Matrix Vesicle Mediated Mineralization - A Review

Abstract

Teeth are composed of the mineralized tissues dentine and cementum, and a mineralized structure, the
dental enamel. The pulp may also mineralize in response to aging processes and/or pathologic aggressions.
The process of mineralization is specific for each dental tissue. Matrix vesicles have been implicated in
the mineralisation of calcified cartilage, bone and dentin. It is an orchestrated sequence of ultrastructural
and biochemical events that lead to crystal nucleation and growth. Matrix vesicles appear to mineralize by
concentrating calcium and phosphate at a protected site close to the inner leaflet of the vesicle membrane.
Calcium may be attracted by its affinity for acidic phospholipids of the vesicle membrane, and phosphate
may be concentrated by the action of transmembrane phosphatases of the matrix vesicle membrane.
Evidence is accumulating to suggest that alkaline phosphatase of the matrix vesicle membrane functions
as a phosphotransferase or phosphate vector, transporting PO4 across the vesicle membrane. The influx of
phosphate ions into the matrix vesicle is mediated by several proteins such as TNAP, ENPP1, Pit1, annexin
and so forth. The catalytic activity of ENPP1 generates pyrophosphate (PPi) using extracellular ATPs as a
substrate, and the resultant PPi prevents crystal overgrowth. However, TNAP hydrolyzes PPi into phosphate
ion monomers, which are then transported into the matrix vesicle through Pit1. Accumulation of Ca2+ and
PO4
3- inside matrix vesicles then induces crystalline nucleation, with calcium phosphate crystals budding off
radially, puncturing the matrix vesicle’s membrane and finally growing out of it to form mineralized nodules.
Their exact role, if any, in the nucleation of hydroxyapatite mineral, and its association with collagen fibres
The organic Matrix has been debated and is controversial. Several hypotheses have been recently introduced
to explain in greater detail how Matrix vesicles function in biomineralization. This review will summarise
recent advances, and ultra-structural and biochemical aspects on Matrix vesicles - mediated mineralization.