FTY720 ameliorates renal fibrosis by simultaneously affecting leucocyte recruitment and TGF-β signalling in fibroblasts

The contribution of the sphingosine 1-phosphate signaling pathway to chronic kidney diseases: recent findings and new perspectives

Chronic kidney disease (CKD) is a multifactorial condition with diverse etiologies, such as diabetes mellitus, hypertension, and genetic disorders, often culminating in end-stage renal disease (ESRD). A hallmark of CKD progression is kidney fibrosis, characterized by the excessive accumulation of extracellular matrix components, for which there is currently no effective anti-fibrotic therapy. Recent literature highlights the critical role of sphingosine 1-phosphate (S1P) signaling in CKD pathogenesis and renal fibrosis. This review provides an in-depth analysis of the latest findings on S1P metabolism and signaling in renal fibrosis and in specific CKDs, including diabetic nephropathy (DN), lupus nephritis (LN), focal segmental glomerulosclerosis (FSGS), Fabry disease (FD), and IgA nephropathy (IgAN). Emerging studies underscore the therapeutic potential of modulating S1P signaling with receptor modulators and inhibitors, such as fingolimod (FTY720) and more selective agents like ozanimod and cenerimod. Additionally, the current knowledge about the effects of established kidney protective therapies such as glucocorticoids and SGLT2 and ACE inhibitors on S1P signaling will be summarized. Furthermore, the review highlights the potential role of S1P as a biomarker for disease progression in CKD models, particularly in Fabry disease and diabetic nephropathy. Advanced technologies, including spatial transcriptomics, are further refining our understanding of S1P's role within specific kidney compartments. Collectively, these insights emphasize the need for continued research into S1P signaling pathways as promising targets for CKD treatment strategies.

Fingolimod (FTY720) Hinders Interferon-γ-Mediated Fibrotic Scar Formation and Facilitates Neurological Recovery After Spinal Cord Injury

Following spinal cord injury (SCI), fibrotic scar inhibits axon regeneration and impairs neurological function recovery. It has been reported that T cell-derived interferon (IFN)-γ plays a pivotal role in promoting fibrotic scarring in neurodegenerative disease. However, the role of IFN-γ in fibrotic scar formation after SCI has not been declared. In this study, a spinal cord crush injury mouse was established. Western blot and immunofluorescence showed that IFN-γ was surrounded by fibroblasts at 3, 7, 14, and 28 days post-injury. Moreover, IFN-γ is mainly secreted by T cells after SCI. Further, in situ injection of IFN-γ into the normal spinal cord resulted in fibrotic scar formation and inflammation response at 7 days post-injection. After SCI, the intraperitoneal injection of fingolimod (FTY720), a sphingosine-1-phosphate receptor 1 (S1PR1) modulator and W146, an S1PR1 antagonist, significantly reduced T cell infiltration, attenuating fibrotic scarring via inhibiting IFN-γ/IFN-γR pathway, while in situ injection of IFN-γ diminished the effect of FTY720 on reducing fibrotic scarring. FTY720 treatment inhibited inflammation, decreased lesion size, and promoted neuroprotection and neurological recovery after SCI. These findings demonstrate that the inhibition of T cell-derived IFN-γ by FTY720 suppressed fibrotic scarring and contributed to neurological recovery after SCI.

CDX-modified chitosan nanoparticles remarkably reduce therapeutic dose of fingolimod in the EAE model of mice

Fingolimod (Fin), an FDA-approved drug, is used to control relapsing-remitting multiple sclerosis (MS). This therapeutic agent faces crucial drawbacks like poor bioavailability rate, risk of cardiotoxicity, potent immunosuppressive effects, and high cost. Here, we aimed to assess the therapeutic efficacy of nano-formulated Fin in a mouse model of experimental autoimmune encephalomyelitis (EAE). Results showed the suitability of the present protocol in the synthesis of Fin-loaded CDX-modified chitosan (CS) nanoparticles (NPs) (Fin@CSCDX) with suitable physicochemical features. Confocal microscopy confirmed the appropriate accumulation of synthesized NPs within the brain parenchyma. Compared to the control EAE mice, INF-γ levels were significantly reduced in the group that received Fin@CSCDX (p < 0.05). Along with these data, Fin@CSCDX reduced the expression of TBX21, GATA3, FOXP3, and Rorc associated with the auto-reactivation of T cells (p < 0.05). Histological examination indicated a low-rate lymphocyte infiltration into the spinal cord parenchyma after the administration of Fin@CSCDX. Of note, HPLC data revealed that the concentration of nano-formulated Fin was about 15-fold less than Fin therapeutic doses (TD) with similar reparative effects. Neurological scores were similar in both groups that received nano-formulated fingolimod 1/15th of free Fin therapeutic amounts. Fluorescence imaging indicated that macrophages and especially microglia can efficiently uptake Fin@CSCDX NPs, leading to the regulation of pro-inflammatory responses. Taken together, current results indicated that CDX-modified CS NPs provide a suitable platform not only for the efficient reduction of Fin TD but also these NPs can target the brain immune cells during neurodegenerative disorders.

Renalase Prevents Renal Fibrosis by Inhibiting Endoplasmic Reticulum Stress and Down-Regulating GSK-3β/Snail Signaling

Background: Treating renal fibrosis is crucial to delaying chronic kidney disease. The glycogen synthase kinase-3β (GSK-3β)/Snail pathway regulates renal fibrosis and Renalase can ameliorate renal interstitial fibrosis. However, it is not clear whether GSK-3β/Snail signaling affects Renalase action. Here, we explored the role and mechanism of GSK-3β/Snail in the anti-fibrosis action of Renalase. Materials and methods: We used mice with complete unilateral ureteral obstruction (UUO) and human proximal renal tubular epithelial (HK-2) cells with transforming growth factor-β1 (TGF-β1)-induced fibrosis to explore the role and regulatory mechanism of the GSK-3β/Snail pathway in the amelioration of renal fibrosis by Renalase. Results: In UUO mice and TGF-β1-induced fibrotic HK-2 cells, the expression of p-GSK-3β-Tyr216/p-GSK-3β-Ser9, GSK-3β and Snail was significantly increased, and endoplasmic reticulum (ER) stress was activated. After Renalase supplementation, fibrosis was alleviated, ER stress was inhibited and p-GSK-3β-Tyr216/p-GSK-3β-Ser9, GSK-3β and Snail were significantly down-regulated. The amelioration of renal fibrosis by Renalase and its inhibitory effect on GSK-3β/Snail were reversed by an ER stress agonist. Furthermore, when an adeno-associated virus or plasmid was used to overexpress GSK-3β, the effect of Renalase on delaying renal fibrosis was counteracted, although ER stress markers did not change. Conclusion: Renalase prevents renal fibrosis by down-regulating GSK-3β/Snail signaling through inhibition of ER stress. Exogenous Renalase may be an effective method of slowing or stopping chronic kidney disease progression.

FTY720 administration results in a M2 associated immunoregulatory effect that positively influences the outcome of alveolar bone repair outcome in mice

The alveolar bone repair process may be influenced by multiple local and systemic factors, which include immune system cells and mediators. Macrophages allegedly play important roles in the repair process, and the transition of an initial inflammatory M1 profile into a pro-reparative M2 profile theoretically contributes to a favorable repair outcome. In this context, considering immunoregulatory molecules as potential targets for improving bone repair, this study evaluated the role of the immunoregulatory molecule FTY720, previously described to favor the development of the M2 phenotype, in the process of alveolar bone healing in C57Bl/6 (WT) mice. Experimental groups submitted to tooth extraction and maintained under control conditions or treated with FTY720 were evaluated by microtomographic (μCT), histomorphometric, immunohistochemical and molecular analysis to characterize healing and host response features at 0, 1, 3, 7 and 14 days. Our results demonstrated that the FTY720 group presented higher bone tissue density, higher bone tissue volume, greater tissue volume fraction, greater number and thickness of trabeculae and a higher number of osteoblasts and osteoclasts than the control group. Accordingly, the bone markers BMP2, BMP7, ALPL, SOST and RANK mRNA expressions increased in the FTY720 treated group. Furthermore, the levels of FIZZ, ARG2 and IL-10 mRNA increased in the FTY720 group together with the presence of CD206⁺ cells, suggesting that the boost of bone formation mediated by FTY720 involves an increased polarization and activity of M2 macrophages in healing sites. Thus, our results demonstrate that FTY720 favored the process of alveolar bone repair, probably trough a strengthened M2 response, associated with an increased expression of markers osteogenic differentiation and activity markers. Immunoregulatory strategies based in the modulation of macrophage polarization profile can comprise effective tools to improve the bone repair process.

Anomaly of cornea and ocular adnexa in spinster homolog 2 (Spns2) knockout mice

Spinster 2 (Spns2) is a transporter that pumps sphingosine-1-phosphate (S1P), a bioactive lipid mediator synthesized in the cytoplasm, out of cells into the inter cellular space. S1P is a signal that modulates cellular behavior during embryonic development, inflammation and tissue repair, etc. A Spns2-null (KO) mouse is born with failure of eyelid closure (eyelid-open-at birth; EOB) and develop corneal fibrosis in adulthood. It remains elusive whether corneal lesion is caused by exposure to keratitis (lagophthalmos) of EOB phenotype or the loss of Spns2 directly perturbs the corneal tissue morphogenesis and intra-eyelid structures. Therefore, we investigated differences between the cornea and ocular adnexa morphogenesis in KO and wild-type (WT) embryos and adults as well. The loss of Spns2 perturbs cornea morphogenesis during embryonic development as early as E16.5 besides EOB phenotype. Histology showed that the corneal stroma was thinner with less extracellular matrix accumulation, e.g., collagen and keratocan in the KO mouse. Epithelial stratification, expression of keratin 12 and formation of desmosomes and hemidesmosomes were also perturbed in these KO corneas. Lacking Spns2 impaired morphogenesis of the Meibomian glands and of orbicularis oculi muscles. KO glands were labeled for ELOVL4 and PPARγ and were Oil-Red O-positive, suggesting KO acinar cells possessed functionality as the glands. This is the first report on the roles of Spns2 in corneal and Meibomian gland morphogenesis. Corneal tissue destruction in an adult KO mouse might be due to not only lagophthalmos but also to an impaired morphogenesis of cornea, Meibomian glands, and orbicularis oculi muscle.

Restoration of atypical protein kinase C ζ function in autosomal dominant polycystic kidney disease ameliorates disease progression

Autosomal dominant polycystic kidney disease (ADPKD) affects more than 500,000 individuals in the United States alone. In most cases, ADPKD is caused by a loss-of-function mutation in the PKD1 gene, which encodes polycystin-1 (PC1). Previous studies reported that PC1 interacts with atypical protein kinase C (aPKC). Here we show that PC1 binds to the ζ isoform of aPKC (PKCζ) and identify two PKCζ phosphorylation sites on PC1's C-terminal tail. PKCζ expression is down-regulated in patients with ADPKD and orthologous and nonorthologous PKD mouse models. We find that the US Food and Drug Administration-approved drug FTY720 restores PKCζ expression in in vitro and in vivo models of polycystic kidney disease (PKD) and this correlates with ameliorated disease progression in multiple PKD mouse models. Importantly, we show that FTY720 treatment is less effective in PKCζ null versions of these PKD mouse models, elucidating a PKCζ-specific mechanism of action that includes inhibiting STAT3 activity and cyst-lining cell proliferation. Taken together, our results reveal that PKCζ down-regulation is a hallmark of PKD and that its stabilization by FTY720 may represent a therapeutic approach to the treat the disease.

Fingolimod Rescues Memory and Improves Pathological Hallmarks in the 3xTg-AD Model of Alzheimer's Disease

Therapeutic strategies for Alzheimer's disease (AD) have largely focused on the regulation of amyloid pathology while those targeting tau pathology, and inflammatory mechanisms are less explored. In this regard, drugs with multimodal and concurrent targeting of Aβ, tau, and inflammatory processes may offer advantages. Here, we investigate one such candidate drug in the triple transgenic 3xTg-AD mouse model of AD, namely the disease-modifying oral neuroimmunomodulatory therapeutic used in patients with multiple sclerosis, called fingolimod. In this study, administration of fingolimod was initiated after behavioral symptoms are known to emerge, at 6 months of age. Treatment continued to 12 months when behavioral tests were performed and thereafter histological and biochemical analysis was conducted on postmortem tissue. The results demonstrate that fingolimod reverses deficits in spatial working memory at 8 and 12 months of age as measured by novel object location and Morris water maze tests. Inflammation in the brain is alleviated as demonstrated by reduced Iba1-positive and CD3-positive cell number, less ramified microglial morphology, and improved cytokine profile. Finally, treatment with fingolimod was shown to reduce phosphorylated tau and APP levels in the hippocampus and cortex. These results highlight the potential of fingolimod as a multimodal therapeutic for the treatment of AD.

Moringa oleifera Lam. seed extract protects kidney function in rats with diabetic nephropathy by increasing GSK-3β activity and activating the Nrf2/HO-1 pathway

BACKGROUND

Moringa oleifera Lam. (M. oleifera) seeds are widely used in traditional folk medicine and as nutritional supplements in the Middle East, Africa, and other regions. Published research showed that M. oleifera seeds (MOS) have pharmacological activities such as blood glucose-lowering, anti-inflammatory, and antitumor effects. However, experimental evidence on the use of MOS to treat diabetic nephropathy and its underlying mechanisms were rarely reported.

PURPOSE

To evaluate the therapeutic effects of MOS extract on the kidneys of high-fat diet (HFD)-fed rats with streptozotocin-induced diabetic nephropathy and reveal its underlying mechanisms.

STUDY DESIGN

HFD-fed rats with streptozotocin-induced diabetic nephropathy and high-glucose induced Human Renal Mesangial Cells (HRMC) were used to explore the protective effect of MOS on diabetic nephropathy in vivo and in vitro.

METHODS

HRMC were used to preliminarily evaluate the effect of MOS extract under high glucose conditions. For the in vivo study, rats were divided into the following 6 groups (n = 5): normal control group (NC), diabetic nephropathy model group (DN), high dose of MOS-treatment group (DN + MOS-H, 200 mg/kg/d); medium dose of MOS-treatment group (DN + MOS-M, 100 mg/kg/d); low dose of MOS-treatment group (DN + MOS-l, 50 mg/kg/d), and metformin-treatment group (DN + MET, 200 mg/kg/d). After 4 weeks of treatment, the damage caused by DN was assessed based on the related parameters of urine and blood. Periodic acid-Schiff (PAS) staining and hematoxylin and eosin (HE) staining were used to assess pathological tissue damage. Immunohistochemistry was used to detect nuclear factor erythroid-derived 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and phosphorylated-glycogen synthase kinase-3beta (P-GSK-3β) levels, whereas western blotting was used to detect Nrf2, HO-1, nephrin, GSK-3β, and p-GSK-3β levels.

RESULTS

MOS extract could inhibit the proliferation of HRMCs induced by high glucose levels. Compared with the rats in the DN group, MOS not only significantly reduced blood glucose levels and oxidative stress in the experimental rats but also improved their kidney function and reduced kidney tissue damage. Additionally, MOS extract increased GSK-3β activity and the expression of Nrf2 and HO-1.

CONCLUSIONS

This study showed that MOS could activate GSK-3β and Nrf2/HO-1 pathways to exert antioxidant and anti-renal fibrosis activities, and delay the progression of diabetic nephropathy.

Backstage players of fibrosis: NOX4, mTOR, HDAC, and S1P; companions of TGF-β

The fibrotic process could be easily defined as a pathological excess of extracellular matrix deposition, leading to disruption of tissue architecture and eventually loss of function; however, this process involves a complex network of several signal transduction pathways. Virtually almost all organs could be affected by fibrosis, the most affected are the liver, lung, skin, kidney, heart, and eyes; in all of them, the transforming growth factor-beta (TGF-β) has a central role. The canonical and non-canonical signal pathways of TGF-β impact the fibrotic process at the cellular and molecular levels, inducing the epithelial-mesenchymal transition (EMT) and the induction of profibrotic gene expression with the consequent increase in proteins such as alpha-smooth actin (α-SMA), fibronectin, collagen, and other extracellular matrix proteins. Recently, it has been reported that some molecules that have not been typically associated with the fibrotic process, such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4), mammalian target of rapamycin (mTOR), histone deacetylases (HDAC), and sphingosine-1 phosphate (S1P); are critical in its development. In this review, we describe and discuss the role of these new players of fibrosis and the convergence with TGF-β signaling pathways, unveiling new insights into the panorama of fibrosis that could be useful for future therapeutic targets.

Dasatinib mitigates renal fibrosis in a rat model of UUO via inhibition of Src/STAT-3/NF-κB signaling

This research aimed to investigate the reno-protective impact of the tyrosine kinase inhibitor dasatinib (DAS) against renal fibrosis induced by unilateral ureteral obstruction (UUO) in rats. DAS administration improved renal function and mitigated renal oxidative stress with paralleled reduction in the ligated kidney mass index, significant retraction in renal histopathological alterations and suppression of renal interstitial fibrosis. Nevertheless, DAS administration attenuated renal expression of phosphorylated Src (p-Src), Abelson (c-Abl) tyrosine kinases, nuclear factor-kappaB (NF-κB) p65, and phosphorylated signal transducer and activator of transcription-3 (p-STAT-3)/STAT-3 with paralleled reduction in renal contents of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and monocyte chemoattractant protein-1 (MCP-1). DAS diminished interstitial macrophage infiltration and decreased renal profibrotic transforming growth factor-β1 (TGF-β1) levels and suppressed interstitial expression of renal α-smooth muscle actin (α-SMA) and fibronectin. Collectively, DAS slowed the progression of renal interstitial fibrosis, possibly via attenuating renal oxidative stress, impairing Src/STAT-3/NF-κB signaling, and reducing renal inflammation.

Nifuroxazide suppresses UUO-induced renal fibrosis in rats via inhibiting STAT-3/NF-κB signaling, oxidative stress and inflammation

The current work explored the influences of nifuroxazide, an in vivo inhibitor of signal transducer and activator of transcription-3 (STAT-3) activation, on tubulointerstitial fibrosis in rats with obstructive nephropathy using unilateral ureteral obstruction (UUO) model. Thirty-two male Sprague Dawley rats were assigned into 4 groups (n = 8/group) at random. Sham and UUO groups were orally administered 0.5% carboxymethyl cellulose (CMC) (2.5 mL/kg/day), while Sham-NIF and UUO-NIF groups were treated with 20 mg/kg/day of NIF (suspended in 0.5% CMC, orally). NIF or vehicle treatments were started 2 weeks after surgery and continued for further 2 weeks. NIF treatment ameliorated kidney function in UUO rats, where it restored serum creatinine, blood urea, serum uric acid and urinary protein and albumin to near-normal levels. NIF also markedly reduced histopathological changes in tubules and glomeruli and attenuated interstitial fibrosis in UUO-ligated kidneys. Mechanistically, NIF markedly attenuated renal immunoexpression of E-cadherin and α-smooth muscle actin (α-SMA), diminished renal oxidative stress (↓ malondialdehyde (MDA) levels and ↑ superoxide dismutase (SOD) activity), lessened renal protein expression of phosphorylated-STAT3 (p-STAT-3), phosphorylated-Src (p-Src) kinase, the Abelson tyrosine kinase (c-Abl) and phosphorylated nuclear factor-kappaB p65 (pNF-κB p65), decreased renal cytokine levels of transforming growth factor-β1 (TGF-β1), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and monocyte chemoattractant protein-1 (MCP-1) and reduced number of cluster of differentiation 68 (CD68) immunolabeled macrophages in UUO renal tissues, compared to levels in untreated UUO kidneys. Taken together, NIF treatment suppressed interstitial fibrosis in UUO renal tissues, probably via inhibiting STAT-3/NF-κB signaling and attenuating renal oxidative stress and inflammation.

Effect of Shenkang on renal fibrosis and activation of renal interstitial fibroblasts through the JAK2/STAT3 pathway

BACKGROUND

Activation of renal fibroblasts is a critical mechanism in the process of renal fibrosis. As a commonly used herbal formula, Shenkang (SK) has been found to attenuate renal fibrosis and renal parenchyma destruction. However, the effect of SK on renal fibroblast activation in unilateral ureteral obstruction (UUO) mice and its molecular mechanism remain undetermined. The present study was performed to elucidate the effect of SK on renal fibroblast activation and renal fibrosis, as well as the potential underlying mechanism, in both NRK-49F cells and UUO mice.

METHODS

NRK-49F cells were stimulated with 10 ng/ml TGF-β1 for 48 h. After SK treatment, the CCK-8 method was used to evaluate cell viability. Thirty-six C57BL/6 mice were randomly divided into the sham group, UUO group, angiotensin receptor blocker (ARB) group, and SK high-, moderate- and low-dose groups. UUO was induced in mice except those in the sham group. Drugs were administered 1 day later. On the 13th day, the fractional anisotropy (FA) value was determined by MRI to evaluate the degree of renal fibrosis. After 14 days, serum indexes were assessed. Hematoxylin and eosin (HE) and Sirius red staining were used to observe pathological morphology and the degree of fibrosis of the affected kidney. Western blotting and PCR were used to assess the expression of related molecules in both cells and animals at the protein and gene levels.

RESULTS

Our results showed that SK reduced extracellular matrix (ECM) and α-smooth muscle actin (α-SMA) expression both in vitro and in vivo and attenuated renal fibrosis and the pathological lesion degree after UUO, suppressing JAK2/STAT3 activation. Furthermore, we found that SK regulated the JAK2/STAT3 pathway regulators peroxiredoxin 5 (Prdx5) in vitro and suppressor of cytokine signaling protein 1 (SOCS1) and SOCS3 in vivo.

CONCLUSIONS

These results indicated that SK inhibited fibroblast activation by regulating the JAK2/STAT3 pathway, which may be a mechanism underlying its protective action in renal fibrosis.

Exaggerated renal fibrosis in lncRNA Gas5-deficient mice after unilateral ureteric obstruction

AIMS

Abnormal expression of long non-coding RNAs (lncRNAs) occurs in several diseases including renal fibrosis. Notably, growth arrest-specific 5 (Gas5) is a lncRNA, which functions as an essential modulator of cell proliferation and growth. However, the role and expression of lncRNA Gas5 associated with renal fibrosis remains controversial. Herein, we investigate the effect of lncRNA Gas5 deficiency in renal fibrosis induced by the operation of unilateral ureteric obstruction (UUO) in mice.

MAIN METHODS

Sera and urine of mice were used to detect markers of renal function. Further, Masson and immunohistochemical staining, western blotting as well as qRT-PCR were performed to observe the distribution and expression of fibrosis marker in the kidney tissue of the mice.

KEY FINDINGS

Unlike the wild type mice, the obstructed kidney in Gas5+/- mice showed more severe renal fibrosis and collagen deposition. In the UUO-Gas5+/- group, the serum levels of uric acid, serum creatinine, and the urine levels of albumin-to-creatinine ratio were higher. Moreover, the expression of mRNA and protein of α-smooth muscle actin (α-SMA), vimentin, collagen IV, fibronectin, and matrix metalloproteinase 9 (MMP9) were higher, whereas that of phosphatase and tensin homolog (PTEN) were lower with the difference being statistically significant (p < 0.05).

SIGNIFICANCE

lncRNA Gas5 was up-regulated in renal fibrosis tissues, and its deficiency exacerbated renal fibrosis in the UUO mice model.

Role of sphingosine 1-phosphate signalling in tissue fibrosis

Fibrosis is characterized by the excessive accumulation of extracellular matrix components, leading to loss of tissue function in affected organs. Although the majority of fibrotic diseases have different origins, they have in common a persistent inflammatory stimulus and lymphocyte-monocyte interactions that determine the production of numerous fibrogenic cytokines. Treatment to contrast fibrosis is urgently needed, since some fibrotic diseases lead to systemic fibrosis and represent a major cause of death. In this article, the role of the bioactive sphingolipid sphingosine 1-phosphate (S1P) and its signalling pathway in the fibrosis of different tissue contexts is extensively reviewed, highlighting that it may represent an innovative and promising pharmacological therapeutic target for treating this devastating multifaceted disease. In multiple tissues S1P influences different aspects of fibrosis modulating the recruitment of inflammatory cells, as well as cell proliferation, migration and transdifferentiation into myofibroblasts, the cell type mainly involved in fibrosis development. Moreover, at the level of fibrotic lesions, S1P metabolism is profoundly influenced by multiple cross-talk with profibrotic mediators, such as transforming growth factor β, thus finely regulating the development of fibrosis. This article is part of a Special Issue entitled "Physiological and pathological roles of bioactive sphingolipids".

Glycogen synthase kinase-3β: a promising candidate in the fight against fibrosis

Fibrosis exists in almost all organs/tissues of the human body, plays an important role in the occurrence and development of diseases and is also a hallmark of the aging process. However, there is no effective prevention or therapeutic method for fibrogenesis. As a serine/threonine (Ser/Thr)-protein kinase, glycogen synthase kinase-3β (GSK-3β) is a vital signaling mediator that participates in a variety of biological events and can inhibit extracellular matrix (ECM) accumulation and the epithelial-mesenchymal transition (EMT) process, thereby exerting its protective role against the fibrosis of various organs/tissues, including the heart, lung, liver, and kidney. Moreover, we further present the upstream regulators and downstream effectors of the GSK-3β pathway during fibrosis and comprehensively summarize the roles of GSK-3β in the regulation of fibrosis and provide several potential targets for research. Collectively, the information reviewed here highlights recent advances vital for experimental research and clinical development, illuminating the possibility of GSK-3β as a novel therapeutic target for the management of tissue fibrosis in the future.

Endothelium-mediated contributions to fibrosis

Fibrosis, characterized by abnormal and excessive deposition of extracellular matrix, results in compromised tissue and organ structure. This can lead to reduced organ function and eventual failure. Although activated fibroblasts, called myofibroblasts, are considered the central players in fibrosis, the contribution of endothelial cells to the inception and progression of fibrosis has become increasingly recognized. Endothelial cells can contribute to fibrosis by acting as a source of myofibroblasts via endothelial-mesenchymal transition (EndoMT), or by becoming senescent, by secretion of profibrotic mediators and pro-inflammatory cytokines, chemokines and exosomes, promoting the recruitment of immune cells, and by participating in vascular rarefaction and decreased angiogenesis. In this review, we provide an overview of the different aspects of fibrosis in which endothelial cells have been implicated.

Sphingosine 1-Phosphate (S1P)/ S1P Receptor Signaling and Mechanotransduction: Implications for Intrinsic Tissue Repair/Regeneration

Tissue damage, irrespective from the underlying etiology, destroys tissue structure and, eventually, function. In attempt to achieve a morpho-functional recover of the damaged tissue, reparative/regenerative processes start in those tissues endowed with regenerative potential, mainly mediated by activated resident stem cells. These cells reside in a specialized niche that includes different components, cells and surrounding extracellular matrix (ECM), which, reciprocally interacting with stem cells, direct their cell behavior. Evidence suggests that ECM stiffness represents an instructive signal for the activation of stem cells sensing it by various mechanosensors, able to transduce mechanical cues into gene/protein expression responses. The actin cytoskeleton network dynamic acts as key mechanotransducer of ECM signal. The identification of signaling pathways influencing stem cell mechanobiology may offer therapeutic perspectives in the regenerative medicine field. Sphingosine 1-phosphate (S1P)/S1P receptor (S1PR) signaling, acting as modulator of ECM, ECM-cytoskeleton linking proteins and cytoskeleton dynamics appears a promising candidate. This review focuses on the current knowledge on the contribution of S1P/S1PR signaling in the control of mechanotransduction in stem/progenitor cells. The potential contribution of S1P/S1PR signaling in the mechanobiology of skeletal muscle stem cells will be argued based on the intriguing findings on S1P/S1PR action in this mechanically dynamic tissue.

Apolipoprotein M suppresses the phenotypes of IgA nephropathy in hyper-IgA mice

Because the association between sphingosine 1-phosphate (S1P)/apolipoprotein M (ApoM) and chronic kidney diseases has not been established, we investigated the involvement of S1P/ApoM in the phenotypes of IgA nephropathy in hyper-IgA (HIGA) mice. The overexpression of ApoM in adenoviral gene transfer ameliorated the phenotypes of IgA nephropathy in HIGA mice, whereas the knockdown of ApoM with siRNA caused deterioration. When ApoM-overexpressing HIGA mice were treated with VPC23019, an antagonist against S1P receptor 1 (S1P1) and 3 (S1P3), we observed that the protective effects of ApoM were reversed, whereas JTE013, an antagonist against S1P2, did not inhibit the effects. We also found that S1P bound to albumin accelerated the proliferation of MES13 cells and the fibrotic changes of HK2 cells, which were inhibited by JTE013, whereas S1P bound to ApoM suppressed these changes, which were inhibited by VPC23019. These results suggest that S1P bound to ApoM possesses properties protective against the phenotypes of IgA nephropathy through S1P1 and S1P3, whereas S1P bound to albumin exerts deteriorating effects through S1P2. ApoM may be useful as a therapeutic target to treat or retard the progression of IgA nephropathy.-Kurano, M., Tsuneyama, K., Morimoto, Y., Nishikawa, M., Yatomi, Y. Apolipoprotein M suppresses the phenotypes of IgA nephropathy in hyper-IgA mice.

FTY720 attenuates behavioral deficits in a murine model of systemic lupus erythematosus

Neuropsychiatric (NP) involvement in systemic lupus erythematosus (SLE) severely impacts patients' quality of life and leads to a poor prognosis. The current therapeutic protocol, corticosteroid administration, can also induce neuropsychiatric disorders. FTY720 is an immunomodulator that selectively confines lymphocytes in lymph nodes and reduces autoreactive T cell recruitment to the central nervous system (CNS). This study aimed to identify a novel therapeutic strategy for NPSLE. B6.MRL-lpr mice were treated with oral administration of FTY720 (2 mg/kg) three times per week for 12 weeks, to evaluate its efficacy in a model of NPSLE. FTY720 significantly attenuated the impulsive and depression-like behavior of B6.MRL-lpr mice. Neuronal damage was reduced in the cortex, hippocampus, and amygdala of the FTY720-treated B6.MRL-lpr mice, as well as in TNF-α-treated HT22 cells. Additionally, FTY720 downregulated levels of inflammatory cytokines, and reduced the infiltration of T cells and neutrophils in the brain parenchyma. FTY720 also acted directly on cerebral endothelial cells and reduced the permeability of the blood-brain barrier (BBB) in B6.MRL-lpr mice, as evidenced by reduced central IgG and albumin levels. Finally, FTY720 significantly inhibited activation of PI3K/Akt/GSK3β/p65 signaling, which further reduced the expression levels of adhesion molecules in bEND.3 cells treated with B6.MRL-lpr mouse serum. Collectively, our data indicate that oral administration of FTY720 at an early stage has beneficial effects in NPSLE-model B6.MRL-lpr mice, suggesting that it may represent an effective new therapeutic strategy for NPSLE.

Central role of dysregulation of TGF-β/Smad in CKD progression and potential targets of its treatment

Chronic kidney disease (CKD) has emerged as a major cause of morbidity and mortality worldwide. Interstitial fibrosis, glomerulosclerosis and inflammation play the central role in the pathogenesis and progression of CKD to end stage renal disease (ESRD). Transforming growth factor-β1 (TGF-β1) is the central mediator of renal fibrosis and numerous studies have focused on inhibition of TGF-β1 and its downstream targets for treatment of kidney disease. However, blockade of TGF-β1 has not been effective in the treatment of CKD patients. This may be, in part due to anti-inflammatory effect of TGF-β1. The Smad signaling system plays a central role in regulation of TGF-β1 and TGF-β/Smad pathway plays a key role in progressive renal injury and inflammation. This review provides an overview of the role of TGF-β/Smad signaling pathway in the pathogenesis of renal fibrosis and inflammation and an effective target of anti-fibrotic therapies. Under pathological conditions, Smad2 and Smad3 expression are upregulated, while Smad7 is downregulated. In addition to TGF-β1, other pathogenic mediators such as angiotensin II and lipopolysaccharide activate Smad signaling through both TGF-β-dependent and independent pathways. Smads also interact with other pathways including nuclear factor kappa B (NF-κB) to regulate renal inflammation and fibrosis. In the context of renal fibrosis and inflammation, Smad3 exerts profibrotic effect, whereas Smad2 and Smad7 play renal protective roles. Smad4 performs its dual functions by transcriptionally promoting Smad3-dependent renal fibrosis but simultaneously suppressing NF-κB-mediated renal inflammation via Smad7-dependent mechanism. Furthermore, TGF-β1 induces Smad3 expression to regulate microRNAs and Smad ubiquitination regulatory factor (Smurf) to exert its pro-fibrotic effect. In conclusion, TGF-β/Smad signaling is an important pathway that mediates renal fibrosis and inflammation. Thus, an effective anti-fibrotic therapy via inhibition of Smad3 and upregulation of Smad7 signaling constitutes an attractive approach for treatment of CKD.

Sphingolipids and Redox Signaling in Renal Regulation and Chronic Kidney Diseases

Significance: Sphingolipids play critical roles in the membrane biology and intracellular signaling events that influence cellular behavior and function. Our review focuses on the cellular mechanisms and functional relevance of the cross talk between sphingolipids and redox signaling, which may be critically implicated in the pathogenesis of different renal diseases. Recent Advances: Reactive oxygen species (ROS) and sphingolipids can regulate cellular redox homeostasis through the regulation of NADPH oxidase, mitochondrial integrity, nitric oxide synthase (NOS), and antioxidant enzymes. Over the last two decades, there have been significant advancements in the field of sphingolipid research, and it was in 2010 for the first time that sphingolipid receptor modulator was exploited as a therapeutic in humans. The cross talk of sphingolipids with redox signaling pathways becomes an important mechanism in the development of many different diseases such as renal diseases. Critical Issues: The critical issues to be addressed in this review are how sphingolipids interact with the redox signaling pathway to regulate renal function and even result in chronic kidney diseases. Ceramide, sphingosine, and sphingosine-1-phosphate (S1P) as main signaling sphingolipids are discussed in more detail. Future Directions: Although sphingolipids and ROS may mediate or modulate cellular responses to physiological and pathological stimuli, more translational studies and mechanistic pursuit in a tissue- or cell-specific way are needed to enhance our understanding of this important topic and to develop effective therapeutic strategies to treat diseases associated with redox signaling and sphingolipid cross talk. Antioxid. Redox Signal. 28, 1008-1026.