Role of the vitamin D receptor in FGF23 action on phosphate metabolism

FGF23 (fibroblast growth factor 23) is a novel phosphaturic factor that influences vitamin D metabolism and renal re-absorption of P(i). The goal of the present study was to characterize the role of the VDR (vitamin D receptor) in FGF23 action using VDR(−/−) (VDR null) mice. Injection of FGF23M (naked DNA encoding the R179Q mutant of human FGF23) into VDR(−/−) and wildtype VDR(+/+) mice resulted in an elevation in serum FGF23 levels, but had no effect on serum calcium or parathyroid hormone levels. In contrast, injection of FGF23M resulted in significant decreases in serum P(i) levels, renal Na/P(i) co-transport activity and type II transporter protein levels in both groups when compared with controls injected with mock vector or with FGFWT (naked DNA encoding wild-type human FGF23). Injection of FGF23M resulted in a decrease in 25-hydroxyvitamin D 1α-hydroxylase mRNA levels in VDR(−/−) and VDR(+/+) mice, while 25-hydroxyvitamin D 24-hydroxylase mRNA levels were significantly increased in FGF23M-treated animals compared with mock vector control- or FGF23WT-treated animals. The degree of 24-hydroxylase induction by FGF23M was dependent on the VDR, since FGF23M significantly reduced the levels of serum 1,25(OH)(2)D(3) [1,25-hydroxyvitamin D(3)] in VDR(+/+) mice, but not in VDR(−/−) mice. We conclude that FGF23 reduces renal P(i) transport and 25-hydroxyvitamin D 1α-hydroxylase levels by a mechanism that is independent of the VDR. In contrast, the induction of 25-hydroxyvitamin D 24-hydroxylase and the reduction of serum 1,25(OH)(2)D(3) levels induced by FGF23 are dependent on the VDR

Hokuriku-plus familial hypercholesterolaemia registry study: rationale and study design

Introduction Familial hypercholesterolaemia (FH) is an autosomal-dominant inherited genetic disease. It carries an extremely high cardiovascular risk associated with significantly elevated low-density lipoprotein (LDL) cholesterol. The diagnostic rate of this disease in some European nations is quite high, due to the presence of multiple prospective registries. On the other hand, few data—and in particular multicentre data—exist regarding this issue among Japanese subjects. Therefore, this study intends to assemble a multicentre registry that aims to comprehensively assess cardiovascular risk among Japanese FH patients while taking into account their genetic backgrounds.Methods and analysis The Hokuriku-plus FH registry is a prospective, observational, multicentre cohort study, enrolling consecutive FH patients who fulfil the clinical criteria of FH in Japan from 37 participating hospitals mostly in Hokuriku region of Japan from April 2020 to March 2024. A total of 1000 patients will be enrolled into the study, and we plan to follow-up participants over 5 years. We will collect clinical parameters, including lipids, physical findings, genetic backgrounds and clinical events covering atherosclerotic and other important events, such as malignancies. The primary endpoint of this study is new atherosclerotic cardiovascular disease (ASCVD) events. The secondary endpoints are as follows: LDL cholesterol, secondary ASCVD events and the occurrence of other diseases including hypertension, diabetes and malignancies.Ethics and dissemination This study is being conducted in compliance with the Declaration of Helsinki, the Ethical Guidelines for Medical and Health Research Involving Human Subjects, and all other applicable laws and guidelines in Japan. This study protocol has been approved by the Institutional Review Board at Kanazawa University. We will disseminate the final results at international conferences and in a peer-reviewed journal.Trial registration number UMIN000038210

The DHR1 Domain of DOCK180 Binds to SNX5 and Regulates Cation-independent Mannose 6-phosphate Receptor Transport

DOCK180 is the archetype of the DOCK180-family guanine nucleotide exchange factor for small GTPases Rac1 and Cdc42. DOCK180-family proteins share two conserved domains, called DOCK homology region (DHR)-1 and -2. Although the function of DHR2 is to activate Rac1, DHR1 is required for binding to phosphoinositides. To better understand the function of DHR1, we searched for its binding partners by direct nanoflow liquid chromatography/tandem mass spectrometry, and we identified sorting nexins (SNX) 1, 2, 5, and 6, which make up a multimeric protein complex mediating endosome-to-trans-Golgi-network (TGN) retrograde transport of the cation-independent mannose 6-phosphate receptor (CI-MPR). Among these SNX proteins, SNX5 was coimmunoprecipitated with DOCK180 most efficiently. In agreement with this observation, DOCK180 colocalized with SNX5 at endosomes. The RNA interference-mediated knockdowns of SNX5 and DOCK180, but not Rac1, resulted in the redistribution of CI-MPR from TGN to endosomes. Furthermore, expression of the DOCK180 DHR1 domain was sufficient to restore the perturbed CI-MPR distribution in DOCK180 knockdown cells. These data suggest that DOCK180 regulates CI-MPR trafficking via SNX5 and that this function is independent of its guanine nucleotide exchange factor activity toward Rac1