LTBP4 Protects Against Renal Fibrosis via Mitochondrial and Vascular Impacts

Inhibiting fatty acid-binding protein 4 reverses inflammation and apoptosis in wasp sting-induced acute kidney injury

Fatty acid-binding protein 4 (FABP4) has been implicated in the pathogenesis of several forms of acute kidney injury (AKI), including rhabdomyolysis, ischemia/reperfusion, sepsis, and cisplatin-induced AKI. However, whether FABP4 inhibition confers a renoprotective effect in wasp sting-induced AKI remains unclear. Therefore, in this study, we investigated the role of FABP4 in wasp sting-induced AKI in vivo and in vitro. We assessed renal dysfunction, mitochondrial injury, cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway-mediated inflammation, and apoptosis. FABP4 expression was significantly higher in wasp sting-induced models of AKI than in the control groups, and pharmacological inhibition of FABP4 attenuated renal dysfunction and tubular injury. Wasp sting-induced AKI was associated with mitochondrial damage induced by excessive mitochondrial fission, which was effectively mitigated by FABP4 inhibition. The FABP4 inhibitor reduced the release of mitochondrial DNA (mtDNA) and cytochrome c (Cyt-c) from damaged mitochondria. cGAS-STING activation induced by mtDNA was downregulated by FABP4 inhibition. Subsequently, inflammation and apoptosis in wasp sting-induced AKI were significantly alleviated, as evidenced by decreased levels of inflammatory mediators and apoptosis-related proteins. In conclusion, FABP4 was found to play a key role in the occurrence and progression of wasp sting-induced AKI.

Extracellular matrix in vascular homeostasis and disease

The extracellular matrix is an essential component and constitutes a dynamic microenvironment of the vessel wall with an indispensable role in vascular homeostasis and disease. From early development through to ageing, the vascular extracellular matrix undergoes various biochemical and biomechanical alterations in response to diverse environmental cues and exerts precise regulatory control over vessel remodelling. Advances in novel technologies that enable the comprehensive evaluation of extracellular matrix components and cell-matrix interactions have led to the emergence of therapeutic strategies that specifically target this fine-tuned network. In this Review, we explore various aspects of extracellular matrix biology in vascular development, disorders and ageing, emphasizing the effect of the extracellular matrix on disease initiation and progression. Additionally, we provide an overview of the potential therapeutic implications of targeting the extracellular matrix microenvironment in vascular diseases.

Tubular MYDGF Slows Progression of Chronic Kidney Disease by Maintaining Mitochondrial Homeostasis

Mitochondrial dysfunction is a key event driving the maladaptive repair of tubular epithelial cells during the transition from acute kidney injury to chronic kidney disease (CKD). Therefore, identifying potential targets involved in mitochondrial dysfunction in tubular epithelial cells is clinically important. Myeloid-derived growth factor (MYDGF), a novel secreted protein, plays important roles in multiple cardiovascular diseases, but the function of MYDGF in tubular epithelial cells remains unknown. In the present study, it is found that MYDGF expression is significantly reduced in the cortex of the kidney, especially in the proximal tubules, from mice with CKD. Notably, lower expression of MYDGF is observed in tubules from patients with CKD and the level of MYDGF correlated with key factors related to kidney fibrosis and estimated glomerular filtration rate (eGFR) in patients with CKD. Tubule-specific deletion of Mydgf exacerbates kidney injury in mice with CKD; however, Mydgf overexpression attenuates kidney fibrosis by remodeling mitochondrial homeostasis in tubular epithelial cells. Mechanistically, renal tubular MYDGF positively regulates the expression of isocitrate dehydrogenase 2 (IDH2), restores mitochondrial homeostasis, and slows CKD progression. Thus, this study indicates that MYDGF derived from tubules may be an effective therapeutic strategy for patients with CKD.

Sanqi oral solution ameliorates renal fibrosis by suppressing fibroblast activation via HIF-1α/PKM2/glycolysis pathway in chronic kidney disease

ETHNOPHARMACOLOGICAL RELEVANCE

Sanqi oral solution (SQ) is a traditional Chinese patent medicine, widely used to treat chronic kidney diseases (CKD) in the clinic in China. Previous studies have confirmed its anti-renal fibrosis effect, but the specific pharmacological mechanism is still unclear.

AIM OF THE STUDY

Focusing on energy metabolism in fibroblasts, the renoprotective mechanism of SQ was investigated in vitro and in vivo.

METHODS

Firstly, the fingerprint of SQ was constructed and its elementary chemical composition was analyzed. In the 5/6Nx rats experiment, the efficacy of SQ on the kidney was evaluated by detecting serum and urine biochemical indexes and pathological staining of renal tissues. Lactic acid and pyruvic acid levels in serum and renal tissues were detected. PCNA protein expression in kidney tissue was detected by immunofluorescence assay and Western blot. Expression levels of HIF-1α, PKM2 and HK2 were determined by immunohistochemistry, Western blot or RT-qPCR assay. In addition, the effect of SQ intervention on cell proliferation and glycolysis was evaluated in TGF-β1-induced NRK-49F cells, and the role of SQ exposure and HIF-1α/PKM2/glycolysis pathway were further investigated by silencing and overexpressing HIF-1α gene in NRK-49F cells.

RESULTS

In 5/6 Nx rats, SQ effectively improved renal function and treated renal injury. It reduced the levels of lactic acid and pyruvic acid in kidney homogenates from CKD rats and decreased the expression levels of HIF-1α, PKM2, HK2, α-SMA, vimentin, collagen I and PCNA in kidney tissues. Similar results were observed in vitro. SQ inhibited NRK-49F cell proliferation, glycolysis and the expression levels of HIF-1α, PKM2 induced by TGF-β1. Furthermore, we established NRK-49F cells transfected with siRNA or pDNA to silence or overexpress the HIF-1α gene. Overexpression of HIF-1α promoted cellular secretion of lactic acid and pyruvic acid in TGF-β1-induced NRK-49F cells, however, this change was reversed by intervention with SQ or silencing the HIF-1α gene. Overexpression of HIF-1α can further induce increased PKM2 expression, while SQ intervention can reduce PKM2 expression. Moreover, PKM2 expression was also inhibited after silencing HIF-1α gene, and SQ was not effective even when given.

CONCLUSION

The mechanism of action of SQ was explored from the perspective of energy metabolism, and it was found to regulate PKM2-activated glycolysis, inhibit fibroblast activation, and further ameliorate renal fibrosis in CKD by targeting HIF-1α.

The Role of Oxidative Stress as a Mechanism in the Pathogenesis of Acute Heart Failure in Acute Kidney Injury

Despite a large amount of research on synchronous and mutually induced kidney and heart damage, the basis of the disease is still not fully clarified. Healthy mitochondria are essential for normal kidney and heart function. Mitochondrial dysfunction occurs when the clearance or process of generation and fragmentation of mitochondria is disturbed. The kidney is the second organ after the heart in terms of the number of mitochondria. Kidney tubules are rich in mitochondria due to the high energy requirements for absorption of large amounts of ultrafiltrate and dissolved substances. The place of action of oxidative stress is the influence on the balance in the production and breakdown of the mitochondrial reactive oxygen species. A more precise determination of the place and role of key factors that play a role in the onset of the disease is necessary for understanding the nature of the onset of the disease and the creation of therapy in the future. This underscores the urgent need for further research. The narrative review integrates results found in previously performed studies that have evaluated oxidative stress participation in cardiorenal syndrome type 3.

Renal tubular epithelial cells response to injury in acute kidney injury

Acute kidney injury (AKI) is a clinical syndrome characterized by a rapid and significant decrease in renal function that can arise from various etiologies, and is associated with high morbidity and mortality. The renal tubular epithelial cells (TECs) represent the central cell type affected by AKI, and their notable regenerative capacity is critical for the recovery of renal function in afflicted patients. The adaptive repair process initiated by surviving TECs following mild AKI facilitates full renal recovery. Conversely, when injury is severe or persistent, it allows the TECs to undergo pathological responses, abnormal adaptive repair and phenotypic transformation, which will lead to the development of renal fibrosis. Given the implications of TECs fate after injury in renal outcomes, a deeper understanding of these mechanisms is necessary to identify promising therapeutic targets and biomarkers of the repair process in the human kidney.

Role of TGFβ-producing regulatory T cells in scleroderma and end-stage organ failure

Regulatory T cells (Tregs) are crucial immune cells that initiate a tolerable immune response. Transforming growth factor-beta (TGFβ) is a key cytokine produced by Tregs and plays a significant role in stimulating tissue fibrosis. Systemic sclerosis, an autoimmune disease characterized by organ fibrosis, is associated with an overrepresentation of regulatory T cells. This review aims to identify Treg-dominant tolerable host immune reactions and discuss their association with scleroderma and end-stage organ failure. End-stage organ failures, including heart failure, liver cirrhosis, uremia, and pulmonary fibrosis, are frequently linked to tissue fibrosis. This suggests that TGFβ-producing Tregs are involved in the pathogenesis of these conditions. However, the exact significance of TGFβ and the mechanisms through which it induces tolerable immune reactions during end-stage organ failure remain unclear. A deeper understanding of these mechanisms could lead to improved preventive and therapeutic strategies for these severe diseases.

RAS protein activator-like 2 (RASAL2) initiates peritubular capillary rarefaction in hypoxic renal interstitial fibrosis

The progression of chronic kidney disease (CKD) often involves renal interstitial fibrosis (RIF) and subsequent loss of peritubular capillaries (PTCs), which enhances disease severity. Despite advancements in our understanding of fibrosis, effective interventions for reversing capillary loss remain elusive. Notably, RIF exhibits reduced capillary density, whereas renal cell carcinoma (RCC) shows robust angiogenesis under hypoxic conditions. Using RNA sequencing and bioinformatics, we identified differentially expressed genes (DEGs) in hypoxic human renal tubular epithelial cells (HK-2) and renal cancer cells (786-0). Analysis of altered Ras and PI3K/Akt pathways coupled with hub gene investigation revealed RAS protein activator-like 2 (RASAL2) as a key candidate. Subsequent in vitro and in vivo studies confirmed RASAL2's early-stage response in RIF, which reduced with fibrosis progression. RASAL2 suppression in HK-2 cells enhanced angiogenesis, as evidenced by increased proliferation, migration, and branching of human umbilical vein endothelial cells (HUVECs) co-cultured with HK-2 cells. In mice, RASAL2 knockdown improved Vascular endothelial growth factor A (VEGFA) and Proliferating cell nuclear antigen (PCNA) levels in unilateral ureteral occlusion (UUO)-induced fibrosis (compared to wild type). Hypoxia-inducible factor 1 alpha (HIF-1α) emerged as a pivotal mediator, substantiated by chromatin immunoprecipitation (ChIP) sequencing, with its induction linked to activation. Hypoxia increased the production of RASAL2-enriched extracellular vesicles (EVs) derived from tubular cells, which were internalized by endothelial cells, contributing to the exacerbation of PTC loss. These findings underscore RASAL2's role in mediating reduced angiogenesis in RIF and reveal a novel EV-mediated communication between hypoxic tubular- and endothelial cells, demonstrating a complex interplay between angiogenesis and fibrosis in CKD pathogenesis.

Role of mitochondria in pathogenesis and therapy of renal fibrosis

Renal fibrosis, specifically tubulointerstitial fibrosis, represents the predominant pathological consequence observed in the context of progressive chronic kidney conditions. The pathogenesis of renal fibrosis encompasses a multifaceted interplay of mechanisms, including but not limited to interstitial fibroblast proliferation, activation, augmented production of extracellular matrix (ECM) components, and impaired ECM degradation. Notably, mitochondria, the intracellular organelles responsible for orchestrating biological oxidation processes in mammalian cells, assume a pivotal role within this intricate milieu. Mitochondrial dysfunction, when manifest, can incite a cascade of events, including inflammatory responses, perturbed mitochondrial autophagy, and associated processes, ultimately culminating in the genesis of renal fibrosis. This comprehensive review endeavors to furnish an exegesis of mitochondrial pathophysiology and biogenesis, elucidating the precise mechanisms through which mitochondrial aberrations contribute to the onset and progression of renal fibrosis. We explored how mitochondrial dysfunction, mitochondrial cytopathy and mitochondrial autophagy mediate ECM deposition and renal fibrosis from a multicellular perspective of mesangial cells, endothelial cells, podocytes, macrophages and fibroblasts. Furthermore, it succinctly encapsulates the most recent advancements in the realm of mitochondrial-targeted therapeutic strategies aimed at mitigating renal fibrosis.

Comprehensive overview of the role of mitochondrial dysfunction in the pathogenesis of acute kidney ischemia-reperfusion injury: a narrative review

Acute kidney ischemia-reperfusion (IR) injury is a life-threatening condition that predisposes individuals to chronic kidney disease. Since the kidney is one of the most energy-demanding organs in the human body and mitochondria are the powerhouse of cells, mitochondrial dysfunction plays a central role in the pathogenesis of IR-induced acute kidney injury. Mitochondrial dysfunction causes a reduction in adenosine triphosphate production, loss of mitochondrial dynamics (represented by persistent fragmentation), and impaired mitophagy. Furthermore, the pathological accumulation of succinate resulting from fumarate reduction under oxygen deprivation (ischemia) in the reverse flux of the Krebs cycle can eventually lead to a burst of reactive oxygen species driven by reverse electron transfer during the reperfusion phase. Accumulating evidence indicates that improving mitochondrial function, biogenesis, and dynamics, and normalizing metabolic reprogramming within the mitochondria have the potential to preserve kidney function during IR injury and prevent progression to chronic kidney disease. In this review, we summarize recent advances in understanding the detrimental role of metabolic reprogramming and mitochondrial dysfunction in IR injury and explore potential therapeutic strategies for treating kidney IR injury.

Latent transforming growth factor beta binding protein 4: A regulator of mitochondrial function in acute kidney injury

Recently, latent transforming growth factor beta binding protein 4 (LTBP4) was implicated in the pathogenesis of renal damage through its modulation of mitochondrial dynamics. The seminal article written by Su et al. entitled "LTBP4 (Latent Transforming Growth Factor Beta Binding Protein 4) Protects Against Renal Fibrosis via Mitochondrial and Vascular Impacts" uncovers LTBP4's renoprotective role against acute kidney injury via modulating mitochondrial dynamics. Recently, LTBP4 has emerged as a driver in the mitochondrial-dependent modulation of age-related organ pathologies. This article aims to expand our understanding of LTBP4's diverse roles in these diseases in the context of these recent findings.