Effect of endocrine and paracrine factors on protein synthesis and cell proliferation in bovine hoof tissue culture

Abstract

Laminitis is a major cause of lameness in dairy cattle, and is widely attributed to a defect in the horny tissue that gives the hoof its mechanical strength. Defective horn is associated with, and may be preceded by, impaired keratin deposition in the hoof epidermis. The cause of abnormal keratin deposition is not easily identified but, like epidermal keratinization in other tissues, is likely to be controlled by hormones and the paracrine action of locally produced growth factors. The hormonal regulation of keratin synthesis and cell proliferation in the bovine hoof was studied using tissue explants in organ culture. As the highest incidence of laminitis is in early lactation, the study focused on insulin, cortisol and prolactin, three hormones implicated in lactogenesis and galactopoiesis. Incubation of tissue explants for 24 h in medium containing insulin (10–5000 ng/ml) stimulated protein synthesis measured by incorporation of 35 S-labelled amino acids. Histochemical examination showed that insulin binding co-localized with the site of protein synthesis. Insulin also stimulated DNA synthesis, an index of cell proliferation, which was measured by incorporation of [3H]methyl thymidine. Cortisol (10–5000 ng/ml) decreased protein synthesis, whereas prolactin (10–5000 ng/ml) had no significant effect on protein or DNA synthesis. Epidermal growth factor (10–200 ng/ml), a potent inhibitor of keratinization in other tissues, stimulated protein synthesis compared with untreated controls. Epidermal growth factor binding was located microscopically to the germinal and differentiating epidermal layers. SDS-PAGE and fluorography showed that the population of proteins synthesized in the presence of any hormone or growth factor combination did not differ from that in untreated controls and included the keratins involved in horn deposition. The results show that bovine hoof keratinization is under endocrine and growth factor control, and suggest that systemic changes in lactogenic hormones may act to inhibit keratin deposition.

Histological and Morphometric Characteristics of the Corneal Layer of Buffalo Hoof Capsules

“…The helical arrangement of the intra tubular keratin, similar to the alfakeratin structure -main protein constituent of the keratinized epidermis -was also described by McKittrick et al (2012). The intercellular cement, second product of keratinization, adhering the keratinocytes and helping in the waterproofing of the hoof capsule and observed in the present study, was not reported in other research with buffaloes (Silva et al), yet it was described in equines (Hendry et al, 1999) (Fig. 4).…”

Relationship of lameness to body condition score, udder health and milk quality in crossbred dairy cattle

“…Maintenance of cows in this period on a high concentrate diet eventually creates hyperinsulinaemia and hyperglycaemia (VERMUNT and GREENOUGH, 1994), a condition in which insulin resistance develops, resulting in inhibition of glucose and amino acid uptake, and producing poor quality hoof horn. However, HENDRY et al (1999) identified the role of other factors, such as epidermal growth factor (EGF), relaxin, prolactin and cortisol levels at the time of late gestation that precipitate the production of poor quality keratin, thus leading to more likelihood of lameness during late lactation.…”

The corticosteroid laminitis story: 2. Science of if, when and how

“…Production of another protein, keratin, is also important for conferring mechanical strength to the hoof wall and laminar interface. In bovine hoof explants cultured in vitro, cortisol significantly decreased keratin synthesis (Hendry et al 1999). Therefore, long-term effects of glucocorticoid use may conceivably produce a weakening of the lamellar bonds or inhibit growth from the coronary band.…”