Decreased expression of p63, a regulator of epidermal stem cells, in the chronic laminitic equine hoof

Abstract

SummaryReasons for performing study: Abnormal epidermal stem cell regulation may contribute to the pathogenesis of equine chronic laminitis. Objective: To analyse the involvement of p63, a regulator of epidermal stem cell proliferative potential, in chronic laminitis. Methods: Epidermal tissues from skin, coronet and lamellae of the dorsal foot were harvested from 5 horses with chronic laminitis and 5 control horses. Tissues were analysed using histopathology, immunofluorescence microscopy and quantitative immunoblotting Results: Hoof lamellae of laminitic horses had a lower frequency of p63 positive cells than control lamellae, particularly in the distal region. Quantitative immunoblotting confirmed reduced p63 expression in the laminitic distal lamellar region. The decreased p63 expression in laminitic epidermal lamellae was most apparent in the abaxial region adjacent to the hoof wall and highly associated with the formation of terminally differentiated, dysplastic and hyperkeratotic epidermis in this region, whereas lamellae from control horses maintained high p63 expression throughout the axial-abaxial axis. Conclusions: Expression of p63 in equine skin resembles that reported in other species, including man and rodents, suggesting that p63 can serve as a marker for the proliferative potential of equine epidermal stem cells. p63 expression was significantly lower in the chronic laminitic hoof than in that of control horses, suggesting laminitic hoof epithelium has more limited proliferative potential with a shift towards differentiation. This may reflect reduced activity of epidermal stem cells in laminitic hoof. It is proposed that p63 contributes to the maintenance of hoof lamellae and that misregulation of p63 expression may lead to epidermal dysplasia during lamellar wedge formation. Potential relevance: This study suggests that loss of epidermal stem cells contributes to the pathogenesis of equine laminitis.

Equine Epidermis: A Source of Epithelial-Like Stem/Progenitor Cells with In Vitro and In Vivo Regenerative Capacities

“…It has been reported that more than 60% of isolated human corneal and limbal epithelial cells were positive for this marker [62]. Unlike previous findings in horse skin [63], it should be mentioned that in this study, using a rabbit polyclonal antibody directed to a mix of p63 isoforms, the expression of p63 was not restricted to the nucleus. Immunoblotting analyses later confirmed crossreactivity of the antibody with our equine EpSCs.…”

“…Dilution optimization, as well as isotype and positive controls further validated these results, revealing cytoplasmic localization (data not shown). By contrast, Carter et al described strictly nuclear signals using mouse monoclonal antibodies directed to the delta N region of the peptide in equine skin samples [63]. It is likely that the noted discrepancies in cellular localization associated with the different antibodies arise from the differences in epitope specificity.…”

The carboxy-terminus of p63 links cell cycle control and the proliferative potential of epidermal progenitor cells

“…Indeed, p63-null mice display severe defects in epithelial development (Mills et al, 1999;Yang et al, 1999). Genetic studies suggest that mutations in p63 contribute to the pathogenesis of a wide range of ectodermal dysplasias (EDs), characterized by ectodermal malformations and hypoplasias (Celli et al, 1999;Koster, 2010;Rinne et al, 2007;van Bokhoven and McKeon, 2002), and we have recently noted decreased p63 expression in chronic equine laminitis in which the proliferative epidermal layers appear dysplastic (Carter et al, 2011). Thus, it is clear that p63 plays a key role in both the normal physiology and pathophysiology of the epidermis.…”

Osteopathology in the Equine Distal Phalanx Associated With the Development and Progression of Laminitis

“…The chronic phase of laminitis is characterized by inadequate tissue healing and aberrant regenerative responses that result in lamellar hyperplasia and dysplasia, which correspond to the gross lesion of a lamellar wedge. 5,9,26 Horses with chronic laminitis and lamellar wedge formation often develop radiographically evident changes in the DP, such as bone remodeling and fractures along the solar margin, whereas in acute stages of laminitis, bone lesions are difficult to detect with routine imaging modalities. …”

“…The chronic phase of laminitis is characterized by inadequate tissue healing and aberrant regenerative responses that result in lamellar hyperplasia and dysplasia, which correspond to the gross lesion of a lamellar wedge. 5,9,26 Horses with chronic laminitis and lamellar wedge formation often develop radiographically evident changes in the DP, such as bone remodeling and fractures along the solar margin, whereas in acute stages of laminitis, bone lesions are difficult to detect with routine imaging modalities. 2,30,34,42 Although magnetic resonance imaging of feet from horses with acute and chronic laminitis has identified evidence of DP bone remodeling and increased fluid within the medullary compartments (sometimes referred to as ''bone marrow edema''), microarchitectural or cellular detail cannot be determined with this imaging modality.…”