Sphingosine-1-phosphate receptor 2 plays a dual role depending on the stage of cell differentiation in renal epithelial cells

Epithelial renal cells have the ability to adopt different cellular phenotypes through epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET). These processes are increasingly recognized as important repair factors following acute renal tubular injury. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid with impact on proliferation, growth, migration, and differentiation which has significant implication in various diseases including cancer and kidney fibrosis. Here we demonstrated that S1P can exert by activating S1P receptor 2 (S1PR2) different functions depending on the stage of cell differentiation. We observed that the differences in the migratory profile of Madin-Darby canine kidney (MDCK) cells depend both on their stage of cell differentiation and the activity of S1PR2, a receptor that can either promote or inhibit the migratory process. Meanwhile in non-differentiated cells S1PR2 activation avoids migration, it is essential on fully differentiated cells. This is the first time that an antagonist effect of S1PR2 was reported for the same cell type. Moreover, in fully differentiated cells, S1PR2 activation is crucial for the progression of EMT - characterized by adherent junctions disassembly, β-catenin and SNAI2 nuclear translocation and vimentin expression- and depends on ERK 1/2 activation and nuclear translocation. These findings provide a new perspective about the different S1PR2 functions depending on the stage of cell differentiation that can be critical to the modulation of renal epithelial cell plasticity, potentially paving the way for innovative research with pathophysiologic relevance.

Synthesis and characterization of [125I]TZ6544, a promising radioligand for investigating sphingosine-1-phosphate receptor 2

INTRODUCTION

Sphingosine-1-phosphate receptor 2 (S1PR2) activation exerts a critical role in biological abnormalities and diseases. A suitable radiotracer will advance our understanding of S1PR2 pathophysiology of diseases. The objective of this study is to evaluate the potential of iodine-125 labeled [¹²⁵I]TZ6544 to be used for screening new compounds binding toward S1PR2, and assessing the changes of S1PR2 expression in the kidney of streptozotocin-induced diabetic rats.

METHODS

[¹²⁵I]TZ6544 was synthesized from borate precursor by copper (II)-catalyzed iodization reaction with [¹²⁵I]NaI. [¹²⁵I]TZ6544 was characterized using human recombinant S1PR2 cell membrane and biodistribution studies of [¹²⁵]TZ6544 were performed on Wistar rats that were euthanized at 5 and 30 min post-injection. A rat model of diabetes was induced by IV injection of streptozotocin (55 mg/kg). In vitro autoradiography studies, immunostaining, and enzyme-linked immunosorbent assay (ELISA) analysis were performed in both diabetic and control rats.

RESULTS

Radiosynthesis of [¹²⁵I]TZ6544 was achieved successfully with good radiochemical yields of ~47% and high radiochemical purity of >99%. [¹²⁵I]TZ6544 is a potent ligand in vitro for S1PR2 with K_d value of 4.31 nM. [¹²⁵I]TZ6544 and [³²P]-labeled endogenous S1P provided comparable IC₅₀ values in radioactive competitive binding assays against known S1PR2 ligands. Compared to control, the kidney of diabetic rats had increased uptake of [¹²⁵I]TZ6544, which could be reduced by a S1PR2 antagonist, JTE-013. Immunostaining and ELISA analysis confirmed that the diabetic rat had increased S1PR2 expression in the kidney.

CONCLUSIONS

[¹²⁵I]TZ6544 was synthesized successfully in high yields, and in vitro evaluation suggested [¹²⁵I]TZ6544 has high potential to be used for screening new S1PR2 compounds and investigating the pathophysiology of S1PR2 functions. The availability of [¹²⁵I]TZ6544 may facilitate the development of therapeutics and imaging agents targeting S1PR2. ADVANCES IN KNOWLEDGE: [¹²⁵I]TZ6544 showed increased expression of S1PR2 in diabetic rat kidney and can be used to determine binding potency of S1PR2 compounds.

Agonist-induced activation of the S1P receptor 2 constitutes a novel osteoanabolic therapy for the treatment of osteoporosis in mice

BACKGROUND AND PURPOSE

Osteoporosis is a worldwide epidemic but pharmacological agents to stimulate new bone formation are scarce. We have shown that increasing tissue levels of sphingosine-1-phosphate (S1P) by blocking its degradation by the S1P lyase has pronounced osteoanabolic effect in mouse osteoporosis models by stimulating osteoblast differentiation through the S1P receptor 2 (S1P2). However, S1P lyase inhibitors have side effects complicating potential clinical use. Here, we tested whether direct S1P2 engagement by the S1P2 agonist CYM5520 exerted osteoanabolic potential in estrogen deficiency-induced osteopenia in mice. We compared its efficacy to LX2931, a novel S1P lyase inhibitor currently tested in rheumatoid arthritis.

EXPERIMENTAL APPROACH

CYM5520, LX2931 or vehicle were administered to ovariectomized mice for 6 weeks beginning 5 weeks after ovariectomy, Bone mass, cellular composition and mechanical strength were assessed by microCT, histomorphometry and three point bending tests. Plasma markers of bone metabolism were analyzed by ELISA.

KEY RESULTS

Therapeutic treatment with CYM5520 and LX2931 clearly increased long bone and vertebral bone mass to impressive 3-5 fold over vehicle in osteopenic ovariectomized mice. As expected, lymphopenia was a side effect of LX2931, whereas none occurred with CYM5520. Consistent with an osteoanabolic effect, CYM5520 increased osteoblast number, osteoid surface and alkaline phosphatase area 2-3 fold over vehicle. Plasma concentrations of the osteoanabolic marker procollagen I C-terminal propeptide were also elevated by CYM5520 and LX2931. LX2931 but not yet CYM5520 increased cortical thickness and mechanical strength without affecting mineral density.

CONCLUSION AND IMPLICATIONS

Treatment with a pharmacological S1P2 agonist corrected ovariectomy-induced osteopenia in mice by inducing new bone formation thus constituting a novel osteoanabolic approach to osteoporosis.

S1PR2 antagonist ameliorate high glucose-induced fission and dysfunction of mitochondria in HRGECs via regulating ROCK1

Aims

Sphingosine-1-phosphate receptor 2 (S1PR2) is a G-protein-coupled receptor that regulates sphingosine-1-phosphate-triggered cellular response. However, the role of S1PR2 in diabetes-induced glomerular endothelial cell dysfunction remains unclear. This study aims to investigate the effect of S1PR2 blockade on the morphology and function of mitochondria in human renal glomerular endothelial cells (HRGECs).

Methods

HRGECs were pretreated with a S1PR2 antagonist (JTE-013) or a Rho-associated coiled coil-containing protein kinase 1 (ROCK1) inhibitor (Y27632) for 30 min and then cultured with normal glucose (5.5 mM) or high glucose (30 mM) for 72 h. The protein expression levels of RhoA, ROCK1, and Dynmin-related protein-1(Drp1) were evaluated by immunoblotting; mitochondrial morphology was observed by electron microscopy; intracellular levels of ATP, ROS, and Ca²⁺ were measured by ATPlite, DCF-DA, and Rhod-2 AM assays, respectively. Additionally, the permeability, apoptosis, and migration of cells were determined to evaluate the effects of S1PR2 and ROCK1 inhibition on high glucose-induced endothelial dysfunction.

Results

High glucose induced mitochondrial fission and dysfunction, indicated by increased mitochondrial fragmentation, ROS generation, and calcium overload but decreased ATP production. High glucose also induced endothelial cell dysfunction, indicated by increased permeability and apoptosis but decreased migration. However, inhibition of either S1PR2 or ROCK1 almost completely blocked these high glucose-mediated cellular responses. Furthermore, inhibiting S1PR2 resulted in the deceased expression of RhoA, ROCK1, and Drp1 while inhibiting ROCK1 led to the downregulated expression of Drp1.

Conclusions

S1PR2 antagonist modulates the morphology and function of mitochondria in HRGECs via the positive regulation of the RhoA/ROCK1/Drp1 signaling pathway, suggesting that the S1PR2/ROCK1 pathway may play a crucial role in high glucose milieu.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1323-0) contains supplementary material, which is available to authorized users.

Sphingosine-1-phosphate signaling and the gut-liver axis in liver diseases

The liver is the central organ involved in lipid metabolism and the gastrointestinal (GI) tract is responsible for nutrient absorption and partitioning. Obesity, dyslipidemia and metabolic disorders are of increasing public health concern worldwide, and novel therapeutics that target both the liver and the GI tract (gut-liver axis) are much needed. In addition to aiding fat digestion, bile acids act as important signaling molecules that regulate lipid, glucose and energy metabolism via activating nuclear receptor, G protein-coupled receptors (GPCRs), Takeda G protein receptor 5 (TGR5) and sphingosine-1-phosphate receptor 2 (S1PR2). Sphingosine-1-phosphate (S1P) is synthesized by two sphingosine kinase isoforms and is a potent signaling molecule that plays a critical role in various diseases such as fatty liver, inflammatory bowel disease (IBD) and colorectal cancer. In this review, we will focus on recent findings related to the role of S1P-mediated signaling pathways in the gut-liver axis.

Bile acids as global regulators of hepatic nutrient metabolism

Bile acids (BA) are synthesized from cholesterol in the liver. They are essential for promotion of the absorption of lipids, cholesterol, and lipid-soluble vitamins from the intestines. BAs are hormones that regulate nutrient metabolism by activating nuclear receptors (farnesoid X receptor (FXR), pregnane X receptor, vitamin D) and G protein-coupled receptors (e.g., TGR5, sphingosine-1-phosphate receptor 2 (S1PR2)) in the liver and intestines. In the liver, S1PR2 activation by conjugated BAs activates the extracellular signal-regulated kinase 1/2 and AKT signaling pathways, and nuclear sphingosine kinase 2. The latter produces sphingosine-1-phosphate (S1P), an inhibitor of histone deacetylases 1/2, which allows for the differential up-regulation of expression of genes involved in the metabolism of sterols and lipids. We discuss here the emerging concepts of the interactions of BAs, FXR, insulin, S1P signaling and nutrient metabolism.

Epithelial cell extrusion: Pathways and pathologies

To remove dying or unwanted cells from an epithelium while preserving the barrier function of the layer, epithelia use a unique process called cell extrusion. To extrude, the cell fated to die emits the lipid Sphingosine 1 Phosphate (S1P), which binds the G-protein-coupled receptor Sphingosine 1 Phosphate receptor 2 (S1P₂) in the neighboring cells that activates Rho-mediated contraction of an actomyosin ring circumferentially and basally. This contraction acts to squeeze the cell out apically while drawing together neighboring cells and preventing any gaps to the epithelial barrier. Epithelia can extrude out cells targeted to die by apoptotic stimuli to repair the barrier in the face of death or extrude live cells to promote cell death when epithelial cells become too crowded. Indeed, because epithelial cells naturally turn over by cell death and division at some of the highest rates in the body, epithelia depend on crowding-induced live cell extrusion to preserve constant cell numbers. If extrusion is defective, epithelial cells rapidly lose contact inhibition and form masses. Additionally, because epithelia act as the first line of defense in innate immunity, preservation of this barrier is critical for preventing pathogens from invading the body. Given its role in controlling constant cell numbers and maintaining barrier function, a number of different pathologies can result when extrusion is disrupted. Here, we review mechanisms and signaling pathways that control epithelial extrusion and discuss how defects in these mechanisms can lead to multiple diseases. We also discuss tactics pathogens have devised to hijack the extrusion process to infect and colonize epithelia.

Pharmacology of bile acid receptors: Evolution of bile acids from simple detergents to complex signaling molecules. Pharmacol Res. 2016;104:9-21. [PMID: 26706784 DOI: 10.1016/j.phrs.2015.12.007]

For many years, bile acids were thought to only function as detergents which solubilize fats and facilitate the uptake of fat-soluble vitamins in the intestine. Many early observations; however, demonstrated that bile acids regulate more complex processes, such as bile acids synthesis and immune cell function through activation of signal transduction pathways. These studies were the first to suggest that receptors may exist for bile acids. Ultimately, seminal studies by many investigators led to the discovery of several bile acid-activated receptors including the farnesoid X receptor, the vitamin D receptor, the pregnane X receptor, TGR5, α5 β1 integrin, and sphingosine-1-phosphate receptor 2. Several of these receptors are expressed outside of the gastrointestinal system, indicating that bile acids may have diverse functions throughout the body. Characterization of the functions of these receptors over the last two decades has identified many important roles for these receptors in regulation of bile acid synthesis, transport, and detoxification; regulation of glucose utilization; regulation of fatty acid synthesis and oxidation; regulation of immune cell function; regulation of energy expenditure; and regulation of neural processes such as gastric motility. Through these many functions, bile acids regulate many aspects of digestion ranging from uptake of essential vitamins to proper utilization of nutrients. Accordingly, within a short time period, bile acids moved beyond simple detergents and into the realm of complex signaling molecules. Because of the important processes that bile acids regulate through activation of receptors, drugs that target these receptors are under development for the treatment of several diseases, including cholestatic liver disease and metabolic syndrome. In this review, we will describe the various bile acid receptors, the signal transduction pathways activated by these receptors, and briefly discuss the physiological processes that these receptors regulate.

Discovery of novel S1P2 antagonists. Part 2: Improving the profile of a series of 1,3-bis(aryloxy)benzene derivatives

Our initial lead compound 2 was modified to improve its metabolic stability. The resulting compound 5 showed excellent metabolic stability in rat and human liver microsomes. We subsequently designed and synthesized a hybrid compound of 5 and the 1,3-bis(aryloxy) benzene derivative 1, which was previously reported by our group to be an S1P2 antagonist. This hybridization reaction gave compound 9, which showed improved S1P2 antagonist activity and good metabolic stability. The subsequent introduction of a carboxylic acid moiety into 9 resulted in 14, which showed potent antagonist activity towards S1P2 with a much smaller species difference between human S1P2 and rat S1P2. Compound 14 also showed good metabolic stability and an improved safety profile compared with compound 9.