NEFL is associated with inhibition of odontoblastic process in odontohypophosphatasia

Hypophosphatasia (HPP) is a rare bone disease caused by pathological variants of ALPL. While hypomineralization of dentin and odontoblast (OD) differentiation defects are known to occur in HPP, the underlying pathophysiology remains poorly understood.

We generated induced pluripotent stem cell (iPSC) lines from patients with perinatal severe HPP (Perinatal) and then isogenic (Rescued) and odontohypophosphatasia type (Odonto) lines using gene editing. These three HPP-iPSC lines were differentiated into OD-like cells via mesenchymal stem cells derived from neural crest cells. The characteristics of the OD-like cells were assessed.

Rescued-OD-like cells demonstrated mineralization ability, increased microtubule-associated protein tau (MAPT) expression, and unidirectional cell processes, while these characteristics were impaired in Perinatal- and Odonto-OD-like cells. These findings suggest that these features are associated with reduced ALP activity. Notably, neurofilament light chain (NEFL) expression was enhanced in Odonto-OD-like cells compared to Perinatal- and Rescued-OD-like cells. NEFL knockdown partially rescued cell process elongation in Odonto-OD-like cells without affecting alkaline phosphatase activity, while NEFL overexpression inhibited cell process elongation in Rescued-OD-like cells.

Enhanced expression of NEFL in Odonto-OD-like cells negatively correlates with OD morphology and may be relevant to odontoblast morphological abnormalities associated with odontohypophosphatasia; however, generalization to other odonto-HPP genotypes requires additional patient-derived lines.