Phosphate sensing

Nickel(II) complexes with covalently attached quinols rely on ligand-derived redox couples to catalyze superoxide dismutation

Although nickel is found in the active sites of a class of superoxide dismutase (SOD), nickel complexes with non-peptidic ligands normally do not catalyze superoxide degradation, and none has displayed activity comparable to those of the best manganese-containing SOD mimics. Here, we find that nickel complexes with polydentate quinol-containing ligands can exhibit catalytic activity comparable to those of the most efficient manganese-containing SOD mimics. The nickel complexes retain a significant portion of their activity in phosphate buffer and under operando conditions and rely on ligand-centered redox processes for catalysis. Although nickel SODs are known to cycle through Ni(II) and Ni(III) species during catalysis, cryo-mass spectrometry studies indicate that the nickel atoms in our catalysts remain in the +2 oxidation state throughout SOD mimicry.

Smartphone-Assisted Fluorescence Determination of Inorganic Phosphorus Using a Samarium Metal-Organic Framework

Inorganic phosphori are widely used in food, whose quantitative detection method is of significance. This work presents a Sm-DDB (H4DDB = 1,3-di(3',5'-dicarboxylphenyl)benzene), which acts as a ratiometric fluorescence sensor to monitor PO43-, H2PO4-, and (PO3)66- with high sensitivity. The determination factors of pH, MOF dosage, and fluorescence response time are optimized as 7.35, 1 mg, and 2 min, respectively. The sensitivity tests show the linear fitting equations of I465/I598 = 0.00363·CP + 1.49183 (I465 and I598: the emission intensities at 465 and 598 nm; Cp = inorganic phosphorus concentration) for PO43-, I465/I598 = 0.00272·CP + 1.55944 for H2PO4-, and I465/I598 = 0.00957·CP + 1.55122 for (PO3)66- with LODs being 1.00 μM for PO43-, 1.33 μM for H2PO4-, and 0.38 μM for (PO3)66-. The detection method was applied in frozen shrimp, marine fish, and bacon, whose fluorescence recoveries of around 100% demonstrate its reliability. The analytical results are close to those determined by the phosphomolybdenum blue method. The Sm-DDB test paper shows an obvious emission color change, whose blue/red (B/R) values can be recognized by a smartphone APP. This work provides a smartphone-assisted visualization detection method for PO43-, H2PO4-, and (PO3)66-.

Cellular Phosphate Sensing and Anion Binding by an Azacrown-Calixpyrrole Hybrid

A hybrid receptor-sensor for anions originating from the merging of positively charged ammonium moieties for electrostatic attraction/stronger binding of azacrowns with directionality of calixpyrrole hydrogen bond donors for selectivity is investigated. As demonstrated this hybrid receptor-sensor shows a remarkable selectivity for orthophosphate even in the presence of other phosphates and anions found in cellular materials (Kassoc H2PO4 ->H2P2O7 2->AMP-≫ADP2- or ATP3- over halides, nitrate, or hydrogen sulfate; all Na+ salts in water) but also cellular polyphosphate or phospholipids. This selectivity is harnessed in a real-time monitoring of cell lysis by lysozyme, which releases orthophosphate and other phosphates and anions from the cells. This sensitive (LOD 0.4 μM) fluorescence-based microscale method compares favorably with the state-of-the-art techniques but can easily be practiced in a high-throughput screening (HTS) manner. The anion binding and selectivity in aqueous solutions were investigated by NMR and put in context with phosphate binding of the parent calix[4]pyrrole. The microscopic understanding of anion binding by the hybrid receptor was then obtained from a combination of density functional theory (DFT), classical molecular dynamics (MD) with explicit water solvation, and ab initio MD (AIMD) simulations. Correlating the NMR and fluorescence binding data with studies of solvation of the receptor, phosphate anion, and the resulting complex confirms the binding is largely driven by entropic component (TΔS) associated with receptor and anion desolvation.

Regulation of eukaryotic transcription initiation in response to cellular stress

Transcription initiation is a vital step in the regulation of eukaryotic gene expression. It can be dysregulated in response to various cellular stressors which is associated with numerous human diseases including cancer. Transcription initiation is facilitated via many gene-specific trans-regulatory elements such as transcription factors, activators, and coactivators through their interactions with transcription pre-initiation complex (PIC). These trans-regulatory elements can uniquely facilitate PIC formation (hence, transcription initiation) in response to cellular nutrient stress. Cellular nutrient stress also regulates the activity of other pathways such as target of rapamycin (TOR) pathway. TOR pathway exhibits distinct regulatory mechanisms of transcriptional activation in response to stress. Like TOR pathway, the cell cycle regulatory pathway is also found to be linked to transcriptional regulation in response to cellular stress. Several transcription factors such as p53, C/EBP Homologous Protein (CHOP), activating transcription factor 6 (ATF6α), E2F, transforming growth factor (TGF)-β, Adenomatous polyposis coli (APC), SMAD, and MYC have been implicated in regulation of transcription of target genes involved in cell cycle progression, apoptosis, and DNA damage repair pathways. Additionally, cellular metabolic and oxidative stressors have been found to regulate the activity of long non-coding RNAs (lncRNA). LncRNA regulates transcription by upregulating or downregulating the transcription regulatory proteins involved in metabolic and cell signaling pathways. Numerous human diseases, triggered by chronic cellular stressors, are associated with abnormal regulation of transcription. Hence, understanding these mechanisms would help unravel the molecular regulatory insights with potential therapeutic interventions. Therefore, here we emphasize the recent advances of regulation of eukaryotic transcription initiation in response to cellular stress.

C/N ratio effect on oily wastewater treatment using column type SBR: machine learning prediction and metagenomics study

The sequencing batch reactor has emerged as a promising technology in treating wastewater; however, its application in the treatment of generated water still needs to be explored. This research gap led to the investigation of various carbon-to-nitrogen (C/N) ratios in a column-type sequencing batch reactor (cSBR). The resulting data and model demonstrated that augmenting the SND process with an external carbon source is effective until the C/N ratio reaches 15, ultimately eliminating nitrogen in the produced water. Conversely, a reduced C/N ratio can limit the ability of polyphosphate-accumulating organisms to incorporate carbon into polyphosphate synthesis, thereby decreasing phosphorus removal efficiency within the cSBR. When the C/N ratio ranged from 6 to 8, and the mixed liquor suspended solids concentration was high, the average phosphate removal was approximately 55%, compared to only around 25% when the C/N ratio was less than 6.

Light Emission from Fe2+-EGTA-H2O2 System Depends on the pH of the Reaction Milieu within the Range That May Occur in Cells of the Human Body

A Fe2+-EGTA(ethylene glycol-bis (β-aminoethyl ether)-N,N,N',N'-tetraacetic acid)-H2O2 system emits photons, and quenching this chemiluminescence can be used for determination of anti-hydroxyl radical (•OH) activity of various compounds. The generation of •OH and light emission due to oxidative damage to EGTA may depend on the buffer and pH of the reaction milieu. In this study, we evaluated the effect of pH from 6.0 to 7.4 (that may occur in human cells) stabilized with 10 mM phosphate buffer (main intracellular buffer) on a chemiluminescence signal and the ratio of this signal to noise (light emission from medium alone). The highest signal (4698 ± 583 RLU) and signal-to-noise ratio (9.7 ± 1.5) were noted for pH 6.6. Lower and higher pH caused suppression of these variables to 2696 ± 292 RLU, 4.0 ± 0.8 at pH 6.2 and to 3946 ± 558 RLU, 5.0 ± 1.5 at pH 7.4, respectively. The following processes may explain these observations: enhancement and inhibition of •OH production in lower and higher pH; formation of insoluble Fe(OH)3 at neutral and alkaline environments; augmentation of •OH production by phosphates at weakly acidic and neutral environments; and decreased regeneration of Fe2+-EGTA in an acidic environment. Fe2+-EGTA-H2O2 system in 10 mM phosphate buffer pH 6.6 seems optimal for the determination of anti-•OH activity.

A phosphate transporter in VIPergic neurons of the suprachiasmatic nucleus gates locomotor activity during the light/dark transition in mice

The suprachiasmatic nucleus (SCN) encodes time of day through changes in daily firing; however, the molecular mechanisms by which the SCN times behavior are not fully understood. To identify factors that could encode day/night differences in activity, we combine patch-clamp recordings and single-cell sequencing of individual SCN neurons in mice. We identify PiT2, a phosphate transporter, as being upregulated in a population of Vip+Nms+ SCN neurons at night. Although nocturnal and typically showing a peak of activity at lights off, mice lacking PiT2 (PiT2-/-) do not reach the activity level seen in wild-type mice during the light/dark transition. PiT2 loss leads to increased SCN neuronal firing and broad changes in SCN protein phosphorylation. PiT2-/- mice display a deficit in seasonal entrainment when moving from a simulated short summer to longer winter nights. This suggests that PiT2 is responsible for timing activity and is a driver of SCN plasticity allowing seasonal entrainment.

The calcium-sensing receptor has only a parathyroid hormone-dependent role in the acute response of renal phosphate transporters to phosphate intake

The kidney controls systemic inorganic phosphate (Pi) levels by adapting reabsorption to Pi intake. Renal Pi reabsorption is mostly mediated by sodium-phosphate cotransporters NaPi-IIa (SLC34A1) and NaPi-IIc (SLC34A3) that are tightly controlled by various hormones including parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23). PTH and FGF23 rise in response to Pi intake and decrease NaPi-IIa and NaPi-IIc brush border membrane abundance enhancing phosphaturia. Phosphaturia and transporter regulation occurs even in the absence of PTH and FGF23 signaling. The calcium-sensing receptor (CaSR) regulates PTH and FGF23 secretion, and may also directly affect renal Pi handling. Here, we combined pharmacological and genetic approaches to examine the role of the CaSR in the acute phosphaturic response to Pi loading. Animals pretreated with the calcimimetic cinacalcet were hyperphosphatemic, had blunted PTH levels upon Pi administration, a reduced Pi-induced phosphaturia, and no Pi-induced NaPi-IIa downregulation. The calcilytic NPS-2143 exaggerated the PTH response to Pi loading but did not abolish Pi-induced downregulation of NaPi-IIa. In mice with a dominant inactivating mutation in the Casr (CasrBCH002), baseline NaPi-IIa expression was higher, whereas downregulation of transporter expression was blunted in double CasrBCH002/PTH knockout (KO) transgenic animals. Thus, in response to an acute Pi load, acute modulation of the CaSR affects the endocrine and renal response, whereas chronic genetic inactivation, displays only subtle differences in the downregulation of NaPi-IIa and NaPi-IIc renal expression. We did not find evidence that the CaSR impacts on the acute renal response to oral Pi loading beyond its role in regulating PTH secretion.NEW & NOTEWORTHY Consumption of phosphate-rich diets causes an adaptive response of the body leading to the urinary excretion of phosphate. The underlying mechanisms are still poorly understood. Here, we examined the role of the calcium-sensing receptor (CaSR) that senses both calcium and phosphate. We confirmed that the receptor increases the secretion of parathyroid hormone involved in stimulating urinary phosphate excretion. However, we did not find any evidence for a role of the receptor beyond this function.

Low phosphorus increases hepatic lipid deposition, oxidative stress and inflammatory response via Acetyl-CoA carboxylase-dependent manner in zebrafish liver cells

Acetyl-CoA carboxylase (ACC) plays a regulatory role in both fatty acid synthesis and oxidation, controlling the process of lipid deposition in the liver. Given that existing studies have shown a close relationship between low phosphorus (P) and hepatic lipid deposition, this study was conducted to investigate whether ACC plays a crucial role in this relationship. Zebrafish liver cell line (ZFL) was incubated under low P medium (LP, P concentration: 0.77 mg/L) or adequate P medium (AP, P concentration: 35 mg/L) for 240 h. The results showed that, compared with AP-treated cells, LP-treated cells displayed elevated lipid accumulation, and reduced fatty acid β-oxidation, ATP content, and mitochondrial mass. Furthermore, transcriptomics analysis revealed that LP-treated cells significantly increased lipid synthesis (Acetyl-CoA carboxylases (acc), Stearyl coenzyme A dehydrogenase (scd)) but decreased fatty acid β-oxidation (Carnitine palmitoyltransferase I (cptI)) and (AMP-activated protein kinase (ampk)) mRNA levels compared to AP-treated cells. The phosphorylation of AMPK and ACC, and the protein expression of CPTI were significantly decreased in LP-treated cells compared with those in AP-treated cells. After 240 h of LP treatment, PF-05175157 (an ACC inhibitor) was supplemented in the LP treatment for an additional 12 h. PF-05175157-treated cells showed higher phosphorylation of ACC, higher protein expression of CPTI, and lower protein expression of FASN, lower TG content, enhanced fatty acid β-oxidation, increased ATP content, and mitochondrial mass compared with LP-treated cells. PF-05175157 also relieved the LP-induced oxidative stress and inflammatory response. Overall, these findings suggest that ACC is a promising target for treating LP-induced elevation of lipid deposition in ZFL, and can alleviate oxidative stress and inflammatory response.

Identification of PPA1 inhibitor candidates for potential repurposing in cancer medicine

Inorganic pyrophosphatase 1 (PPA1) is pivotal to cellular metabolism as it facilitates the hydrolysis of PPi-a by-product of various metabolic processes that influence cell growth and differentiation. Overexpression of PPA1 enzyme has been linked to diminished patient survival and was shown to influence tumor cell dynamics, thereby positioning it as a potential therapy target for a variety of cancers including colorectal cancer, diffuse large B-cell lymphoma, and lung adenocarcinoma. Despite this therapeutic promise, there are no known inhibitors of PPA1 as of today. In this study, we searched for potential PPA1 inhibitors using a molecular docking screen of 30 470 compounds with a history of clinical trials and/or US Food and Drug Administration approval. We specifically targeted the active pocket that coincides with the established catalytic domain. Our screen identified promising hits, which we further subjected to ADMET (absorption, distribution, metabolism, excretion, and toxicity) filtering. Subsequent molecular dynamics (MD) analyses were conducted on devazepide, quinotolast, and tarazepide-the three substances that successfully navigated all filters. MD analyses reinforced the stability of the protein-ligand complexes and confirmed ligand binding, as substantiated by our root mean square deviation, radius of gyration and secondary structures of proteins analyses. Furthermore, Molecular Mechanics Poisson-Boltzmann Surface Area calculations post-MD identified devazepide and quinotolast as showing higher binding affinities; being supported by principal component analysis, free energy landscape, and dynamic cross-correlation matrix results. Overall, our study reveals devazepide and quinotolast as potential candidates for PPA1 inhibition which could be considered for repurposing studies that need further experimental validation. These results not only reveal a potential for clinical repurposing for PPA1 inhibition but they also offer valuable insights into the development of future compounds for targeting the crucial PPA1 enzyme.

Kidney glycolysis serves as a mammalian phosphate sensor that maintains phosphate homeostasis

How phosphate levels are detected in mammals is unknown. The bone-derived hormone fibroblast growth factor 23 (FGF23) lowers blood phosphate levels by reducing kidney phosphate reabsorption and 1,25(OH)2D production, but phosphate does not directly stimulate bone FGF23 expression. Using PET scanning and LC-MS, we found that phosphate increases kidney-specific glycolysis and synthesis of glycerol-3-phosphate (G-3-P), which then circulates to bone to trigger FGF23 production. Further, we found that G-3-P dehydrogenase 1 (Gpd1), a cytosolic enzyme that synthesizes G-3-P and oxidizes NADH to NAD+, is required for phosphate-stimulated G-3-P and FGF23 production and prevention of hyperphosphatemia. In proximal tubule cells, we found that phosphate availability is substrate-limiting for glycolysis and G-3-P production and that increased glycolysis and Gpd1 activity are coupled through cytosolic NAD+ recycling. Finally, we show that the type II sodium-dependent phosphate cotransporter Npt2a, which is primarily expressed in the proximal tubule, conferred kidney specificity to phosphate-stimulated G-3-P production. Importantly, exogenous G-3-P stimulated FGF23 production when Npt2a or Gpd1 were absent, confirming that it was the key circulating factor downstream of glycolytic phosphate sensing in the kidney. Together, these findings place glycolysis at the nexus of mineral and energy metabolism and identify a kidney-bone feedback loop that controls phosphate homeostasis.

Calcium signaling in plant immunity: a spatiotemporally controlled symphony

Calcium ions (Ca²⁺) are prominent intracellular messengers in all eukaryotic cells. Recent studies have emphasized the crucial roles of Ca²⁺ in plant immunity. Here, we review the latest progress on the spatiotemporal control of Ca²⁺ function in plant immunity. We discuss discoveries of how Ca²⁺ influx is triggered upon the activation of immune receptors, how Ca²⁺-permeable channels are activated, how Ca²⁺ signals are decoded inside plant cells, and how these signals are switched off. Despite recent advances, many open questions remain and we highlight the existing toolkit and the new technologies to address the outstanding questions of Ca²⁺ signaling in plant immunity.

Diquinol Functionality Boosts the Superoxide Dismutase Mimicry of a Zn(II) Complex with a Redox-Active Ligand while Maintaining Catalyst Stability and Enhanced Activity in Phosphate Solution

In the current work, we demonstrate ligand design concepts that significantly improve the superoxide dismutase (SOD) activity of a zinc complex; the catalysis is enhanced when two quinol groups are present in the polydentate ligand. We investigate the mechanism through which the quinols influence the catalysis and determine the impact of entirely removing a chelating group from the original hexadentate ligand. Our results suggest that SOD mimicry with these compounds requires a ligand that coordinates Zn(II) strongly in both its oxidized and reduced forms and that the activity proceeds through Zn(II)-semiquinone complexes. The complex with two quinols displays greatly enhanced catalytic ability, with the activity improving by as much as 450% over a related complex with a single quinol. In the reduced form of the diquinol complex, one quinol appears to coordinate to the zinc much more weakly than the other. We believe that superoxide can more readily displace this portion of the ligand, facilitating its coordination to the metal center and thereby hastening the SOD reactivity. Despite the presence of two redox-active groups that may communicate through intramolecular hydrogen bonding and redox tautomerism, only one quinol undergoes two-electron oxidation to a para-quinone during the catalysis. After the formation of the para-quinone, the remaining quinol deprotonates and binds tightly to the metal, ensuring that the complex remains intact in its oxidized state, thereby maintaining its catalytic ability. The Zn(II) complex with the diquinol ligand is highly unusual for a SOD mimic in that it performs more efficiently in phosphate solution.

Single-Atomic Iron Doped Carbon Dots with Both Photoluminescence and Oxidase-Like Activity

Multifunctional nanozymes can benefit biochemical analysis via expanding sensing modes and enhancing analytical performance, but designing multifunctional nanozymes to realize the desired sensing of targets is challenging. In this work, single-atomic iron doped carbon dots (SA Fe-CDs) are designed and synthesized via a facile in situ pyrolysis process. The small-sized CDs not only maintain their tunable fluorescence, but also serve as a support for loading dispersed active sites. Monoatomic Fe offers SA Fe-CDs exceptional oxidase-mimetic activity to catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation with fast response (V_max  = 10.4 nM s^-1 ) and strong affinity (K_m  = 168 µM). Meanwhile, their photoluminescence is quenched by the oxidation product of TMB due to inner filter effect. Phosphate ions (Pi) can suppress the oxidase-mimicking activity and restore the photoluminescence of SA Fe-CDs by interacting with Fe active sites. Based on this principle, a dual-mode colorimetric and fluorescence assay of Pi with high sensitivity, selectivity, and rapid response is established. This work paves a path to develop multifunctional enzyme-like catalysts, and offers a simple but efficient dual-mode method for phosphate monitoring, which will inspire the exploration of multi-mode sensing strategies based on nanozyme catalysis.

A novel fluorescence method for detection of phosphate anions based on porphyrin metalation

In this work, a novel fluorescence method for the detection of phosphate anions (PO₄^3-) was developed based on porphyrin metalation. Through catalysis by G-quadruplex (G4), Cu²⁺ could insert into the porphyrins to quench their fluorescence. G4 simultaneously improved the fluorescence of the porphyrins but not that of Cu²⁺-porphyrin. In the absence of PO₄^3-, the porphyrins were metallized by Cu²⁺, and no fluorescence was observed. In the presence of PO₄^3-, PO₄^3- could coordinate with Cu²⁺ to prevent porphyrin metalation. Free porphyrin could bind with G4 to emit strong fluorescence. By comparing four common porphyrins, we found that G4 had the greatest effect on increasing the fluorescence intensity of N-methylmesoporphyrin IX (NMM). Thus, NMM/G4 was chosen for the design of a biosensor. Under optimal experimental conditions, this method showed high sensitivity and satisfactory selectivity for PO₄^3- with a detection limit of 44 nM in a linear range of 0.01-1.0 μM. The recovery experiments showed recovery rates of 93.75-106.00%, suggesting a great potential for measuring PO₄^3- in real samples.

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

Acute adaptation of renal phosphate transporters in the murine kidney to oral phosphate intake requires multiple signals

AIMS

Dietary inorganic phosphate (Pi) modulates renal Pi reabsorption by regulating the expression of the NaPi-IIa and NaPi-IIc Pi transporters. Here, we aimed to clarify the role of several Pi-regulatory mechanisms including parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23) and inositol hexakisphosphate kinases (IP6-kinases) in the acute regulation of NaPi-IIa and NaPi-IIc.

METHODS

Wildtype (WT) and PTH-deficient mice (PTH-KO) with/without inhibition of FGF23 signalling were gavaged with Pi/saline and examined at 1, 4 and 12 h.

RESULTS

Pi-gavage elevated plasma Pi and decreased plasma Ca²⁺ in both genotypes after 1 h Within 1 h, Pi-gavage decreased NaPi-IIa abundance in WT and PTH-KO mice. NaPi-IIc was downregulated 1 h post-administration in WT and after 4 h in PTH-KO. PTH increased after 1 h in WT animals. After 4 h Pi-gavage, FGF23 increased in both genotypes being higher in the KO group. PTHrp and dopamine were not altered by Pi-gavage. Blocking FGF23 signalling blunted PTH upregulation in WT mice and reduced NaPi-IIa downregulation in PTH-KO mice 4 h after Pi-gavage. Inhibition of IP6-kinases had no effect.

CONCLUSIONS

(1) Acute downregulation of renal Pi transporters in response to Pi intake occurs also in the absence of PTH and FGF23 signalling, (2) when FGF23 signalling is blocked, a partial contribution of PTH is revealed, (3) IP6 kinases, intracellular Pi-sensors in yeast and bacteria, are not involved, and (4) Acute Pi does not alter PTHrp and dopamine. Thus, signals other than PTH, PTHrp, FGF23 and dopamine contribute to renal adaption.

Hydrogen phosphate selectively induces MDA MB 231 triple negative breast cancer cell death in vitro

Phosphate ions are the most abundant anions inside the cells, and they are increasingly gaining attention as key modulators of cellular function and gene expression. However, little is known about the effect of inorganic phosphate ions on cancer cells, particularly breast cancer cells. Here, we investigated the toxicity of different phosphate compounds to triple-negative human breast cancer cells, particularly, MDA-MB-231, and compared it to that of human monocytes, THP-1. We found that, unlike dihydrogen phosphate (H₂PO₄⁻), hydrogen phosphate (HPO₄²⁻) at 20 mM or lower concentrations induced breast cancer cell death more than immune cell death, mainly via apoptosis. We correlate this effect to the fact that phosphate in the form of HPO₄²⁻ raises pH levels to alkaline levels which are not optimum for transport of phosphate into cancer cells. The results in this study highlight the importance of further exploring hydrogen phosphate (HPO₄²⁻) as a potential therapeutic for the treatment of breast cancer.

Uremic Toxin Lanthionine Induces Endothelial Cell Mineralization In Vitro

Vascular calcification (VC) is a pathological event caused by the unusual deposition of minerals in the vascular system, representing the leading cause of cardiovascular mortality in chronic kidney disease (CKD). In CKD, the deregulation of calcium and phosphate metabolism, along with the effect of several uremic toxins, act as key processes conveying altered mineralization. In this work, we tested the ability of lanthionine, a novel uremic toxin, to promote calcification in human endothelial cell cultures (Ea.hy926). We evaluated the effects of lanthionine, at a concentration similar to that actually detected in CKD patients, alone and under pro-calcifying culture conditions using calcium and phosphate. In pro-calcific culture conditions, lanthionine increased both the intracellular and extracellular calcium content and induced the expression of Bone Morphogenetic Protein 2 (BMP2) and RUNX Family Transcription Factor 2 (RUNX2). Lanthionine treatment, in pro-calcifying conditions, raised levels of tissue-nonspecific alkaline phosphatase (ALPL), whose expression also overlapped with Dickkopf WNT Signaling Pathway Inhibitor 1 (DKK1) gene expression, suggesting a possible role of the latter gene in the activation of ALPL. In addition, treatment with lanthionine alone or in combination with calcium and phosphate reduced Inorganic Pyrophosphate Transport Regulator (ANKH) gene expression, a protective factor toward the mineralizing process. Moreover, lanthionine in a pro-calcifying condition induced the activation of ERK1/2, which is not associated with an increase in DKK1 protein levels. Our data underscored a link between mineral disease and the alterations of sulfur amino acid metabolisms at a cell and molecular level. These results set the basis for the understanding of the link between uremic toxins and mineral-bone disorder during CKD progression.

Phosphate Starvation by Energy Metabolism Disturbance in Candida albicansvip1Δ/Δ Induces Lipid Droplet Accumulation and Cell Membrane Damage

Phosphorus in the form of phosphate (Pi) is an essential element for metabolic processes, including lipid metabolism. In yeast, the inositol polyphosphate kinase vip1 mediated synthesis of inositol heptakisphosphate (IP₇) regulates the phosphate-responsive (PHO) signaling pathway, which plays an important role in response to Pi stress. The role of vip1 in Pi stress and lipid metabolism of Candida albicans has not yet been studied. We found that when vip1Δ/Δ was grown in glucose medium, if Pi was supplemented in the medium or mitochondrial Pi transporter was overexpressed in the strain, the lipid droplet (LD) content was reduced and membrane damage was alleviated. However, further studies showed that neither the addition of Pi nor the overexpression of the Pi transporter affected the energy balance of vip1Δ/Δ. In addition, the LD content of vip1Δ/Δ grown in Pi limitation medium PNMC was lower than that grown in SC, and the metabolic activity of vip1Δ/Δ grown in PNMC was also lower than that grown in SC medium. This suggests that the increase in Pi demand by a high energy metabolic rate is the cause of LD accumulation in vip1Δ/Δ. In addition, in the vip1Δ/Δ strains, the core transcription factor PHO4 in the PHO pathway was transported to the vacuole and degraded, which reduced the pathway activity. However, this does not mean that knocking out vip1 completely blocks the activation of the PHO pathway, because the LD content of vip1Δ/Δ grown in the medium with β-glycerol phosphate as the Pi source was significantly reduced. In summary, the increased Pi demand and the decreased PHO pathway activity in vip1Δ/Δ ultimately lead to LD accumulation and cell membrane damage.

Tuning Receptor Properties of Metal-Amyloid Beta Complexes. Studies on the Interaction between Ni(II)-Aβ5-9 and Phosphates/Nucleotides

Amyloid-beta (Aβ) peptides, potentially relevant in the pathology of Alzheimer's disease, possess distinctive coordination properties, enabling an effective binding of transition-metal ions, with a preference for Cu(II). In this work, we found that a N-truncated Aβ analogue bearing a His-2 motif, Aβ5-9, forms a stable Ni(II) high-spin octahedral complex at a physiological pH of 7.4 with labile coordination sites and facilitates ternary interactions with phosphates and nucleotides. As the pH increased above 9, a spin transition from a high-spin to a low-spin square-planar Ni(II) complex was observed. Employing electrochemical techniques, we showed that interactions between the binary Ni(II)-Aβ5-9 complex and phosphate species result in significant changes in the Ni(II) oxidation signal. Thus, the Ni(II)-Aβ5-9 complex could potentially serve as a receptor in electrochemical biosensors for phosphate species. The obtained results could also be important for nickel toxicology.

The emerging role of phosphorus in human health

Phosphorus, an essential nutrient, performs vital functions in skeletal and non-skeletal tissues and is pivotal for energy production. The last two decades of research on the physiological importance of phosphorus have provided several novel insights about its dynamic nature as a nutrient performing functions as a phosphate ion. Phosphorous also acts as a signaling molecule and induces complex physiological responses. It is recognized that phosphorus homeostasis is critical for health. The intake of phosphorus by the general population world-wide is almost double the amount required to maintain health. This increase is attributed to the incorporation of phosphate containing food additives in processed foods purchased by consumers. Research findings assessed the impact of excessive phosphorus intake on cells' and organs' responses, and highlighted the potential pathogenic consequences. Research also identified a new class of bioactive phosphates composed of polymers of phosphate molecules varying in chain length. These polymers are involved in metabolic responses including hemostasis, brain and bone health, via complex mechanism(s) with positive or negative health effects, depending on their chain length. It is amazing, that phosphorus, a simple element, is capable of exerting multiple and powerful effects. The role of phosphorus and its polymers in the renal and cardiovascular system as well as on brain health appear to be important and promising future research directions.

Cycles, sources, and sinks: Conceptualizing how phosphate balance modulates carbon flux using yeast metabolic networks

Phosphates are ubiquitous molecules that enable critical intracellular biochemical reactions. Therefore, cells have elaborate responses to phosphate limitation. Our understanding of long-term transcriptional responses to phosphate limitation is extensive. Contrastingly, a systems-level perspective presenting unifying biochemical concepts to interpret how phosphate balance is critically coupled to (and controls) metabolic information flow is missing. To conceptualize such processes, utilizing yeast metabolic networks we categorize phosphates utilized in metabolism into cycles, sources and sinks. Through this, we identify metabolic reactions leading to putative phosphate sources or sinks. With this conceptualization, we illustrate how mass action driven flux towards sources and sinks enable cells to manage phosphate availability during transient/immediate phosphate limitations. We thereby identify how intracellular phosphate availability will predictably alter specific nodes in carbon metabolism, and determine signature cellular metabolic states. Finally, we identify a need to understand intracellular phosphate pools, in order to address mechanisms of phosphate regulation and restoration.

Stoichiometric niche, nutrient partitioning and resource allocation in a solitary bee are sex-specific and phosphorous is allocated mainly to the cocoon

Life histories of species may be shaped by nutritional limitations posed on populations. Yet, populations contain individuals that differ according to sex and life stage, each of which having different nutritional demands and experiencing specific limitations. We studied patterns of resource assimilation, allocation and excretion during the growth of the solitary bee Osmia bicornis (two sexes) under natural conditions. Adopting an ecological perspective, we assert that organisms ingest mutable organic molecules that are transformed during physiological processes and that the immutable atoms of the chemical elements composing these molecules may be allocated to specific functions, thereby influencing organismal fitness and life history. Therefore, using the framework of ecological stoichiometry, we investigated the multielemental (C, N, S, P, K, Na, Ca, Mg, Fe, Zn, Mn, Cu) compositions of six components of the bee elemental budget: food (pollen), eggs, pupae, adults, cocoons and excreta. The sexes differed fundamentally in the assimilation and allocation of acquired atoms, elemental phenotypes, and stoichiometric niches for all six components. Phosphorus, which supports larval growth, was allocated mainly (55-75%) to the cocoon after larval development was complete. Additionally, the majority (60-99%) of the Mn, Ca, Mg and Zn acquired during larval development was allocated to the cocoon, probably influencing bee fitness by conferring protection. We conclude that for holometabolous insects, considering only the chemical composition of the adult body within the context of nutritional ecology does not provide a complete picture. Low ratios of C to other nutrients, low N:P and high Na concentrations in excreta and cocoons may be important for local-scale nutrient cycling. Limited access to specific nutritional elements may hinder bee development in a sex-dependent manner, and N and P limitations, commonly considered elsewhere, may not play important roles in O. bicornis. Sexual dimorphism in nutritional limitations due to nutrient scarcity during the larval stage may influence bee population function and should be considered in bee conservation efforts.

A single Na+-Pi cotransporter in Toxoplasma plays key roles in phosphate import and control of parasite osmoregulation

Inorganic ions such as phosphate, are essential nutrients required for a broad spectrum of cellular functions and regulation. During infection, pathogens must obtain inorganic phosphate (P_i) from the host. Despite the essentiality of phosphate for all forms of life, how the intracellular parasite Toxoplasma gondii acquires P_i from the host cell is still unknown. In this study, we demonstrated that Toxoplasma actively internalizes exogenous P_i by exploiting a gradient of Na⁺ ions to drive P_i uptake across the plasma membrane. The Na⁺-dependent phosphate transport mechanism is electrogenic and functionally coupled to a cipargarmin sensitive Na⁺-H⁺-ATPase. Toxoplasma expresses one transmembrane P_i transporter harboring PHO4 binding domains that typify the PiT Family. This transporter named TgPiT, localizes to the plasma membrane, the inward buds of the endosomal organelles termed VAC, and many cytoplasmic vesicles. Upon P_i limitation in the medium, TgPiT is more abundant at the plasma membrane. We genetically ablated the PiT gene, and ΔTgPiT parasites are impaired in importing P_i and synthesizing polyphosphates. Interestingly, ΔTgPiT parasites accumulate 4-times more acidocalcisomes, storage organelles for phosphate molecules, as compared to parental parasites. In addition, these mutants have a reduced cell volume, enlarged VAC organelles, defects in calcium storage and a slightly alkaline pH. Overall, these mutants exhibit severe growth defects and have reduced acute virulence in mice. In survival mode, ΔTgPiT parasites upregulate several genes, including those encoding enzymes that cleave or transfer phosphate groups from phosphometabolites, transporters and ions exchangers localized to VAC or acidocalcisomes. Taken together, these findings point to a critical role of TgPiT for P_i supply for Toxoplasma and also for protection against osmotic stresses.

Inorganic phosphate (P_i) is indispensable for the biosynthesis of key cellular components, and is involved in many metabolic and signaling pathways. Transport across the plasma membrane is the first step in the utilization of P_i. The import mechanism of P_i by the intracellular parasite Toxoplasma is unknown. We characterized a transmembrane, high-affinity Na⁺-P_i cotransporter, named TgPiT, expressed by the parasite at the plasma membrane for P_i uptake. Interestingly, TgPiT is also localized to inward buds of the endosomal VAC organelles and some cytoplasmic vesicles. Loss of TgPiT results in a severe reduction in P_i internalization and polyphosphate levels, but stimulation of the biogenesis of phosphate-enriched acidocalcisomes. ΔTgPiT parasites have a shrunken cell body, enlarged VAC organelles, poor release of stored calcium and a mildly alkaline pH, suggesting a role for TgPiT in the maintenance of overall ionic homeostasis. ΔTgPiT parasites are poorly infectious in vitro and in mice. The mutant appears to partially cope with the absence of TgPiT by up-regulating genes coding for ion transporters and enzymes catalyzing phosphate group transfer. Our data highlight a scenario in which the role of TgPiT in P_i and Na⁺ transport is functionally coupled with osmoregulation activities central to sustain Toxoplasma survival.

Phosphate Metabolism in Health and Disease

Phosphorus, a 5A element with atomic weight of 31, comprises just over 0.6% of the composition by weight of plants and animals. Three isotopes are available for studying phosphorus metabolism and kinetics. ³¹P is stable, whereas the radioactive isotope ³³P has a half-life of 25 days and ³²P has a half-life of 14 days. Phosphate ester and phosphoanhydride are common chemical linkages and phosphorus is a key element in organic molecules involved in a wide variety of essential cellular functions. These include biochemical energy transfer via adenosine triphosphate (ATP), maintenance of genetic information with nucleotides DNA and RNA, intracellular signaling via cyclic adenosine monophosphate (cAMP), and membrane structural integrity via glycerophospholipids. However, this review focuses on the metabolism of inorganic phosphorus (Pi) acting as a weak acid. Phosphoric acid has all three hydrogens attached to oxygen and is a weak diprotic acid. It has 3 pKa values: pH 2.2, pH 7.2, and pH 12.7. At physiological pH of 7.4, Pi exists as both H₂PO₄^(-) and HPO₄^(2-) and acts as an extracellular fluid (ECF) buffer. Pi is the form transported across tissue compartments and cells. Measurement of Pi in biological fluids is based on its reaction with ammonium molybdate which does not measure organic phosphorus. In humans, 80% of the body phosphorus is present in the form of calcium phosphate crystals (apatite) that confer hardness to bone and teeth, and function as the major phosphorus reservoir (Fig. 1). The remainder is present in soft tissues and ECF. Dietary phosphorus, comprising both inorganic and organic forms, is digested in the upper gastrointestinal tract. Absorbed Pi is transported to and from bone, skeletal muscle and soft tissues, and kidney at rates determined by ECF Pi concentration, rate of blood flow, and activity of cell Pi transporters (Fig. 2). During growth, there is net accretion of phosphorus, and with aging, net loss of phosphorus occurs. The bone phosphorus reservoir is depleted and repleted by overall phosphorus requirement. Skeletal muscle is rich in phosphorus used in essential biochemical energy transfer. Kidney is the main regulator of ECF Pi concentration by virtue of having a tubular maximum reabsorptive capacity for Pi (TmPi) that is under close endocrine control. It is also the main excretory pathway for Pi surplus which is passed in urine. Transcellular and paracellular Pi transports are performed by a number of transport mechanisms widely distributed in tissues, and particularly important in gut, bone, and kidney. Pi transporters are regulated by a hormonal axis comprising fibroblast growth factor 23 (FGF23), parathyroid hormone (PTH), and 1,25 dihydroxy vitamin D (1,25D). Pi and calcium (Ca) metabolism are intimately interrelated, and clinically neither can be considered in isolation. Diseases of Pi metabolism affect bone as osteomalacia/rickets, soft tissues as ectopic mineralization, skeletal muscle as myopathy, and kidney as nephrocalcinosis and urinary stone formation. Fig. 1 Content of phosphorus in human adult: skeleton, soft tissue, and extracellular fluid (grams, log scale). Corresponding data for calcium are shown for comparison Fig. 2 Phosphate (Pi) transport to and from tissue compartments in mg/24 h. At a dietary phosphorus of 1400 mg, 1120 mg is absorbed in upper intestine to the ECF, 210 mg returned to intestine by endogenous secretion, resulting in 910 mg net Pi absorption and 490 mg fecal excretion. At bone, 180 mg is deposited by bone formation and 180 mg return to the ECF by bone resorption. At kidney, 5040 mg is filtered at the glomerulus and 4130 mg return to the ECF by tubular reabsorption with 910 mg excreted in the urine. In soft tissue, Pi is exchanged between ECF and cells.

Mechanistic Insight of Sensing Hydrogen Phosphate in Aqueous Medium by Using Lanthanide(III)-Based Luminescent Probes

The development of synthetic lanthanide luminescent probes for selective sensing or binding anions in aqueous medium requires an understanding of how these anions interact with synthetic lanthanide probes. Synthetic lanthanide probes designed to differentiate anions in aqueous medium could underpin exciting new sensing tools for biomedical research and drug discovery. In this direction, we present three mononuclear lanthanide-based complexes, EuLCl₃ (1), SmLCl₃ (2), and TbLCl₃ (3), incorporating a hexadentate aminomethylpiperidine-based nitrogen-rich heterocyclic ligand L for sensing anion and establishing mechanistic insight on their binding activities in aqueous medium. All these complexes are meticulously studied for their preferential selectivities towards different anions such as HPO₄²⁻, SO₄²⁻, CH₃COO⁻, I⁻, Br⁻, Cl⁻, F⁻, NO₃⁻, CO₃²⁻/HCO₃⁻, and HSO₄⁻ at pH 7.4 in aqueous HEPES (2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid) buffer. Among the anions scanned, HPO₄²⁻ showed an excellent luminescence change with all three complexes. Job’s plot and ESI-MS support the 1:2 association between the receptors and HPO₄²⁻. Systematic spectrophotometric titrations of 1–3 against HPO₄²⁻ demonstrates that the emission intensities of 1 and 2 were enhanced slightly upon the addition of HPO₄²⁻ in the range 0.01–1 equiv and 0.01–2 equiv., respectively. Among the three complexes, complex 3 showed a steady quenching of luminescence throughout the titration of hydrogen phosphate. The lower and higher detection limits of HPO₄²⁻ by complexes 1 and 2 were determined as 0.1–4 mM and 0.4–3.2 mM, respectively, while complex 3 covered 0.2–100 μM. This concludes that all complexes demonstrated a high degree of sensitivity and selectivity towards HPO₄²⁻.

Lack of PTEN in osteocytes increases circulating phosphate concentrations by decreasing intact fibroblast growth factor 23 levels

Fibroblast growth factor 23 (FGF23) has been centric to the regulation of phosphate (Pi) metabolism; however, the regulatory network of FGF23 in osteocytes has not yet been defined in detail. We herein investigated the role of PTEN (phosphatase and tensin homolog deleted from chromosome 10) in this regulation. We created mice lacking PTEN expression mainly in osteocytes by crossing Pten-flox mice with Dmp1-Cre mice. The lack of PTEN in the osteocytes of these mice was associated with decreased skeletal and serum intact FGF23 levels, which, in turn, resulted in reductions of urinary Pi excretion and elevations of serum Pi levels. Mechanistically, the knockdown of PTEN expression in osteoblastic UMR106 cells activated the AKT/mTORC1 (mechanistic target of rapamycin complex 1) pathway and this was associated with reductions in Fgf23 expression. Furthermore, the suppression of Fgf23 expression by PTEN knockdown or insulin simulation in UMR106 cells was partially restored by the treatment with the mTORC1 inhibitor, rapamycin. These results suggest that FGF23 expression in osteoblastic cells is in part regulated through the AKT/mTORC1 pathway and provide new insights into our understanding of the regulatory network of Pi metabolism.

Modulating phosphate consumption, a novel therapeutic approach for the control of cancer cell proliferation and tumorigenesis

Phosphorus, often in the form of inorganic phosphate (Pi), is critical to cellular function on many levels; it is required as an integral component of kinase signaling, in the formation and function of DNA and lipids, and energy metabolism in the form of ATP. Accordingly, crucial aspects of cell mitosis - such as DNA synthesis and ATP energy generation - elevate the cellular requirement for Pi, with rapidly dividing cells consuming increased levels. Mechanisms to sense, respond, acquire, accumulate, and potentially seek Pi have evolved to support highly proliferative cellular states such as injury and malignant transformation. As such, manipulating Pi availability to target rapidly dividing cells presents a novel strategy to reduce or prevent unrestrained cell growth. Currently, limited knowledge exists regarding how modulating Pi consumption by pre-cancerous cells might influence the initiation of aberrant growth during malignant transformation, and if reducing the bioavailability or suppressing Pi consumption by malignant cells could alter tumorigenesis. The concept of targeting Pi-regulated pathways and/or consumption by pre-cancerous or tumor cells represents a novel approach to cancer prevention and control, although current data remains insufficient as to rigorously assess the therapeutic value and physiological relevance of this strategy. With this review, we present a critical evaluation of the paradox of how an element critical to essential cellular functions can, when available in excess, influence and promote a cancer phenotype. Further, we conjecture how Pi manipulation could be utilized as a therapeutic intervention, either systemically or at the cell level, to ultimately suppress or treat cancer initiation and/or progression.

Inorganic Phosphate (Pi) Signaling in Endothelial Cells: A Molecular Basis for Generation of Endothelial Microvesicles in Uraemic Cardiovascular Disease

Hyperphosphataemia increases cardiovascular mortality in patients with kidney disease. Direct effects of high inorganic phosphate (Pi) concentrations have previously been demonstrated on endothelial cells (ECs), including generation of procoagulant endothelial microvesicles (MVs). However, no mechanism directly sensing elevated intracellular Pi has ever been described in mammalian cells. Here, we investigated the hypothesis that direct inhibition by Pi of the phosphoprotein phosphatase PP2A fulfils this sensing role in ECs, culminating in cytoskeleton disruption and MV generation. ECs were treated with control (1 mM [Pi]) vs. high (2.5 mM [Pi]), a condition that drives actin stress fibre depletion and MV generation demonstrated by confocal microscopy of F-actin and NanoSight Nanoparticle tracking, respectively. Immuno-blotting demonstrated that high Pi increased p-Src, p-PP2A-C and p-DAPK-1 and decreased p-TPM-3. Pi at 100 μM directly inhibited PP2A catalytic activity. Inhibition of PP2A enhanced inhibitory phosphorylation of DAPK-1, leading to hypophosphorylation of Tropomyosin-3 at S284 and MV generation. p-Src is known to perform inhibitory phosphorylation on DAPK-1 but also on PP2A-C. However, PP2A-C can itself dephosphorylate (and therefore inhibit) p-Src. The direct inhibition of PP2A-C by Pi is, therefore, amplified by the feedback loop between PP2A-C and p-Src, resulting in further PP2A-C inhibition. These data demonstrated that PP2A/Src acts as a potent sensor and amplifier of Pi signals which can further signal through DAPK-1/Tropomyosin-3 to generate cytoskeleton disruption and generation of potentially pathological MVs.

High phosphate actively induces cytotoxicity by rewiring pro-survival and pro-apoptotic signaling networks in HEK293 and HeLa cells

Inorganic phosphate (Pi) is an essential nutrient for human health. Due to the changes in our dietary pattern, dietary Pi overload engenders systemic phosphotoxicity, including excessive Pi-related vascular calcification and chronic tissue injury. The molecular mechanisms of the seemingly distinct phenotypes remain elusive. In this study, we investigated Pi-mediated cellular response in HEK293 and HeLa cells. We found that abnormally high Pi directly mediates diverse cellular toxicity in a dose-dependent manner. Up to 10 mM extracellular Pi promotes cell proliferation by activating AKT signaling cascades and augmenting cell cycle progression. By introducing additional Pi, higher than the concentration of 40 mM, we observed significant cell damage caused by the interwoven Pi-related biological processes. Elevated Pi activates mitogen-activated protein kinase (MAPK) signaling, encompassing extracellular signal-regulated kinase 1/2 (ERK1/2), p38 and Jun amino-terminal kinase (JNK), which consequently potentiates Pi triggered lethal epithelial-mesenchymal transition (EMT). Synergistically, high Pi-caused endoplasmic reticulum (ER) stress also contributes to apparent apoptosis. To counteract, Pi-activated AKT signaling promotes cell survival by activating the mammalian target of rapamycin (mTOR) signaling and blocking ER stress. Pharmacologically or genetically abrogating Pi transport, the impact of high Pi-induced cytotoxicity could be reduced. Taken together, abnormally high extracellular Pi results in a broad spectrum of toxicity by rewiring complicated signaling networks that control cell growth, cell death, and homeostasis.

Clinical Potential of Targeting Fibroblast Growth Factor-23 and αKlotho in the Treatment of Uremic Cardiomyopathy

Chronic kidney disease is highly prevalent, affecting 10% to 15% of the adult population worldwide and is associated with increased cardiovascular morbidity and mortality. As chronic kidney disease worsens, a unique cardiovascular phenotype develops characterized by heart muscle disease, increased arterial stiffness, atherosclerosis, and hypertension. Cardiovascular risk is multifaceted, but most cardiovascular deaths in patients with advanced chronic kidney disease are caused by heart failure and sudden cardiac death. While the exact drivers of these deaths are unknown, they are believed to be caused by uremic cardiomyopathy: a specific pattern of myocardial hypertrophy, fibrosis, with both diastolic and systolic dysfunction. Although the pathogenesis of uremic cardiomyopathy is likely to be multifactorial, accumulating evidence suggests increased production of fibroblast growth factor-23 and αKlotho deficiency as potential major drivers of cardiac remodeling in patients with uremic cardiomyopathy. In this article we review the increasing understanding of the physiology and clinical aspects of uremic cardiomyopathy and the rapidly increasing knowledge of the biology of both fibroblast growth factor-23 and αKlotho. Finally, we discuss how dissection of these pathological processes is aiding the development of therapeutic options, including small molecules and antibodies, directly aimed at improving the cardiovascular outcomes of patients with chronic kidney disease and end-stage renal disease.

Coumarin-based colorimetric-fluorescent sensors for the sequential detection of Zn2+ ion and phosphate anions and applications in cell imaging

Two novel coumarin based fluorescent sensors CHP and CHS have been synthesized for the sequential detection of Zn²⁺ ion and phosphate anion (PA) in DMF/HEPES buffer medium (1/5 v/v, 10 mM, pH = 7.4). On the addition of Zn²⁺ ion to the solution of CHP or CHS resulted in a pronounced fluorescence enhancement, accompanying noticeable color change (under UV or daylight), while there was hardly obvious change with other competing metal ions co-existing. The detection limits (DL) of CHP and CHS toward Zn²⁺ were separately determined as 1.03 × 10^-7 (R² = 0.9886) and 1.87 × 10^-7 (R² = 0.9902). The PET binding processes were affirmed by spectroscopic techniques, HRMS experiments and theoretical calculations. Subsequently, the CHP-Zn²⁺ or CHS-Zn²⁺ complexes showed high selectivity fluorescence quenching toward PA by snatching Zn²⁺ ion from its complex and the binding processes were reversible. DLs were calculated as 2.07 × 10^-7 M (R² = 0.9928) and 2.63 × 10^-7 M (R² = 0.9954), respectively. Furthermore, the cell imaging experiments demonstrated that the sensors were capable of detecting of Zn²⁺ and PA in vitro cells.

How do we sense phosphate to regulate serum phosphate level?

Abnormal phosphate levels result in several pathological conditions such as rickets/osteomalacia and ectopic calcification indicating that there must be a system that regulates phosphate level within a narrow range. FGF23 has been shown to be an essential hormone regulating serum phosphate level. FGF23 binds to Klotho-FGF receptor complex to reduce serum phosphate level. Several reports suggested that FGF receptor is involved in the regulation of FGF23 production. It has been also shown that high extracellular phosphate can activate several intracellular signaling pathways. However, it has been unclear whether and how phosphate regulates FGF23 production in vivo. Our recent results indicate that high extracellular phosphate directly activates FGF receptor 1 and the downstream intracellular signaling enhances FGF23 production. Thus, there is a negative feedback system for the regulation of serum phosphate level involving FGF receptor and FGF23. We propose that FGF receptor works at least as one of phosphate sensors in the maintenance of serum phosphate level.

Phosphoproteomic Profiling Reveals the Importance of CK2, MAPKs and CDPKs in Response to Phosphate Starvation in Rice

Phosphorus is one of the most important macronutrients required for plant growth and development. The importance of phosphorylation modification in regulating phosphate (Pi) homeostasis in plants is emerging. We performed phosphoproteomic profiling to characterize proteins whose degree of phosphorylation is altered in response to Pi starvation in rice root. A subset of 554 proteins, including 546 down-phosphorylated and eight up-phosphorylated proteins, exhibited differential phosphorylation in response to Pi starvation. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis with the differentially phosphorylated proteins indicated that RNA processing, transport, splicing and translation and carbon metabolism played critical roles in response to Pi starvation in rice. Levels of phosphorylation of four mitogen-activated protein kinases (MAPKs), including OsMAPK6, five calcium-dependent protein kinases (CDPKs) and OsCK2β3 decreased in response to Pi starvation. The decreased phosphorylation level of OsMAPK6 was confirmed by Western blotting. Mutation of OsMAPK6 led to Pi accumulation under Pi-sufficient conditions. Motif analysis indicated that the putative MAPK, casein kinase 2 (CK2) and CDPK substrates represented about 54.4%, 21.5% and 4.7%, respectively, of the proteins exhibiting differential phosphorylation. Based on the motif analysis, 191, 151 and 46 candidate substrates for MAPK, CK2 and CDPK were identified. These results indicate that modification of phosphorylation profiles provides complementary information on Pi-starvation-induced processes, with CK2, MAPK and CDPK protein kinase families playing key roles in these processes in rice.

A Control Region Near the Fibroblast Growth Factor 23 Gene Mediates Response to Phosphate, 1,25(OH)2D3, and LPS In Vivo

Fibroblast growth factor 23 (FGF23) is a bone-derived hormone involved in the control of phosphate (P) homeostasis and vitamin D metabolism. Despite advances, however, molecular details of this gene's regulation remain uncertain. In this report, we created mouse strains in which four epigenetically marked FGF23 regulatory regions were individually deleted from the mouse genome using CRISPR/Cas9 gene-editing technology, and the consequences of these mutations were then assessed on Fgf23 expression and regulation in vivo. An initial analysis confirmed that bone expression of Fgf23 and circulating intact FGF23 (iFGF23) were strongly influenced by both chronic dietary P treatment and acute injection of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. However, further analysis revealed that bone Fgf23 expression and iFGF23 could be rapidly upregulated by dietary P within 3 and 6 hours, respectively; this acute upregulation was lost in the FGF23-PKO mouse containing an Fgf23 proximal enhancer deletion but not in the additional enhancer-deleted mice. Of note, prolonged dietary P treatment over several days led to normalization of FGF23 levels in the FGF23-PKO mouse, suggesting added complexity associated with P regulation of FGF23. Treatment with 1,25(OH)2D3 also revealed a similar loss of Fgf23 induction and blood iFGF23 levels in this mouse. Finally, normal lipopolysaccharide (LPS) induction of Fgf23 expression was also compromised in the FGF23-PKO mouse, a result that, together with our previous report, indicates that the action of LPS on Fgf23 expression is mediated by both proximal and distal Fgf23 enhancers. These in vivo data provide key functional insight into the genomic enhancers through which Fgf23 expression is mediated.

In situ polymerization on nanoscale metal-organic frameworks for enhanced physiological stability and stimulus-responsive intracellular drug delivery

Metal-organic framework (MOF) nanoparticles have shown great potential as carrier platforms in theranostic applications. However, their poor physiological stability in phosphate-based media has limited their biological applications. Here, we studied the dissociation of MOF nanoparticles under physiological conditions, both in vitro and in vivo, and developed an in situ polymerization strategy on MOF nanoparticles for enhanced stability under physiological conditions and stimulus-responsive intracellular drug release. With polymer wrapped on the surface serving as a shield, the nanoscale MOFs were protected from decomposition by phosphate ions or acid and prevented the loaded cargos from leaking. An in vivo positron emission tomography (PET) study of 64Cu-labelled porphyrinic MOF indicated prolonged circulation time of the in situ polymerized MOF nanoparticles and greater tumor accumulation than unmodified MOF nanoparticles. With enhanced stability, cargos loaded into MOF nanoparticles or prodrugs conjugated on the surface can be efficiently delivered and released upon stimulus-responsive cleavage.

Fibroblast growth factor 23 and α-Klotho co-dependent and independent functions

PURPOSE OF REVIEW

The current review examines what is known about the FGF-23/α-Klotho co-dependent and independent pathophysiological effects, and whether FGF-23 and/or α-Klotho are potential therapeutic targets.

RECENT FINDINGS

FGF-23 is a hormone derived mainly from bone, and α-Klotho is a transmembrane protein. Together they form a trimeric signaling complex with FGFRs in target tissues to mediate the physiological functions of FGF-23. Local and systemic factors control FGF-23 release from osteoblast/osteocytes in bone, and circulating FGF-23 activates FGFR/α-Klotho complexes in kidney proximal and distal renal tubules to regulate renal phosphate excretion, 1,25 (OH)2D metabolism, sodium and calcium reabsorption, and ACE2 and α-Klotho expression. The resulting bone-renal-cardiac-immune networks provide a new understanding of bone and mineral homeostasis, as well as identify other biological effects FGF-23. Direct FGF-23 activation of FGFRs in the absence of α-Klotho is proposed to mediate cardiotoxic and adverse innate immune effects of excess FGF-23, particularly in chronic kidney disease, but this FGF-23, α-Klotho-independent signaling is controversial. In addition, circulating soluble Klotho (sKl) released from the distal tubule by ectodomain shedding is proposed to have beneficial health effects independent of FGF-23.

SUMMARY

Separation of FGF-23 and α-Klotho independent functions has been difficult in mammalian systems and understanding FGF-23/α-Klotho co-dependent and independent effects are incomplete. Antagonism of FGF-23 is important in treatment of hypophosphatemic disorders caused by excess FGF-23, but its role in chronic kidney disease is uncertain. Administration of recombinant sKl is an unproven therapeutic strategy that theoretically could improve the healt span and lifespan of patients with α-Klotho deficiency.

Endocrine regulation of MFS2 by branchless controls phosphate excretion and stone formation in Drosophila renal tubules

How inorganic phosphate (Pi) homeostasis is regulated in Drosophila is currently unknown. We here identify MFS2 as a key Pi transporter in fly renal (Malpighian) tubules. Consistent with its role in Pi excretion, we found that dietary Pi induces MFS2 expression. This results in the formation of Malpighian calcium-Pi stones, while RNAi-mediated knockdown of MFS2 increases blood (hemolymph) Pi and decreases formation of Malpighian tubule stones in flies cultured on high Pi medium. Conversely, microinjection of adults with the phosphaturic human hormone fibroblast growth factor 23 (FGF23) induces tubule expression of MFS2 and decreases blood Pi. This action of FGF23 is blocked by genetic ablation of MFS2. Furthermore, genetic overexpression of the fly FGF branchless (bnl) in the tubules induces expression of MFS2 and increases Malpighian tubule stones suggesting that bnl is the endogenous phosphaturic hormone in adult flies. Finally, genetic ablation of MFS2 increased fly life span, suggesting that Malpighian tubule stones are a key element whereby high Pi diet reduces fly longevity previously reported by us. In conclusion, MFS2 mediates excretion of Pi in Drosophila, which is as in higher species under the hormonal control of FGF-signaling.

Phosphate Assay Kit in One Cell for Electrochemical Detection of Intracellular Phosphate Ions at Single Cells

In this paper, phosphate assay kit in one cell is realized for the electrochemical detection of intracellular phosphate ions at single cells. The components of the phosphate assay kit, including maltose phosphorylase, maltose, mutarotase, and glucose oxidase, are electrochemically injected into a living cell through a nanometer-sized capillary with the ring electrode at the tip. These components react with phosphate ions inside the cell to generate hydrogen peroxide that is electrochemically oxidized at the ring electrode for the qualification of intracellular phosphate ions. An average 1.7 nA charge was collected from eight individual cells, suggesting an intracellular phosphate concentration of 2.1 mM. The establishment in the electrochemical measurement of phosphate ions provides a special strategy to monitor the fluctuation of intracellular phosphate at single cells, which is significant for the future investigation of phosphate signal transduction pathway.

Tissue nonspecific alkaline phosphatase promotes calvarial progenitor cell cycle progression and cytokinesis via Erk1,2

Bone growth is dependent upon the presence of self-renewing progenitor cell populations. While the contribution of Tissue Nonspecific Alkaline Phosphatase (TNAP) enzyme activity in promoting bone mineralization when expressed in differentiated bone forming cells is well understood, little is known regarding the role of TNAP in bone progenitor cells. We previously found diminished proliferation in the calvarial MC3T3E1 cell line upon suppression of TNAP by shRNA, and in calvarial cells and tissues of TNAP^-/- mice. These findings indicate that TNAP promotes cell proliferation. Here we investigate how TNAP mediates this effect. Results show that TNAP is essential for calvarial progenitor cell cycle progression and cytokinesis, and that these effects are mediated by inorganic phosphate and Erk1/2. Levels of active Erk1/2 are significantly diminished in TNAP deficient cranial cells and tissues even in the presence of inorganic phosphate. Moreover, in the absence of TNAP, FGFR2 expression levels are high and FGF2 rescues phospho-Erk1/2 levels and cell cycle abnormalities to a significantly greater extent than inorganic phosphate. Based upon the data we propose a model in which TNAP stimulates Erk1/2 activity via both phosphate dependent and independent mechanisms to promote cell cycle progression and cytokinesis in calvarial bone progenitor cells. Concomitantly, TNAP feeds back to inhibit FGFR2 expression. These results identify a novel mechanism by which TNAP promotes calvarial progenitor cell renewal and indicate that converging pathways exist downstream of FGF signaling and TNAP activity to control craniofacial skeletal development.

Nephronectin Expression is Inhibited by Inorganic Phosphate in Osteoblasts

Nephronectin (Npnt), an extracellular matrix protein, is known to be a ligand of integrin α8β1, and it has also been known to play critical roles as various organs. In the present study, elevated extracellular inorganic phosphate (Pi) strongly inhibited the expression of Npnt in MC3T3-E1 cells, while the existence of extracellular calcium (Ca) was indispensable for its effect. Furthermore, Pi-induced inhibition of Npnt gene expression was recovered by inhibitors of both sodium-dependent Pi transporter (Pit) and fibroblast growth factor receptors (Fgfrs). These results demonstrated that Npnt gene expression is regulated by extracellular Pi via Pit and Fgfrs.

Enzymatic Transition States and Drug Design

Transition state theory teaches that chemically stable mimics of enzymatic transition states will bind tightly to their cognate enzymes. Kinetic isotope effects combined with computational quantum chemistry provides enzymatic transition state information with sufficient fidelity to design transition state analogues. Examples are selected from various stages of drug development to demonstrate the application of transition state theory, inhibitor design, physicochemical characterization of transition state analogues, and their progress in drug development.

Role of phosphate sensing in bone and mineral metabolism

Inorganic phosphate (P_i) is essential for signal transduction and cell metabolism, and is also an essential structural component of the extracellular matrix of the skeleton. P_i is sensed in bacteria and yeast at the plasma membrane, which activates intracellular signal transduction to control the expression of P_i transporters and other genes that control intracellular P_i levels. In multicellular organisms, P_i homeostasis must be maintained in the organism and at the cellular level, requiring an endocrine and metabolic P_i-sensing mechanism, about which little is currently known. This Review will discuss the metabolic effects of P_i, which are mediated by P_i transporters, inositol pyrophosphates and SYG1-Pho81-XPR1 (SPX)-domain proteins to maintain cellular phosphate homeostasis in the musculoskeletal system. In addition, we will discuss how P_i is sensed by the human body to regulate the production of fibroblast growth factor 23 (FGF23), parathyroid hormone and calcitriol to maintain serum levels of P_i in a narrow range. New findings on the crosstalk between iron and P_i homeostasis in the regulation of FGF23 expression will also be outlined. Mutations in components of these metabolic and endocrine phosphate sensors result in genetic disorders of phosphate homeostasis, cardiomyopathy and familial basal ganglial calcifications, highlighting the importance of this newly emerging area of research.

Phosphate as a Signaling Molecule and Its Sensing Mechanism

In mammals, phosphate balance is maintained by influx and efflux via the intestines, kidneys, bone, and soft tissue, which involves multiple sodium/phosphate (Na+/Pi) cotransporters, as well as regulation by several hormones. Alterations in the levels of extracellular phosphate exert effects on both skeletal and extra-skeletal tissues, and accumulating evidence has suggested that phosphate itself evokes signal transduction to regulate gene expression and cell behavior. Several in vitro studies have demonstrated that an elevation in extracellular Piactivates fibroblast growth factor receptor, Raf/MEK (mitogen-activated protein kinase/ERK kinase)/ERK (extracellular signal-regulated kinase) pathway and Akt pathway, which might involve the type III Na+/Picotransporter PiT-1. Excessive phosphate loading can lead to various harmful effects by accelerating ectopic calcification, enhancing oxidative stress, and dysregulating signal transduction. The responsiveness of mammalian cells to altered extracellular phosphate levels suggests that they may sense and adapt to phosphate availability, although the precise mechanism for phosphate sensing in mammals remains unclear. Unicellular organisms, such as bacteria and yeast, use some types of Pitransporters and other molecules, such as kinases, to sense the environmental Piavailability. Multicellular animals may need to integrate signals from various organs to sense the phosphate levels as a whole organism, similarly to higher plants. Clarification of the phosphate-sensing mechanism in humans may lead to the development of new therapeutic strategies to prevent and treat diseases caused by phosphate imbalance.

Superoxide dismutase activity enabled by a redox-active ligand rather than metal

Reactive oxygen species are integral to many physiological processes. Although their roles are still being elucidated, they seem to be linked to a variety of disorders and may represent promising drug targets. Mimics of superoxide dismutases, which catalyse the decomposition of O₂^•- to H₂O₂ and O₂, have traditionally used redox-active metals, which are toxic outside of a tightly coordinating ligand. Purely organic antioxidants have also been investigated but generally require stoichiometric, rather than catalytic, doses. Here, we show that a complex of the redox-inactive metal zinc(II) with a hexadentate ligand containing a redox-active quinol can catalytically degrade superoxide, as demonstrated by both reactivity assays and stopped-flow kinetics studies of direct reactions with O₂^•- and the zinc(II) complex. The observed superoxide dismutase catalysis has an important advantage over previously reported work in that it is hastened, rather than impeded, by the presence of phosphate, the concentration of which is high under physiological conditions.