PPARα/β Activation Alleviates Age-Associated Renal Fibrosis in Sprague Dawley Rats

c-Jun N-terminal kinase signaling in aging

Aging encompasses a wide array of detrimental effects that compromise physiological functions, elevate the risk of chronic diseases, and impair cognitive abilities. However, the precise underlying mechanisms, particularly the involvement of specific molecular regulatory proteins in the aging process, remain insufficiently understood. Emerging evidence indicates that c-Jun N-terminal kinase (JNK) serves as a potential regulator within the intricate molecular clock governing aging-related processes. JNK demonstrates the ability to diminish telomerase reverse transcriptase activity, elevate β-galactosidase activity, and induce telomere shortening, thereby contributing to immune system aging. Moreover, the circadian rhythm protein is implicated in JNK-mediated aging. Through this comprehensive review, we meticulously elucidate the intricate regulatory mechanisms orchestrated by JNK signaling in aging processes, offering unprecedented molecular insights with significant implications and highlighting potential therapeutic targets. We also explore the translational impact of targeting JNK signaling for interventions aimed at extending healthspan and promoting longevity.

Proteomics reveals defective peroxisomal fatty acid oxidation during the progression of acute kidney injury and repair

Acute kidney injury (AKI) is characterized by a rapid decrease in renal function with high mortality and risk of progression to chronic kidney disease (CKD). Ischemia and reperfusion injury (IRI) is one of the major causes of AKI. However, the cellular and molecular responses of the kidney to IRI are complex and not fully understood. Herein, we conducted unbiased proteomics and bioinformatics analyses in an IRI mouse model on days 3, 7, and 21, and validated the results using IRI, unilateral ureteral obstruction (UUO), and biopsies from patients with AKI or CKD. The results indicated an obvious temporal expression profile of differentially expressed proteins and highlighted impaired lipid metabolism during the progression of AKI to CKD. Acyl-coenzyme A oxidase 1 (Acox1), the first rate-limiting enzyme of peroxisomal fatty acid beta-oxidation, was then selected, and its disturbed expression in the two murine models validated the proteomic findings. Accordingly, Acox1 expression was significantly downregulated in renal biopsies from patients with AKI or CKD, and its expression was negatively correlated with kidney injury score. Furthermore, in contrast to the decreased Acox1 expression, lipid droplet accumulation was remarkably increased in these renal tissues, suggesting dysregulation of fatty acid oxidation. In conclusion, our results suggest that defective peroxisomal fatty acid oxidation might be a common pathological feature in the transition from AKI to CKD, and that Acox1 is a promising intervention target for kidney injury and repair.

Sex-Mediated Differences in TNF Signaling- and ECM-Related Gene Expression in Aged Rat Kidney

Aging leads to the functional decline of an organism, which is associated with age and sex. To understand the functional change of kidneys depending on age and sex, we carried out a transcriptome analysis using RNA sequencing (RNA-Seq) data from rat kidneys. Four differentially expressed gene (DEG) sets were generated according to age and sex, and Gene Ontology analysis and overlapping analysis of Kyoto Encyclopedia of Genes and Genomes pathways were performed for the DEG sets. Through the analysis, we revealed that inflammation- and extracellular matrix (ECM)-related genes and pathways were upregulated in both males and females during aging, which was more prominent in old males than in old females. Furthermore, quantitative real-time PCR analysis confirmed that the expression of tumor necrosis factor (TNF) signaling-related genes, Birc3, Socs3, and Tnfrsf1b, and ECM-related genes, Cd44, Col3a1, and Col5a2, which showed that the genes were markedly upregulated in males and not females during aging. Also, hematoxylin-eosin (H&E) staining for histological analysis showed that renal damage was highly shown in old males rather than old females. In conclusion, in the rat kidney, the genes involved in TNF signaling and ECM accumulation are upregulated in males more than in females during aging. These results suggest that the upregulation of the genes may have a higher contribution to age-related kidney inflammation and fibrosis in males than in females.

Fatty Acid β-Oxidation in Kidney Diseases: Perspectives on Pathophysiological Mechanisms and Therapeutic Opportunities

The kidney is a highly metabolic organ and requires a large amount of ATP to maintain its filtration-reabsorption function, and mitochondrial fatty acid β-oxidation serves as the main source of energy to meet its functional needs. Reduced and inefficient fatty acid β-oxidation is thought to be a major mechanism contributing to kidney diseases, including acute kidney injury, chronic kidney disease and diabetic nephropathy. PPARα, AMPK, sirtuins, HIF-1, and TGF-β/SMAD3 activation have all been shown to play key roles in the regulation of fatty acid β-oxidation in kidney diseases, and restoration of fatty acid β-oxidation by modulation of these molecules can ameliorate the development of such diseases. Here, we disentangle the lipid metabolism regulation properties and potential mechanisms of mesenchymal stem cells and their extracellular vesicles, and emphasize the role of mesenchymal stem cells on lipid metabolism. This review aims to highlight the important role of fatty acid β-oxidation in the progression of kidney diseases, and to explore the fatty acid β-oxidation effects and therapeutic potential of mesenchymal stem cells for kidney diseases.

Druggability of lipid metabolism modulation against renal fibrosis

Renal fibrosis contributes to progressive damage to renal structure and function. It is a common pathological process as chronic kidney disease develops into kidney failure, irrespective of diverse etiologies, and eventually leads to death. However, there are no effective drugs for renal fibrosis treatment at present. Lipid aggregation in the kidney and consequent lipotoxicity always accompany chronic kidney disease and fibrosis. Numerous studies have revealed that restoring the defective fatty acid oxidation in the kidney cells can mitigate renal fibrosis. Thus, it is an important strategy to reverse the dysfunctional lipid metabolism in the kidney, by targeting critical regulators of lipid metabolism. In this review, we highlight the potential "druggability" of lipid metabolism to ameliorate renal fibrosis and provide current pre-clinical evidence, exemplified by some representative druggable targets and several other metabolic regulators with anti-renal fibrosis roles. Then, we introduce the preliminary progress of noncoding RNAs as promising anti-renal fibrosis drug targets from the perspective of lipid metabolism. Finally, we discuss the prospects and deficiencies of drug targeting lipid reprogramming in the kidney.

Protocol for a preclinical systematic review and meta-analysis of pharmacological targeting of peroxisome proliferator-activated receptors in experimental renal injury

INTRODUCTION

Impaired lipid metabolism in the renal tubule plays a prominent role in the progression of renal fibrosis following acute kidney injury (AKI) and in chronic kidney disease (CKD). Peroxisome proliferator-activated receptors (PPARs) are promising druggable targets to mitigate renal fibrosis by redirecting metabolism, including restoration of fatty acid oxidation (FAO) capacity. We aim to synthesise evidence from preclinical studies of pharmacological PPAR targeting in experimental renal injury, and inform the design of future studies evaluating PPAR-mediated restoration of FAO in AKI and CKD.

METHODS AND ANALYSIS

Studies reporting on the impact of pharmacological PPAR modulation in animal models of renal injury will be collected from MEDLINE (Ovid), Embase and Web of Science databases. Predefined eligibility criteria will exclude studies testing medications which are not specific ligands of one or more PPARs and studies involving multimodal pharmacological treatment. The Systematic Review Centre for Laboratory Animal Experimentation risk of bias tool and Collaborative Approach to Meta-Analysis and Review of Animal Experimental Studies checklist will be used to assess quality of the included studies. Data extraction will be followed by a narrative synthesis of the data and meta-analysis where feasible. Analysis will be performed separately for AKI, CKD and renal transplant models. Subgroup analyses will be performed based on study design characteristics, PPAR isotype(s) targeted, and classes of PPAR-targeting medications used. Risk of publication bias will be assessed using funnel plotting, Egger's regression and trim-and-fill analysis.

ETHICS AND DISSEMINATION

Ethical approval is not required. Findings will be published in a peer-reviewed journal and presented at scientific meetings.

PROSPERO REGISTRATION NUMBER

CRD42021265550.

Targeting fatty acid metabolism for fibrotic disorders

Fibrosis is defined by abnormal accumulation of extracellular matrix, which can affect virtually every organ system under diseased conditions. Fibrotic tissue remodeling often leads to organ dysfunction and is highly associated with increased morbidity and mortality. The disease burden caused by fibrosis is substantial, and the medical need for effective antifibrotic therapies is essential. Significant progress has been made in understanding the molecular mechanism and pathobiology of fibrosis, such as transforming growth factor-β (TGF-β)-mediated signaling pathways. However, owing to the complex and dynamic properties of fibrotic disorders, there are currently no therapeutic options that can prevent or reverse fibrosis. Recent studies have revealed that alterations in fatty acid metabolic processes are common mechanisms and core pathways that play a central role in different fibrotic disorders. Excessive lipid accumulation or defective fatty acid oxidation is associated with increased lipotoxicity, which directly contributes to the development of fibrosis. Genetic alterations or pharmacologic targeting of fatty acid metabolic processes have great potential for the inhibition of fibrosis development. Furthermore, mechanistic studies have revealed active interactions between altered metabolic processes and fibrosis development. Several well-known fibrotic factors change the lipid metabolic processes, while altered metabolic processes actively participate in fibrosis development. This review summarizes the recent evidence linking fatty acid metabolism and fibrosis, and provides new insights into the pathogenesis of fibrotic diseases for the development of drugs for fibrosis prevention and treatment.

Advances in Understanding of the Role of Lipid Metabolism in Aging

During aging, body adiposity increases with changes in the metabolism of lipids and their metabolite levels. Considering lipid metabolism, excess adiposity with increased lipotoxicity leads to various age-related diseases, including cardiovascular disease, cancer, arthritis, type 2 diabetes, and Alzheimer's disease. However, the multifaceted nature and complexities of lipid metabolism make it difficult to delineate its exact mechanism and role during aging. With advances in genetic engineering techniques, recent studies have demonstrated that changes in lipid metabolism are associated with aging and age-related diseases. Lipid accumulation and impaired fatty acid utilization in organs are associated with pathophysiological phenotypes of aging. Changes in adipokine levels contribute to aging by modulating changes in systemic metabolism and inflammation. Advances in lipidomic techniques have identified changes in lipid profiles that are associated with aging. Although it remains unclear how lipid metabolism is regulated during aging, or how lipid metabolites impact aging, evidence suggests a dynamic role for lipid metabolism and its metabolites as active participants of signaling pathways and regulators of gene expression. This review describes recent advances in our understanding of lipid metabolism in aging, including established findings and recent approaches.

Alginate Oligosaccharide Ameliorates D-Galactose-Induced Kidney Aging in Mice through Activation of the Nrf2 Signaling Pathway

Aging is an independent risk factor for the development of age-related progressive kidney injury. As a part of the aging process, kidney aging has been indicated to be associated with oxidative stress-induced damage. Ameliorating oxidative damage is therefore considered a promising strategy for delaying kidney aging. Alginate oligosaccharide (AOS) has been reported to have a wide range of biological and pharmacological activities. However, no studies have focused on the role of AOS in delaying the kidney aging process. In this study, we aimed to evaluate the potential effects of AOS on kidney aging and its possible mechanisms. Subcutaneous injection of D-galactose (D-gal) (200 mg·kg⁻¹·d⁻¹) in C57BL/6J mice for 8 weeks was used to establish the aging model. AOS (200 mg·kg⁻¹·d⁻¹) was administered via oral gavage for the last four weeks. As a result, AOS inhibited the D-gal-induced upregulation of aging markers and significantly improved the kidney index and kidney function of D-gal-induced mice. In addition, AOS ameliorated the degree of tissue damage and fibrosis in the aging kidney. To further explore the potential mechanisms by which AOS attenuates the kidney aging process, the associated oxidative stress-induced damage was analyzed in depth. The data showed that AOS upregulated the expression of Klotho and decreased malondialdehyde levels by increasing the expression of antioxidant enzymes. Furthermore, our results suggested that AOS activated the nuclear factor erythrogen-2 associated factor 2 (Nrf2) pathway by promoting Nrf2 nuclear translocation in aging mice and upregulated the downstream expression of heme oxygenase-1 (HO-1) and NADPH quinone oxidoreductase 1 (NQO1). In conclusion, the present study demonstrated that AOS is a promising agent for attenuating kidney aging, and the underlying molecular mechanisms are related to the activation of the Nrf2 signaling pathway.

Potential ameliorative effects of epigallocatechin-3-gallate against cigarette smoke exposure induced renal and hepatic deficits

The environmental pollution caused by cigarette smoke (CS) seriously endangers people's health. Epigallocatechin-3-gallate (EGCG) is the most abundant catechin in green tea. In this study, rats were exposed to CS for 90 days. Kidney function was evaluated by detecting the levels of serum creatinine and blood urea nitrogen. Liver function was evaluated by detecting the activities of alanine aminotransferase and aspartate transaminase. The renal and hepatic oxidative stress and inflammation were assessed by detecting the levels of malondialdehyde, reduced glutathione, antioxidant enzymes (superoxide dismutase and glutathione peroxidase) and proinflammatory cytokines. Organ fibrosis was evaluated by observing collagen deposition via masson staining, by examining the hydroxyproline level, by measuring the mRNA levels of fibrosis-associated genes collagen (Col)-1A1 and Col-3A1, as well as by assessing the activity of profibrotic TGF-β1 pathway. Additionally, renal and hepatic epithelial-mesenchymal transition (EMT) were evaluated. It was observed that EGCG ameliorated the renal and hepatic oxidative stress, inflammation, EMT, as well as inhibited the activation of TGF-β1 signaling pathway induced by CS. These results showed that EGCG could attenuate CS-induced renal and hepatic fibrosis.