Browsing by Subject "Phosphates"
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Item ACKR3–arrestin2/3 complexes reveal molecular consequences of GRK-dependent barcoding(bioRxiv, 2023-07-19) Chen, Qiuyan; Schafer, Christopher T.; Mukherjee, Somnath; Gustavsson, Martin; Agrawal, Parth; Yao, Xin-Qiu; Kossiakoff, Anthony A.; Handel, Tracy M.; Tesmer, John J. G.; Biochemistry and Molecular Biology, School of MedicineAtypical chemokine receptor 3 (ACKR3, also known as CXCR7) is a scavenger receptor that regulates extracellular levels of the chemokine CXCL12 to maintain responsiveness of its partner, the G protein-coupled receptor (GPCR), CXCR4. ACKR3 is notable because it does not couple to G proteins and instead is completely biased towards arrestins. Our previous studies revealed that GRK2 and GRK5 install distinct distributions of phosphates (or "barcodes") on the ACKR3 carboxy terminal tail, but how these unique barcodes drive different cellular outcomes is not understood. It is also not known if arrestin2 (Arr2) and 3 (Arr3) bind to these barcodes in distinct ways. Here we report cryo-electron microscopy structures of Arr2 and Arr3 in complex with ACKR3 phosphorylated by either GRK2 or GRK5. Unexpectedly, the finger loops of Arr2 and 3 directly insert into the detergent/membrane instead of the transmembrane core of ACKR3, in contrast to previously reported "core" GPCR-arrestin complexes. The distance between the phosphorylation barcode and the receptor transmembrane core regulates the interaction mode of arrestin, alternating between a tighter complex for GRK5 sites and heterogenous primarily "tail only" complexes for GRK2 sites. Arr2 and 3 bind at different angles relative to the core of ACKR3, likely due to differences in membrane/micelle anchoring at their C-edge loops. Our structural investigations were facilitated by Fab7, a novel Fab that binds both Arr2 and 3 in their activated states irrespective of receptor or phosphorylation status, rendering it a potentially useful tool to aid structure determination of any native GPCR-arrestin complex. The structures provide unprecedented insight into how different phosphorylation barcodes and arrestin isoforms can globally affect the configuration of receptor-arrestin complexes. These differences may promote unique downstream intracellular interactions and cellular responses. Our structures also suggest that the 100% bias of ACKR3 for arrestins is driven by the ability of arrestins, but not G proteins, to bind GRK-phosphorylated ACKR3 even when excluded from the receptor cytoplasmic binding pocket.Item Item Bone mineral density reductions after tenofovir disoproxil fumarate initiation and changes in phosphaturia: a secondary analysis of ACTG A5224s(Oxford Academic, 2017-07-01) Gupta, Samir K.; Yeh, Eunice; Kitch, Douglas W.; Brown, Todd T.; Venuto, Charles S.; Morse, Gene D.; Ha, Belinda; Melbourne, Kathleen; McComsey, Grace A.; Medicine, School of MedicineBackground: It is unknown if the greater reductions in bone mineral density (BMD) associated with initiation of tenofovir disoproxil fumarate compared with abacavir in previously untreated HIV-infected participants in the ACTG A5224s clinical trial were associated with potentially worsening tenofovir-related phosphaturia. Methods: We correlated changes in BMD at the hip and spine with changes in phosphaturia [transtubular reabsorption of phosphorus (TRP) and tubular maximum phosphate reabsorption per glomerular filtration rate (TmP/GFR)] from entry through week 96 in those initiating tenofovir ( n = 134) versus abacavir ( n = 135) with efavirenz or atazanavir/ritonavir in A5224s. We also correlated changes in BMD with tenofovir AUC measured between weeks 4 and 24. Results: Changes in TRP and TmP/GFR through week 96 between the tenofovir and abacavir arms were not significantly different (both P ≥ 0.70) and did not differ with use of efavirenz versus atazanavir/ritonavir. There were no significant correlations between changes in either TRP or TmP/GFR and with either hip or spine BMD in the tenofovir arms. Tenofovir AUC was significantly correlated with changes in hip BMD, but not spine BMD, at week 24 ( r = -0.22, P = 0.028) and week 48 ( r = -0.26, P = 0.010), but not at week 96 ( r = -0.14, P = 0.18). Conclusions: Changes in phosphaturia were not different between the tenofovir and abacavir arms in A5224s. Changes in hip and spine BMD with tenofovir were not related to changes in phosphaturia. However, tenofovir exposure was weakly associated with changes in hip BMD through week 48.Item Conventional Therapy in Adults With XLH Improves Dental Manifestations, But Not Enthesopathy.(The Endocrine Society, 2015-10) Econs, Michael J.; Department of Medical and Molecular Genetics, IU School of MedicineItem Coupling fibroblast growth factor 23 production and cleavage: iron deficiency, rickets, and kidney disease(Ovid Technologies (Wolters Kluwer) - Lippincott Williams & Wilkins, 2014-07) Wolf, Myles; White, Kenneth E.; Department of Medical & Molecular Genetics, IU School of MedicinePURPOSE OF REVIEW: High levels of fibroblast growth factor 23 (FGF23) cause the rare disorders of hypophosphatemic rickets and are a risk factor for cardiovascular disease and death in patients with chronic kidney disease (CKD). Despite major advances in understanding FGF23 biology, fundamental aspects of FGF23 regulation in health and in CKD remain mostly unknown. RECENT FINDINGS: Autosomal dominant hypophosphatemic rickets (ADHR) is caused by gain-of-function mutations in FGF23 that prevent its proteolytic cleavage, but affected individuals experience a waxing and waning course of phosphate wasting. This led to the discovery that iron deficiency is an environmental trigger that stimulates FGF23 expression and hypophosphatemia in ADHR. Unlike osteocytes in ADHR, normal osteocytes couple increased FGF23 production with commensurately increased FGF23 cleavage to ensure that normal phosphate homeostasis is maintained in the event of iron deficiency. Simultaneous measurement of FGF23 by intact and C-terminal assays supported these breakthroughs by providing minimally invasive insight into FGF23 production and cleavage in bone. These findings also suggest a novel mechanism of FGF23 elevation in patients with CKD, who are often iron deficient and demonstrate increased FGF23 production and decreased FGF23 cleavage, consistent with an acquired state that mimics the molecular pathophysiology of ADHR. SUMMARY: Iron deficiency stimulates FGF23 production, but normal osteocytes couple increased FGF23 production with increased cleavage to maintain normal circulating levels of biologically active hormone. These findings uncover a second level of FGF23 regulation within osteocytes, failure of which culminates in elevated levels of biologically active FGF23 in ADHR and perhaps CKD.Item Dietary Phosphorus and FGF23: Is More Restriction Better?(American Society of Nephrology, 2019-10-01) Gallant, Kathleen M. Hill; Medicine, School of MedicineItem High carbonate level of apatite in kidney stones underlines infection, but is it predictive?(Springer, 2013) Englert, Kate M.; McAteer, James A.; Lingeman, James E.; Williams, James C., Jr.; Anatomy, Cell Biology and Physiology, School of MedicineThe presence of infectious microorganisms in urinary stones is commonly inferred from stone composition, especially by the presence of struvite in a stone. The presence of highly carbonated apatite has also been proposed as a marker of the presence of bacteria within a stone. We retrospectively studied 368 patients who had undergone percutaneous nephrolithotomy (PCNL), and who also had culture results for both stone and urine. Urine culture showed no association with stone mineral content, but stone culture was more often positive in struvite-containing stones (73 % positive) and majority apatite stones (65 %) than in other stone types (54 %, lower than the others, P < 0.02). In 51 patients in whom the carbonate content of apatite could be measured, carbonate in the apatite was weakly predictive of positive stone culture with an optimal cutoff value of 13.5 % carbonate (sensitivity 0.61, specificity 0.80). In positive cultures of stones (all mineral types combined), organisms that characteristically produce urease were present in 71 % of the cases, with no difference in this proportion among different types of stone. In summary, the type of mineral in the stone was predictive of positive stone culture, but this correlation is imperfect, as over half of non-struvite, non-apatite stones were found to harbor culturable organisms. We conclude that mineral type is an inadequate predictor of whether a stone contains infectious organisms, and that stone culture is more likely to provide information useful to the management of patients undergoing PCNL.Item Meta-analysis: randomized controlled trials of 4-L polyethylene glycol and sodium phosphate solution as bowel preparation for colonoscopy(Wiley Blackwell (Blackwell Publishing), 2010-07) Juluri, R.; Eckert, G.; Imperiale, T. F.; Department of Medicine, IU School of MedicineBACKGROUND: Randomized controlled trials (RCTs) comparing polyethylene glycol (PEG) with sodium phosphate (NaP) are inconsistent. AIM: To compare the efficacy of and tolerance to PEG vs. NaP for bowel preparation. METHODS: We used MEDLINE and EMBASE to identify English-language RCTs published between 1990 and 2008 comparing 4-L PEG with two 45 mL doses of NaP in adults undergoing elective colonoscopy. We calculated the pooled odds ratios (ORs) for preparation quality and proportion of subjects completing the preparation. RESULTS: From 18 trials (n = 2792), subjects receiving NaP were more likely to have an excellent or good quality preparation than those receiving PEG (82% vs. 77%; OR = 1.43; 95% CI, 1.01-2.00). Among a subgroup of 10 trials in which prep quality was reported in greater detail, there were no differences in the proportions of excellent, good, fair or poor preparation quality. Among nine trials that assessed preparation completion rates, patients receiving NaP were more likely to complete the preparation than patients receiving 4-L PEG (3.9% vs. 9.8% respectively did not complete the preparation; OR = 0.40; CI, 0.17-0.88). CONCLUSION: Among 18 head-to-head RCTs of NaP vs. 4-L PEG, NaP was more likely to be completed and to result in an excellent or good quality preparation.Item Molecular Genetic Analysis of FGF23 Bioactivity in the Bone-Kidney Endocrine Axis(2009-06-23T21:29:44Z) Farrow, Emily; White, KennethHeritable disorders of phosphate handling are the most common cause of hypophosphatemic rickets in developed countries. Isolated renal phosphate wasting and subsequent low serum phosphate concentrations may result from a number of genetic disorders that include: autosomal dominant hypophosphatemic rickets (ADHR), X-linked hypophosphatemic rickets (XLH), and autosomal recessive hypophosphatemic rickets (ARHR). Fibroblast growth factor-23 (FGF23), identified as the causative gene in ADHR, is produced in bone and plays a central role in kidney phosphate regulation. Increased serum concentrations of FGF23 lead to renal phosphate wasting through down regulation of renal sodium-phosphate co-transporters. However, the molecular mechanisms of FGF23 bioactivity in hormonal phosphate regulation are largely unknown. An experimental focus of this dissertation was to investigate the molecular mechanisms of FGF23-mediated phosphate regulation in the bone-kidney hormonal axis. To this end, the role of Dentin Matrix Protein 1 (DMP1), newly identified as the gene responsible for ARHR, was further defined by the identification of a novel large deletion as well as testing the molecular consequences of DMP1 mutations. FGF23 requires a signaling complex composed of Klotho and an FGFR for bioactivity, however, the location and composition of the signaling complex is unknown. Klotho localizes to the renal distal convoluted tubule, whereas the sodium phosphate co-transporters are expressed within the renal proximal tubules. The molecular mechanisms of FGF23 signaling were investigated by isolating a novel marker of FGF23 bioactivity using array technology, determining the location of initial FGF23 signaling in the kidney, and by identifying a novel mutation in a receptor upstream of FGF23 production. Taken together, these results increase the knowledge of the molecular mechanisms of phosphate homeostasis in relation to FGF23 bioactivity, leading to the identification of potentially novel therapeutic targets.Item Oh, My Gut! New insights on the role of the gastrointestinal tract and the gut microbiome in chronic kidney disease-mineral and bone disorder(Wolters Kluwer, 2024) Mirmohammadali, Seyedeh Nooshan; Hill Gallant, Kathleen M.; Biruete, Annabel; Medicine, School of MedicinePurpose of review: The aim of this review is to highlight recent evidence on the role of the gastrointestinal tract and gut microbiome on chronic kidney disease-mineral bone disorder (CKD-MBD) outcomes, including intestinal phosphorus absorption and sensing, and the effect of gut-oriented therapies. Recent findings: Recent evidence has revealed a complex interplay among mineral metabolism and novel gut-related factors, including paracellular intestinal phosphate absorption, the gut microbiome, and the immune system, prompting a reevaluation of treatment approaches for CKD-MBD. The inhibition of NHE3 limits phosphate transport in the intestine and may lead to changes in the gut microbiome. A study in rats with CKD showed that the supplementation of the fermentable dietary inulin delayed CKD-MBD, lowering circulating phosphorus and parathyroid hormone, reducing bone remodeling and improving cortical parameters, and lowering cardiovascular calcifications. In non-CKD preclinical studies, probiotics and prebiotics improved bone formation mediated through the effect of butyrate facilitating the differentiation of T cells into Tregs, and Tregs stimulating the osteogenic Wnt10b, and butyrate was also necessary for the parathyroid hormone (PTH) bone effects. Summary: Recent findings support multiple possible roles for gut-oriented therapies in addressing CKD-MBD prevention and management that should be further explored through clinical and translational studies.