Poster N9 - Determination of Altered Mineralization within TBCK-deficient Enamel to Predict Neurodegenerative Phenotype Severity

Introduction: Neurodevelopmental disorders (NDDs) encompass conditions disrupting the nervous system and cerebral development, often causing significant cognitive, social, and behavioural challenges. Despite genetic research advancements, early NDD diagnosis and trajectory prediction remain difficult, impeding timely intervention and personalized treatments. Our previous studies have focused on a rare neurogenetic disorder called TBC1 Domain-Containing Kinase (TBCK) Syndrome, characterized by severe neurodegeneration and craniofacial abnormalities, notably affecting dental structure.
Tooth enamel and neuronal development share intricate systems during fetal growth, reliant on significant membrane turnover for differentiation, migration, and signalling. The mTOR signalling pathway, particularly PI3-AKT, regulates lysosome acidification, with TBCK pivotal in mTOR signalling and lysosomal transport. Therefore, it is significant to establish TBCK syndrome as a proof-of-concept model that aims to explore whether the interruption of the PI3K-AKT signalling pathway affects both teeth and neurons lacking functional TBCK.

Materials and

Methods: The mineralization patterns of tooth enamel will be assessed using mandible samples from TBCK +/+ (wild-type), TBCK +/- (heterozygous), and TBCK -/- (knockout) mice. Nanoindentation testing will evaluate mechanical properties such as elastic modulus and hardness in specific mandible regions. Focused-ion beam scanning electron microscopy (FIB/SEM) coupled with energy-dispersive spectroscopy (EDS) will map elemental distribution within developing and mature enamel. Additionally, Raman spectroscopy will analyze molecular bonding to reveal alterations in enamel composition due to TBCK deficiency.
To elucidate TBCK's role in mTOR signalling via the PI3K-AKT pathway in neural and enamel development, TBCK-/- mice and in vitro models lacking TBCK in neurons and ameloblasts will undergo treatment with PI3K and AKT inhibitors to target crucial functions of TBCK within the PI3K-AKT pathway. By utilizing a multi-omics approach, we will conduct single-nuclei RNA sequencing and quantitative mass spectrometry analyses on brain and tooth tissues obtained from TBCK mice. This methodology aims to unveil common pathways and potential interactions between PI3K-AKT signalling and other pathways involved in neurogenesis and amelogenesis.

Results, Conclusions, and Discussions: Initial findings from ultrasonic vocalizations (USV) suggest that TBCK-/- pups display distinctive vocalization patterns, indicating neurological disruptions that can be quantitatively monitored alongside dental development. Preliminary investigations into TBCK-/- teeth reveal both delayed and hypomineralized enamel using micro-computed tomography (µCT). The mechanical properties, including modulus and hardness, are lower in the enamel and dentin in TBCK-/- mandibles compared with TBCK+/-.
By establishing tooth enamel as an accessible and non-invasive diagnostic tool that can be routinely evaluated, we can revolutionize the way we approach diagnosis, monitoring, and early intervention for a wide spectrum of neurodevelopmental disorders. Moreover, this research bridges the traditionally separate domains of medicine and dentistry, forging essential bonds between these professions to enhance patient care and pediatric oral health outcomes.
Through the validation of tooth enamel as an accessible and non-invasive diagnostic tool, routinely assessable, there exists an opportunity to revolutionize the diagnostic, monitoring, and early intervention strategies for a broad spectrum of neurological dysfunction.

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