A G protein-coupled, IP3/protein kinase C pathway controlling the synthesis of phosphaturic hormone FGF23

Potential Targeting Mechanisms for Bone-Directed Therapies

Bone development is characterized by complex regulation mechanisms, including signal transduction and transcription factor-related pathways, glycobiological processes, cellular interactions, transportation mechanisms, and, importantly, chemical formation resulting from hydroxyapatite. Any abnormal regulation in the bone development processes causes skeletal system-related problems. To some extent, the avascularity of cartilage and bone makes drug delivery more challenging than that of soft tissues. Recent studies have implemented many novel bone-targeting approaches to overcome drawbacks. However, none of these strategies fully corrects skeletal dysfunction, particularly in growth plate-related ones. Although direct recombinant enzymes (e.g., Vimizim for Morquio, Cerezyme for Gaucher, Elaprase for Hunter, Mepsevii for Sly diseases) or hormone infusions (estrogen for osteoporosis and osteoarthritis), traditional gene delivery (e.g., direct infusion of viral or non-viral vectors with no modifications on capsid, envelope, or nanoparticles), and cell therapy strategies (healthy bone marrow or hematopoietic stem cell transplantation) partially improve bone lesions, novel delivery methods must be addressed regarding target specificity, less immunogenicity, and duration in circulation. In addition to improvements in bone delivery, potential regulation of bone development mechanisms involving receptor-regulated pathways has also been utilized. Targeted drug delivery using organic and inorganic compounds is a promising approach in mostly preclinical settings and future clinical translation. This review comprehensively summarizes the current bone-targeting strategies based on bone structure and remodeling concepts while emphasizing potential approaches for future bone-targeting systems.

Both enantiomers of β-aminoisobutyric acid BAIBA regulate Fgf23 via MRGPRD receptor by activating distinct signaling pathways in osteocytes

With exercise, muscle and bone produce factors with beneficial effects on brain, fat, and other organs. Exercise in mice increased fibroblast growth factor 23 (FGF23), urine phosphate, and the muscle metabolite L-β-aminoisobutyric acid (L-BAIBA), suggesting that L-BAIBA may play a role in phosphate metabolism. Here, we show that L-BAIBA increases in serum with exercise and elevates Fgf23 in osteocytes. The D enantiomer, described to be elevated with exercise in humans, can also induce Fgf23 but through a delayed, indirect process via sclerostin. The two enantiomers both signal through the same receptor, Mas-related G-protein-coupled receptor type D, but activate distinct signaling pathways; L-BAIBA increases Fgf23 through Gαs/cAMP/PKA/CBP/β-catenin and Gαq/PKC/CREB, whereas D-BAIBA increases Fgf23 indirectly through sclerostin via Gαi/NF-κB. In vivo, both enantiomers increased Fgf23 in bone in parallel with elevated urinary phosphate excretion. Thus, exercise-induced increases in BAIBA and FGF23 work together to maintain phosphate homeostasis.

Organic phosphate but not inorganic phosphate regulates Fgf23 expression through MAPK and TGF-ꞵ signaling

One of the main regulators of phosphate homeostasis is fibroblast growth factor 23 (FGF23), secreted by osteocytes. The effects of organic versus inorganic dietary phosphate on this homeostasis are unclear. This study used MC3T3-E1 FGF23-producing cells to examine the transcriptomic responses to these phosphates. Most importantly, the expression and secretion of FGF23 were only increased in response to organic phosphate. Gene ontology terms related to a response to environmental change were only enriched in cells treated with organic phosphate while cells treated with inorganic phosphate were enriched for terms associated with regulation of cellular phosphate metabolism. Inhibition of MAPK signaling diminished the response of Fgf23 to organic phosphate, suggesting it activates FGF23. TGF-β signaling inhibition increased Fgf23 expression after the addition of organic phosphate, while the negative TGF-β regulator Skil decreased this response. In summary, the observed differential response of FGF23-producing to phosphate types may have consequences for phosphate homeostasis.

Hypericin Alleviates Chronic Kidney Disease-induced Left Ventricular Hypertrophy by Regulation of FGF23-FGFR4 Signaling Pathway

ABSTRACT

Chronic kidney disease (CKD) is a significant global health threat that imposes a substantial burden on both individuals and societies. CKD frequently correlates with cardiovascular events, particularly left ventricular hypertrophy (LVH), which contributes to the high mortality rate associated with CKD. Fibroblast growth factor 23 (FGF23), a hormone primarily involved in regulating calcium and phosphorus metabolism, has been identified as a major risk factor for LVH in CKD patients. Elevated serum FGF23 levels are known to induce LVH and myocardial fibrosis by activating the fibroblast growth factor receptor 4 (FGFR4) signal pathway. Therefore, targeting FGFR4 and its downstream signaling pathways holds potential as a treatment strategy for cardiac dysfunction in CKD. In our current study, we have discovered that Hypericin, a key component derived from Hypericum perforatum , has the ability to alleviate CKD-related LVH by targeting the FGFR4/phospholipase C gamma 1 (PLCγ1) signaling pathway. Through in vitro experiments using rat cardiac myocyte H9c2 cells, we observed that Hypericin effectively inhibits FGF23-induced hypertrophy and fibrosis by suppressing the FGFR4/PLCγ1/calcineurin/nuclear factor of activated T-cell (NFAT3) signaling pathway. In addition, our in vivo studies using mice on a high-phosphate diet and rat models of 5/6 nephrectomy demonstrated that Hypericin has therapeutic effects against CKD-induced LVH by modulating the FGFR4/PLCγ1/calcineurin/NFAT3 signaling pathway. In conclusion, our research highlights the potential of Hypericin as a candidate for the treatment of CKD-induced cardiomyopathy. By suppressing the FGFR4/PLCγ1 signaling pathway, Hypericin shows promise in attenuating LVH and myocardial fibrosis associated with CKD.

Gα11 deficiency increases fibroblast growth factor 23 levels in a mouse model of familial hypocalciuric hypercalcemia

Fibroblast growth factor 23 (FGF23) production has recently been shown to increase downstream of Gαq/11-PKC signaling in osteocytes. Inactivating mutations in the gene encoding Gα11 (GNA11) cause familial hypocalciuric hypercalcemia (FHH) due to impaired calcium-sensing receptor signaling. We explored the effect of Gα11 deficiency on FGF23 production in mice with heterozygous (Gna11+/-) or homozygous (Gna11-/-) ablation of Gna11. Both Gna11+/- and Gna11-/- mice demonstrated hypercalcemia and mildly raised parathyroid hormone levels, consistent with FHH. Strikingly, these mice also displayed increased serum levels of total and intact FGF23 and hypophosphatemia. Gna11-/- mice showed augmented Fgf23 mRNA levels in the liver and heart, but not in bone or bone marrow, and also showed evidence of systemic inflammation with elevated serum IL-1β levels. Furin gene expression was significantly increased in the Gna11-/- liver, suggesting enhanced FGF23 cleavage despite the observed rise in circulating intact FGF23 levels. Gna11-/- mice had normal renal function and reduced serum levels of glycerol-3-phosphate, excluding kidney injury as the primary cause of elevated intact FGF23 levels. Thus, Gα11 ablation caused systemic inflammation and excess serum FGF23 in mice, suggesting that patients with FHH - at least those with GNA11 mutations - may be at risk for these complications.

PKC regulates αKlotho gene expression in MDCK and NRK-52E cells

Particularly expressed in the kidney, αKlotho is a transmembrane protein that acts together with bone hormone fibroblast growth factor 23 (FGF23) to regulate renal phosphate and vitamin D homeostasis. Soluble Klotho (sKL) is released from the transmembrane form and controls various cellular functions as a paracrine and endocrine factor. αKlotho deficiency accelerates aging, whereas its overexpression favors longevity. Higher αKlotho abundance confers a better prognosis in cardiovascular and renal disease owing to anti-inflammatory, antifibrotic, or antioxidant effects and tumor suppression. Serine/threonine protein kinase C (PKC) is ubiquitously expressed, affects several cellular responses, and is also implicated in heart or kidney disease as well as cancer. We explored whether PKC is a regulator of αKlotho. Experiments were performed in renal MDCK or NRK-52E cells and PKC isoform and αKlotho expression determined by qRT-PCR and Western Blotting. In both cell lines, PKC activation with phorbol ester phorbol-12-myristate-13-acetate (PMA) downregulated, while PKC inhibitor staurosporine enhanced αKlotho mRNA abundance. Further experiments with PKC inhibitor Gö6976 and RNA interference suggested that PKCγ is the major isoform for the regulation of αKlotho gene expression in the two cell lines. In conclusion, PKC is a negative regulator of αKlotho gene expression, an effect which may be relevant for the unfavorable effect of PKC on heart or kidney disease and tumorigenesis.

The role of genetic and epigenetic GNAS alterations in the development of early-onset obesity

BACKGROUND

GNAS (guanine nucleotide-binding protein, alpha stimulating) is an imprinted gene that encodes Gsα, the α subunit of the heterotrimeric stimulatory G protein. This subunit mediates the signalling of a diverse array of G protein-coupled receptors (GPCRs), including the melanocortin 4 receptor (MC4R) that serves a pivotal role in regulating food intake, energy homoeostasis, and body weight. Genetic or epigenetic alterations in GNAS are known to cause pseudohypoparathyroidism in its different subtypes and have been recently associated with isolated, early-onset, severe obesity. Given the diverse biological functions that Gsα serves, multiple molecular mechanisms involving various GPCRs, such as MC4R, β2- and β3-adrenoceptors, and corticotropin-releasing hormone receptor, have been implicated in the pathophysiology of severe, early-onset obesity that results from genetic or epigenetic GNAS changes.

SCOPE OF REVIEW

This review examines the structure and function of GNAS and provides an overview of the disorders that are caused by defects in this gene and may feature early-onset obesity. Moreover, it elucidates the potential molecular mechanisms underlying Gsα deficiency-induced early-onset obesity, highlighting some of their implications for the diagnosis, management, and treatment of this complex condition.

MAJOR CONCLUSIONS

Gsα deficiency is an underappreciated cause of early-onset, severe obesity. Therefore, screening children with unexplained, severe obesity for GNAS defects is recommended, to enhance the molecular diagnosis and management of this condition.

GNAS locus: bone related diseases and mouse models

GNASis a complex locus characterized by multiple transcripts and an imprinting effect. It orchestrates a variety of physiological processes via numerous signaling pathways. Human diseases associated with the GNAS gene encompass fibrous dysplasia (FD), Albright's Hereditary Osteodystrophy (AHO), parathyroid hormone(PTH) resistance, and Progressive Osseous Heteroplasia (POH), among others. To facilitate the study of the GNAS locus and its associated diseases, researchers have developed a range of mouse models. In this review, we will systematically explore the GNAS locus, its related signaling pathways, the bone diseases associated with it, and the mouse models pertinent to these bone diseases.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

A Naturally Occurring Membrane-Anchored Gαs Variant, XLαs, Activates Phospholipase Cβ4

Extra-large stimulatory Gα (XLα_s) is a large variant of G protein α_s subunit (Gα_s) that uses an alternative promoter and thus differs from Gα_s at the first exon. XLα_s activation by G protein–coupled receptors mediates cAMP generation, similarly to Gα_s; however, Gα_s and XLα_s have been shown to have distinct cellular and physiological functions. For example, previous work suggests that XLα_s can stimulate inositol phosphate production in renal proximal tubules and thereby regulate serum phosphate levels. In this study, we show that XLα_s directly and specifically stimulates a specific isoform of phospholipase Cβ (PLCβ), PLCβ4, both in transfected cells and with purified protein components. We demonstrate that neither the ability of XLα_s to activate cAMP generation nor the canonical G protein switch II regions are required for PLCβ stimulation. Furthermore, this activation is nucleotide independent but is inhibited by Gβγ, suggesting a mechanism of activation that relies on Gβγ subunit dissociation. Surprisingly, our results indicate that enhanced membrane targeting of XLα_s relative to Gα_s confers the ability to activate PLCβ4. We also show that PLCβ4 is required for isoproterenol-induced inositol phosphate accumulation in osteocyte-like Ocy454 cells. Taken together, we demonstrate a novel mechanism for activation of phosphoinositide turnover downstream of G_s-coupled receptors that may have a critical role in endocrine physiology.

Fibroblast Growth Factor 23 Regulation and Acute Kidney Injury

Elevated fibroblast growth factor 23 (FGF23) levels are markers and potential mediators, of adverse outcomes in acute kidney injury (AKI). We recently identified glycerol-3-phosphate (G-3-P), a glycolysis byproduct, as a kidney-derived factor that circulates to bone and bone marrow and triggers FGF23 production in ischemic AKI. This kidney-to-bone signaling axis was further shown to require the conversion of G-3-P to lysophosphatidic acid (LPA) in bone marrow, followed by LPA signaling through the LPAR1 receptor. These findings highlight discrete steps potentially amenable to therapeutic targeting in conditions of FGF23 excess, although more work is required to determine the specificity and safety of targeting specific enzyme and receptor isoforms. Importantly, the initial metabolomic screen that identified a strong correlation between renal vein G-3-P and circulating FGF23 was conducted in human subjects undergoing elective catheterization, none with AKI. This raises the question of whether G-3-P might also modulate FGF23 homeostasis in patients with more mild or chronic decrements in kidney function, or under normal physiologic conditions - a question that is reinforced by a growing body of literature highlighting functional roles for a range of circulating metabolites traditionally thought to function exclusively inside cells.

Regulation of FGF23: Beyond Bone

PURPOSE OF REVIEW

Fibroblast growth factor 23 (FGF23) is a bone- and bone marrow-derived hormone that is critical to maintain phosphate homeostasis. The principal actions of FGF23 are to reduce serum phosphate levels by decreasing kidney phosphate reabsorption and 1,25-dihydroxyvitamin D synthesis. FGF23 deficiency causes hyperphosphatemia and ectopic calcifications, while FGF23 excess causes hypophosphatemia and skeletal defects. Excess FGF23 also correlates with kidney disease, where it is associated with increased morbidity and mortality. Accordingly, FGF23 levels are tightly regulated, but the mechanisms remain incompletely understood.

RECENT FINDINGS

In addition to bone mineral factors, additional factors including iron, erythropoietin, inflammation, energy, and metabolism regulate FGF23. All these factors affect Fgf23 expression, while some also regulate FGF23 protein cleavage. Conversely, FGF23 may have a functional role in regulating these biologic processes. Understanding the bi-directional relationship between FGF23 and non-bone mineral factors is providing new insights into FGF23 regulation and function.

FAM20C Overview: Classic and Novel Targets, Pathogenic Variants and Raine Syndrome Phenotypes

FAM20C is a gene coding for a protein kinase that targets S-X-E/pS motifs on different phosphoproteins belonging to diverse tissues. Pathogenic variants of FAM20C are responsible for Raine syndrome (RS), initially described as a lethal and congenital osteosclerotic dysplasia characterized by generalized atherosclerosis with periosteal bone formation, characteristic facial dysmorphisms and intracerebral calcifications. The aim of this review is to give an overview of targets and variants of FAM20C as well as RS aspects. We performed a wide phenotypic review focusing on clinical aspects and differences between all lethal (LRS) and non-lethal (NLRS) reported cases, besides the FAM20C pathogenic variant description for each. As new targets of FAM20C kinase have been identified, we reviewed FAM20C targets and their functions in bone and other tissues, with emphasis on novel targets not previously considered. We found the classic lethal and milder non-lethal phenotypes. The milder phenotype is defined by a large spectrum ranging from osteonecrosis to osteosclerosis with additional congenital defects or intellectual disability in some cases. We discuss our current understanding of FAM20C deficiency, its mechanism in RS through classic FAM20C targets in bone tissue and its potential biological relevance through novel targets in non-bone tissues.

Glycerol-3-phosphate and fibroblast growth factor 23 regulation

PURPOSE OF REVIEW

Both classical and nonclassical factors regulate fibroblast growth factor 23 (FGF23), with impacts on gene expression and proteolytic cleavage. Here, we review recent publications that extend current knowledge on these factors.

RECENT FINDINGS

Emerging nonclassical FGF23 regulators such as erythropoietin cause a balanced increase in FGF23 expression and cleavage, with minimal or no increase in biologically active intact FGF23 (iFGF23) in blood. However, circulating FGF23 profiles may not reflect the bone marrow microenvironment. For example, granulocyte colony-stimulating factor increases local marrow iFGF23 levels without impacting circulating iFGF23 levels. The view that phosphate does not increase bone FGF23 production also warrants reconsideration, as phosphate can reduce iFGF23 cleavage and phosphate-containing calciprotein particles increase FGF23 expression. Finally, a screen of renal venous plasma identifies glycerol-3-phosphate as a kidney-derived molecule that circulates to bone and bone marrow, where it is converted to lysophosphatidic acid and signals through a G-protein coupled receptor to increase FGF23 synthesis.

SUMMARY

FGF23 regulation is complex, requiring consideration of known and emerging stimuli, expression and cleavage, and circulating and local levels. Recent work identifies glycerol-3-phosphate as an FGF23 regulator derived from the injured kidney; whether it participates in FGF23 production downstream of classical or nonclassical factors requires further study.

Maternal GNAS Contributes to the Extra-Large G Protein α-Subunit (XLαs) Expression in a Cell Type-Specific Manner

GNAS encodes the stimulatory G protein alpha-subunit (Gsα) and its large variant XLαs. Studies have suggested that XLαs is expressed exclusively paternally. Thus, XLαs deficiency is considered to be responsible for certain findings in patients with paternal GNAS mutations, such as pseudo-pseudohypoparathyroidism, and the phenotypes associated with maternal uniparental disomy of chromosome 20, which comprises GNAS. However, a study of bone marrow stromal cells (BMSC) suggested that XLαs could be biallelically expressed. Aberrant BMSC differentiation due to constitutively activating GNAS mutations affecting both Gsα and XLαs is the underlying pathology in fibrous dysplasia of bone. To investigate allelic XLαs expression, we employed next-generation sequencing and a polymorphism common to XLαs and Gsα, as well as A/B, another paternally expressed GNAS transcript. In mouse BMSCs, Gsα transcripts were 48.4 ± 0.3% paternal, while A/B was 99.8 ± 0.2% paternal. In contrast, XLαs expression varied among different samples, paternal contribution ranging from 43.0 to 99.9%. Sample-to-sample variation in paternal XLαs expression was also detected in bone (83.7-99.6%) and cerebellum (83.8 to 100%) but not in cultured calvarial osteoblasts (99.1 ± 0.1%). Osteoblastic differentiation of BMSCs shifted the paternal XLαs expression from 83.9 ± 1.5% at baseline to 97.2 ± 1.1%. In two human BMSC samples grown under osteoinductive conditions, XLαs expression was also predominantly monoallelic (91.3 or 99.6%). Thus, the maternal GNAS contributes significantly to XLαs expression in BMSCs but not osteoblasts. Altered XLαs activity may thus occur in certain cell types irrespective of the parental origin of a GNAS defect.

Gs/Gq signaling switch in β cells defines incretin effectiveness in diabetes

By restoring glucose-regulated insulin secretion, glucagon-like peptide-1-based (GLP-1-based) therapies are becoming increasingly important in diabetes care. Normally, the incretins GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) jointly maintain normal blood glucose levels by stimulation of insulin secretion in pancreatic β cells. However, the reason why only GLP-1-based drugs are effective in improving insulin secretion after presentation of diabetes has not been resolved. ATP-sensitive K+ (KATP) channels play a crucial role in coupling the systemic metabolic status to β cell electrical activity for insulin secretion. Here, we have shown that persistent membrane depolarization of β cells due to genetic (β cell-specific Kcnj11-/- mice) or pharmacological (long-term exposure to sulfonylureas) inhibition of the KATP channel led to a switch from Gs to Gq in a major amplifying pathway of insulin secretion. The switch determined the relative insulinotropic effectiveness of GLP-1 and GIP, as GLP-1 can activate both Gq and Gs, while GIP only activates Gs. The findings were corroborated in other models of persistent depolarization: a spontaneous diabetic KK-Ay mouse and nondiabetic human and mouse β cells of pancreatic islets chronically treated with high glucose. Thus, a Gs/Gq signaling switch in β cells exposed to chronic hyperglycemia underlies the differential insulinotropic potential of incretins in diabetes.

New and Old Osteocytic Cell Lines and 3D Models

The aim of this review was to compile a list of tools currently available to study bone cells and in particular osteocytes. As the interest (and importance) in osteocyte biology has greatly expanded over the past decade, new tools and techniques have become available to study these elusive cells, RECENT FINDINGS: Osteocytes are the main orchestrators of bone remodeling. They control both osteoblasts and osteoclast activities via cell-to cell communication or through secreted factors. Osteocytes are also the mechanosensors of the bone and they orchestrate skeletal adaptation to loads. Recent discoveries have greatly expanded our knowledge and understanding of these cells and new models are now available to further uncover the functions of osteocytes. Novel osteocytic cell lines, primary cultures, and 3D scaffolds are now available to investigators to further unravel the functions and roles of these cells.

Osteocytic FGF23 and Its Kidney Function

Osteocytes, which represent up to 95% of adult skeletal cells, are deeply embedded in bone. These cells exhibit important interactive abilities with other bone cells such as osteoblasts and osteoclasts to control skeletal formation and resorption. Beyond this local role, osteocytes can also influence the function of distant organs due to the presence of their sophisticated lacunocanalicular system, which connects osteocyte dendrites directly to the vasculature. Through these networks, osteocytes sense changes in circulating metabolites and respond by producing endocrine factors to control homeostasis. One critical function of osteocytes is to respond to increased blood phosphate and 1,25(OH)2 vitamin D (1,25D) by producing fibroblast growth factor-23 (FGF23). FGF23 acts on the kidneys through partner fibroblast growth factor receptors (FGFRs) and the co-receptor Klotho to promote phosphaturia via a downregulation of phosphate transporters, as well as the control of vitamin D metabolizing enzymes to reduce blood 1,25D. In the first part of this review, we will explore the signals involved in the positive and negative regulation of FGF23 in osteocytes. In the second portion, we will bridge bone responses with the review of current knowledge on FGF23 endocrine functions in the kidneys.

A paternally inherited non-sense variant c.424G>T (p.G142*) in the first exon of XLαs in an adult patient with hypophosphatemia and osteopetrosis

XLαs, the extra-large isoform of alpha-subunit of the stimulatory guanine nucleotide-binding protein (Gsα), is paternally expressed. The significance of XLαs in humans remains largely unknown. Here, we report a patient who presented with increased bone mass, hypophosphatemia, and elevated parathyroid hormone (PTH) levels. His serum calcium was in the lower limit of the normal range. Whole exome sequencing of this subject found a novel non-sense variant c.424G>T (p. G142*) in the first exon of XLαs, which was inherited from his father and transmitted to his daughter. This variant was predicted to exclusively influence the expression of XLαs, while possibly having no significant effects on other gene products of this locus. Ellsworth-Howard test revealed normal renal response to PTH in proband. Human SaOS2 cells transfected with mutant XLαs failed to generate cyclic adenosine monophosphate under PTH stimulation, indicating skeletal resistance to this hormone. This subject showed higher circulating sclerostin, dickkopf1, and osteoprotegerin (OPG) levels, while lower receptor activator of nuclear factor kappa-B ligand/OPG ratio, leading to reduced bone resorption. Our findings indicate that XLαs plays a critical role in bone metabolism and GNAS locus should be considered as a candidate gene for high bone mass.

Extra-Large Gα Protein (XLαs) Deficiency Causes Severe Adenine-Induced Renal Injury with Massive FGF23 Elevation

Fibroblast growth factor-23 (FGF23) is critical for phosphate and vitamin D homeostasis. Cellular and molecular mechanisms underlying FGF23 production remain poorly defined. The extra-large Gα subunit (XLαs) is a variant of the stimulatory G protein alpha-subunit (Gsα), which mediates the stimulatory action of parathyroid hormone in skeletal FGF23 production. XLαs ablation causes diminished FGF23 levels in early postnatal mice. Herein we found that plasma FGF23 levels were comparable in adult XLαs knockout (XLKO) and wild-type littermates. Upon adenine-rich diet-induced renal injury, a model of chronic kidney disease, both mice showed increased levels of plasma FGF23. Unexpectedly, XLKO mice had markedly higher FGF23 levels than WT mice, with higher blood urea nitrogen and more severe tubulopathy. FGF23 mRNA levels increased substantially in bone and bone marrow in both genotypes; however, the levels in bone were markedly higher than in bone marrow. In XLKO mice, a positive linear correlation was observed between plasma FGF23 and bone, but not bone marrow, FGF23 mRNA levels, suggesting that bone, rather than bone marrow, is an important contributor to severely elevated FGF23 levels in this model. Upon folic acid injection, a model of acute kidney injury, XLKO and WT mice exhibited similar degrees of tubulopathy; however, plasma phosphate and FGF23 elevations were modestly blunted in XLKO males, but not in females, compared to WT counterparts. Our findings suggest that XLαs ablation does not substantially alter FGF23 production in adult mice but increases susceptibility to adenine-induced kidney injury, causing severe FGF23 elevations in plasma and bone.