IADR Abstract Archives
Extracellular Matrix Remodeling in the Apical Papilla
Objectives: The apical papilla is a collagen and stem cell rich tissue which is involved in dental root maturation. Here, we investigate cellular heterogeneity in the medulla of the apical papilla and determine their role in extracellular matrix (ECM) remodeling.
Methods: Apical papillae were dissected from 13 human third molars (13-26 years), embedded in paraffin and stained for haematoxylin-eosin to investigate cellularity. Immunocytochemistry was performed to identify cellular phenotypes (vimentin, CD44), apoptosis (cleaved caspase-3), calcium and lipid binding (Annexin V), enzymes involved in ECM degradation (MMP-1, FAP-α) and collagen crosslinking (lysyl oxidase, osteopontin). Stem cells of the apical papilla (SCAPs) were isolated using the tissue explant method. Functional capacity of SCAPs to contract collagen was determined in 3-D floating collagen gels and second harmonic generation microscopy (SHG) was implemented to evaluate collagen type I organization.
Results: Macroscopical analysis revealed a reduction in apical papilla size during root elongation. Cellularity remained stable but decreased significantly when reaching full elongation. Regional phenotypical analysis identified vimentin+/CD44+ SCAPs in the outer medulla and vimentin-/CD44- as largest population in the inner medulla. High apoptotic activity as indicated by cleaved caspase-3 was shown in SCAPs and coincided with nuclear translocation of Annexin V. Cytosolic Annexin V expression was noted in the vimentin-/CD44- cell population suggesting differential calcium influx. SCAPs showed strong expression of lysyl oxidase and osteopontin in situ and in vitro but was absent in cells of the inner medulla. Moreover, SCAPs demonstrated a high contraction and crosslinking capacity after re-introduction in floating collagen gels. SHG imaging confirmed collagen crosslinking in the vicinity of SCAPs. Alternatively, SCAPs degraded ECM as indicated by the marked FAP-α and MMP-1 staining.
Conclusions: Our results revealed that SCAPs have the capacity to remodel the ECM during root elongation suggesting a novel role in dental root maturation.
Methods: Apical papillae were dissected from 13 human third molars (13-26 years), embedded in paraffin and stained for haematoxylin-eosin to investigate cellularity. Immunocytochemistry was performed to identify cellular phenotypes (vimentin, CD44), apoptosis (cleaved caspase-3), calcium and lipid binding (Annexin V), enzymes involved in ECM degradation (MMP-1, FAP-α) and collagen crosslinking (lysyl oxidase, osteopontin). Stem cells of the apical papilla (SCAPs) were isolated using the tissue explant method. Functional capacity of SCAPs to contract collagen was determined in 3-D floating collagen gels and second harmonic generation microscopy (SHG) was implemented to evaluate collagen type I organization.
Results: Macroscopical analysis revealed a reduction in apical papilla size during root elongation. Cellularity remained stable but decreased significantly when reaching full elongation. Regional phenotypical analysis identified vimentin+/CD44+ SCAPs in the outer medulla and vimentin-/CD44- as largest population in the inner medulla. High apoptotic activity as indicated by cleaved caspase-3 was shown in SCAPs and coincided with nuclear translocation of Annexin V. Cytosolic Annexin V expression was noted in the vimentin-/CD44- cell population suggesting differential calcium influx. SCAPs showed strong expression of lysyl oxidase and osteopontin in situ and in vitro but was absent in cells of the inner medulla. Moreover, SCAPs demonstrated a high contraction and crosslinking capacity after re-introduction in floating collagen gels. SHG imaging confirmed collagen crosslinking in the vicinity of SCAPs. Alternatively, SCAPs degraded ECM as indicated by the marked FAP-α and MMP-1 staining.
Conclusions: Our results revealed that SCAPs have the capacity to remodel the ECM during root elongation suggesting a novel role in dental root maturation.