Involvement of YTHDF1 in renal fibrosis progression via up-regulating YAP

The hippo-YAP1/HIF-1α pathway mediates arsenic-induced renal fibrosis

Epidemiological evidence reveals that arsenic increases the risk of chronic kidney disease (CKD) in humans, but its mechanism of action has so far been unclear. Fibrosis is the manifestation of end-stage renal disease. Hypoxia is recognized as a vital event accompanying the progression of renal fibrosis. KM mice were exposed to 0, 20, 40, and 80 mg/L NaAsO2 for 12 weeks. HK-2 cells were treated with 1 μM NaAsO2 for 4 weeks. The results showed that arsenic increased the expression of hypoxia-inducible factor 1α (HIF-1α) (P < 0.05), which is involved in inorganic arsenic-induced renal fibrosis. The Hippo signaling pathway is the upstream signal of HIF-1α and the kinase cascade of Large tumor suppressor kinase 1 (LATS1) and Yes-associated protein 1 (YAP1) is the heart of the Hippo pathway. Our results showed that protein expressions of LATS1 and phosphorylated YAP1 were decreased, and dephosphorylated YAP1 expression increased in arsenic-treated mouse kidneys and human HK-2 cells (P < 0.05). Our research manifested that arsenic treatment suppressed the Hippo signaling and induced high expression of YAP1 into the nucleus. We also found that YAP1 was involved in arsenic-induced renal fibrosis by forming a complex with HIF-1α and maintaining HIF-1α stability. Our findings indicate that YAP1 is a potential target for molecular-based therapy for arsenic-mediated renal fibrosis.

Targeted delivery of type I TGF-β receptor-mimicking peptide to fibrotic kidney for improving kidney fibrosis therapy via enhancing the inhibition of TGF-β1/Smad and p38 MAPK pathways

Renal fibrosis is a representative pathological feature of various chronic kidney diseases, and efficient treatment is needed. Interstitial myofibroblasts are a key driver of kidney fibrosis, which is dependent on the binding of TGF-β1 to type I TGF-β receptor (TβRI) and TGF-β1-related signaling pathways. Therefore, attenuating TGF-β1 activity by competing with TGF-β1 in myofibroblasts is an ideal strategy for treating kidney fibrosis. Recently, a novel TβRI-mimicking peptide RIPΔ demonstrated a high affinity for TGF-β1. Thus, it could be speculated that RIPΔ may be used for anti-fibrosis therapy. Platelet-derived growth factor β receptor (PDGFβR) is highly expressed in fibrotic kidney. In this study, we found that target peptide Z-RIPΔ, which is RIPΔ modified with PDGFβR-specific affibody ZPDGFβR, was specifically and highly taken up by TGF-β1-activated NIH3T3 fibroblasts. Moreover, Z-RIPΔ effectively inhibited the myofibroblast proliferation, migration and fibrosis response in vitro. In vivo and ex vivo experiments showed that Z-RIPΔ specifically targeted fibrotic kidney, improved the damaged renal function, and ameliorated kidney histopathology and renal fibrosis in UUO mice. Mechanistic studies showed that Z-RIPΔ hold the stronger inhibition of the TGF-β1/Smad and TGF-β1/p38 pathways than unmodified RIPΔ in vitro and in vivo. Furthermore, systemic administration of Z-RIPΔ to UUO mice led to minimal toxicity to major organs. Taken together, RIPΔ modified with ZPDGFβR increased its therapeutic efficacy and reduced its systemic toxicity, making it a potential candidate for targeted therapy for kidney fibrosis.

m6A RNA methylation: The latent string-puller in fibrosis

Fibrosis is a pathological phenomenon characterized by the aberrant accumulation of extracellular matrix (ECM) in tissues. Fibrosis is a universally age-related disease involving that many organs and is the final stage of many chronic inflammatory diseases, which often threaten the patient's health. Undoubtedly, fibrosis has become a serious economic and health burden worldwide, However, the pathogenesis of fibrosis is complex. Further, the key molecules still remain to be unraveled. Hence, so far, there have been no effective treatments designed against the key targets of fibrosis. The methylation modification on the nitrogen atom at position 6 of adenine (m6A) is the most common mRNA modification in mammals. There is increasing evidence that m6A is actively involved in the pathogenesis of fibrosis. This review aims to highlight m6A-associated mechanisms and functions in several organic fibrosis, which implies that m6A is universal and critical for fibrosis and summarize the outlook of m6A in the treatment of fibrosis. This may light up the unknown aspects of this condition for researchers interested to explore fibrosis further.

PDGFβ receptor-targeted delivery of truncated transforming growth factor β receptor type II for improving the in vitro and in vivo anti-renal fibrosis activity via strong inactivation of TGF-β1/Smad signaling pathway

Truncated transforming growth factor β receptor type II (tTβRII), serving as a trap for binding excessive transforming growth factor β1 (TGF-β1) by means of competing with wild-type TβRII, is a promising strategy for the treatment of kidney fibrosis. Platelet-derived growth factor β receptor (PDGFβR) is highly expressed in interstitial myofibroblasts in kidney fibrosis. This study identified the interaction between a novel tTβRII variant Z-tTβRII (PDGFβR-specific affibody ZPDGFβR fused to the N-terminus of tTβRII) and TGF-β1. Moreover, Z-tTβRII highly targeted to TGF-β1-activated NIH3T3 cells and UUO-induced fibrotic kidney, but less to normal cells, tissues, and organs. Furthermore, Z-tTβRII significantly inhibited cell proliferation and migration, and reduced fibrosis markers expression and phosphorylation level of Smad2/3 in activated NIH3T3 cells. Meanwhile, Z-tTβRII markedly alleviated the kidney histopathology and fibrotic responses, and inhibited the TGF-β1/Smad signaling pathway in UUO mice. Besides, Z-tTβRII showed good safety performance in the treatment of UUO mice. In conclusion, these results demonstrated that Z-tTβRII may be a potential candidate for a targeting therapy on renal fibrosis due to the high potential of fibrotic kidney-targeting and strong anti-renal fibrosis activity.

Emerging role of m6A modification in fibrotic diseases and its potential therapeutic effect

Fibrosis can occur in a variety of organs such as the heart, lung, liver and kidney, and its pathological changes are mainly manifested by an increase in fibrous connective tissue and a decrease in parenchymal cells in organ tissues, and continuous progression can lead to structural damage and organ hypofunction, or even failure, seriously threatening human health and life. N6-methyladenosine (m6A) modification, as one of the most common types of internal modifications of RNA in eukaryotes, exerts a multifunctional role in physiological and pathological processes by regulating the metabolism of RNA. With the in-depth understanding and research of fibrosis, we found that m6A modification plays an important role in fibrosis, and m6A regulators can further participate in the pathophysiological process of fibrosis by regulating the function of specific cells. In our review, we summarized the latest research advances in m6A modification in fibrosis, as well as the specific functions of different m6A regulators. In addition, we focused on the mechanisms and roles of m6A modification in cardiac fibrosis, liver fibrosis, pulmonary fibrosis, renal fibrosis, retinal fibrosis and oral submucosal fibrosis, with the aim of providing new insights and references for finding potential therapeutic targets for fibrosis. Finally, we discussed the prospects and challenges of targeted m6A modification in the treatment of fibrotic diseases.

METTL3-mediated m6A RNA methylation induces the differentiation of lung resident mesenchymal stem cells into myofibroblasts via the miR-21/PTEN pathway

BACKGROUND

The accumulation of myofibroblasts is the key pathological feature of pulmonary fibrosis (PF). Aberrant differentiation of lung-resident mesenchymal stem cells (LR-MSCs) has been identified as a critical source of myofibroblasts, but the molecular mechanisms underlying this process remain largely unknown. In recent years, N6-methyladenosine (m6A) RNA modification has been implicated in fibrosis development across diverse organs; however, its specific role in promoting the differentiation of LR-MSCs into myofibroblasts in PF is not well defined.

METHODS

In this study, we examined the levels of m6A RNA methylation and the expression of its regulatory enzymes in both TGF-β1-treated LR-MSCs and fibrotic mouse lung tissues. The downstream target genes of m6A and their related pathways were identified according to a literature review, bioinformatic analysis and experimental verification. We also assessed the expression levels of myofibroblast markers in treated LR-MSCs and confirmed the involvement of the above-described pathway in the aberrant differentiation direction of LR-MSCs under TGF-β1 stimulation by overexpressing or knocking down key genes within the pathway.

RESULTS

Our results revealed that METTL3-mediated m6A RNA methylation was significantly upregulated in both TGF-β1-treated LR-MSCs and fibrotic mouse lung tissues. This process directly led to the aberrant differentiation of LR-MSCs into myofibroblasts by targeting the miR-21/PTEN pathway. Moreover, inhibition of METTL3 or miR-21 and overexpression of PTEN could rescue this abnormal differentiation.

CONCLUSION

Our study demonstrated that m6A RNA methylation induced aberrant LR-MSC differentiation into myofibroblasts via the METTL3/miR-21/PTEN signaling pathway. We indicated a novel mechanism to promote PF progression. Targeting METTL3-mediated m6A RNA methylation and its downstream targets may present innovative therapeutic approaches for the prevention and treatment of PF.

METTL3-mediated N6-methyladenosine modification stimulates mitochondrial damage and ferroptosis of kidney tubular epithelial cells following acute kidney injury by modulating the stabilization of MDM2-p53-LMNB1 axis

N6-methyladenosine (m6A) and MELLT3 assume a role in the development of acute kidney injury (AKI). However, their mechanism in AKI remains under-explored. On this basis, this study explored the mechanism of MELLT3 in mitochondrial damage and ferroptosis of kidney tubular epithelial cells after AKI. HK-2 cells were induced by lipopolysaccharide (LPS) to simulate AKI, followed by gain and loss of function of genes, detection of mitochondrial damage and ferroptosis indicators, and analysis of gene interactions. An AKI mouse model was developed using the cecal ligation and puncture (CLP) method to investigate the effect of METTL3 knockdown on kidney injury. MDM2 and LMNB1 were upregulated and p53 was downregulated in LPS-treated HK-2 cells. Mechanistically, the E3 ubiquitin ligase MDM2 increased p53 ubiquitination to activate LMNB1. METTL3 knockdown decreased m6A methylation of MDM2, thus diminishing YTHDF1-mediated MDM2 mRNA stability and translation in LPS-treated HK-2 cells. Knockdown of LMNB1, MDM2, or METTL3 reduced NO, MDA, iron ion, and ROS levels as well as mitochondrial damage and raised SOD, GSH, XCT, GPX4, FPN1, and TFR1 levels in LPS-treated HK-2 cells. The in vivo results showed that METTL3 knockdown reduced renal injury and ferroptosis in CLP mice. METTL3 knockdown prevents mitochondrial damage and ferroptosis of kidney tubular epithelial cells after AKI via the MDM2-p53-LMNB1 axis.

YTHDF1 mitigates acute kidney injury via safeguarding m6A-methylated mRNAs in stress granules of renal tubules

Acute kidney injury (AKI) presents a daunting challenge with limited therapeutic options. To explore the contribution of N6-methyladenosine (m6A) in AKI development, we have investigated m6A-modified mRNAs within renal tubular cells subjected to injuries induced by diverse stressors. Notably, while the overall level of m6A-modified RNA remains unaltered in renal tubular cells facing stress, a distinct phenomenon emerges-mRNAs bearing m6A methylation exhibit a pronounced tendency to accumulate within stress granules (SGs), structures induced in response to these challenges. Cumulation of m6A-modified mRNA in SGs is orchestrated by YTHDF1, a m6A 'reader' closely associated with SGs. Strikingly, AKI patients and various mouse AKI models showcase elevated levels of renal tubular YTHDF1. Depleting YTHDF1 within renal tubular cells leads to a marked reduction in m6A-modified mRNA accumulation within SGs, accompanied by an escalation in cell apoptosis under stress challenges. The significance of YTHDF1's protective role is further underscored by findings in AKI mouse models triggered by cisplatin or renal ischemia-reperfusion treatments. In particular, renal tubular-specific YTHDF1 knockout mice exhibit heightened AKI severity when contrasted with their wild-type counterparts. Mechanistic insights reveal that YTHDF1 fulfills a crucial function by safeguarding m6A-modified mRNAs that favor cell survival-exemplified by SHPK1-within SGs amid stress-challenged renal tubular cells. Our findings collectively shed light on the pivotal role of YTHDF1 in shielding renal tubules against AKI, through its adeptness in recruiting and preserving m6A-modified mRNAs within stress-induced SGs.

N6-methyladenosine methylation in kidney injury

Multiple mechanisms are involved in kidney damage, among which the role of epigenetic modifications in the occurrence and development of kidney diseases is constantly being revealed. However, N6-methyladenosine (M6A), a well-known post-transcriptional modification, has been regarded as the most prevalent epigenetic modifications in higher eukaryotic, which is involved in various biological processes of cells such as maintaining the stability of mRNA. The role of M6A modification in the mechanism of kidney damage has attracted widespread attention. In this review, we mainly summarize the role of M6A modification in the progression of kidney diseases from the following aspects: the regulatory pattern of N6-methyladenosine, the critical roles of N6-methyladenosine in chronic kidney disease, acute kidney injury and renal cell carcinoma, and then reveal its potential significance in the diagnosis and treatment of various kidney diseases. A better understanding of this field will be helpful for future research and clinical treatment of kidney diseases.

YAP/TAZ: Molecular pathway and disease therapy

The Yes-associated protein and its transcriptional coactivator with PDZ-binding motif (YAP/TAZ) are two homologous transcriptional coactivators that lie at the center of a key regulatory network of Hippo, Wnt, GPCR, estrogen, mechanical, and metabolism signaling. YAP/TAZ influences the expressions of downstream genes and proteins as well as enzyme activity in metabolic cycles, cell proliferation, inflammatory factor expression, and the transdifferentiation of fibroblasts into myofibroblasts. YAP/TAZ can also be regulated through epigenetic regulation and posttranslational modifications. Consequently, the regulatory function of these mechanisms implicates YAP/TAZ in the pathogenesis of metabolism-related diseases, atherosclerosis, fibrosis, and the delicate equilibrium between cancer progression and organ regeneration. As such, there arises a pressing need for thorough investigation of YAP/TAZ in clinical settings. In this paper, we aim to elucidate the signaling pathways that regulate YAP/TAZ and explore the mechanisms of YAP/TAZ-induce diseases and their potential therapeutic interventions. Furthermore, we summarize the current clinical studies investigating treatments targeting YAP/TAZ. We also address the limitations of existing research on YAP/TAZ and propose future directions for research. In conclusion, this review aims to provide fresh insights into the signaling mediated by YAP/TAZ and identify potential therapeutic targets to present innovative solutions to overcome the challenges associated with YAP/TAZ.

Hippo signaling in acute kidney injury to chronic kidney disease transition: current understandings and future targets

Acute kidney injury (AKI)-to-chronic kidney disease (CKD) transition is a slow but persistent progression toward end-stage kidney disease. Earlier reports have shown that Hippo components, such as Yes-associated protein (YAP) and its homolog TAZ (Transcriptional coactivator with PDZ-binding motif), regulate inflammation and fibrogenesis during the AKI-to-CKD transition. Notably, the roles and mechanisms of Hippo components vary during AKI, AKI-to-CKD transition, and CKD. Hence, it is important to understand these roles in detail. This review addresses the potential of Hippo regulators or components as future therapeutic targets for halting the AKI-to-CKD transition.

Dapagliflozin delays renal fibrosis in diabetic kidney disease by inhibiting YAP/TAZ activation

In diabetic kidney disease (DKD), the long-term hyperactivation of yes-associated protein (YAP)/transcriptional coactivator PDZ-binding motif (TAZ) in renal proximal tubule epithelial cells (RPTCs) plays an important role in progressive tubulointerstitial fibrosis. Sodium-glucose cotransporter 2 (SGLT2) is highly expressed in RPTCs, but its relationship with YAP/TAZ in tubulointerstitial fibrosis in DKD is still unknown. The purpose of this study was to clarify whether the SGLT2 inhibitor (SGLT2i) dapagliflozin could alleviate renal tubulointerstitial fibrosis in DKD by regulating YAP/TAZ. We examined 58 patients with DKD confirmed by renal biopsy and found that the expression and nuclear translocation of YAP/TAZ increased with the exacerbation of chronic kidney disease classification. In models of DKD, dapagliflozin showed similar effects to verteporfin, an inhibitor of YAP/TAZ, in reducing the activation of YAP/TAZ and downregulating the expression of their target genes, connective tissue growth factor (CTGF) and amphiregulin in vivo and in vitro. Silencing SGLT2 also confirmed this effect. Importantly, dapagliflozin showed a better effect than verteporfin in inhibiting inflammation, oxidative stress and fibrosis in the kidney in DKD rats. Taken together, this study proved for the first time that dapagliflozin delayed tubulointerstitial fibrosis at least partly by inhibiting YAP/TAZ activation, which further enriched the antifibrotic effect of SGLT2i.

Bayesian mixed model analysis uncovered 21 risk loci for chronic kidney disease in boxer dogs

Chronic kidney disease (CKD) affects 10% of the human population, with only a small fraction genetically defined. CKD is also common in dogs and has been diagnosed in nearly all breeds, but its genetic basis remains unclear. Here, we performed a Bayesian mixed model genome-wide association analysis for canine CKD in a boxer population of 117 canine cases and 137 controls, and identified 21 genetic regions associated with the disease. At the top markers from each CKD region, the cases carried an average of 20.2 risk alleles, significantly higher than controls (15.6 risk alleles). An ANOVA test showed that the 21 CKD regions together explained 57% of CKD phenotypic variation in the population. Based on whole genome sequencing data of 20 boxers, we identified 5,206 variants in LD with the top 50 BayesR markers. Following comparative analysis with human regulatory data, 17 putative regulatory variants were identified and tested with electrophoretic mobility shift assays. In total four variants, three intronic variants from the MAGI2 and GALNT18 genes, and one variant in an intergenic region on chr28, showed alternative binding ability for the risk and protective alleles in kidney cell lines. Many genes from the 21 CKD regions, RELN, MAGI2, FGFR2 and others, have been implicated in human kidney development or disease. The results from this study provide new information that may enlighten the etiology of CKD in both dogs and humans.

RNA N6 -methyladenosine modifications and potential targeted therapeutic strategies in kidney disease

Epigenetic modifications have received increasing attention and have been shown to be extensively involved in kidney development and disease progression. Among them, the most common RNA modification, N⁶ -methyladenosine (m⁶ A), has been shown to dynamically and reversibly exert its functions in multiple ways, including splicing, export, decay and translation initiation efficiency to regulate mRNA fate. Moreover, m⁶ A has also been reported to exert biological effects by destabilizing base pairing to modulate various functions of RNAs. Most importantly, an increasing number of kidney diseases, such as renal cell carcinoma, acute kidney injury and chronic kidney disease, have been found to be associated with aberrant m⁶ A patterns. In this review, we comprehensively review the critical roles of m⁶ A in kidney diseases and discuss the possibilities and relevance of m⁶ A-targeted epigenetic therapy, with an integrated comprehensive description of the detailed alterations in specific loci that contribute to cellular processes that are associated with kidney diseases.

Silencing of YTHDF1 Attenuates Cerebral Stroke by Inducing PTEN Degradation and Activating the PTEN/AKT/mTOR Pathway

N6-methyladenosine (m6A) methylation regulates pathological processes of cerebral stroke, which can lead to disability and death. Herein, we explored the role of a m6A "reader" YTHDF1 in stroke. MCAO (middle cerebral artery occlusion) rat model and hypoxia/reoxygenation (H/R)-induced neurocytes cell model were established. TTC staining assay assessed the infarction area and TUNEL assay analyzed apoptosis. Neurological score was analyzed to evaluate the brain function. Cell counting kit-8, LDH release, and flow cytometry assessed cellular proliferation, cell death, and cell apoptosis in vitro. The expression of YTHDF1, PTEN, and the factors in the PI3K/AKT/mTOR pathway was measured using western blot. The interaction between YTHDF1 and PTEN was confirmed luciferase assay and RNA immunoprecipitation assay. The results indicated that YTHDF1 was upregulated in the brain tissues of MCAO mice and H/R-treated cells. Knockdown of YTHDF1 inhibited the infarct area, neuron damage, and apoptosis. Additionally, YTHDF1 depletion promoted viability and inhibited apoptosis of H/R-treated cells. Moreover, YTHDF1 inactivated the PI3K/AKT/mTOR pathway. Mechanistically, YTHDF1 binds to PTEN to increase PTEN mRNA stability. Overexpressing PTEN rescued the effects of YTHDF1 depletion on cell viability and apoptosis. In conclusion, silencing of YTHDF1 decelerated the progression of cerebral stroke through promoting PTEN degradation and activating the PTEN/AKT/mTOR pathway, suggesting that YTHDF1 has the potential to be a therapeutic target for stroke.

N6-methyladenine RNA Methylation Epigenetic Modification and Kidney Diseases

RNA methylation modification is a rapidly developing field in epigenetics. N6-methyladensine (m⁶A) is the most common internal modification in eukaryotic mRNA. m⁶A group regulates RNA splicing, stability, translocation, and translation. Enzymes catalyzing this process were termed as writers, erasers, and readers. Recent studies have focused on exploring the role of RNA methylation in human diseases. RNA methylation modifications, particularly m⁶A, play important roles in the pathogenesis of kidney diseases. In this review, we provide a brief description of m⁶A and summarize the impact of m⁶A on acute and chronic kidney disease (CKD) and possible future study directions for this research.