition of the corresponding tissues and of the cytokeratin distribution in these tissues with the aid of one- and twodimensional electrophoresis and immunohistochemistry, respectively.In horses with acute laminitis, inhibited differentiation of keratinocytes in the zone of cornification of the hoof wall and chestnut was observed morphologically. Further, there was an increased rate ofproliferation in the stratum internum ofthe hoofwall as well as in the strata medium and externum and to some extent also in the chestnut. Moreover, in those horses with laminitis with inhibited differentiation of keratinocytes in the zone of cornification of the hoof wall and chestnut, the basal cell layer was affected at the same time. The bio- and immunohistochemical studies in horses with laminitis showed that the types of cytokeratins present in the hoof wall and chestnut were identical to those in normal horses, but there was a change regarding the cell layers in which they were expressed.Taken together, the increased rate of proliferation among epidermal cells, the change regarding the cell layers in which cytokeratins were expressed, the less differentiated appearance of the suprabasal cells and the probably primary changes in the zone of cornification that were observed early in acute spontaneous laminitis indicate that primary inhibition of differentiation ofthe hoof keratinocytes occurs in laminitis.The observed change in the tissue distribution of cytokeratins was most likely caused by an increased proliferation among the epidermal cells. No “new” types of cytokeratins were produced in the tissues examined; hence it appears natural to consider the role of the cysteine-rich keratin-associated proteins in acute laminitis, and this issue is discussed in the present thesis.