Abstract
This study aimed to elucidate the role of the Sonic hedgehog (Shh)–Patched (Ptch)–Gli signaling pathway in maintaining dental epithelial and pulp stem/progenitor cells and regulating the function of odontoblasts. Doxycycline (dox)-inducible histone 2B (H2B)–green fluorescent protein (GFP) transgenic mice ingested dox at prenatal embryonic days 14.5 or 15.5 and their offspring were collected from postnatal day 1 (P1) to week 3 (P3W). Immunohistochemistry for Gli1, Ptch1, and Ptch2 andin situhybridization forShhandPtch1were conducted. Mandibular incisors of postnatal day 2 H2B-GFP transgenic and wild-type mice were cultivated in a nutrient medium with Shh antibody for 4 days and subsequently processed for immunohistochemistry for Sox2. In molars, dense H2B-GFP-label-retaining cells (H2B-GFP-LRCs) were densely distributed throughout the dental pulp during P1 to postnatal week 2 (P2W) and decreased in number by postnatal P3W, whereas the number of dense H2B-GFP-LRCs in the subodontoblastic layer increased in number at P2W. Gli1+and Pthc1+cells were distributed throughout the enamel organ and dental pulp, including the odontoblast and subodontoblastic layers.ShhmRNA was expressed in the inner enamel epithelium and shifted into odontoblasts after dentin deposition.Ptch1mRNA was expressed in the inner enamel epithelium and cuspal pulpal tissue on P1 and decreased in intensity from postnatal week 1 to P3W. In incisors, the apical bud contained H2B-GFP-LRCs, Gli1+cells, and Ptch1+cells. The addition of Shh antibody to explants induced a decrease in the number of Sox2+cells due to the increase in apoptotic cells in the apical bud. Thus, the Shh–Ptch–Gli signaling pathway plays a role in maintaining quiescent adult stem cells and regulating the function of odontoblasts.
Highlights
IntroductionAdult stem cells, exist in renewal tissues such as the epidermis, intestinal crypt, and bone marrow and are crucial for physiological tissue renewal and regeneration after injury [1]
Committed multipotent stem cells, or adult stem cells, exist in renewal tissues such as the epidermis, intestinal crypt, and bone marrow and are crucial for physiological tissue renewal and regeneration after injury [1]
Sonic hedgehog (Shh) expression and Ki67+ cells were observed in the apical bud and inner enamel epithelium in both the control and 5E1 groups (Figures 4A–D) in B6 mice
Summary
Adult stem cells, exist in renewal tissues such as the epidermis, intestinal crypt, and bone marrow and are crucial for physiological tissue renewal and regeneration after injury [1]. The prenatal BrdU labeling method, in which BrdU is injected into the pregnant mother to label proliferative cells in the prenatal stages, enables us to identify long-term labelretaining cells (LRCs) in the perivascular niche [5, 6] These LRCs are considered to be quiescent stem cells that actively proliferate following exogenous stimuli [5, 7, 8] and play an important role in pulpal homeostasis and the reparative process. These cells maintain their regenerative capability throughout life and are capable of producing odontoblast-like cells to repair injured dentin. The localization of stem/progenitor cells in the dental pulp, the differences in their differentiation capacity in different cell populations, and the mechanisms maintaining their niches are not fully understood
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