Ameloblastin promotes polarization of ameloblast cell lines in a 3-D cell culture system

Studies on animal models with mutations in ameloblastin gene have suggested that the extracellular matrix protein ameloblastin (AMBN) plays important roles in controlling cell-matrix adhesion and amelo-blast polarization during amelogenesis. In order to examine the function of AMBN in cell polarization and morphology, we developed an in vitro 3D cell culture model to examine the effect of AMBN and ameloge-nin (AMEL) addition on ameloblast cell lines. We further used high resolution confocal microscopy to detect expression of polarization markers in response to AMBN addition. Addition of AMBN to the 3D cul-ture matrix resulted in the clustering and elongation (higher aspect ratio) of ALC in a dose dependent manner. The molar concentration of AMEL required to exact this response from ALC was 2.75-times greater than that of AMBN. This polarization effect of ameloblastin was attributable directly to an evolu-tionary conserved domain within its exon 5-encoded region. The lack of exon 6-encoded region also influ-enced AMBN-cell interactions but to a lesser extent. The clusters formed with AMBN were polarized with expression of E-cadherin, Par3 and Cldn1 assembly at the nascent cell-cell junctions. The elongation effect was specific to epithelial cells of ameloblastic lineage ALC and LS8 cells. Our data suggest that AMBN may play critical signaling roles in the initiation of cell polarity by acting as a communicator between cell-cell and cell-matrix interactions. Our investigation has important implications for understand-ing the function of ameloblastin in enamel-cell matrix adhesion and the outcomes may contribute to efforts to develop strategies for enamel tissue regeneration. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

Studies on animal models have shown that ameloblastin (AMBN) is involved in cell-matrix adhesion and cell polarization during enamel formation. In this study, an in vitro 3D cell culture model was developed to investigate the role of AMBN in cell polarization and morphology. The addition of AMBN to the culture matrix resulted in the clustering and elongation of ameloblast cell lines in a dose-dependent manner. AMBN plays a critical signaling role in the initiation of cell polarity by acting as a communicator between cell-cell and cell-matrix interactions.