Pathobiochemical impact of human xylosyltransferase-I in bone homeostasis

• Applicant: Dr. Isabel Faust
• Subject Area: Toxicology, Laboratory Medicine ; Cell Biology
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 316628156

Proteoglycans (PG) are component parts of the extracellular matrix (ECM) of bone and regulate proliferation as well as differentiation of bone-remodeling cells by modulating the bioavailability of growth factors and cytokines. Furthermore, PG define collagen fibril assembly and consequently exert influence on mechanical integrity of the skeleton. The rate-limiting step of PG-glycosylation is catalyzed by human xylosyltransferase-I and -II (XT-I and -II). As recently published by our group, serum XT activity reflects the PG synthesis rate and thus is a powerful non-invasive biomarker.In the course of our first funding period, we demonstrated that XT-I-deficiency is associated with abnormal ECM remodeling and cellular senescence in primary human dermal fibroblasts. Our resulting hypothesis of a strong pathophysiological relevance of XT-I-deficiency gets reinforced by the descripton of several pathogenic XYLT1 mutations being associated with skeletal dysplasia. So the aim of this study is to unravel the pathobiochemical impact of XT-I in bone homeostasis using primary human mesenchymal stem cells (hMSC) and osteoclasts.In total, our study addresses four issues. To evaluate the influence of XT-I-deficiency on cellular functionality of hMSC, we will perform a CRISPR-(clustered regularly interspaced short palindromic repeats)-Cas9-based XYLT1 knockout. Gene edited hMSC will further be used to study the differentiation potential of these cells as well as the ECM remodeling of osteoblasts and chondrocytes generated from hMSC. In the second project we will examine the influence of XT-I-deficiency on cellular functionality of osteoclasts. In addition, we will analyze whether serum XT-activity qualifies to be a biomarker for osteoporosis and aberrant osteolysis. In the last issue we will look closely at the association of XT-I-deficiency and cellular senescence by studying XT regulation during ageing of hMSC and by characterizing the phenotype of XT-I-deficient hMSC.For the long term our results will not only contribute to a better understanding of molecular mechanisms of bone homeostasis but will also reveal putative therapeutic interventions for XT-associated skeletal diseases.

• DFG Programme: Research Grants