Autosomal-Recessive Mutations in MESD Cause Osteogenesis Imperfecta

Area of Science:

• Genetics
• Molecular Biology
• Developmental Biology

Background:

• Osteogenesis imperfecta (OI) is a group of genetic disorders characterized by brittle bones.
• The Wingless-related integration site (WNT) signaling pathway is crucial for skeletal development.
• MESD is an endoplasmic reticulum chaperone for WNT receptors LRP5 and LRP6.

Purpose of the Study:

• To investigate the genetic basis of a deforming type of Osteogenesis Imperfecta.
• To understand the functional consequences of MESD mutations on WNT signaling.
• To explore potential therapeutic strategies for MESD-associated OI.

Main Methods:

• Genetic analysis of five families with OI to identify mutations.
• Expression studies of wild-type and mutant MESD in HEK293T cells.
• Assessment of LRP5 and LRP6 trafficking and WNT signaling.

Main Results:

• Four novel homozygous mutations in MESD were identified in affected individuals.
• Mutant MESD showed impaired ER retention, leading to reduced LRP5/LRP6 trafficking.
• Despite reduced WNT signaling, key developmental processes remained intact, suggesting tissue-specific sensitivity.

Conclusions:

• MESD mutations cause a hypomorphic allele, resulting in Osteogenesis Imperfecta through impaired WNT signaling.
• Bone and dental development are particularly sensitive to reduced WNT signaling.
• Targeting LRP5/LRP6-mediated WNT signaling may offer therapeutic benefits for MESD-associated OI.