The realm of vitamin K – more than only coagulation

• Applicant: Dr. Katrin Jeannette Czogalla-Nitsche
• Subject Area: Hematology, Oncology ; Cell Biology
• Term: from 2018 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405008087

Vitamin K is an essential vitamin that was discovered in 1941 due to its procoagulatory properties. The function in blood coagulation has been extensively researched, where vitamin K is reduced by vitamin k epoxide reductases (VKOR) and then used for the carboxylation of vitamin K dependent clotting proteins. However, vitamin K has more roles than in coagulation only due to the facts that there are also many other vitamin K-dependent proteins (VKDPs) with various functions, two VKOR enzymes (VKORC1 and VKORC1L1), and because there are different vitamin K derivates (vitamin K1 and K2) with antioxidant effects. The aim of this grant proposal is to investigate the function of vitamin K beyond blood coagulation. Therefore, our research group aims to study the yet unknown function of VKORC1L1. Our prelimanary data show that VKORC1L1 is involved in lipophagy, a process where lipid droplets are degraded through autophagy. Our knockout models develop NAFLD in mice and super-sized lipid droplets in HepG2 cells when VKORC1L1 is absent. Thus, we would like to further study the function of VKORC1L1 in lipophagy by using several techniques as STED microscopy and lipidomic studies, where WT vs KO tissue and cells will be analyzed. Additionally, we aim to clarify whether the administration of vitamin K can compensate for the NAFLD phenotype in mice. This could be of great benefit in the therapy of fatty liver diseases. Lipophagy plays a role in white adipose tissue also. Since our Vkorc1l1-/- show a decrease in white fat mass we would like to further analyze the function of VKORC1L1 in adipocytes using for example VKORC1L1 knockout adipocyte cell line. Finally, we are the first to show that VKORC1L1 is also a mitochondrial protein and VKORC1L1 KO cells have increased maximum respiration. Further investigations into the function of VKORC1 in mitochondria, such as Seahorse measurements, are planned with this research proposal. Another project is to investigate iPS cells from patients with a mutation in VKORC1 or GGCX. These cells will be differentiated into various cell types such as vascular smooth muscle cells (iVSMCs), osteoblasts, and chondrocytes. We have already shown that a knockout of VKORC1 in iPS cells prevents differentiation into iVSMCs. Therefore, we want to investigate whether this is due to a lack of vitamin K reduction or under-carboxylation of a specific VKDP. Furthermore, the iPS cells will be differentiated into osteoblasts and chondrocytes, as patients exhibit facial hypoplasia and reduced growth, among other symptoms. This will provide insight into which VKDPs are not carboxylated and whether vitamin K supplementation can potentially correct the phenotype.

• DFG Programme: Independent Junior Research Groups