Matrix protein Tenascin-C promotes kidney fibrosis via STAT3 activation in response to tubular injury

Inhibition of PKM2 by shikonin impedes TGF-β1 expression by repressing histone lactylation to alleviate renal fibrosis

BACKGROUND

Macrophage-myofibroblast transition (MMT) plays a significant role in the progression of renal fibrosis in chronic kidney disease (CKD), making inhibition of MMT a promising therapeutic strategy. Pyruvate kinase M2 (PKM2) and its metabolite lactate are implicated in the pathogenesis of renal fibrosis; however, the mechanisms through which they contribute to this process remain poorly understood.

PURPOSE

To investigate the effects of PKM2 inhibition by shikonin on renal fibrosis and the underly mechanisms.

METHODS

Mice were subjected to unilateral ureteral obstruction (UUO) to establish a CKD model. Renal fibrosis was assessed using histochemistry and western blotting. The MMT and histone lactylation levels were evaluated by immunofluorescence and western blotting. The interaction between the Tgfb1 promoter and lactylated histone H3 (K18) was examined using chromatin Immunoprecipitation (ChIP).

RESULTS

PKM2 expression was significantly elevated in the renal tubular cells of UUO mouse kidneys, resulting in increased pyruvate and lactate production. Similarly, lactate levels were elevated in TGF-β1-treated TCMK-1 cells and in the serum of CKD patients. In UUO mice, treatment with shikonin, a potent PKM2 inhibitor, effectively reduced lactate production, alleviated renal fibrosis, decreased TGF-β1 expression, and suppressed the MMT process. Mechanistic studies revealed that lactate treatment stimulates Tgfb1 expression in TCMK-1 cells. Consequently, TGF-β1 in conditioned media from lactate-treated TCMK-1 cells promoted M2 macrophage polarization and upregulated fibrotic gene expression in RAW264.7 cells. Pharmacological intervention demonstrated that TGF-β1 activates the Smad3 pathway to drive the MMT process. In TCMK-1 cells, both lactate treatment and PKM2 overexpression induced Tgfb1 expression by promoting histone H3K18 lactylation.

CONCLUSIONS

Our findings indicate that PKM2-induced excessive lactate production renal tubular cells contributes to renal fibrosis. Lactate promotes histone lactylation, leading to TGF-β1 expression in these cells, which subsequently activates the Smad3 pathway in macrophages, driving the MMT and fibrosis in the kidney. Therefore, targeting PKM2, as with shikonin treatment, may represent an effective therapeutic strategy for managing renal fibrosis in CKD.

RNA-seq analysis and in vivo experiments identified the protective effect of kaempferol on idiopathic pulmonary fibrosis by regulating the PPARG/TNC signaling pathway to reduce ECM deposition

Idiopathic pulmonary fibrosis (IPF) is a chronic age-related lung disease with a high mortality rate. Kaempferol (KMP), an active ingredient in common plants and foods with anti-inflammatory, antioxidant and immunomodulatory properties, has been shown to be effective against fibrotic diseases. However, the molecular mechanisms underlying the treatment of IPF with KMP remain unclear. Therefore, IPF mice were established by intratracheal instillation of bleomycin (BLM) to explore the efficacy and underlying mechanism of KMP in the treatment of IPF. We found that KMP improved the body weight changes of BLM-induced IPF mice, alleviated inflammatory infiltration and collagen deposition, and decreased the expression levels of hydroxyproline, α-SMA, Col3a1, Mmp2, Timp1, Vim, Fn, TNF-α, TGF-β1, IL-6 and IL-8, while up-regulating the expression E-cadherin in lung tissues. The transcriptomic results showed that KMP may exert therapeutic effects against IPF by regulating the PPARG/TNC signaling pathway to reduce extracellular matrix (ECM) deposition. Interestingly, ROC curve analysis suggested that TNC and PPARG had good diagnostic performance for IPF, and TF prediction revealed that PPARG is an important upstream gene regulating TNC, and the IF experiment confirmed the co-localization of TNC and PPARG. Molecular docking showed that KMP bound well to PPARG and TNC, and IF results revealed that KMP significantly reduced the interaction between PPARG and TNC. Furthermore, RT-PCR, WB, IHC and IF experiments confirmed that KMP elevated the expression of PPARG and inhibited the expression of TNC, thus inhibiting the ECM-receptor interaction pathway and ultimately serving as a therapeutic treatment for IPF mice. These findings revealed that KMP reduced inflammatory infiltration and collagen deposition in the lungs of IPF mice and that the PPARG/TNC signaling pathway may be an important mechanism for the treatment of IPF with KMP, which provides a new perspective for the development of therapeutic approaches for IPF.

Microparticle Mediated Delivery of Apelin Improves Heart Function in Post Myocardial Infarction Mice

BACKGROUND

Apelin is an endogenous prepropeptide that regulates cardiac homeostasis and various physiological processes. Intravenous injection has been shown to improve cardiac contractility in patients with heart failure. However, its short half-life prevents studying its impact on left ventricular remodeling in the long term. Here, we aim to study whether microparticle-mediated slow release of apelin improves heart function and left ventricular remodeling in mice with myocardial infarction (MI).

METHODS

A cardiac patch was fabricated by embedding apelin-containing microparticles in a fibrin gel scaffold. MI was induced via permanent ligation of the left anterior descending coronary artery in adult C57BL/6J mice followed by epicardial patch placement immediately after (acute MI) or 28 days (chronic MI) post-MI. Four groups were included in this study, namely sham, MI, MI plus empty microparticle-embedded patch treatment, and MI plus apelin-containing microparticle-embedded patch treatment. Cardiac function was assessed by transthoracic echocardiography. Cardiomyocyte morphology, apoptosis, and cardiac fibrosis were evaluated by histology. Cardioprotective pathways were determined by RNA sequencing, quantitative polymerase chain reaction, and Western blot.

RESULTS

The level of endogenous apelin was largely reduced in the first 7 days after MI induction and it was normalized by day 28. Apelin-13 encapsulated in poly(lactic-co-glycolic acid) microparticles displayed a sustained release pattern for up to 28 days. Treatment with apelin-containing microparticle-embedded patch inhibited cardiac hypertrophy and reduced scar size in both acute and chronic MI models, which is associated with improved cardiac function. Data from cellular and molecular analyses showed that apelin inhibits the activation and proliferation of cardiac fibroblasts by preventing transforming growth factor-β-mediated activation of Smad2/3 (supporessor of mothers against decapentaplegic 2/3) and downstream profibrotic gene expression.

CONCLUSIONS

Poly(lactic-co-glycolic acid) microparticles prolonged the apelin release time in the mouse hearts. Epicardial delivery of the apelin-containing microparticle-embedded patch protects mice from both acute and chronic MI-induced cardiac dysfunction, inhibits cardiac fibrosis, and improves left ventricular remodeling.

Unraveling the nexus of NAD+ metabolism and diabetic kidney disease: insights from murine models and human data

Background

Nicotinamide adenine dinucleotide (NAD+) is a critical coenzyme involved in kidney disease, yet its regulation in diabetic kidney disease (DKD) remains inadequately understood.

Objective

Therefore, we investigated the changes of NAD+ levels in DKD and the underlying mechanism.

Methods

Alternations of NAD+ levels and its biosynthesis enzymes were detected in kidneys from streptozotocin-induced diabetic mouse model by real-time PCR and immunoblot. The distribution of NAD+ de novo synthetic enzymes was explored via immunohistochemical study. NAD+ de novo synthetic metabolite was measured by LC-MS. Human data from NephroSeq were analyzed to verify our findings.

Results

The study showed that NAD+ levels were decreased in diabetic kidneys. Both mRNA and protein levels of kynurenine 3-monooxygenase (KMO) in NAD+ de novo synthesis pathway were decreased, while NAD+ synthetic enzymes in salvage pathway and NAD+ consuming enzymes remained unchanged. Further analysis of human data suggested KMO, primarily expressed in the proximal tubules shown by our immunohistochemical staining, was consistently downregulated in human diabetic kidneys.

Conclusion

Our study demonstrated KMO of NAD+ de novo synthesis pathway was decreased in diabetic kidney and might be responsible for NAD+ reduction in diabetic kidneys, offering valuable insights into complex regulatory mechanisms of NAD+ in DKD.

Cell-cell communication in kidney fibrosis

Kidney fibrosis is a common outcome of a wide variety of chronic kidney diseases, in which virtually all kinds of renal resident and infiltrating cells are involved. As such, well-orchestrated intercellular communication is of vital importance in coordinating complex actions during renal fibrogenesis. Cell-cell communication in multicellular organisms is traditionally assumed to be mediated by direct cell contact or soluble factors, including growth factors, cytokines and chemokines, through autocrine, paracrine, endocrine and juxtacrine signaling mechanisms. Growing evidence also demonstrates that extracellular vesicles, lipid bilayer-encircled particles naturally released from almost all types of cells, can act as a vehicle to transfer a diverse array of biomolecules including proteins, mRNA, miRNA and lipids to mediate cell-cell communication. We recently described a new mode of intercellular communication via building a special extracellular niche by insoluble matricellular proteins. Kidney cells, upon injury, produce and secrete different matricellular proteins, which incorporate into the local extracellular matrix network, and regulate the behavior, trajectory and fate of neighboring cells in a spatially confined fashion. This extracellular niche-mediated cell-cell communication is unique in that it restrains the crosstalk between cells within a particular locality. Detailed delineation of this unique manner of intercellular communication will help to elucidate the mechanism of kidney fibrosis and could offer novel insights in developing therapeutic intervention.

Extracellular Matrix-Derived Damage-Associated Molecular Patterns (DAMP): Implications in Systemic Sclerosis and Fibrosis

Damage-associated molecular patterns (DAMPs) are intracellular molecules released under cellular stress or recurring tissue injury, which serve as endogenous ligands for toll-like receptors (TLRs). Such DAMPs are either actively secreted by immune cells or passively released into the extracellular environment from damaged cells or generated as alternatively spliced mRNA variants of extracellular matrix (ECM) glycoproteins. When recognized by pattern recognition receptors (PRRs) such as TLRs, DAMPs trigger innate immune responses. Currently, the best-characterized PRRs include, in addition to TLRs, nucleotide-binding oligomerization domain-like receptors, RIG-I-like RNA helicases, C-type lectin receptors, and many more. Systemic sclerosis (SSc) is a chronic autoimmune condition characterized by inflammation and progressive fibrosis in multiple organs. Using an unbiased survey for SSc-associated DAMPs, we have identified the ECM glycoproteins fibronectin-containing extra domain A and tenascin C as the most highly upregulated in SSc skin and lung biopsies. These DAMPs activate TLR4 on resident stromal cells to elicit profibrotic responses and sustained myofibroblasts activation resulting in progressive fibrosis. This review summarizes the current understanding of the complex functional roles of DAMPs in the progression and failure of resolution of fibrosis in general, with a particular focus on SSc, and considers viable therapeutic approaches targeting DAMPs.

[Study of urinary markers of different podocytopathies by proteomic analysis]

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) is a primary podocytopathy characterized by primary podocyte detection and high proteinuria. The search for biomarkers and factors associated with the progression of this disease is an important task nowdays.

AIM

To assess the proteomic profile of urine in patients with FSGS and to isolate urinary biomarkers of podocytopathies.

MATERIALS AND METHODS

The study included 41 patients diagnosed with chronic glomerulonephritis, 27 men and 14 women. According to the morphological study, 28 patients were diagnosed with FSGS, 9 with steroid-sensitive nephrotic syndrome and 14 with steroid-resistant nephrotic syndrome. The comparison group included 13 patients with membranous nephropathy. The study of the urinary proteome was carried out by targeted liquid chromatography-mass spectrometry using multiple reaction monitoring with synthetic stable isotope labelled peptide standards.

RESULTS

The main differences in the protein profile of urine were found in the subgroups of steroid-sensitive (SS) and steroid-resistant (SR) FSGS. In the FSGS SR group, at the onset of the disease, there was a high concentration of proteins reflecting damage to the glomerular filter (apo-lipoprotein A-IV, orosomucoid, cadherin, hemopexin, vitronectin), as well as proteins associated with tubulo-interstitial inflammation and accumulation of extracellular matrix (retinol- and vitamin D-binding proteins, kininogen-1, lumican and neurophilin-2). Compared with the membranous nephropathy group, FSGS patients had significantly higher urinary concentrations of carnosinase, orosomucoid, cadherin-13, tenascin X, osteopontin, and zinc-alpha-2-glycoprotein.

CONCLUSION

Thus, in patients with SR FSGS, the proteomic profile of urine includes more proteins at elevated concentrations, which reflects severe damage to various parts of the nephron compared with patients with SS FSGS and membranous nephropathy.