Autocrine production of prostaglandin F2αenhances phenotypic transformation of normal rat kidney fibroblasts

CYP24A1 and TRPC3 Gene Expression in Kidneys and Their Involvement in Calcium and Phosphate Metabolism in Laying Hens

Ca and P homeostasis across the egg-laying cycle is a complex process involving absorption in the small intestine, reabsorption/excretion in the kidneys, and eggshell gland secretion. Diets with inadequate calcium and phosphorus can interfere with their absorption and digestibility, resulting in eggshell quality losses and reduced productive life, affecting egg production and welfare. A better understanding of gene expression profiles in the kidneys of laying hens during the late egg-laying period could clarify the renal role in mineral metabolism at this late stage. Therefore, the performance, egg quality and bone integrity-related traits, and expression profiles of kidney candidate genes were evaluated in 73-week-old laying hens receiving different Ca and P ratios in their diet: a high Ca/P ratio (HR, 22.43), a low ratio (LR, 6.71), and a medium ratio (MR, 11.43). The laying hens receiving the HR diet had improved egg production and eggshell quality traits compared to the other two groups. Humerus length was shorter in the HR than in the other groups. The CYP24A1 and TRPC3 genes were differentially expressed (p.adj ≤ 0.05) among the groups. Therefore, their expression profiles could be involved in calcium and phosphate transcellular transport in 73-week-old laying hens as a way to keep mineral absorption at adequate levels.

Droplet Digital PCR Is a Novel Screening Method Identifying Potential Cardiac G-Protein-Coupled Receptors as Candidate Pharmacological Targets in a Rat Model of Pressure-Overload-Induced Cardiac Dysfunction

The identification of novel drug targets is needed to improve the outcomes of heart failure (HF). G-protein-coupled receptors (GPCRs) represent the largest family of targets for already approved drugs, thus providing an opportunity for drug repurposing. Here, we aimed (i) to investigate the differential expressions of 288 cardiac GPCRs via droplet digital PCR (ddPCR) and bulk RNA sequencing (RNAseq) in a rat model of left ventricular pressure-overload; (ii) to compare RNAseq findings with those of ddPCR; and (iii) to screen and test for novel, translatable GPCR drug targets in HF. Male Wistar rats subjected to transverse aortic constriction (TAC, n = 5) showed significant systolic dysfunction vs. sham operated animals (SHAM, n = 5) via echocardiography. In TAC vs. SHAM hearts, RNAseq identified 69, and ddPCR identified 27 significantly differentially expressed GPCR mRNAs, 8 of which were identified using both methods, thus showing a correlation between the two methods. Of these, Prostaglandin-F2α-receptor (Ptgfr) was further investigated and localized on cardiomyocytes and fibroblasts in murine hearts via RNA-Scope. Antagonizing Ptgfr via AL-8810 reverted angiotensin-II-induced cardiomyocyte hypertrophy in vitro. In conclusion, using ddPCR as a novel screening method, we were able to identify GPCR targets in HF. We also show that the antagonism of Ptgfr could be a novel target in HF by alleviating cardiomyocyte hypertrophy.

Epithelial-fibroblast cross talk aggravates the impact of the nephrotoxin ochratoxin A

BACKGROUND

Chronic nephropathies result from different pathogenic agents, including nutritional factors triggering vicious pathophysiological cycles. Ochratoxin A (OTA) is a globally occurring nephrotoxic mycotoxin detectable in a variety of foodstuff and suspected to cause tubulointerstitial damage. The underlying mechanisms are not sufficiently understood, compromising risk assessment. Because crosstalk of proximal tubule cells with fibroblasts is crucial for tubulointerstitial damage, we investigated the effects of OTA in co-culture of these two cell types.

METHODS

Rat renal proximal tubule cells (NRK-52E) and renal fibroblasts (NRK-49F) were exposed to nanomolar OTA concentrations under mono- and/or co-culture conditions for up to 48 h. We determined the impact on inflammation-, EMT- and fibrosis-associated proteins as well as microRNAs by western blot or qPCR, respectively. Alterations in cell morphology were quantitatively assessed. The roles of miRs, COX-2 and ERK1/2 in OTA-induced effects were investigated by specific inhibition.

FINDINGS

Only under co-culture condition, OTA caused an increase of vimentin, fibronectin and miR-21 and a decrease of collagen III, E-cadherin, COX-2 and WISP1 mRNA abundance in NRK-52E cells. In NRK-49F cells, OTA induced an increase of N-cadherin, COX-2, WISP1 in co-culture only. The OTA-induced increase of fibronectin in NRK-52E cells was prevented by simultaneous inhibition of miR-21 and -200a, COX-2 or ERK1/2. The OTA-induced increase of COX-2 in NRK-49F cells was prevented by inhibition of miR-21 and -200a or ERK1/2.

INTERPRETATION

Our results show that the complete nephropathic potential of nanomolar OTA, leading to EMT, is unveiled when cellular crosstalk is possible. In monoculture, the nephropathic potential is underestimated.

RESEARCH IN CONTEXT

Chronic nephropathies are a severe health burden and the result of different pathogenic mechanisms, including nutritional factors that trigger vicious pathophysiological cycles. Ochratoxin A (OTA) is a ubiquitous, globally occurring nephrotoxic mycotoxin detectable in a variety of foodstuff and suspected to cause tubulointerstitial damage. Because underlying pathomechanisms are unclear, risk assessment is problematic. Crosstalk of proximal tubule cells (the main target of OTA) with fibroblasts is crucial for the development of tubulointerstitial damage. We show that during co-culture of proximal tubule cells and fibroblasts, OTA-induced effects (e.g. epithelial-mesenchymal transition (EMT)) change significantly as compared to monoculture. Our results show that the complete nephropathic potential of OTA is unveiled when cellular crosstalk is possible. In monoculture, the nephropathic potential of OTA is underestimated.

Adhesion Stabilized en Masse Intracellular Electrical Recordings from Multicellular Assemblies

Coordinated collective electrochemical signals in multicellular assemblies, such as ion fluxes, membrane potentials, electrical gradients, and steady electric fields, play an important role in cell and tissue spatial organization during many physiological processes like wound healing, inflammatory responses, and hormone release. This mass of electric actions cumulates in an en masse activity within cell collectives which cannot be deduced from considerations at the individual cell level. However, continuously sampling en masse collective electrochemical actions of the global electrochemical activity of large-scale electrically coupled cellular assemblies with intracellular resolution over long time periods has been impeded by a lack of appropriate recording techniques. Here we present a bioelectrical interface consisting of low impedance vertical gold nanoelectrode interfaces able to penetrate the cellular membrane in the course of cellular adhesion, thereby allowing en masse recordings of intracellular electrochemical potentials that transverse electrically coupled NRK fibroblast, C2C12 myotube assemblies, and SH-SY5Y neuronal networks of more than 200,000 cells. We found that the intracellular electrical access of the nanoelectrodes correlates with substrate adhesion dynamics and that penetration, stabilization, and sealing of the electrode-cell interface involves recruitment of surrounding focal adhesion complexes and the anchoring of actin bundles, which form a caulking at the electrode base. Intracellular recordings were stable for several days, and monitoring of both basal activity as well as pharmacologically altered electric signals with high signal-to-noise ratios and excellent electrode coupling was performed.

Stimulation of fibrotic processes by the infrapatellar fat pad in cultured synoviocytes from patients with osteoarthritis: a possible role for prostaglandin f2α

OBJECTIVE

Stiffening of the joint is a feature of knee osteoarthritis (OA) that can be caused by fibrosis of the synovium. The infrapatellar fat pad (IPFP) present in the knee joint produces immune-modulatory and angiogenic factors. The goal of the present study was to investigate whether the IPFP can influence fibrotic processes in synovial fibroblasts, and to determine the role of transforming growth factor β (TGFβ) and prostaglandin F2α (PGF2α ) in these processes.

METHODS

Batches of fat-conditioned medium (FCM) were made by culturing pieces of IPFP obtained from the knees of 13 patients with OA. Human OA fibroblast-like synoviocytes (FLS) (from passage 3) were cultured in FCM with or without inhibitors of TGFβ/activin receptor-like kinase 5 or PGF2α for 4 days. The FLS were analyzed for production of collagen and expression of the gene for procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2; encoding lysyl hydroxylase 2b, an enzyme involved in collagen crosslinking) as well as the genes encoding α-smooth muscle actin and type I collagen α1 chain. In parallel, proliferation and migration of the synoviocytes were analyzed.

RESULTS

Collagen production and PLOD2 gene expression by the FLS were increased 1.8-fold (P < 0.05) and 6.0-fold (P < 0.01), respectively, in the presence of FCM, relative to control cultures without FCM. Moreover, the migration and proliferation of synoviocytes were stimulated by FCM. Collagen production was positively associated with PGF2α levels in the FCM (R = 0.89, P < 0.05), and inhibition of PGF2α levels reduced the extent of FCM-induced collagen production and PLOD2 expression. Inhibition of TGFβ signaling had no effect on the profibrotic changes.

CONCLUSION

These results indicate that the IPFP can contribute to the development of synovial fibrosis in the knee joint by increasing collagen production, PLOD2 expression, cell proliferation, and cell migration. In addition, whereas the findings showed that TGFβ is not involved, the more recently discovered profibrotic factor PGF2α appears to be partially involved in the regulation of profibrotic changes.

Purified culture systems for bovine oviductal stromal cells

Isolated stromal cells from the ampullary and isthmic parts of bovine oviductal tissues were cultured in monolayer and spheroid (cell aggregate) systems. Prostaglandin F2α (PGF) plays a crucial role in oviductal contraction and is produced by oviductal epithelial cells in cattle. Since stromal cells of many organs produce PGF, PGF production by bovine oviductal stromal cells was investigated. After PGF synthesis was confirmed, the utility of isolation and culture methods for oviductal stromal cells was evaluated by PGF production in the present study. The homogeneity of the cells was > 99%. PGF production of the cells was increased by tumor necrosis factor-α. The stromal cells aggregated and formed a spheroid by the treatments with several reagents. PGF production was higher in the spheroid culture than in the monolayer culture. The isolation and culture methods described here will facilitate studies of the physiological function of bovine oviductal stromal cells.

Role of Trpc channels, Stim1 and Orai1 in PGF(2α)-induced calcium signaling in NRK fibroblasts

Normal rat kidney (NRK) fibroblasts exhibit growth-dependent changes in electrophysiological properties and intracellular calcium dynamics. The transition from a quiescent state to a density-arrested state results in altered calcium entry characteristics. This coincides with modulation of the expression of the genes encoding the calcium channels Trpc1, Trpc6 and Orai1, and of the intracellular calcium sensor Stim1. In the present study we have used gene selective short hairpin (sh) RNAs against these various genes to investigate their role in (a) capacitative store-operated calcium entry (SOCE); (b) non-capacitative OAG-induced receptor-operated calcium entry (ROCE); and (c) prostaglandin F(2α) (PGF(2α))-induced Ca(2+)-oscillations in NRK fibroblasts. Intracellular calcium measurements revealed that knockdown of the genes encoding Trpc1, Orai1 and Stim1 each caused a significant reduction of SOCE in NRK cells, whereas knockdown of the gene encoding Trpc6 reduced only the OAG-induced ROCE. Furthermore, our data show that knockdown of the genes encoding Trpc1, Orai1 and Stim1, but not Trpc6, substantially reduced the frequency (up to 60%) of PGF(2α)-induced Ca(2+) oscillations in NRK cells. These results indicate that in NRK cells distinct calcium channels control the processes of SOCE, ROCE and PGF(2α)-induced Ca(2+) oscillations.

HPLC/MS/MS-based approaches for detection and quantification of eicosanoids

Eicosanoids are oxygenated, endogenous, unsaturated fatty acids derived from arachidonic acid. Detection and quantification of these compounds are of great interest because they play important roles in a number of significant diseases, including asthma, chronic obstructive pulmonary disease (COPD), cardiovascular disease, and cancer. Because the endogenous levels of eicosanoids are quite low, sensitive and specific analytical methods are required to reliably quantify these compounds. High-performance liquid chromatography mass spectrometry (HPLC/MS) has emerged as one of the main techniques used in eicosanoid profiling. Herein, we describe the main LC/MS techniques and principles as well as their application in eicosanoid analysis. In addition, a protocol is given for extracting eicosanoids from biological samples, using bronchoalveolar lavage fluid (BALF) as an example. The method and instrument optimization procedures are presented, followed by the analysis of eicosanoid standards using reverse phase HPLC interfaced with an ion trap mass spectrometer (LC/MS/MS). This protocol is intended to provide a broad description of the field for readers looking for an introduction to the methodologies involved in eicosanoid quantification.

Bimatoprost-induced calcium signaling in human T-cells does not involve prostanoid FP or TP receptors

PURPOSE

The prostamide bimatoprost and prostanoid FP receptor agonists are highly efficacious drugs for glaucoma treatment. The presence of both prostamide and prostanoid FP receptors in bimatoprost-sensitive preparations has made prostamide receptor classification difficult. This study investigated a novel bimatoprost-sensitive preparation.

METHODS

Human peripheral blood T lymphoblasts (Molt-3) and human osteoblasts (hFOB) were cultured for intracellular calcium signaling studies and quantitative real-time PCR analysis of RNA.

RESULTS

Bimatoprost stimulated concentration-related increases in [Ca(2 +)](i) in a human T-cell line that does not express human FP receptor/variants, according to PCR analysis. The calcium signal induced by bimatoprost was not antagonized by prostanoid FP receptor antagonist/partial agonist AL-8810 or selective TP receptor antagonist SQ 29548. Conversely, bimatoprost did not elevate [Ca(2 +)](i) in human osteoblasts, which were confirmed to contain RNA of human FP receptor/variants.

CONCLUSIONS

Molt-3 cells have been identified as a bimatoprost-sensitive preparation in which the activity of bimatoprost is independent of prostanoid FP receptors.

Role of the prostanoid FP receptor in action potential generation and phenotypic transformation of NRK fibroblasts

By using an shRNA approach to knockdown the expression of the prostaglandin (PG)-F(2alpha) receptor (FP-R), the role of PGF(2alpha) in the process of phenotypic transformation of normal rat kidney (NRK) fibroblasts has been studied. Our data show that PGF(2alpha) up-regulates Cox-2 expression both at the mRNA and protein level, indicating that activation of FP-R in NRK fibroblasts induces a positive feedback loop in the production PGF(2alpha). Knockdown of FP-R expression fully impaired the ability of PGF(2alpha) to induce a calcium response and subsequent depolarization in NRK cells. However, these cells could still undergo phenotypic transformation when treated with a combination of EGF and retinoic acid, but in contrast to the wild-type cells, this process was not accompanied by a membrane depolarization to -20 mV. Knockdown of FP-R expression also impaired the spontaneous firing of calcium action potentials by density-arrested NRK cells. These data show that a membrane depolarization is not a prerequisite for the acquisition of a transformed phenotype. Furthermore, our data provide the first direct evidence that activity of PGF(2alpha) by putative pacemaker cells underlies the generation of calcium action potentials in NRK monolayers.

Synthetic FP-prostaglandin-induced contraction of rat uterus smooth muscle in vitro

Numerous synthetic FP-class prostaglandin (PG) analogs stimulated the contraction of isolated non-pregnant female rat uterus in a concentration-dependent manner with the following agonist potencies: bimatoprost acid (17-phenyl-trinor PGF(2alpha); EC(50)=0.68+/-0.06 nM)=cloprostenol (EC(50)=0.73+/-0.01 nM)>travoprost acid (EC(50)=1.3+/-0.07 nM)>latanoprost acid (EC(50)=2.7+/-0.08 nM)>PGF(2alpha) (EC(50)=52+/-11 nM)>unoprostone (UF-021; EC(50)=310+/-101 nM)>S-1033 (EC(50)=610+/-4 nM)>bimatoprost (EC(50)=1130+/-173 nM). The FP-receptor antagonist, AL-8810, antagonized the contractile effects of PGF(2alpha) (K(i)=2.9+/-0.2 microM), travoprost acid (K(i)=0.6+/-0.1 microM) and bimatoprost (K(i)=0.2+/-0.02 microM). Agonist and antagonist potencies for rat uterus contraction by these PGs compared well with their potencies for inducing/blocking functional responses in other systems (r=0.83-0.94) except with bovine iris sphincter (r=0.2; p<0.7). In conclusion, the rat uterus contains functionally active FP-receptors whose activation by a variety of free acid and an amide forms of synthetic PGs leads to the contraction of this tissue and which can be pharmacologically blocked by an FP-receptor antagonist, AL-8810.

Prostaglandins in the kidney: developments since Y2K

There are five major PGs (prostaglandins/prostanoids) produced from arachidonic acid via the COX (cyclo-oxygenase) pathway: PGE(2), PGI(2) (prostacyclin), PGD(2), PGF(2alpha) and TXA(2) (thromboxane A(2)). They exert many biological effects through specific G-protein-coupled membrane receptors, namely EP (PGE(2) receptor), IP (PGI(2) receptor), DP (PGD(2) receptor), FP (PGF(2alpha) receptor) and TP (TXA(2) receptor) respectively. PGs are implicated in physiological and pathological processes in all major organ systems, including cardiovascular function, gastrointestinal responses, reproductive processes, renal effects etc. This review highlights recent insights into the role of each prostanoid in regulating various aspects of renal function, including haemodynamics, renin secretion, growth responses, tubular transport processes and cell fate. A thorough review of the literature since Y2K (year 2000) is provided, with a general overview of PGs and their synthesis enzymes, and then specific considerations of each PG/prostanoid receptor system in the kidney.

Stabilizing role of calcium store-dependent plasma membrane calcium channels in action-potential firing and intracellular calcium oscillations

In many biological systems, cells display spontaneous calcium oscillations (CaOs) and repetitive action-potential firing. These phenomena have been described separately by models for intracellular inositol trisphosphate (IP3)-mediated CaOs and for plasma membrane excitability. In this study, we present an integrated model that combines an excitable membrane with an IP3-mediated intracellular calcium oscillator. The IP3 receptor is described as an endoplasmic reticulum (ER) calcium channel with open and close probabilities that depend on the cytoplasmic concentration of IP3 and Ca2+. We show that simply combining this ER model for intracellular CaOs with a model for membrane excitability of normal rat kidney (NRK) fibroblasts leads to instability of intracellular calcium dynamics. To ensure stable long-term periodic firing of action potentials and CaOs, it is essential to incorporate calcium transporters controlled by feedback of the ER store filling, for example, store-operated calcium channels in the plasma membrane. For low IP3 concentrations, our integrated NRK cell model is at rest at -70 mV. For higher IP3 concentrations, the CaOs become activated and trigger repetitive firing of action potentials. At high IP3 concentrations, the basal intracellular calcium concentration becomes elevated and the cell is depolarized near -20 mV. These predictions are in agreement with the different proliferative states of cultures of NRK fibroblasts. We postulate that the stabilizing role of calcium channels and/or other calcium transporters controlled by feedback from the ER store is essential for any cell in which calcium signaling by intracellular CaOs involves both ER and plasma membrane calcium fluxes.