AMP-activated protein kinase/myocardin-related transcription factor-A signaling regulates fibroblast activation and renal fibrosis

Circadian clock regulation of myofibroblast fate

Fibrosis-related disorders represent an increasing medical and economic burden on a worldwide scale, accounting for one-third of all disease-related deaths with limited therapeutic options. As central mediators in fibrosis development, myofibroblasts have been gaining increasing attention in the last 20 years as potential targets for fibrosis attenuation and reversal. While various aspects of myofibroblast physiology have been proposed as treatment targets, many of these approaches have shown limited long-term efficacy so far. However, ongoing research is uncovering new potential strategies for targeting myofibroblast activity, offering hope for more effective treatments in the future. The circadian molecular clock is a feature of almost every cell in the human body that dictates the rhythmic nature of various aspects of human physiology and behavior in response to changes in the surrounding environment. The dysregulation of these rhythms with aging is considered to be one of the underlying reasons behind the development of multiple aging-related chronic disorders, with fibrotic tissue scarring being a common pathological complication among the majority of them. Myofibroblast dysregulation due to skewed circadian clockwork might significantly contribute to fibrotic scar persistence. In the current review, we highlight the role of the circadian clock in the context of myofibroblast activation and deactivation and examine its dysregulation as a driver of fibrogenesis.

AMPK is dispensable for physiological podocyte and glomerular functions but prevents glomerular fibrosis in experimental diabetes

AMP-activated protein kinase (AMPK) has been postulated to be crucial in regulating various renal physiology and pathophysiology processes, including energy metabolism, ion and water transport, inflammation, and hypertrophy. However, the specific roles of AMPK in the podocyte, a cell critical for maintaining glomerular filtration, have not been fully explored using genetic model animals. In this study, we generated mice lacking both AMPK α1 and α2 catalytic subunits in glomerular podocytes (pmut). Our findings revealed that, surprisingly, AMPK is dispensable for normal podocyte function. These knockout mice could live as long as their wild-type littermates without showing any pathological alterations in their glomeruli or glomerular function at two years of age. However, under type 1 diabetic conditions, the diabetic pmut mice exhibited increased lipid and collagen accumulation and an elevated expression of mesenchymal proteins in their glomeruli. They also showed more significant albuminuria compared to control diabetic mice. Under high glucose culture conditions, glomeruli isolated from pmut mice demonstrated a reduced expression of mitochondrial genes (e.g., Ndufv2) and increased leakage of mitochondrial components. Additionally, there was heightened expression of genes associated with nucleotide sensing and pro-inflammatory pathways (including mb21d2, IL-1 beta, and NF-kB). These observations suggest that while AMPK is not necessary for podocyte function in healthy kidneys, it is crucial for preventing glomerular fibrosis resulting from lipotoxicity and inflammation under diabetic conditions.

Matrix stiffness regulates nucleus pulposus cell glycolysis by MRTF-A-dependent mechanotransduction

Increased matrix stiffness of nucleus pulposus (NP) tissue is a main feature of intervertebral disc degeneration (IVDD) and affects various functions of nucleus pulposus cells (NPCs). Glycolysis is the main energy source for NPC survival, but the effects and underlying mechanisms of increased extracellular matrix (ECM) stiffness on NPC glycolysis remain unknown. In this study, hydrogels with different stiffness were established to mimic the mechanical environment of NPCs. Notably, increased matrix stiffness in degenerated NP tissues from IVDD patients was accompanied with impaired glycolysis, and NPCs cultured on rigid substrates exhibited a reduction in glycolysis. Meanwhile, RNA sequencing analysis showed altered cytoskeleton-related gene expression in NPCs on rigid substrates. Myocardin-related transcription factor A (MRTF-A) is a transcriptional coactivator in mechanotransduction mainly responding to cytoskeleton remodeling, which was activated and translocated to the nucleus under rigid substrate and was upregulated during IVDD progression. Furthermore, gas chromatography-mass spectrometry (GC-MS) analysis revealed that MRTF-A overexpression reduced NPC glycolytic metabolite abundance and identified a correlation with AMPK pathway. Mechanistically, rigid substrates and MRTF-A overexpression inhibited Kidins220 expression and AMPK phosphorylation in NPCs, whereas MRTF-A inhibition, treated with the MRTF-A inhibitor CCG, partially rescued NP tissue degeneration and glycolytic enzyme expression. Our data demonstrate that MRTF-A is a critical regulator that responds to increased matrix stiffness in IVDD, and MRTF-A activation reduces NPC glycolysis by down-regulating Kidins220 and inhibiting AMPK phosphorylation.

Myofibroblast-derived exosomes enhance macrophages to myofibroblasts transition and kidney fibrosis

A critical event in the pathogenesis of kidney fibrosis is the transition of macrophages into myofibroblasts (MMT). Exosomes play an important role in crosstalk among cells in the kidney and the development of renal fibrosis. However, the role of myofibroblast-derived exosomes in the process of MMT and renal fibrosis progression remains unknown. Here, we examined the role of myofibroblast-derived exosomes in MMT and kidney fibrogenesis. In vitro, transforming growth factor-β1 stimulated the differentiation of kidney fibroblasts into myofibroblasts and promoted exosome release from myofibroblasts. RAW264.7 cells were treated with exosomes derived from myofibroblasts. We found purified exosomes from myofibroblasts trigger the MMT. By contrast, inhibition of exosome production with GW4869 or exosome depletion from the conditioned media abolished the ability of myofibroblasts to induce MMT. Mice treatment with myofibroblast-derived exosomes (Myo-Exo) exhibited severe fibrotic lesion and more abundant MMT cells in kidneys with folic acid (FA) injury, which was negated by TANK-banding kinase-1 inhibitor. Furthermore, suppression of exosome production reduced collagen deposition, extracellular matrix protein accumulation, and MMT in FA nephropathy. Collectively, Myo-Exo enhances the MMT and kidney fibrosis. Blockade of exosomes mediated myofibroblasts-macrophages communication may provide a novel therapeutic target for kidney fibrosis.

ULK1-regulated AMP sensing by AMPK and its application for the treatment of chronic kidney disease

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a central kinase involved in energy homeostasis. Increased intracellular AMP levels result in AMPK activation through the binding of AMP to the γ-subunit of AMPK. Recently, we reported that AMP-induced AMPK activation is impaired in the kidneys in chronic kidney disease (CKD) despite an increase in the AMP/ATP ratio. However, the mechanisms by which AMP sensing is disrupted in CKD are unclear. Here, we identified mechanisms of energy homeostasis in which Unc-51-like kinase 1 (ULK1)-dependent phosphorylation of AMPKγ1 at Ser260/Thr262 promoting AMP sensitivity of AMPK. AMPK activation by AMP was impaired in Ulk1 knockout mice despite an increased AMP/ATP ratio. ULK1 expression is markedly downregulated in CKD kidneys, leading to AMP sensing failure. Additionally, MK8722, an allosteric AMPK activator, stimulated AMPK in the kidneys of a CKD mouse model (5/6th nephrectomy) via a pathway that is independent of AMP sensing. Thus, our study shows that MK8722 treatment significantly attenuates the deterioration of kidney function in CKD and may be a potential therapeutic option in CKD therapeutics.

Reprogramming of Energy Metabolism in Human PKD1 Polycystic Kidney Disease: A Systems Biology Analysis

Multiple alterations of cellular metabolism have been documented in experimental studies of autosomal dominant polycystic kidney disease (ADPKD) and are thought to contribute to its pathogenesis. To elucidate the molecular pathways and transcriptional regulators associated with the metabolic changes of renal cysts in ADPKD, we compared global gene expression data from human PKD1 renal cysts, minimally cystic tissues (MCT) from the same patients, and healthy human kidney cortical tissue samples. We found gene expression profiles of PKD1 renal cysts were consistent with the Warburg effect with gene pathway changes favoring increased cellular glucose uptake and lactate production, instead of pyruvate oxidation. Additionally, mitochondrial energy metabolism was globally depressed, associated with downregulation of gene pathways related to fatty acid oxidation (FAO), branched-chain amino acid (BCAA) degradation, the Krebs cycle, and oxidative phosphorylation (OXPHOS) in renal cysts. Activation of mTORC1 and its two target proto-oncogenes, HIF-1α and MYC, was predicted to drive the expression of multiple genes involved in the observed metabolic reprogramming (e.g., GLUT3, HK1/HK2, ALDOA, ENO2, PKM, LDHA/LDHB, MCT4, PDHA1, PDK1/3, MPC1/2, CPT2, BCAT1, NAMPT); indeed, their predicted expression patterns were confirmed by our data. Conversely, we found AMPK inhibition was predicted in renal cysts. AMPK inhibition was associated with decreased expression of PGC-1α, a transcriptional coactivator for transcription factors PPARα, ERRα, and ERRγ, all of which play a critical role in regulating oxidative metabolism and mitochondrial biogenesis. These data provide a comprehensive map of metabolic pathway reprogramming in ADPKD and highlight nodes of regulation that may serve as targets for therapeutic intervention.

Critical Role of histone deacetylase 3 in the regulation of kidney inflammation and fibrosis

Chronic kidney disease (CKD) is characterized by kidney inflammation and fibrosis. However, the precise mechanisms leading to kidney inflammation and fibrosis are poorly understood. Since histone deacetylase is involved in inflammation and fibrosis in other tissues, we examined the role of histone deacetylase 3 (HDAC3) in the regulation of inflammation and kidney fibrosis. HDAC3 is induced in the kidneys of animal models of CKD but mice with conditional HDAC3 deletion exhibit significantly reduced fibrosis in the kidneys compared with control mice. The expression of proinflammatory and profibrotic genes was significantly increased in the fibrotic kidneys of control mice, which was impaired in mice with HDAC3 deletion. Genetic deletion or pharmacological inhibition of HDAC3 reduced the expression of proinflammatory genes in cultured monocytes/macrophages. Mechanistically, HDAC3 deacetylates Lys122 of NF-κB p65 subunit turning on transcription. RGFP966, a selective HDAC3 inhibitor, reduced fibrosis in cells and in animal models by blocking NF-κB p65 binding to κB-containing DNA sequences. Thus, our study identified HDAC3 as a critical regulator of inflammation and fibrosis of the kidney through deacetylation of NF-κB unlocking its transcriptional activity. Hence, targeting HDAC3 could serve as a novel therapeutic strategy for CKD.

Melatonin inhibits fibroblast cell functions and hypertrophic scar formation by enhancing autophagy through the MT2 receptor-inhibited PI3K/Akt /mTOR signaling

Hypertrophic scar (HS) is a fibrotic skin condition and characterized by abnormal proliferation of myofibroblasts and accumulation of extracellular matrix. Melatonin, an endogenous hormone, can alleviate fibrosis in multiple models of diseases. This study examined the effect of melatonin on fibrosis in primary fibroblasts from human HS (HSFs) and a rabbit ear model and potential mechanisms. Melatonin treatment significantly decreased the migration and contraction capacity, collagen and α-smooth muscle actin (α-SMA) production in HSFs. RNA-sequencing and bioinformatic analyses indicated that melatonin modulated the expression of genes involved in autophagy and oxidative stress. Mechanistically, melatonin treatment attenuated the AKT/mTOR activation through affecting the binding of MT2 receptor with PI3K to enhance autophagy, decreasing fibrogenic factor production in HSFs. Moreover, melatonin treatment inhibited HS formation in rabbit ears by enhancing autophagy. The anti-fibrotic effects of melatonin were abrogated by treatment with an autophagy inhibitor (3-methyladenine, 3-MA), an Akt activator (SC79), or an MT2 selective antagonist (4-phenyl-2propionamidotetralin, 4-P-PDOT). Therefore, melatonin may be a potential drug for prevention and treatment of HS.

Glycyrrhizic Acid Protects Glomerular Podocytes Induced by High Glucose by Modulating SNARK/AMPK Signaling Pathway

OBJECTIVE

Diabetic nephropathy is one of the most important microvascular complications of diabetes, which mainly refers to glomerular capillary sclerosis. Podocytes are an important part of glomerular capillaries. Previous clinical and basic studies have shown that fibrosis is the main factor of diabetic nephropathy. This study aimed to assess the protective mechanism of glycyrrhizic acid (GA) on glomerular podocytes induced by high glucose as we hypothesized that GA may have antifibrotic and anti-inflammatory effects on podocytes through regulation of the adenosine 5'-monophosphate-activated protein kinase (AMPK)/sucrose nonfermenting AMPK-related kinase (SNARK) signaling pathway.

METHODS

SNARK siRNA was used to transfect podocytes. Real-time quantitative polymerase chain reaction and immunofluorescence staining assays were used for molecular and pathological analysis. The expression levels of key pathway proteins (including TGF-β1, α-SMA, SITR1, AMPKα, LKB1, PGC-1α, NF-κB, IL-6, and TNF-α) were verified by Western blotting. The expression of inflammatory factors in podocytes was detected by ELISA.

RESULTS

We demonstrated that GA decreased the expression of podocyte fibrosis signaling pathway-related factors by upregulating the AMPK pathway and its related factors. However, after transfection of podocytes with SNARK siRNA, there was an increased expression of fibrosis-related factors and inflammation-related factors.

CONCLUSION

GA can protect podocytes and alleviate fibrosis and inflammation induced by high glucose, which is related to the AMPK signaling pathway. Meanwhile, knockdown of SNARK protein can inhibit the AMPK signaling pathway, aggravate fibrosis, and increase inflammation.

Genome-Wide Association Study for eGFR in a Taiwanese Population

BACKGROUND AND OBJECTIVES

Chronic kidney disease (CKD) is a global public health issue associated with large economic burdens. CKD contributes to higher risks of cardiovascular complications, kidney failure, and mortality. The incidence and prevalence rates of kidney failure in Taiwan have remained the highest in the world.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Assessing genetic factors that influence kidney function in specific populations has substantial clinical relevance. We investigated associations of genetic variants with eGFR. The quality control filtering and genotype imputation resulted in 10,008 Taiwan Biobank participants and 6,553,511 variants for final analyses. We examined these loci with in silico replication in individuals of European and African ancestry.

RESULTS

Our results revealed one significant locus (4q21.1) and three suggestive significant loci (17q23.2, 22q13.2, and 3q29) for eGFR in the Taiwanese population. In total, four conditional-independent single nucleotide polymorphisms were identified as the most important variants within these regions, including rs55948430 (Coiled-Coil Domain Containing 158), rs1010269 (BCAS3), rs56108505 (MKL1), and rs34796810 (upstream of DLG1). By performing a meta-analysis, we found that the 4q21.1 and 17q23.2 loci were successfully replicated in the European population, whereas only the 17q23.2 locus was replicated in African ancestry. Therefore, these two loci are suggested to be transethnic loci, and the other two eGFR-associated loci (22q13.2 and 3q29) are likely population specific.

CONCLUSIONS

We identified four susceptibility loci on 4q21.1, 17q23.2, 22q13.2, and 3q29 that associated with kidney-related traits in a Taiwanese population. The 22q13.2 (MKL1) and 3q29 (DLG1) were prioritized as critical candidates. Functional analyses delineated novel pathways related to kidney physiology in Taiwanese and East Asian ancestries.

Pharmacological Inhibition of S100A4 Attenuates Fibroblast Activation and Renal Fibrosis

The TGF-β/Smad3 signaling pathway is an important process in the pathogenesis of kidney fibrosis. However, the molecular mechanisms are not completely elucidated. The current study examined the functional role of S100A4 in regulating TGF-β/Smad3 signaling in fibroblast activation and kidney fibrosis development. S100A4 was upregulated in the kidney in a murine model of renal fibrosis induced by folic acid nephropathy. Further, S100A4 was predominant in the tubulointerstitial cells of the kidney. Pharmacological inhibition of S100A4 with niclosamide significantly attenuated fibroblast activation, decreased collagen content, and reduced extracellular matrix protein expression in folic acid nephropathy. Overexpression of S100A4 in cultured renal fibroblasts significantly facilitated TGF-β1-induced activation of fibroblasts by increasing the expression of α-SMA, collagen-1 and fibronectin. In contrast, S100A4 knockdown prevented TGF-β1-induced activation of fibroblast and transcriptional activity of Smad3. Mechanistically, S100A4 interacts with Smad3 to stabilize the Smad3/Smad4 complex and promotes their translocation to the nucleus. In conclusion, S100A4 facilitates TGF-β signaling via interaction with Smad3 and promotes kidney fibrosis development. Manipulating S100A4 may provide a beneficial therapeutic strategy for chronic kidney disease.

Adiponectin Alleviates Intestinal Fibrosis by Enhancing AMP-Activated Protein Kinase Phosphorylation

BACKGROUND

Intestinal fibrosis is a common complication of Crohn's disease (CD). Adiponectin reportedly exerts anti-inflammatory effects in various disease models, including colitis models.

AIMS

In this study, we aimed to determine the effects of adiponectin on intestinal fibrosis and the underlying mechanisms.

METHODS

A murine model of intestinal fibrosis was established by administering increasing doses of 2,4,6-trinitrobenzene sulfonic acid to Balb/c mice via enema for 7 weeks. Primary human fibroblasts were isolated from the colon tissues of patients with CD. The fibroblasts were incubated with transforming growth factor (TGF)-β1 to establish a fibrosis model in vitro. Pathway inhibitors were used to verify the potential signaling pathways involved in the anti-fibrogenic effect of adiponectin.

RESULTS

Compared with the normal mesentery, adiponectin expression was significantly increased in the hypertrophic mesentery of patients with CD. Intraperitoneal injection of adiponectin significantly decreased the activity of myeloperoxidase and the expression of pro-inflammatory cytokines (tumor necrosis factor α and interleukin 6) in the colon of fibrosis model mice, whereas the expression of the anti-inflammatory cytokine interleukin 10 was substantially increased. Moreover, adiponectin treatment inhibited colon shortening, decreased colon weight, and reduced fibrotic protein deposition in the model mice. Adiponectin reduced the phosphorylation of Smad2 and collagen deposition induced by TGF-β1 in primary human intestinal fibroblasts, with an increase in AMP-activated protein kinase (AMPK) phosphorylation. Furthermore, this phenomenon was reversed by the AMPK inhibitor.

CONCLUSIONS

Adiponectin can protect against intestinal fibrosis by enhancing the phosphorylation of AMPK and inhibiting the activity of the TGF-β1/Smad signaling pathway.

The adipokine orosomucoid alleviates adipose tissue fibrosis via the AMPK pathway

The excess deposition of underlying extracellular matrix (ECM) in adipose tissue is defined as adipose tissue fibrosis that is a major contributor to metabolic disorder such as obesity and type 2 diabetes. Anti-fibrosis therapy has received much attention in the treatment of metabolic disorders. Orosomucoid (ORM) is an acute-phase protein mainly produced by liver, which is also an adipokine. In this study, we investigated the effects of ORM on adipose tissue fibrosis and the potential mechanisms. We showed that ORM1-deficient mice exhibited an obese phenotype, manifested by excessive collagen deposition in adipose tissues and elevated expression of ECM regulators such as metalloproteinases (MMP-2, MMP-13, MMP-14) and tissue inhibitors of metalloproteinases (TIMP-1, TIMP-2, TIMP-3). Administration of exogenous ORM (50 mg· kg^-1· d^-1, ip) for 7 consecutive days in high-fat diet (HFD)-fed mice and leptin receptor (LepR)-deficient db/db mice attenuated these abnormal expressions. Meanwhile, ORM administration stimulated AMP-activated protein kinase (AMPK) phosphorylation and decreased transforming growth factor-β1 (TGF-β1) level in adipose tissues of the mice. In TGF-β1-treated 3T3-L1 fibroblasts, ORM (10 μg/mL) improved the impaired expression profiles of fibrosis-related genes, whereas a selective AMPK inhibitor dorsomorphin (1 μmol/mL) abolished these effects. Together, our results suggest that ORM exerts a direct anti-fibrosis effect in adipose tissue via AMPK activation. ORM is expected to become a novel target for the treatment of adipose tissue fibrosis.

Myeloid PTEN deficiency aggravates renal inflammation and fibrosis in angiotensin II-induced hypertension

Hypertension is a major cause of chronic kidney disease. However, the pathogenesis of hypertensive kidney disease is not fully understood. Recently, we have shown that CXCL16/phosphoinositide-3 kinase γ (PI3Kγ) plays an important role in the development of renal inflammation and fibrosis in angiotensin II (AngII) induced hypertensive nephropathy. In the present study, we examined the role of phosphatase and tensin homolog (PTEN), a major regulator of PI3K signaling, in the pathogenesis of renal inflammation and fibrosis in an experimental model of hypertension induced by AngII. We generated myeloid PTEN conditional knockout mice by crossing PTEN^flox/flox mice with LysM-driven Cre mice. Littermate LysM-Cre^-/- PTEN^flox/flox mice were used as a control. Both myeloid PTEN knockout mice and their littermate control mice exhibited similar blood pressure at baseline. AngII treatment resulted in an increase in blood pressure that was comparable between myeloid PTEN knockout mice and littermate control mice. Compared with littermate control mice, myeloid PTEN knockout mice developed more severe kidney dysfunction, proteinuria, and fibrosis following AngII treatment. Furthermore, myeloid PTEN deficiency exacerbated total collagen deposition and extracellular matrix protein production and enhanced myeloid fibroblast accumulation and myofibroblast formation in the kidney following AngII treatment. Finally, myeloid PTEN deficiency markedly augmented infiltration of F4/80⁺ macrophages and CD3⁺ T cells into the kidneys of AngII-treated mice. Taken together, these results indicate that PTEN plays a crucial role in the pathogenesis of renal inflammation and fibrosis through the regulation of infiltration of myeloid fibroblasts, macrophages, and T lymphocytes into the kidney.

Inhibition of RhoA/MRTF-A signaling alleviates nucleus pulposus fibrosis induced by mechanical stress overload

PURPOSE/AIM

: Intervertebral disc degeneration (IDD) is the leading cause of lower back pain, and clinically useful drugs for IDD are unavailable. Mechanical stress overload-induced fibrosis plays a critical role in IDD. RhoA/MRTF-A signaling is known to regulate tissue fibrosis; however, the effect of RhoA/MRTF-A on the development of IDD is unclear.

MATERIALS AND METHODS

: The expression of aggrecan, collagen I, collagen II, MMP-12, CTGF, and MRTF-A in nucleus pulposus (NP) samples from IDD patients and controls was detected by immunohistochemical staining. Primary nucleus pulposus cells (NPCs) were isolated and cultured to establish an overload strain model treated with or without CCG-1423. The protein levels of RhoA, ROCK2, MRTF-A, CTGF, and MMP-12 as well as fibrosis-associated proteins were detected by western blotting and immunofluorescence.

RESULTS

: Collagen I, MMP-12, and CTGF were significantly upregulated, and aggrecan and collagen II were significantly downregulated in the IDD samples. The cellular localization of MRTF-A was associated with intervertebral disc (IVD) degeneration. Overloaded strain enhanced the nuclear translocation of MRTF-A and changed the NPC morphology from spindle-shaped to long strips. Additional experiments showed that RhoA, ROCK2, MRTF-A, SRF, MMP-12, and CTGF were upregulated; however, aggrecan and collagen II were downregulated in NPCs under overload strain. CCG-1423, a RhoA/MRTF-A pathway inhibitor, reversed strain-induced fibrosis.

CONCLUSION

: Mechanical stress activates RhoA/MRTF-A signaling to promote extracellular matrix (ECM) degeneration in the NP, which is associated with the development of IDD. Our findings suggest that the RhoA/MRTF-A inhibitor CCG-1423 can alleviate NPC degeneration caused by overload stress and has potential as a therapeutic agent for IDD.

P53 mediates the protective effects of metformin in inflamed lung endothelial cells

The endothelial barrier regulates interstitial fluid homeostasis by transcellular and paracellular means. Dysregulation of this semipermeable barrier may lead to vascular leakage, edema, and accumulation of pro-inflammatory cytokines, inducing microvascular hyperpermeability. Investigating the molecular pathways involved in those events will most probably provide novel therapeutic possibilities in pathologies related to endothelial barrier dysfunction. Metformin (MET) is an anti-diabetic drug, opposes malignancies, inhibits cellular transformation, and promotes cardiovascular protection. In the current study, we assess the protective effects of MET in LPS-induced lung endothelial barrier dysfunction and evaluate the role of P53 in mediating the beneficial effects of MET in the vasculature. We revealed that this biguanide (MET) opposes the LPS-induced dysregulation of the lung microvasculature, since it suppressed the formation of filamentous actin stress fibers, and deactivated cofilin. To investigate whether P53 is involved in those phenomena, we employed the fluorescein isothiocyanate (FITC) - dextran permeability assay, to measure paracellular permeability. Our observations suggest that P53 inhibition increases paracellular permeability, and MET prevents those effects. Our results contribute towards the understanding of the lung endothelium and reveal the significant role of P53 in the MET-induced barrier enhancement.

STAT6 Deficiency Attenuates Myeloid Fibroblast Activation and Macrophage Polarization in Experimental Folic Acid Nephropathy

Renal fibrosis is a pathologic feature of chronic kidney disease, which can lead to end-stage kidney disease. Myeloid fibroblasts play a central role in the pathogenesis of renal fibrosis. However, the molecular mechanisms pertaining to myeloid fibroblast activation remain to be elucidated. In the present study, we examine the role of signal transducer and activator of transcription 6 (STAT6) in myeloid fibroblast activation, macrophage polarization, and renal fibrosis development in a mouse model of folic acid nephropathy. STAT6 is activated in the kidney with folic acid nephropathy. Compared with folic-acid-treated wild-type mice, STAT6 knockout mice had markedly reduced myeloid fibroblasts and myofibroblasts in the kidney with folic acid nephropathy. Furthermore, STAT6 knockout mice exhibited significantly less CD206 and PDGFR-β dual-positive fibroblast accumulation and M2 macrophage polarization in the kidney with folic acid nephropathy. Consistent with these findings, STAT6 knockout mice produced less extracellular matrix protein, exhibited less severe interstitial fibrosis, and preserved kidney function in folic acid nephropathy. Taken together, these results have shown that STAT6 plays a critical role in myeloid fibroblasts activation, M2 macrophage polarization, extracellular matrix protein production, and renal fibrosis development in folic acid nephropathy. Therefore, targeting STAT6 may provide a novel therapeutic strategy for fibrotic kidney disease.

Pharmacological Inhibition of STAT6 Ameliorates Myeloid Fibroblast Activation and Alternative Macrophage Polarization in Renal Fibrosis

A hallmark of chronic kidney disease is renal fibrosis, which can result in progressive loss of kidney function. Currently, there is no effective therapy for renal fibrosis. Therefore, there is an urgent need to identify potential drug targets for renal fibrosis. In this study, we examined the effect of a selective STAT6 inhibitor, AS1517499, on myeloid fibroblast activation, macrophage polarization, and development of renal fibrosis in two experimental murine models. To investigate the effect of STAT6 inhibition on myeloid fibroblast activation, macrophage polarization, and kidney fibrosis, wild-type mice were subjected to unilateral ureteral obstruction or folic acid administration and treated with AS1517499. Mice treated with vehicle were used as control. At the end of experiments, kidneys were harvested for analysis of myeloid fibroblast activation, macrophage polarization, and renal fibrosis and function. Unilateral ureteral obstruction or folic acid administration induced STAT6 activation in interstitial cells of the kidney, which was significantly abolished by AS1517499 treatment. Mice treated with AS1517499 accumulated fewer myeloid fibroblasts and myofibroblasts in the kidney with ureteral obstruction or folic acid nephropathy compared with vehicle-treated mice. Moreover, AS1517499 significantly suppressed M2 macrophage polarization in the injured kidney. Furthermore, AS1517499 markedly reduced the expression levels of extracellular matrix proteins, and development of kidney fibrosis and dysfunction. These findings suggest that AS1517499 inhibits STAT6 activation, suppresses myeloid fibroblast activation, reduces M2 macrophage polarization, attenuates extracellular matrix protein production, and preserves kidney function. Therefore, targeting STAT6 with AS1517499 is a novel therapeutic approach for chronic kidney disease.

MRTF: Basic Biology and Role in Kidney Disease

A lesser known but crucially important downstream effect of Rho family GTPases is the regulation of gene expression. This major role is mediated via the cytoskeleton, the organization of which dictates the nucleocytoplasmic shuttling of a set of transcription factors. Central among these is myocardin-related transcription factor (MRTF), which upon actin polymerization translocates to the nucleus and binds to its cognate partner, serum response factor (SRF). The MRTF/SRF complex then drives a large cohort of genes involved in cytoskeleton remodeling, contractility, extracellular matrix organization and many other processes. Accordingly, MRTF, activated by a variety of mechanical and chemical stimuli, affects a plethora of functions with physiological and pathological relevance. These include cell motility, development, metabolism and thus metastasis formation, inflammatory responses and—predominantly-organ fibrosis. The aim of this review is twofold: to provide an up-to-date summary about the basic biology and regulation of this versatile transcriptional coactivator; and to highlight its principal involvement in the pathobiology of kidney disease. Acting through both direct transcriptional and epigenetic mechanisms, MRTF plays a key (yet not fully appreciated) role in the induction of a profibrotic epithelial phenotype (PEP) as well as in fibroblast-myofibroblast transition, prime pathomechanisms in chronic kidney disease and renal fibrosis.

1,25-(OH)2D3 ameliorates renal interstitial fibrosis in UUO rats through the AMPKα/mTOR pathway

Objective

To investigate the effects of 1,25(OH)₂D₃ on renal fibrosis associated with the AMP-activated protein kinase (AMPK)α/mechanistic target of rapamycin (mTOR) signalling pathway in a rat model of unilateral ureteral obstruction (UUO).

Methods

A total of 54 male Sprague Dawley rats were randomly divided into three groups: sham-operation group, UUO group, and UUO plus calcitriol (3 ng/100 g) group. Renal tissue was excised for histological examination by immunohistochemistry and Western blot, and for gene expression analysis using real-time polymerase chain reaction.

Results

1,25(OH)₂D₃ enhanced AMPKα levels, inhibited mTOR levels and slowed the development of interstitial fibrosis in kidney tissue. Compared with the UUO plus calcitriol group, UUO rats demonstrated more severe renal damage characterized by marked tubular atrophy, interstitial fibrosis and significant induction of fibrogenic transforming growth factor-β1 and increased extra-cellular matrix proteins (α-smooth muscle actin and collagen type III), and decreased E-cadherin.

Conclusion

Treatment with 1,25(OH)₂D₃ altered the AMPKα/mTOR signalling pathway to suppress excessive fibroblast activation observed in UUO rats. This may serve as a novel mechanism to ameliorate renal dysfunction and fibrotic lesions.

Emodin induces collagen type I synthesis in Hs27 human dermal fibroblasts

Fibrillar collagen and elastic fibers are the main components of the dermal extracellular matrix (ECM), which confers mechanical strength and resilience to the skin. In particular, type I collagen produced by fibroblasts is the most abundant collagen that determines the general strength of the ECM, thereby contributing to the prevesntion of the skin-aging process. Although the natural anthraquinone derivative emodin (1,3,8-trihydroxy-6-methylanthraquinone) exerts numerous beneficial effects, including antiviral, anticancer, anti-inflammatory and wound-healing effects in diverse cells, the effect of emodin on collagen expression or skin aging is not fully understood. The present study demonstrated that exposure to emodin increased type I collagen synthesis in a concentration- and time-dependent manner in Hs27 human dermal fibroblasts. Subsequent experiments showed that emodin strongly increased collagen type I levels without altering cell proliferation or cellular matrix metalloproteinase-1 (MMP-1) expression. Additionally, it was determined that increased phosphorylation of 5' AMP-activated protein kinase, following emodin treatment, was responsible for increased type I collagen synthesis. These findings clearly indicate that emodin plays an important role in collagen type I synthesis in dermal fibroblasts, thereby making it a potential drug candidate for treating skin aging and wrinkles.

Compound C Protects Against Cisplatin-Induced Nephrotoxicity Through Pleiotropic Effects

AICAR (Acadesine/AICA riboside) as an activator of AMPK, can protect renal tubular cells from cisplatin induced apoptosis. But in our experiment, the dorsomorphin (compound C, an inhibitor of AMPK) also significantly reduced cisplatin induced renal tubular cells apoptosis. Accordingly, we tested whether compound C can protect cisplatin-induced nephrotoxicity and the specific mechanism. Here, we treated Boston University mouse proximal tubular cells (BUMPT-306) with cisplatin and/or different dosages of AICAR (Acadesine/AICA riboside) or compound C to confirm the effect of AICAR and compound C in vitro. The AMPK-siRNA treated cells to evaluate whether the protective effect of compound C was through inhibiting AMPK. Male C57BL/6 mice were used to verify the effect of compound C in vivo. Both compound C and AICAR can reduce renal tubular cells apoptosis in dose-dependent manners, and compound C decreased serum creatinine and renal tubular injury induced by cisplatin. Mechanistically, compound C inhibited P53, CHOP and p-IREα during cisplatin treatment. Our results demonstrated that compound C inhibited AMPK, but the renal protective effects of compound C were not through AMPK. Instead, compound C protected cisplatin nephrotoxicity by inhibiting P53 and endoplasmic reticulum (ER) stress. Therefore, compound C may protect against cisplatin-induced nephrotoxicity through pleiotropic effects.

AMP-activated protein kinase contributes to cisplatin-induced renal epithelial cell apoptosis and acute kidney injury

Cisplatin, a commonly used anticancer drug, has been shown to induce acute kidney injury, which limits its clinical use in cancer treatment. Emerging evidence has suggested that AMP-activated protein kinase (AMPK), which functions as a cellular energy sensor, is activated by various cellular stresses that deplete cellular ATP. However, the potential role of AMPK in cisplatin-induced apoptosis of renal tubular epithelial cells has not been studied. In this study, we demonstrated that cisplatin activates AMPK (Thr¹⁷² phosphorylation) in cultured renal tubular epithelial cells in a time-dependent manner, which was associated with p53 phosphorylation. Compound C, a selective AMPK inhibitor, suppressed cisplatin-induced AMPK activation, p53 phosphorylation, Bax induction, and caspase 3 activation. Furthermore, silencing AMPK expression by siRNA attenuated cisplatin-induced p53 phosphorylation, Bax induction, and caspase 3 activation. In a mouse model of cisplatin-induced kidney injury, compound C inhibited p53 phosphorylation, Bax expression, caspase 3 activation, and apoptosis, protecting the kidney from injury and dysfunction. Taken together, these results suggest that the AMPK-p53-Bax signaling pathway plays a crucial role in cisplatin-induced tubular epithelial cell apoptosis.

Apigenin Alleviates Renal Fibroblast Activation through AMPK and ERK Signaling Pathways In Vitro

OBJECTIVE

Renal fibrosis is a common pathway leading to the progression of chronic kidney disease. Activated fibroblasts contribute remarkably to the development of renal fibrosis. Although apigenin has been demonstrated to play a protective role from fibrotic diseases, its pharmacological effect on renal fibroblast activation remains largely unknown.

MATERIALS AND METHODS

Here, we examined the functional role of apigenin in the activation of renal fibroblasts response to transforming growth factor (TGF)-β1 and its potential mechanisms. Cultured renal fibroblasts (NRK-49F) were exposed to apigenin (1, 5, 10 and 20 μM), followed by the stimulation of TGF-β1 (2 ng/mL) for 24 h. The markers of fibroblast activation were determined. In order to confirm the anti-fibrosis effect of apigenin, the expression of fibrosis-associated genes in renal fibroblasts was assessed. As a consequence, apigenin alleviated fibroblast proliferation and fibroblastmyofibroblast differentiation induced by TGF-β1.

RESULTS

Notably, apigenin significantly inhibited the fibrosis-associated genes expression in renal fibroblasts. Moreover, apigenin treatment significantly increased the phosphorylation of AMP-activated protein kinase (AMPK). Apigenin treatment also obviously reduced TGF-β1 induced phosphorylation of ERK1/2 but not Smad2/3, p38 and JNK MAPK in renal fibroblasts.

CONCLUSION

In a summary, these results indicate that apigenin inhibits renal fibroblast proliferation, differentiation and function by AMPK activation and reduced ERK1/2 phosphorylation, suggesting it could be an attractive therapeutic potential for the treatment of renal fibrosis.

Multifunctional Natural Polymer Nanoparticles as Antifibrotic Gene Carriers for CKD Therapy

BACKGROUND

Progressive fibrosis is the underlying pathophysiological process of CKD, and targeted prevention or reversal of the profibrotic cell phenotype is an important goal in developing therapeutics for CKD. Nanoparticles offer new ways to deliver antifibrotic therapies to damaged tissues and resident cells to limit manifestation of the profibrotic phenotype.

METHODS

We focused on delivering plasmid DNA expressing bone morphogenetic protein 7 (BMP7) or hepatocyte growth factor (HGF)-NK1 (HGF/NK1) by encapsulation within chitosan nanoparticles coated with hyaluronan, to safely administer multifunctional nanoparticles containing the plasmid DNA to the kidneys for localized and sustained expression of antifibrotic factors. We characterized and evaluated nanoparticles in vitro for biocompatibility and antifibrotic function. To assess antifibrotic activity in vivo, we used noninvasive delivery to unilateral ureteral obstruction mouse models of CKD.

RESULTS

Synthesis of hyaluronan-coated chitosan nanoparticles containing plasmid DNA expressing either BMP7 or NGF/NKI resulted in consistently sized nanoparticles, which-following endocytosis driven by CD44⁺ cells-promoted cellular growth and inhibited fibrotic gene expression in vitro. Intravenous tail injection of these nanoparticles resulted in approximately 40%-45% of gene uptake in kidneys in vivo. The nanoparticles attenuated the development of fibrosis and rescued renal function in unilateral ureteral obstruction mouse models of CKD. Gene delivery of BMP7 reversed the progression of fibrosis and regenerated tubules, whereas delivery of HGF/NK1 halted CKD progression by eliminating collagen fiber deposition.

CONCLUSIONS

Nanoparticle delivery of HGF/NK1 conveyed potent antifibrotic and proregenerative effects. Overall, this research provided the proof of concept on which to base future investigations for enhanced targeting and transfection of therapeutic genes to kidney tissues, and an avenue toward treatment of CKD.

AdipoRon Protects against Tubular Injury in Diabetic Nephropathy by Inhibiting Endoplasmic Reticulum Stress

Endoplasmic reticulum (ER) stress has been reported to play a pivotal role in diabetic nephropathy (DN). AdipoRon is a newly developed adiponectin receptor agonist that provides beneficial effects for diabetic mice; however, its underlying mechanism remains to be delineated. Here, we demonstrated increased expression levels of ER stress markers, accompanied by upregulated levels of proinflammatory cytokines and increased expression of collagen I, fibronectin, Bax, and cleaved caspase 3 in the kidneys of db/db mice compared with control mice. Decreased expression of adiponectin receptor 1 (AdipoR1) and phosphorylated 5′AMP-activated kinase (p-AMPK) was also observed in the kidneys of db/db mice. However, these alterations were partially reversed by intragastric gavage with AdipoRon. In vitro, AdipoRon alleviated high-glucose-induced ER stress, oxidative stress, and apoptosis in HK-2 cells, a human tubular cell line. Moreover, AdipoRon restored the expression of AdipoR1 and p-AMPK in HK-2 cells exposed to high-glucose conditions. Additionally, these effects were partially abrogated by pretreatment with AdipoR1 siRNA, but this abrogation was ameliorated by cotreatment with AICAR, an AMPK activator. Furthermore, the effects of AdipoRon were also partially abolished by cotreatment with compound C. Together, these results suggest that AdipoRon exerts favorable effects on diabetes-induced tubular injury in DN by inhibiting ER stress mediated by the AdipoR1/p-AMPK pathway.

Pulmonary Silicosis Alters MicroRNA Expression in Rat Lung and miR-411-3p Exerts Anti-fibrotic Effects by Inhibiting MRTF-A/SRF Signaling

To identify potential therapeutic targets for pulmonary fibrosis induced by silica, we studied the effects of this disease on the expression of microRNAs (miRNAs) in the lung. Rattus norvegicus pulmonary silicosis models were used in conjunction with high-throughput screening of lung specimens to compare the expression of miRNAs in control and pulmonary silicosis tissues. A total of 70 miRNAs were found to be differentially expressed between control and pulmonary silicosis tissues. This included 41 miRNAs that were upregulated and 29 that were downregulated relative to controls. Among them, miR-292-5p, miR-155-3p, miR-1193-3p, miR-411-3p, miR-370-3p, and miR-409a-5p were found to be similarly altered in rat lung and transforming growth factor (TGF)-β1-induced cultured fibroblasts. Using miRNA mimics and inhibitors, we found that miR-1193-3p, miR-411-3p, and miR-370-3p exhibited potent anti-fibrotic effects, while miR-292-5p demonstrated pro-fibrotic effects in TGF-β1-stimulated lung fibroblasts. Moreover, we also found that miR-411-3p effectively reduced pulmonary silicosis in the mouse lung by regulating Mrtfa expression, as demonstrated using biochemical and histological assays. In conclusion, our findings indicate that miRNA expression is perturbed in pulmonary silicosis and suggest that therapeutic interventions targeting specific miRNAs might be effective in the treatment of this occupational disease.

Disruption of CXCR6 Ameliorates Kidney Inflammation and Fibrosis in Deoxycorticosterone Acetate/Salt Hypertension

Circulating cells have a pathogenic role in the development of hypertensive nephropathy. However, how these cells infiltrate into the kidney are not fully elucidated. In this study, we investigated the role of CXCR6 in deoxycorticosterone acetate (DOCA)/salt-induced inflammation and fibrosis of the kidney. Following uninephrectomy, wild-type and CXCR6 knockout mice were treated with DOCA/salt for 3 weeks. Blood pressure was similar between wild-type and CXCR6 knockout mice at baseline and after treatment with DOCA/salt. Wild-type mice develop significant kidney injury, proteinuria, and kidney fibrosis after three weeks of DOCA/salt treatment. CXCR6 deficiency ameliorated kidney injury, proteinuria, and kidney fibrosis following treatment with DOCA/salt. Moreover, CXCR6 deficiency inhibited accumulation of bone marrow–derived fibroblasts and myofibroblasts in the kidney following treatment with DOCA/salt. Furthermore, CXCR6 deficiency markedly reduced the number of macrophages and T cells in the kidney after DOCA/salt treatment. In summary, our results identify a critical role of CXCR6 in the development of inflammation and fibrosis of the kidney in salt-sensitive hypertension.

Mangiferin Alleviates Renal Interstitial Fibrosis in Streptozotocin-Induced Diabetic Mice through Regulating the PTEN/PI3K/Akt Signaling Pathway

Renal interstitial fibrosis is considered to be the typical manifestation of diabetic nephropathy (DN). Mangiferin has shown positive effect on the prevention or treatment of diabetes and its complications. The aim of this study was to explore the inhibitive effect and mechanism of mangiferin on renal interstitial fibrosis in diabetic mice. Streptozotocin- (STZ-) induced diabetic mice were treated with mangiferin (15, 30, and 60 mg/kg/d) for 4 weeks. The morphology of kidneys was observed by Masson's trichrome staining, and the biochemical parameters (fasting blood glucose (FBG), triglyceride (TG), total cholesterol (TC), blood urea nitrogen (BUN), serum creatinine (SCr), and urine protein) were determined by kits. In addition, the levels of inflammatory cytokines (tumor necrosis factor-α (TNF-α), interleukin- (IL-) 6, and IL-1β), antioxidant enzymes (SOD, CAT, and GSH-Px), MDA, and ROS were assessed. Furthermore, the expressions of fibronectin (FN), collagen I (Col I), and α-SMA were measured by immunohistochemistry. Regulations of TGF-β1 and the PTEN/PI3K/Akt pathway were detected by Western blotting. Treatment with mangiferin significantly ameliorated renal dysfunction in diabetic mice, as evidenced by the increase in body weight and decreases in FBG, TG, TC, BUN, SCr, urine protein, and the kidney to body weight ratio (KW/BW). Furthermore, mangiferin treatment prevented renal interstitial fibrosis evidenced by decreases in the positive expression of FN, Col I, and α-SMA, in comparison with morphological changes in the renal tissue. Meanwhile, mangiferin increased antioxidant enzymes, reduced the TNF-α, IL-6, and IL-1β, as well as MDA and ROS. Additionally, mangiferin administration also downregulated TGF-β1, upregulated PTEN, and decreased the phosphorylation of both PI3K and Akt. These findings demonstrate that mangiferin may reduce inflammation and oxidative stress in DN, thereby inhibiting the renal interstitial fibrosis by reducing the TGF-β1-mediated elevation of Col I, FN, and α-SMA through the PTEN/PI3K/Akt pathway.

Patient with a PRKAG2 mutation who developed Immunoglobulin A nephropathy: a case report

Background

PRKAG2 syndrome (PS) is a rare, early-onset autosomal dominant inherited disease caused by mutations in PRKAG2, the gene encoding the regulatory γ2 subunit of adenosine monophosphate-activated protein kinase. PRKAG2 syndrome is associated with many cardiac manifestations, including pre-excitation, arrhythmias, left ventricular hypertrophy, and chronotropic incompetence frequently leading to early pacemaker placement. A meta-analysis of genome-wide association data in subjects with chronic kidney disease (CKD) identified a susceptibility locus in an intron of PRKAG2, which has been replicated in other studies. However, CKD has not been reported in patients with PS or mutations in PRKAG2.

Case summary

We report a case of a woman diagnosed at age 27 with PS when she presented with atrial fibrillation and pre-excitation on electrocardiogram. By age 35, she had developed mild renal insufficiency and a biopsy demonstrated IgA nephropathy (IGAN).

Discussion

This is the first reported case of IGAN in a patient with PS. We discuss both PS and IGAN and the potential mechanisms by which they could be related.

Pomolic Acid Ameliorates Fibroblast Activation and Renal Interstitial Fibrosis through Inhibition of SMAD-STAT Signaling Pathways

Fibrosis is a common pathological feature in most kinds of chronic kidney disease. Transforming growth factor β1 (TGF-β1) signaling is the master pathway regulating kidney fibrosis pathogenesis, in which mothers against decapentaplegic homolog 3 (SMAD3) with signal transducer and activator of transcription 3 (STAT3) act as the integrator of various pro-fibrosis signals. We examine the effects of pomolic acid (PA) on mice with unilateral ureteral obstruction (UUO) and TGF-β1 stimulated kidney fibroblast cells. UUO mice were observed severe tubular atrophy, and tubulointerstitial fibrosis and extracellular matrix (ECM) deposition at seven days postoperatively. However, PA-treated UUO mice demonstrated only moderate injury, minimal fibrosis, and larger reductions in the expression of ECM protein and epithelial-mesenchymal transition (EMT) progress. PA inhibited the SMAD-STAT phosphorylation in UUO mice. PA effects were also confirmed in TGF-β1 stimulated kidney fibroblast cells. In this study, we first demonstrated that PA ameliorates fibroblast activation and renal interstitial fibrosis. Our results indicate that PA may be useful as a potential candidate in the prevention of chronic kidney disease.

Myocardin-related transcription factor A (MRTF-A) contributes to acute kidney injury by regulating macrophage ROS production

A host of pathogenic factors induce acute kidney injury (AKI) leading to insufficiencies of renal function. In the present study we evaluated the role of myocardin-related transcription factor A (MRTF-A) in the pathogenesis of AKI. We report that systemic deletion of MRTF-A or inhibition of MRTF-A activity with CCG-1423 significantly attenuated AKI in mice induced by either ischemia-reperfusion or LPS injection. Of note, MRTF-A deficiency or suppression resulted in diminished renal ROS production in AKI models with down-regulation of NAPDH oxdiase 1 (NOX1) and NOX4 expression. In cultured macrophages, MRTF-A promoted NOX1 transcription in response to either hypoxia-reoxygenation or LPS treatment. Interestingly, macrophage-specific MRTF-A deletion ameliorated AKI in mice. Mechanistic analyses revealed that MRTF-A played a role in regulating histone H4K16 acetylation surrounding the NOX gene promoters by interacting with the acetyltransferase MYST1. MYST1 depletion repressed NOX transcription in macrophages. Finally, administration of a MYST1 inhibitor MG149 alleviated AKI in mice. Therefore, we data illustrate a novel epigenetic pathway that controls ROS production in macrophages contributing to AKI. Targeting the MRTF-A-MYST1-NOX axis may yield novel therapeutic strategies to combat AKI.