Involvement of the Klotho Protein in Dentin Formation and Mineralization

Abstract

Klotho-deficient mice exhibit multiple pathological conditions resembling human aging. Our previous study showed alterations in the distribution of osteocytes and in the bone matrix synthesis in klotho-deficient mice. Although the bone and tooth share morphological features such as mineralization processes and components of the extracellular matrix, little information is available on how klotho deletion influences tooth formation. The present study aimed to elucidate the altered histology of incisors of klothodeficient mice-comparing the findings with those from their wild-type littermates, by using immunohistochemistry for alkaline phosphatase (ALP), osteopontin, and dentin matrix protein-1 (DMP-1), terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) detection for apoptosis, and electron probe microanalyzer (EPMA) analysis on calcium (Ca), phosphate (P), and magnesium (Mg). Klotho-deficient incisors exhibited disturbed layers of odontoblasts, predentin, and dentin, resulting in an obscure dentin-predentinal border at the labial region. Several odontoblast-like cells without ALP activity were embedded in the labial dentin matrix, and immunopositivity for DMP-1 and osteopontin was discernible in the matrix surrounding these embedded odontoblast-like cells. TUNEL detection demonstrated an apoptotic reaction in the embedded odontoblast-like cells and pulpal cells in the klotho-deficient mice. EPMA revealed lower concentrations of Ca, P, and Mg in the klotho-deficient dentin, except for the dentin around abnormal odontoblast-like cells. These findings suggest the involvement of the klotho gene in dentinogenesis and its mineralization.

Dentin matrix protein 1 and phosphate homeostasis are critical for postnatal pulp, dentin and enamel formation

“…14,15 Similarly, a dystrophic pulp calcification, root dilaceration, and a thistle shaped pulp have been reported in the tumoral calcinosis patients who are deficient in FGF23 and have increased phosphate levels. 31,32 This ectopic ossification is linked to an increase in apoptosis of the odontoblasts.…”

“…11,13 Both Fgf23- null and Klotho -deficient mice are reported to have mild dentin malformation and increased apoptosis in odontoblasts, which is due to a high phosphate level. 14,15 …”

Role of the Klotho Gene in Bone and Mineral Metabolism

“…On the other hand, osteoblasts show an impairment in the expression of alkaline phosphatase and the ability to form mineralized nodules [13,14]. Histological studies have also revealed some abnormalities in osteoid and dentin mineralization [15,16]. The impaired osteoclastogenesis appears to be associated with an up-regulation of osteoprotegerin synthesis, an inhibitor of osteoclast precursor differentiation, and indeed it is partially rescued by deleting the osteoprotegerin gene [17].…”

Clinical, Cellular and Molecular Phenotypes of Aging Bone

“…Klotho functions as an aging-suppressor and has been reported to be a regulator of oxidative stress and senescence [86]; in fact, loss of klotho leads to enhanced apoptosis in odontoblasts and disturbed mineralization in teeth [87]. In contrast to what had been described originally [81], it has been shown more recently by micro-CT that, in 3-month-old klotho-/-mice, trabecular bone mass at the tibia actually increases over wild type littermates [88].…”