Epidermal cell proliferation in the equine hoof wall

Abstract

Summary Reasons for performing study: Current theories explaining how the hoof wall ‘grows’ and moves past the stationary distal phalanx are speculative and based on incomplete evidence. Movement in the lamellar region could occur by cell proliferation or an enzyme‐based remodelling process. Since laminitis pathogenesis appears to involve increased transcription and activation of enzymes normally involved in tissue remodelling, it is important to know precisely which process dominates the lamellar region of the hoof. Objectives: T o investigate epidermal cell proliferation in the equine hoof wall and calculate a proliferative index (PI) for the coronet, lamellae and toe. Methods: An analogue of thymidine, 5‐bromo‐2′‐deoxyuridine (BRdU), was infused i.v. into 5 ponies. After tissue harvesting, BRdU (and therefore basal cell proliferation) was detected immunohistochemically using mouse anti‐BRdU. PIs were calculated for the coronet and 10 levels of the dorsal hoof wall lamellae. Results: The highest PIs (mean ± s.e.) were in the coronet; 12.04%± 1.59 and proximal lamellae (7.13%± 1.92) and are therefore growth zones of the proximal hoof wall. PIs of more distal lamellae were 0.11%± 0.04 to 0.97%± 0.29; significantly lower (P = 0.05) than the lamellar growth zone. Conclusions: A 20‐fold PI decrease between proximal and more distal lamellae suggests that the majority of the normal lamellae are nonproliferative and their main function is to suspend the distal phalanx within the hoof capsule. Remodelling within the hoof wall epidermal lamellae, which must occur as the hoof wall moves past the stationary distal phalanx, is a process not requiring epidermal cell proliferation. Potential relevance: A hoof lamellar epidermis that remodels using the same MMPs involved in laminitis pathogenesis implies that laminitis is a normal process out of control. Understanding MMP control and how the normal lamellar epidermis achieves this will help in the development of better laminitis preventative and treatment strategies.

Morphological study of the hoof in yak

“…The observations of Daradka and Pollitt [6], who stated that the terminal part of the digital artery enters the solar canal of the distal phalanx via the paired sole foramina and unites with the artery of the opposite side to form the terminal arch deep within the bone, could not be supported by our findings, which showed that there was turning angle instead of terminal arch in yak hoof. Our findings resemble that in cattle [27].…”

“…The hooves in equine have been frequently mentioned [6,10,13,[15][16][17], the hoof wall consists of three layers: the stratum externum, stratum medium, and stratum internum. The stratum medium is the thickest of the three layers and is characterised by its tubular and intertubular horn structure.…”

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

“…Tissue homeostasis is possible due to the presence of ESCs, which have the capacity both for self‐renewal and generation of differentiated cells of the epidermal tissue (Blanpain and Fuchs 2009). In the case of the equine hoof, continuous growth is necessary to replace hoof lost at the ground surface (Daradka and Pollitt 2004). This growth is supported mainly by proliferation of epidermal cells (ECs) of proximal (coronary) regions of the hoof, with very low levels of proliferation in mid‐lamellar regions, as demonstrated in ponies using 5‐bromo‐2′‐deoxyuridine (BrdU) incorporation (Daradka and Pollitt 2004).…”

Histologic evaluation of the diversity of epidermal laminae in hooves of horses without clinical signs of laminitis

“…10,11 The PEL-types I and II could have been the predominant morphologic type of PEL within tissue sections because these types were detected grouped together, whereas PEL-type III was detected on its own. 10,11 The PEL-types I and II could have been the predominant morphologic type of PEL within tissue sections because these types were detected grouped together, whereas PEL-type III was detected on its own.…”