The Effects of Sialoadenectomy and Exogenous EGF on Taste Bud Morphology and Maintenance

Abstract

Taste buds on the dorsal tongue surface are continually bathed in saliva rich in epidermal growth factor (EGF). In the following experiment, taste bud number and morphology were monitored following submandibular and sublingual salivary gland removal (sialoadenectomy), to determine if EGF plays a role in the maintenance and formation of taste buds. Adult male rats were divided into four groups: sialoadenectomized (SX, n = 4); sialoadenectomized with EGF replacement (SX + EGF, n = 5); sham-operated (SH, n = 4); and sham-operated with exogenous EGF (SH + EGF, n = 5). After a 3 week recovery, SX + EGF and SH + EGF animals were given 50 microg/day EGF in their drinking water for 14 days. At day 14, saliva was collected, the animals were killed and the presence of EGF determined by radioligand-binding assay. Tongues were removed and histologically examined for the presence and morphology of taste buds on fungiform and circumvallate papillae, or immunostained for the presence of EGF, TGFalpha (transforming growth factor alpha) and EGFR (EGF receptor). The removal of submandibular and sublingual salivary glands resulted in the loss of fungiform taste buds and normal fungiform papillae morphology. These effects were reversed by EGF supplementation, indicating a role for EGF in fungiform taste bud maintenance. In addition, supplementation of EGF to sham-operated animals increased the size of fungiform taste buds. In contrast, removal of salivary glands had no effect on the size, numbers, or morphology of circumvallate taste buds, suggesting that the formation and maintenance of taste buds in fungiform and circumvallate papillae may involve different and distinct processes. EGF, TGFalpha and EGFR were localized to distinct layers of the dorsal epithelium and to within both fungiform and circumvallate taste buds. Their expression within the epithelium or taste buds was not altered with sialoadenectomy, indicating that the actions of endogenous EGF and TGFalpha are distinct and not regulated by exogenous EGF and TGFalpha supplied in saliva.

Reduced Oral Wound Healing in the NOD Mouse Model for Type 1 Autoimmune Diabetes and Its Reversal by Epidermal Growth Factor Supplementation

“…Restoration of normal rates of healing in diabetic mice by EGF treatment supports the concept that reduced saliva-derived EGF is a major contributor in the pathogenic complication of decreased wound healing associated with diabetes. A direct action for EGF in the healing processes of the lingual surface is supported further by the presence of the EGF receptor in the epithelial cells that form the taste buds as well as the need for saliva-derived EGF to maintain the presence and morphology of this tissue (38).…”

In Utero and Lactational Exposure to Low-Dose Genistein-Vinclozolin Mixture Affects the Development and Growth Factor mRNA Expression of the Submandibular Salivary Gland in Immature Female Rats

“…Nerve growth factor acts on the sympathetic nervous system, particularly under stress conditions, whereas EGF acts primarily on mammary gland morphogenesis, uterine growth, and gametogenesis (Rougeot et al 2000). In addition, EGF protects the oral cavity epithelium and maintains taste bud integrity (Morris-Wiman et al 2000), whereas NGF is more involved in taste perception (Suzuki et al 2007), behavior, and brain plasticity (Saruta et al 2010). As a consequence, SSG sialoadenectomy results in taste loss, oral illness, and reproductive disorders (e.g., increased abortion rate and spermatogenesis impairment), which demonstrates that salivary secretions contribute to the regulation of many physiological processes, including sensory perception and immune and inflammatory reactions, but also reproductive and peripheral organ development and/or regeneration (Mathison 1995).…”

Effect of exogenous epidermal growth factor (EGF) on nonenzymatic antioxidant capacities and MPO activity of wound tissue

“…The integrity of oral and digestive mucosa was maintained by salivary components, such as EGF, nerve growth factor (NGF), transforming growth factor alpha (TGF-a) (Egéa et al, 2005). EGF in saliva is responsible for the maintenance of normal taste bud morphology (Morris-Wiman et al, 2000). EGF facilitates epidermal cell regeneration and plays an essential role in process of wound healing through stimulation of proliferation and migration of keratinocytes (Barrandon and Green, 1987).…”