Vps4b heterozygous mice do not develop tooth defects that replicate human dentin dysplasia I

Abstract

BackgroundVacuolar protein sorting-associated protein 4B (VPS4B) is a member of the ATP enzyme AAA protein family, and is mainly involved in protein degradation and cell membrane fusion. Recently, a dominant mutation in this gene was identified in human dentin dysplasia type I (DD-I). Herein, we report the generation of Vps4b knockout (Vps4b KO) mice; however, the homozygous Vps4b KO mutation was embryonic lethal at the early stages of embryo development, and we therefore report the results of heterozygous mutant mice.ResultsMice heterozygous for Vps4b did not develop tooth defects replicating human DD-I. Immunohistochemistry showed that gene KO was successful, as there was decreased expression of Vps4b in heterozygous mice; hematoxylin and eosin (H&E) staining also showed that the width of the pre-dentin zone was increased in heterozygous mice, although the arrangement of the odontoblasts was not significantly different from wild-type (WT) mice. However, H&E staining showed no obvious abnormalities in the bones of heterozygous mice. Moreover, stereomicroscopic and X-ray radiography results indicated no abnormal manifestations in teeth or bones. Furthermore, statistical analysis of the volume and density of dentin and enamel, as well as skeletal analysis, including the volume and separation of trabecular bone analyzed by micro-CT, all showed no differences between Vps4b heterozygotes and WT mice. In addition, there also were no significant differences in bone or cartilage mineralization as evaluated by Alcian blue–Alizarin red staining.ConclusionsThe heterozygous Vps4b KO mice do not develop tooth defects that replicate human DD-I and this is likely to be due to differences in tooth development between the two species. Consequently, further studies are needed to determine whether mice are an appropriate animal model for human tooth diseases.

Adding Some “Splice” to Stress Eating: Autophagy, ESCRT and Alternative Splicing Orchestrate the Cellular Stress Response

“…Alternative splicing also plays a role in the induction and maintenance of autophagy directly by altering splicing of autophagy-associated genes like Beclin1 [65] (Table 1) or indirectly via the splicing of genes such as Heh1 that modulate subcellular recruitment of the yeast homolog of CHMP7, Chmp7 [83] (Figure 2). Furthermore, alternative and/or mis-splicing of ESCRT genes that affect autophagy play roles in the pathogenesis of several diseases, including TSG101 in cancer and CHMP2B and VPS4B mis-splicing in the pathogenesis of FLTD and dental dysplasia I (respectively) [101,141] (Figure 4). These findings also have implications for therapy.…”

“…These results together indicate that VPS4B mis-splicing results in a loss-of-function scenario. However, when a heterozygous Vps4b KO was made in mice that that better modelled the heterogeneous genetic nature of DDI, there was no phenotype in tooth or bone development observed [141]. These results suggest that although the role of Vps4 in tooth development is conserved between fish and humans, its function in mouse tooth development is less prominent or lost.…”

Vacuolar protein sorting 4B regulates the proliferation and odontoblastic differentiation of human dental pulp stem cells through the Wnt-β-catenin signalling pathway

“…An experimental knockdown of Vsp4b expression in zebrafish reduced the number of teeth and also shortened the length of the teeth, thereby mimicking the DD-I phenotype. Moreover, a Vps4b knockout mouse model has proven that complete loss of VPS4B in mice results in placental death during the early stages of embryonic development, whereas Vsp4b þ/-(heterozygous) mice feature a widened predentin zone [11]. Because these studies have highlighted defects in dentin and pulp canal obliteration in both DD-I patients and animal models, we hypothesized that VPS4B deficiency is associated with imperfect dentinogenesis and might play a differential role in the disruption of the development of this mineralized tissue.…”