👤 Petra Simic

Dysregulated actions of the bone-derived phosphaturic hormone, fibroblast growth factor-23 (FGF23), underlie the pathophysiology of several diseases. FGF23 is synthesized primarily in osteocytes in response to various endogenous molecules; however, the mechanisms governing FGF23 production are incompletely understood. Glycerol-3-phosphate (G3P), a glycolytic by-product originating from the kidney, critically controls skeletal FGF23 synthesis via its conversion in bone to lysophosphatidic acid (LPA), which stimulates osteocyte FGF23 production. The bioactive vitamin D, 1,25-dihydroxyvitamin D (1,25D), also promotes FGF23 production in osteocytes. We herein demonstrated that LPA requires 1,25D action to raise FGF23 levels in mouse bone explants and mice. RNA sequencing of osteocyte-like Ocy454 cells identified differentially expressed genes (DEGs) uniquely induced by LPA/1,25D co-treatment. These unique DEGs were enriched for the ribosome biogenesis pathway. DEGs concurrently induced by individual LPA and 1,25D treatments were enriched for MAPK signaling, and inhibiting this pathway obliterated LPA/1,25D-induced FGF23 production. DEGs following LPA/1,25D co-treatment were enriched for the cytokine-cytokine receptor interaction pathway. Moreover, LPA/1,25D co-treatment, but not individual LPA and 1,25D treatments, rapidly induced the expression of Il12a, the gene encoding the pro-inflammatory cytokine interleukin-12 alpha-subunit, which responded solely to 1,25D at later times and required MAPK-ERK1/2 signaling. Inhibiting cytokine signaling or knocking down Il12a inhibited, while overexpressing Il12a enhanced LPA/1,25D-induced FGF23 production. However, challenging Ocy454 cells with recombinant bioactive interleukin-12 failed to enhance FGF23 production, suggesting that Il12a plays a noncanonical role. Our results reveal a mechanism of skeletal FGF23 synthesis involving synergistic actions of LPA and 1,25D, advancing our understanding of FGF23 regulation. Show less

High-density lipoprotein cholesterol (HDL-C) is inversely related to cardiovascular risk. HDL-C raising ester transfer protein (CETP) inhibitors, are novel therapeutics. We studied the effects of CETP inhibitors anacetrapib and evacetrapib on triglycerides, cholesterol and lipoproteins, cholesterol efflux, paraoxonase activity (PON-1), reactive oxygen species (ROS), and endothelial function in E3L and E3L.CETP mice. Triglycerides and cholesterol were measured at weeks 5, 14 and 21 in E3L.CETP mice on high cholesterol diet and treated with anacetrapib (3 mg/kg/day), evacetrapib (3 mg/kg/day) or placebo. Cholesterol efflux was assessed ex-vivo in mice treated with CETP inhibitors for 3 weeks on a normal chow diet. Endothelial function was analyzed at week 21 in isolated aortic rings, and serum lipoproteins assessed by fast-performance liquid chromatography. Anacetrapib and evacetrapib increased HDL-C levels (5- and 3.4-fold, resp.) and reduced triglycerides (-39% vs. placebo, p = 0.0174). Total cholesterol levels were reduced only in anacetrapib-treated mice (-32%, p = 0.0386). Cholesterol efflux and PON-1 activity (+45% and +35% vs. control, p < 0.005, resp.) were increased, while aortic ROS production was reduced with evacetrapib (-49% vs. control, p = 0.020). Anacetrapib, but not evacetrapib, impaired endothelium dependent vasorelaxation (p < 0.05). In contrast, no such effects were observed in E3L mice for all parameters tested. Notwithstanding a marked rise in HDL-C, evacetrapib did not improve endothelial function, while anacetrapib impaired it, suggesting that CETP inhibition does not provide vascular protection. Anacetrapib exerts unfavorable endothelial effects beyond CETP inhibition, which may explain the neutral results of large clinical trials in spite of increased HDL-C. Show less