The early formation of irregular secondary dentine in progeria

Expression of the Hutchinson-Gilford Progeria Mutation Leads to Aberrant Dentin Formation

Hutchinson-Gilford progeria syndrome (HGPS) is a rare accelerated senescence disease, manifesting dental abnormalities and several symptoms suggestive of premature aging. Although irregular secondary dentin formation in HGPS patients has been reported, pathological mechanisms underlying aberrant dentin formation remain undefined. In this study, we analyzed the mandibular molars of a tissue-specific mouse model that overexpresses the most common HGPS mutation (LMNA, c.1824C > T, p.G608G) in odontoblasts. In the molars of HGPS mutant mice at postnatal week 13, targeted expression of the HGPS mutation in odontoblasts results in excessive dentin formation and pulp obliteration. Circumpulpal dentin of HGPS mutants was clearly distinguished from secondary dentin of wild-type (WT) littermates and its mantle dentin by considering the irregular porous structure and loss of dentinal tubules. However, the dentin was significantly thinner in the molars of HGPS mutants at postnatal weeks 3 and 5 than in those of WT mice. In vitro analyses using MDPC-23, a mouse odontoblastic cell line, showed cellular senescence, defects of signaling pathways and consequential downregulation of matrix protein expression in progerin-expressing odontoblasts. These results indicate that expression of the HGPS mutation in odontoblasts disturbs physiological secondary dentin formation. In addition, progerin-expressing odontoblasts secrete paracrine factors that can stimulate odontogenic differentiation of dental pulp cells. Taken together, our results suggest that the aberrant circumpulpal dentin of HGPS mutants results from defects in physiological secondary dentin formation and consequential pathologic response stimulated by paracrine factors from neighboring progerin-expressing odontoblasts.

Expression of the Hutchinson-Gilford progeria mutation during osteoblast development results in loss of osteocytes, irregular mineralization, and poor biomechanical properties

Hutchinson-Gilford progeria syndrome (HGPS) is a very rare genetic disorder that is characterized by multiple features of premature aging and largely affects tissues of mesenchymal origin. In this study, we describe the development of a tissue-specific mouse model that overexpresses the most common HGPS mutation (LMNA, c.1824C>T, p.G608G) in osteoblasts. Already at the age of 5 weeks, HGPS mutant mice show growth retardation, imbalanced gait and spontaneous fractures. Histopathological examination revealed an irregular bone structure, characterized by widespread loss of osteocytes, defects in mineralization, and a hypocellular red bone marrow. Computerized tomography analysis demonstrated impaired skeletal geometry and altered bone structure. The skeletal defects, which resemble the clinical features reported for bone disease in HGPS patients, was associated with an abnormal osteoblast differentiation. The osteoblast-specific expression of the HGPS mutation increased DNA damage and affected Wnt signaling. In the teeth, irregular dentin formation, as was previously demonstrated in human progeria cases, caused severe dental abnormalities affecting the incisors. The observed phenotype also shows similarities to reported bone abnormalities in aging mice and may therefore help to uncover general principles of the aging process.

The effect of aging on tooth morphology: a study on impacted teeth

The effect of age on dental tissues was studied on histologic sections of totally impacted teeth obtained from patients between 11 and 76 years of age. Impacted teeth were used in order to obviate the influence of the environmental effects prevalent in the oral cavity. The presence of concentric denticles and diffuse calcifications was determined, and the width of secondary dentin, predentin, and cementum was measured. The width of predentin and cementum increased linearly with age, whereas the aging process of secondary dentin formation and diffuse calcifications followed a different pattern. The incidence of concentric denticles was identical for all age groups.