Immunolocalization of cathepsin D in dental tissues

Lysosomal protease expression in mature enamel

The enamel matrix proteins (amelogenin, enamelin and ameloblastin) are degraded by matrix metalloproteinase-20 and kallikrein-4 during enamel development and mature enamel is virtually protein free. The precise mechanism of removal and degradation of the enamel protein cleavage products from the matrix, however, remains poorly understood. It has been proposed that receptor-mediated endocytosis allows for the cleaved proteins to be removed from the matrix during enamel formation and then transported to the lysosome for further degradation. This study aims to identify lysosomal proteases that are present in maturation-stage enamel organ. RNA from first molars of 11-day-old mice was collected and expression was initially assessed by RT-PCR and then quantified by qPCR. The pattern of expression of selected proteases was assessed by immunohistochemical staining of demineralized mouse incisors. With the exception of cathepsin G, all lysosomal proteases assessed were expressed in maturation-stage enamel organ. Identified proteases included cathepsins B, D, F, H, K, L, O, S and Z. Tripeptidyl peptidases I and II as well as dipeptidyl peptidases I, II, III and IV were also found to be expressed. Immunohistochemical staining confirmed that the maturation-stage ameloblasts express cathepsins L and S and tripeptidyl peptidase II. Our results suggest that the ameloblasts are enriched by a large number of lysosomal proteases at maturation that are likely involved in the degradation of the organic matrix.

Dipeptidyl-peptidase II and cathepsin B activities in amelogenesis of the rat incisor

A body of published evidence suggests that a significant portion of enamel matrix protein synthesized by ameloblasts localises in the lysosomal-endosomal organelles of these enamel organ cells. Little is known regarding the lysosomal proteolytic activities during amelogenesis. The aims of this study were to detect and measure the activities of lysosomal peptidases cathepsin B (E.C. 3.4.22.1) and dipeptidyl-peptidase II (E.C. 3.4.14.2) in the enamel organ of the rat incisor and to ascertain whether rat enamel matrix proteins are degraded by these peptidases in vitro. Whole enamel organs were dissected from rat mandibular incisors. Enamel protein was also collected from the rat teeth. Analysis indicated that the rat incisor enamel organs contained specific activities of both dipeptidyl-peptidase II and cathepsin B at levels comparable with those of kidney which is rich in both these lysosomal peptidases. Gel electrophoresis and immunoblotting demonstrated that both cathepsin B and dipeptidyl-peptidase II were able to substantially degrade the rat enamel proteins in vitro. Based on these observations, we propose that lysosomal proteases have roles in amelogenesis in the intracellular degradation of amelogenins.

Molecular pathogenesis of root dentin caries

Human dentin has a higher content of organic matrix and more non-ideal hydroxyapatite than human enamel. Ultrastructural studies indicate that root caries involves both mineral dissolution and breakdown of the organic matrix. Factors involved in the root caries process seem more complicated than those in enamel caries. Moreover, the distinct roles of acids and enzymes and the sequence of events in the root caries process are not well-understood. Although Streptococcus mutans and Actinomyces viscosus are considered to be major pathogenic micro-organisms of root caries, their roles in degradation of the organic matrix components of root dentin need clarification. The purpose of this paper is to review the basic composition of root dentin and the roles of acids and both endogenous and bacterial enzymes in the root caries process.

Anti-cathepsin D chicken IgY antibodies: characterisation, cross-species reactivity and application in immunogold labelling of human splenic neutrophils and fibroblasts

Hyperexpression, alteration of trafficking and secretion of cathepsin D has been linked with tumour invasion and inflammation. To study these phenomena in a variety of cells large quantities of anti-cathepsin D antibodies and the appropriate immunogen are required. As the human immunogen for studies on human tissue is less easily accessed, antibodies to both human and porcine cathepsin D were raised in chickens, as high levels of antibody may be recovered from egg yolks, and the potential cross-reactivity of the anti-porcine cathepsin D IgY antibody was assessed. This preparation cross-reacted strongly with human cathepsin D, comparing favourably with the reactivity of the chicken antibody to the human immunogen. The necessity for isolating human immunogen can thus be circumvented. The cross-species-reacting chicken IgY was successfully used to localise cathepsin D in immunogold labelling of human tissues. To our knowledge, IgY antibodies have not previously been used by other researchers for this purpose. Application of the cross-reacting antibody to human splenic neutrophils (PMNs) has confirmed the presence of cathepsin D in some granules. Double labelling has shown these to be novel subpopulations of azurophil granules. Cathepsin D may, therefore, be relevant in the invasive and inflammatory activities of PMNs and a target for therapeutic strategies.

Dentinogenesis

The formation of dentin, dentinogenesis, comprises a sophisticated interplay between several factors in the tissue, cellular as well as extracellular. Dentin may be regarded as a calcified connective tissue. In this respect, as well as in its mode of formation, it is closely related to bone. Using dentinogenesis as an experimental model to study biomineralization provides several practical advantages, and the results may be extrapolated to understand similar processes in other tissues, primarily bone. After describing dentin structure and composition, this review discusses items such as the morphology of dentinogenesis; the dentinogenically active odontoblast, transport, and concentrations of mineral ions; the constituents of the dentin organic matrix; and the presumed mechanisms involved in mineral formation.

Cytochemical localization of dipeptidyl peptidase II activity in rat incisor tooth ameloblasts

Dipeptidyl peptidase II (DPP II), E.C. 3.4.14.2, a serine class endopeptidase, is widely used as a lysosomal marker in cytochemical studies. To date most ultrastructural studies of ameloblasts use the presence of acid phosphatase activity to identify cellular organelles to be lysosomal. Using decalcified rat mandibles, with kidney tissue as a positive control, DPP II activity, was assessed with specific substrate Lysyl-alanine-4-methoxy-2-naphthylamide in ameloblasts at an ultrastructural level. Reaction product (RP) indicative of DPP II activity was observed only within lysosome-like organelles. These RP-labelled organelles were only localized in the supra- or para-nuclear regions of the ameloblasts, which corresponds with previous studies using acid phosphatase cytochemistry. However, in contrast with these studies, RP was not detected in the distal region of the ameloblasts, viz., in the Tomes' processes of the secretory ameloblasts or near the ruffled border in the maturation ameloblasts. The transitional ameloblasts were notable for the intensity of staining of their RP-labelled organelles. We propose that DPP II may have a role in programmed cell death which is thought to occur in this transition zone. Biochemical analysis of rat incisor enamel organ homogenates, indicated tissue fixation resulted in an 82% reduction in DPP II activity, although the specific activity of DPP II was not affected.