Role of the mTOR signalling pathway in salivary gland development

Abstract

Development of the salivary gland is characterized by extensive branching morphogenesis. Although various molecules have been implicated in salivary gland development, the role of the mammalian target of rapamycin (mTOR) signalling pathway, including both mTOR complexes 1 and 2 (mTORC1 and 2), in salivary gland development is unknown. Here, we examined protein expression levels related to the mTOR signalling pathway using an ex vivo submandibular salivary gland (SMG) organ culture. We showed that branching buds in the salivary glands were substantially decreased and phosphorylation of mTORC1 signalling pathway related proteins (mTOR, p70 ribosomal protein S6 kinase 1 and eukaryotic initiation factor 4E‐binding protein 1) was inhibited by rapamycin (an mTOR inhibitor). In addition, AKT, which is an upstream protein kinase of mTORC1 and is downstream of mTORC2, is inhibited by LY294002 (a phosphatidylinositol 3‐kinase inhibitor), but not by rapamycin. Moreover, rapamycin‐treated ICR neonatal mice exhibited a reduction in both body weight and salivary glands compared with vehicle‐treated neonatal mice. The present data indicate that the mTOR signalling pathway, including both mTORC1 and mTORC2, plays a critical role in salivary gland development both in ex vivo SMG organ culture and ICR neonatal mice in vivo.

The HIF‐1α pathway plays a critical role in salivary gland development in ex vivo organ cultures

“…During development, SMG branching morphogenesis is regulated by various factors and cytokines via many signaling cascades [8], but the role of the HIF-1arelated signaling pathway in salivary gland development has not been investigated. Using ex vivo SMG organ culture, we found that the HIF-1a-related signaling pathway regulates branching morphogenesis during SMG development.…”

“…6A,B). Therefore, we investigated the effect of hypoxic conditions on cell proliferation and cell death, as previous studies have reported the role of cell proliferation and cell death during salivary gland development [7,8]. We investigated the expression of PCNA, Cyclin D1, Cleaved-caspase-3, Procaspase-3, and LC3B1/2 by western blot analysis.…”

“…Saliva has digestive, antibacterial, mucosal protective, and bolus-forming properties and hence plays an important role in maintaining the environment and function of the oral cavity and the body as a whole [5]. During the development of some organs including salivary glands, a branching process which begins on embryonic day 12 (E12) is necessary [6][7][8]. Early organs are simple epithelial buds that gradually develop into polycystic structures.…”

“…Bud branching continues during early fetal development and peaks between E13 and E15. We previously used ex vivo submandibular salivary gland (SMG) organ cultures to observe SMG branching morphogenesis between E13 and E15 [7,8]. Many researchers have used our method to investigate the interactions between cells and matrices, cell proliferation, and cell death.…”

“…Many researchers have used our method to investigate the interactions between cells and matrices, cell proliferation, and cell death. Various factors are involved in salivary gland morphogenesis during embryonic development [8][9][10]. Embryos are exposed to low oxygen levels during development, and hence, HIF-1a plays an important role in embryonic development [11,12].…”