Osteogenesis imperfecta caused by TMEM38B mutation: a deep investigation of cellular and extracellular consequences to identify new therapeutic targets

Project Summary
There is no cure for osteogenesis imperfecta (OI or brittle bone disease), a group of heritable genetic disorders
affecting 1:15,000 births. The most evident clinical hallmarks of OI are bone fragility and skeletal deformities.
Mutations in trimeric intracellular cation channel B (TRIC-B), an endoplasmic reticulum potassium (K+) channel
encoded by transmembrane protein 38 B (TMEM38B) gene and modulating Calcium (Ca2+) flux, cause the rare
recessive form of the disease, namely OI type XIV. How a potassium channel is responsible for a heritable bone
disease is puzzling the field. Calcium is indispensable for several cell activities including signal transduction
pathways that regulate osteoblast differentiation and function.
We here plan to identify the intra and extra-cellular mechanisms responsible for the skeletal defects and fragility
caused by loss-of-function mutations in TRIC-B, with the goal to unveil a druggable target for OI therapy. We
recently proved that the Calcium flux impairment due to osteoblast TRIC-B loss-of-function compromises the
TGF-β/SMAD signaling. Based on preliminary data, we hypothesize that TMEM38B mutation generates an
impairment of β-catenin/WNT pathway and of cell adhesion, which results in an increased bone fragility by
compromising bone matrix structure and composition, thus reducing strength and toughness. Specific aims are
to: 1) dissect TRIC-B role in osteoblast intracellular signaling affecting activity and adhesion; 2) determine the
mechanism by which osteoblast specific absence of TRIC-B develops bone fragility.
To address TRIC-B bone function, we generated an osteoblast specific TRIC-B knock-out mouse that
reproduces patients’ skeletal outcome. The consequence of loss of TRIC-B on osteoblast WNT pathways and
cell adhesion will be investigated by advanced molecular, biochemical and high-resolution imaging techniques
(AIM 1). Bone strength and fracture toughness combined with second harmonic generation microscopy and
spectroscopic analysis of the bone tissue collagen fiber structure and composition, respectively, will inform on
the mechanism through which depletion of Tmem38b generates bone fragility (AIM 2). This work will shed light
on TRIC-B role in osteoblasts and extracellular matrix to identify a druggable target for OI.

Grant Number: 1R03AR084261-01A1
NIH Institute/Center: NIH
Principal Investigator: Alessandra Carriero