Immunohistochemical study of lysosome-associated membrane proteins during periodontal ligament development

Amelogenin is an enamel matrix protein also expressed in periodontal tissues. Recent studies suggest that lysosome-associated membrane proteins (LAMPs) can bind cell surface amelogenin and act as signaling receptors for amelogenin in periodontal ligament (PDL) cells and cementoblasts in vitro. However, whether amelogenin and LAMPs are involved in the development of periodontal tissues is unclear. To address this issue, we used immunohistochemistry to profile LAMPs and amelogenin expression during periodontal tissue development. Paraffin sections from mice at embryonic day 15 (E15) and 1, 2, and 4 weeks were made, and serial sections at each age were stained with hematoxylin-eosin, followed by immunostaining with antiamelogenin, LAMP-1, and LAMP-3. At E15, dental follicle cells, which are the source of periodontal tissues, were amelogenin-positive and weakly positive for LAMP-1 and LAMP-3. At 1 week, dental follicle cells were immunopositive for amelogenin and LAMP-1 but weakly positive for LAMP-3. At 2 weeks, PDL cells were positive for amelogenin and LAMP-1 but negative for LAMP-3. At 4 weeks, PDL cells were immunopositive for both amelogenin and LAMP-1. These results suggest that LAMP-1 is expressed in both the dental follicle and PDL, and that LAMP-1 and LAMP-3 have temporally distinct roles as signaling receptors for amelogenin.