Hypoxia-inducible factor signaling in the development of tissue fibrosis

Cellular crosstalk in fibrosis: insights into macrophage and fibroblast dynamics

Pathological fibrosis, the excessive deposition of extracellular matrix and tissue stiffening that causes progressive organ dysfunction, underlies diverse chronic diseases. The fibrotic microenvironment is driven by the dynamic microenvironmental interaction between various cell types; macrophages and fibroblasts play central roles in fibrotic disease initiation, maintenance, and progression. Macrophage functional plasticity to microenvironmental stimuli modulates fibroblast functionality by releasing pro-inflammatory cytokines, growth factors, and matrix remodeling enzymes that promote fibroblast proliferation, activation, and differentiation into myofibroblasts. Activated fibroblasts and myofibroblasts serve as the fibrotic effector cells, secreting extracellular matrix components and initiating microenvironmental contracture. Fibroblasts also modulate macrophage function through the release of their own pro-inflammatory cytokines and growth factors, creating bidirectional crosstalk that reinforces the chronic fibrotic cycle. The intricate interplay between macrophages and fibroblasts, including their secretomes and signaling interactions, leads to tissue damage and pathological loss of tissue function. In this review, we examine macrophage-fibroblast reciprocal dynamic interactions in pathological fibrotic conditions. We discuss the specific lineages and functionality of macrophages and fibroblasts implicated in fibrotic progression, with focus on their signal transduction pathways and secretory signalling that enables their pro-fibrotic behaviour. We then finish with a set of recommendations for future experimentation with the goal of developing a set of potential targets for anti-fibrotic therapeutic candidates. Understanding the cellular interactions between macrophages and fibroblasts provides valuable insights into potential therapeutic strategies to mitigate fibrotic disease progression.

Mechanism of Mitophagy to Protect Yak Kidney from Hypoxia-Induced Fibrosis Damage by Regulating Ferroptosis Pathway

Renal fibrosis is a critical pathological feature of various chronic kidney diseases, with hypoxia being recognized as an important factor in inducing fibrosis. Yaks have long inhabited high-altitude hypoxic environments and do not exhibit fibrotic damage under chronic hypoxia. However, the underlying protective mechanisms remain unclear. This study compared the renal tissue structure and collagen volume between low-altitude cattle and high-altitude yaks, revealing that yaks possess a significantly higher number of renal tubules than cattle, though collagen volume showed no significant difference. Under hypoxic treatment, we observed that chronic hypoxia induced renal fibrosis in cattle, but did not show a significant effect in yaks, suggesting that the hypoxia adaptation mechanisms in yaks may have an anti-fibrotic effect. Further investigation demonstrated a significant upregulation of P-AMPK/AMPK, Parkin, PINK1, LC3Ⅱ/Ⅰ, and BECN1, alongside a downregulation of P-mTOR/mTOR in yak kidneys. Additionally, hypoxia-induced renal tubular epithelial cells (RTECs) showed increased expression of mitophagy-related proteins, mitochondrial membrane depolarization, and an increased number of lysosomes, indicating that hypoxia induces mitophagy. By regulating the mitophagy pathway through drugs, we found that under chronic hypoxia, activation of mitophagy upregulated E-cadherin protein expression while downregulating the expression of Vimentin, α-SMA, Collagen I, and Fibronectin. Simultaneously, there was an increase in SLC7A11, GPX4, and GSH levels, and a decrease in ROS, MDA, and Fe2⁺ accumulation. Inhibition of mitophagy produced opposite effects on protein expression and cellular markers. Further studies identified ferroptosis as a key mechanism promoting renal fibrosis. Moreover, in renal fibrosis models, mitophagy reduced the accumulation of ROS, MDA, and Fe2⁺, thereby alleviating ferroptosis-induced renal fibrosis. These findings suggest that chronic hypoxia protects yaks from hypoxia-induced renal fibrosis by activating mitophagy to inhibit the ferroptosis pathway.

Crosstalk between glomeruli and tubules

Models of kidney injury have classically concentrated on glomeruli as the primary site of injury leading to glomerulosclerosis or on tubules as the primary site of injury leading to tubulointerstitial fibrosis. However, current evidence on the mechanisms of progression of chronic kidney disease indicates that a complex interplay between glomeruli and tubules underlies progressive kidney injury. Primary glomerular injury can clearly lead to subsequent tubule injury. For example, damage to the glomerular filtration barrier can expose tubular cells to serum proteins, including complement and cytokines, that would not be present in physiological conditions and can promote the development of tubulointerstitial fibrosis and progressive decline in kidney function. In addition, although less well-studied, increasing evidence suggests that tubule injury, whether primary or secondary, can also promote glomerular damage. This feedback from the tubule to the glomerulus might be mediated by changes in the reabsorptive capacity of the tubule, which can affect the glomerular filtration rate, or by mediators released by injured proximal tubular cells that can induce damage in both podocytes and parietal epithelial cells. Examining the crosstalk between the various compartments of the kidney is important for understanding the mechanisms underlying kidney pathology and identifying potential therapeutic interventions.

Process-Specific Blood Biomarkers and Outcomes in COVID-19 Versus Non-COVID-19 ARDS (APEL-COVID Study): A Prospective, Observational Cohort Study

Background: Severe acute respiratory syndrome (SARS) and acute respiratory distress syndrome (ARDS) are often considered separate clinico-radiological entities. Whether these conditions also present a single process-specific systemic biomolecular phenotype and how this relates to patient outcomes remains unknown. A prospective cohort study was conducted, including adult patients admitted to the ICU and general floors for COVID-19-related (COVID+) or non-COVID-19-related (COVID-) acute respiratory failure during the main phase of the pandemic. The primary objective was to study blood biomarkers and outcomes among different groups and severity subsets. Results: A total of 132 patients were included, as follows: 67 COVID+, 54 COVID- (with 11 matched control subjects for biomarker reference), and 58 of these patients allowed for further pre- and post-analysis. The baseline apelin (APL) levels were higher in COVID+ patients (p < 0.0001 vs. COVID- patients) and in SARS COVID+ patients (p ≤ 0.02 vs. ARDS), while the IL-6 levels were higher in ARDS COVID- patients (p ≤ 0.0001 vs. SARS). Multivariable logistic regression analyses with cohort biomarkers and outcome parameters revealed the following: (i) log-transformed neprilysin (NEP) activity was significantly higher in COVID+ patients (1.11 [95% CI: 0.4-1.9] vs. 0.37 [95% CI: 0.1-0.8], fold change (FC): 1.43 [95% CI: 1.04-1.97], p = 0.029) and in SARS patients (FC: 1.65 [95% CI: 1.05-2.6], p = 0.032 vs. non-SARS COVID+ patients, and 1.73 [95% CI: 1.19-2.5], p = 0.005 vs. ARDS COVID- patients) and (ii) higher lysyl oxidase (LOX) activity and APL levels were respectively associated with death and a shorter length of hospital stay in SARS COVID+ patients (Odds Ratios (OR): 1.01 [1.00-1.02], p = 0.05, and OR: -0.007 [-0.013-0.0001], p = 0.048). Conclusion: Process-specific blood biomarkers exhibited distinct profiles between COVID+ and COVID- patients, and across stages of severity. NEP and LOX activities, as well as APL levels, are particularly linked to COVID+ patients and their outcomes (ClinicalTrials.gov Identifier: NCT04632732).

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.

Paradoxes: Cholesterol and Hypoxia in Preeclampsia

Preeclampsia, a hypertensive disease of pregnancy of unknown etiology, is intensely studied as a model of cardiovascular disease (CVD) not only due to multiple shared pathologic elements but also because changes that develop over decades in CVD appear and resolve within days in preeclampsia. Those affected by preeclampsia and their offspring experience increased lifetime risks of CVD. At the systemic level, preeclampsia is characterized by increased cellular, membrane, and blood levels of cholesterol; however, cholesterol-dependent signaling, such as canonical Wnt/βcatenin, Hedgehog, and endothelial nitric oxide synthase, is downregulated indicating a cholesterol deficit with the upregulation of cholesterol synthesis and efflux. Hypoxia-related signaling in preeclampsia also appears to be paradoxical with increased Hypoxia-Inducible Factors in the placenta but measurably increased oxygen in maternal blood in placental villous spaces. This review addresses the molecular mechanisms by which excessive systemic cholesterol and deficient cholesterol-dependent signaling may arise from the effects of dietary lipid variance and environmental membrane modifiers causing the cellular hypoxia that characterizes preeclampsia.

Comparative Tensile Properties and Collagen Patterns in Domestic Cat (Felis catus) and Dog (Canis lupus familiaris) Ovarian Cortical Tissues

The importance of the ovarian extracellular environment and tissue rigidity on follicle survival and development has gained attention in recent years. Our laboratory has anecdotally observed differences in the rigidity of domestic cat and dog ovarian cortical tissues, which have been postulated to underlie the differences in in vitro culture responses between the species, wherein cat ovarian tissues display higher survival in extended incubation. Here, the tensile strengths of cat and dog ovarian cortical tissues were compared via micropipette aspiration. The underlying collagen patterns, including fiber length, thickness, alignment, curvature, branch points and end points, and overall tissue lacunary and high-density matrix (HDM) were quantified via picrosirius red staining and TWOMBLI analysis. Finally, we explored the potential of MMP (-1 and -9) and TIMP1 supplementation in modulating tissue rigidity, collagen structure, and follicle activation in vitro. No differences in stiffness were observed between cat or dog cortical tissues, or pre- versus post-pubertal status. Cat ovarian collagen was characterized by an increased number of branch points, thinner fibers, and lower HDM compared with dog ovarian collagen, and cat tissues exposed to MMP9 in vitro displayed a reduced Young's modulus. Yet, MMP exposure had a minor impact on follicle development in vitro in either species. This study contributes to our growing understanding of the interactions among the physical properties of the ovarian microenvironment, collagen patterns, and follicle development in vitro.

cGAS-STING signaling pathway promotes hypoxia-induced renal fibrosis by regulating PFKFB3-mediated glycolysis

Hypoxia has long been considered to play an active role in the progression of fibrosis in chronic kidney disease, but its specific mechanism is not fully understood. The stimulator of interferon genes (STING) has been a research hotspot in the fields of tumor, immunity, and infection in recent years, and its role in immune and inflammatory responses related to kidney disease has gradually attracted attention. This study mainly explores the role and mechanism of STING in hypoxia-related renal fibrosis. To address this issue, we stimulated human proximal tubular epithelial (HK-2) cells with hypoxia for 48 h to construct cell models. Meanwhile, C57BL/6J male mice were used to establish a renal fibrosis model induced by renal ischemia-reperfusion injury (IRI). In our present study, we found that the GMP-AMP synthase (cGAS)-STING signaling pathway can promote the progression of renal fibrosis after hypoxic exposure, and this effect is closely related to 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 3 (PFKFB3)-mediated glycolysis. Furthermore, inhibition of both STING and its downstream interferon regulatory factor 3 (IRF3) reversed elevated PFKFB3 expression, thereby attenuating hypoxia-induced renal fibrosis. Taken together, our data suggest that the cGAS-STING-IRF3-PFKFB3 signaling pathway activated under hypoxia may provide new ideas and targets for the treatment of early renal fibrosis.

Lysyl oxidase like-2 in fibrosis and cardiovascular disease

Fibrosis is an important and essential reparative response to injury that, if left uncontrolled, results in the excessive synthesis, deposition, remodeling, and stiffening of the extracellular matrix, which is deleterious to organ function. Thus, the sustained activation of enzymes that catalyze matrix remodeling and cross linking is a fundamental step in the pathology of fibrotic diseases. Recent studies have implicated the amine oxidase lysyl oxidase like-2 (LOXL2) in this process and established significantly elevated expression of LOXL2 as a key component of profibrotic conditions in several organ systems. Understanding the relationship between LOXL2 and fibrosis as well as the mechanisms behind these relationships can offer significant insights for developing novel therapies. Here, we summarize the key findings that demonstrate the link between LOXL2 and fibrosis and inflammation, examine current therapeutics targeting LOXL2 for the treatment of fibrosis, and discuss future directions for experiments and biomedical engineering.

Leptospirosis kidney disease: Evolution from acute to chronic kidney disease

Leptospirosis is a neglected bacterial disease caused by leptospiral infection that carries a substantial mortality risk in severe cases. Research has shown that acute, chronic, and asymptomatic leptospiral infections are closely linked to acute and chronic kidney disease (CKD) and renal fibrosis. Leptospires affect renal function by infiltrating kidney cells via the renal tubules and interstitium and surviving in the kidney by circumventing the immune system. The most well-known pathogenic molecular mechanism of renal tubular damage caused by leptospiral infection is the direct binding of the bacterial outer membrane protein LipL32 to toll-like receptor-2 expressed in renal tubular epithelial cells (TECs) to induce intracellular inflammatory signaling pathways. These pathways include the production of tumor necrosis factor (TNF)-α and nuclear factor kappa activation, resulting in acute and chronic leptospirosis-related kidney injury. Few studies have investigated the relationship between acute and chronic renal diseases and leptospirosis and further evidence is necessary. In this review, we intend to discuss the roles of acute kidney injury (AKI) to/on CKD in leptospirosis. This study reviews the molecular pathways underlying the pathogenesis of leptospirosis kidney disease, which will assist in concentrating on potential future research directions.

Hypoxia-Induced HIF-1α Expression Promotes Neurogenic Bladder Fibrosis via EMT and Pyroptosis

BACKGROUND

Neurogenic bladder (NB) patients exhibit varying degrees of bladder fibrosis, and the thickening and hardening of the bladder wall induced by fibrosis will further affect bladder function and cause renal failure. Our study aimed to investigate the mechanism of bladder fibrosis caused by a spinal cord injury (SCI).

METHODS

NB rat models were created by cutting the bilateral lumbar 6 (L6) and sacral 1 (S1) spinal nerves. RNA-seq, Western blotting, immunofluorescence, cell viability and ELISA were performed to assess the inflammation and fibrosis levels.

RESULTS

The rats showed bladder dysfunction, upper urinary tract damage and bladder fibrosis after SCI. RNA-seq results indicated that hypoxia, EMT and pyroptosis might be involved in bladder fibrosis induced by SCI. Subsequent Western blot, ELISA and cell viability assays and immunofluorescence of bladder tissue confirmed the RNA-seq findings. Hypoxic exposure increased the expression of HIF-1α and induced EMT and pyroptosis in bladder epithelial cells. Furthermore, HIF-1α knockdown rescued hypoxia-induced pyroptosis, EMT and fibrosis.

CONCLUSION

EMT and pyroptosis were involved in the development of SCI-induced bladder fibrosis via the HIF-1α pathway. Inhibition of the HIF-1α pathway may serve as a potential target to alleviate bladder fibrosis caused by SCI.

Metabolic reprogramming of pulmonary fibrosis

Pulmonary fibrosis is a progressive and intractable lung disease with fibrotic features that affects alveoli elasticity, which leading to higher rates of hospitalization and mortality worldwide. Pulmonary fibrosis is initiated by repetitive localized micro-damages of the alveolar epithelium, which subsequently triggers aberrant epithelial-fibroblast communication and myofibroblasts production in the extracellular matrix, resulting in massive extracellular matrix accumulation and interstitial remodeling. The major cell types responsible for pulmonary fibrosis are myofibroblasts, alveolar epithelial cells, macrophages, and endothelial cells. Recent studies have demonstrated that metabolic reprogramming or dysregulation of these cells exerts their profibrotic role via affecting pathological mechanisms such as autophagy, apoptosis, aging, and inflammatory responses, which ultimately contributes to the development of pulmonary fibrosis. This review summarizes recent findings on metabolic reprogramming that occur in the aforementioned cells during pulmonary fibrosis, especially those associated with glucose, lipid, and amino acid metabolism, with the aim of identifying novel treatment targets for pulmonary fibrosis.

Susceptibility of renal fibrosis in diabetes: Role of hypoxia inducible factor-1

Diabetes may prevent kidney repair and sensitize the kidney to fibrosis or scar formation. To test this possibility, we examined renal fibrosis induced by unilateral ureteral obstruction (UUO) in diabetic mouse models. Indeed, UUO induced significantly more renal fibrosis in both Akita and STZ-induced diabetic mice than in nondiabetic mice. The diabetic mice also had more apoptosis and interstitial macrophage infiltration during UUO. In vitro, hypoxia induced higher expression of the fibrosis marker protein fibronectin in high glucose-conditioned renal tubular cells than in normal glucose cells. Mechanistically, hypoxia induced significantly more hypoxia-inducible factor-1 α (HIF-1 α) in high glucose cells than in normal glucose cells. Inhibition of HIF-1 attenuated the expression of fibronectin induced by hypoxia in high-glucose cells. Consistently, UUO induced significantly higher HIF-1α expression along with fibrosis in diabetic mice kidneys than in nondiabetic kidneys. The increased expression of fibrosis induced by UUO in diabetic mice was diminished in proximal tubule-HIF-1α-knockout mice. Together, these results indicate that diabetes sensitizes kidney tissues and cells to fibrogenesis probably by enhancing HIF-1 activation.

Role of Tumor Microenvironment in Cancer Stem Cells Resistance to Radiotherapy

Cancer is a chronic disorder that involves several elements of both the tumor and the host stromal cells. At present, the complex relationship between the various factors presents in the tumor microenvironment (TME) and tumor cells, as well as immune cells located within the TME, is still poorly known. Within the TME, the crosstalk of these factors and immune cells essentially determines how a tumor reacts to the treatment and how the tumor can ultimately be destroyed, remain dormant, or develop and metastasize. Also, in TME, reciprocal crosstalk between cancer-associated fibroblasts (CAFs), extracellular matrix (ECM), hypoxia-inducible factor (HIF) intensifies the proliferation capacity of cancer stem cells (CSCs). CSCs are subpopulation of cells that reside within the tumor bulk and have the capacity to self-renew, differentiate, and repair DNA damage. These characteristics make CSCs develop resistance to a variety of treatments, such as radiotherapy (RT). RT is a frequent and often curative treatment for local cancer which mediates tumor elimination by cytotoxic actions. Also, cytokines and growth factors that are released into TME, have been involved in the activation of tumor radioresistance and the induction of different immune cells, altering local immune responses. In this review, we discuss the pivotal role of TME in resistance of CSCs to RT.

Hypoxia modulates human mast cell adhesion to hyaluronic acid

Hypoxia is an inherent factor in the inflammatory process and is important in the regulation of some immune cell functions, including the expression of mast cell pro- and anti-inflammatory mediators. Hypoxia also influences cell adhesion to the extracellular matrix (ECM). Hyaluronic acid is one of the major components of the ECM that is involved in inflammatory and tissue regeneration processes in which mast cells play a prominent role. This prompted us to investigate the effects of hypoxia on the expression of hyaluronic acid receptors in mast cells and mast cell adhesion to this ECM component. We found that human LAD2 mast cells spontaneously adhered to hyaluronic acid in a CD44-dependent manner and that reduced oxygen concentrations inhibited or even completely abolished this adhesion process. The mechanism of hypoxia downregulation of mast cell adhesion to hyaluronic acid did not involve a decrease in CD44 expression and hyaluronidase-mediated degradation of adhesion substrates but rather conformational changes in the avidity of CD44 to hyaluronic acid. Hypoxia-mediated regulation of mast cell adhesion to extracellular matrix components might be involved in the pathogenic accumulation of mast cells observed in the course of certain diseases including rheumatoid arthritis and cancer.

Contribution of Oxidative Stress to HIF-1-Mediated Profibrotic Changes during the Kidney Damage

Hypoxia and oxidative stress are the common causes of various types of kidney injury. During recent years, the studies on hypoxia inducible factor- (HIF-) 1 attract more and more attention, which can not only mediate hypoxia adaptation but also contribute to profibrotic changes. Through analyzing related literatures, we found that oxidative stress can regulate the expression and activity of HIF-1α through some signaling molecules, such as prolyl hydroxylase domain-containing protein (PHD), PI-3K, and microRNA. And oxidative stress can take part in inflammation, epithelial-mesenchymal transition, and extracellular matrix deposition mediated by HIF-1 via interacting with classical NF-κB and TGF-β signaling pathways. Therefore, based on previous literatures, this review summarizes the contribution of oxidative stress to HIF-1-mediated profibrotic changes during the kidney damage, in order to further understand the role of oxidative stress in renal fibrosis.

Pharmaceutical targeting of succinate dehydrogenase in fibroblasts controls bleomycin-induced lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by excessive deposition of extracellular matrix in the lung with fibroblast-to-myofibroblast transition, leading to chronically compromising lung function and death. However, very little is known about the metabolic alterations of fibroblasts in IPF, and there is still a lack of pharmaceutical agents to target the metabolic dysregulation. Here we show a glycolysis upregulation and fatty acid oxidation (FAO) downregulation in fibroblasts from fibrotic lung, and perturbation of glycolysis and FAO affects fibroblasts transdifferentiation. In addition, there is a significant accumulation of succinate both in fibrotic lung tissues and myofibroblasts, where succinate dehydrogenase (SDH) operates in reverse by reducing fumarate to succinate. Then succinate contributes to glycolysis upregulation and FAO downregulation by stabilizing HIF-1α, which promotes the development of lung fibrosis. In addition, we identify a near-infrared small molecule dye, IR-780, as a targeting agent which stimulates mild inhibition of succinate dehydrogenase subunit A (SDHA) in fibroblasts, and which inhibits TGF-β1 induced SDH and succinate elevation, then to prevent fibrosis formation and respiratory dysfunction. Further, enhanced cell retention of IR-780 is shown to promote severe inhibition of SDHA in myofibroblasts, which may contribute to excessive ROS generation and selectively induces myofibroblasts to apoptosis, and then therapeutically improves established lung fibrosis in vivo. These findings indicate that targeting metabolic dysregulation has significant implications for therapies aimed at lung fibrosis and succinate dehydrogenase is an exciting new therapeutic target to treat IPF.

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Glycolysis upregulation and fatty acid oxidation (FAO) downregulation in fibroblasts lead to lung fibrosis.

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Succinate contributes to metabolic dysregulation of fibroblasts by stabilizing HIF-1α.

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Succinate dehydrogenase is an exciting new therapeutic target to treat IPF.

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IR-780 can be a promising agent to control lung fibrosis by targeting succinate dehydrogenase.

Hypoxia - as a Possible Regulator of the Activity of Epicardial Mesothelial Cells After Myocardial Infarction

Aim      To study the effect of hypoxia on the activity of epithelial-mesenchymal transition (EMT) in epicardial cells, which provides formation of a specialized microenvironment.Material and methods   This study used a model of experimental myocardial infarction created by ligation of the anterior descendent coronary artery. The activity of epicardial cells after a hypoxic exposure was studied with the hypoxia marker, pimonidazole, bromodeoxyuridine, immunofluorescent staining of heart cryosections, and in vitro mesothelial cell culture.Results The undamaged heart maintained the quiescent condition of mesothelial cells and low levels of their proliferation, extracellular matrix protein production, and of the EMT activity. Acute ischemic injury induced moderate hypoxia in the epicardial/subepicardial region. This caused a global rearrangement of this region due to the initiation of EMT in cells, changes in the cell composition, and accumulation of extracellular matrix proteins. We found that the initiation of EMT in mesothelial cells may result in the formation of smooth muscle cell precursors, fibroblasts, and a population of Sca-1+ cardiac progenitor cells, which may both participate in construction of new blood vessels and serve as a mesenchymal link for the paracrine support of microenvironmental cells. In in vitro experiments, we showed that 72‑h hypoxia facilitated activation of EMT regulatory genes, induced dissembling of intercellular contacts, cell uncoupling, and increased cell plasticity.Conclusion      The epicardium of an adult heart serves as a "reparative reserve" that can be reactivated by a hypoxic exposure. This creates a basis for an approach to influence the epicardium to modulate its activity for regulating reparative processes.

Molecular profiling reveals a hypoxia signature in breast implant-associated anaplastic large cell lymphoma

Breast implant-associated anaplastic large cell lymphoma (BIAALCL) is a recently characterized T-cell malignancy that has raised significant patient safety concerns and led to worldwide impact on the implants used and clinical management of patients undergoing reconstructive or cosmetic breast surgery. Molecular signatures distinguishing BIA-ALCL from other anaplastic large cell lymphomas have not been fully elucidated and classification of BIA-ALCL as a World Health Organization entity remains provisional. We performed RNA sequencing and gene set enrichment analysis comparing BIA-ALCL to non-BIAALCL and identified dramatic upregulation of hypoxia signaling genes including the hypoxia-associated biomarker CA9 (carbonic anyhydrase- 9). Immunohistochemistry validated CA9 expression in all BIA-ALCL, with only minimal expression in non-BIA-ALCL. Growth induction in BIA-ALCL-derived cell lines cultured under hypoxic conditions was proportional to upregulation of CA9 expression, and RNA sequencing demonstrated induction of the same gene signature observed in BIAALCL tissue samples compared to non-BIA-ALCL. CA9 silencing blocked hypoxia-induced BIA-ALCL cell growth and cell cycle-associated gene expression, whereas CA9 overexpression in BIA-ALCL cells promoted growth in a xenograft mouse model. Furthermore, CA9 was secreted into BIA-ALCL cell line supernatants and was markedly elevated in human BIA-ALCL seroma samples. Finally, serum CA9 concentrations in mice bearing BIA-ALCL xenografts were significantly elevated compared to those in control serum. Together, these findings characterize BIA-ALCL as a hypoxia-associated neoplasm, likely attributable to the unique microenvironment in which it arises. These data support classification of BIA-ALCL as a distinct entity and uncover opportunities for investigating hypoxia-related proteins such as CA9 as novel biomarkers and therapeutic targets in this disease.

SIRT1 attenuates renal fibrosis by repressing HIF-2α

Sirtuin 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD⁺)-dependent deacetylase belonging to class III histone deacetylases. Previous studies have shown that SIRT1 is involved in kidney physiology regulation and protects the kidney from various pathological factors. However, the underlying mechanisms behind its function have yet to be fully elucidated. In our study, we found that ablation of Sirt1 in renal interstitial cells resulted in more severe renal damage and fibrosis in unilateral ureteral obstruction (UUO) model mice. We also observed that hypoxia-inducible factor (HIF)-2α expression was increased in Sirt1 conditional knockout mice, suggesting that HIF-2α might be a substrate of SIRT1, mediating its renoprotective roles. Therefore, we bred Hif2a deficient mice and subjected them to renal trauma through UUO surgery, ultimately finding that Hif2a ablation attenuated renal fibrogenesis induced by UUO injury. Moreover, in cultured NRK-49F cells, activation of SIRT1 decreased HIF-2α and fibrotic gene expressions, and inhibition of SIRT1 stimulated HIF-2α and fibrotic gene expressions. Co-immunoprecipitation analysis revealed that SIRT1 directly interacted with and deacetylated HIF-2α. Together, our data indicate that SIRT1 plays a protective role in renal damage and fibrosis, which is likely due to inhibition of HIF-2α.

Pathologic HIF1α signaling drives adipose progenitor dysfunction in obesity

Adipose precursor cells (APCs) exhibit regional variation in response to obesity, for unclear reasons. Here, we reveal that HIFα-induced PDGFRβ signaling within murine white adipose tissue (WAT) PDGFRβ⁺ cells drives inhibitory serine 112 (S112) phosphorylation of PPARγ, the master regulator of adipogenesis. Levels of PPARγ S112 phosphorylation in WAT PDGFRβ⁺ cells are depot dependent, with levels of PPARγ phosphorylation in PDGFRβ⁺ cells inversely correlating with their capacity for adipogenesis upon high-fat-diet feeding. HIFα suppression in PDGFRβ⁺ progenitors promotes subcutaneous and intra-abdominal adipogenesis, healthy WAT remodeling, and improved metabolic health in obesity. These metabolic benefits are mimicked by treatment of obese mice with the PDGFR antagonist Imatinib, which promotes adipocyte hyperplasia and glucose tolerance in a progenitor cell PPARγ-dependent manner. Our studies unveil a mechanism underlying depot-specific responses of APCs to high-fat feeding and highlight the potential for APCs to be targeted pharmacologically to improve metabolic health in obesity.

Connexin 43 prevents the progression of diabetic renal tubulointerstitial fibrosis by regulating the SIRT1-HIF-1α signaling pathway

Hyperglycemia-induced renal epithelial-to-mesenchymal transition (EMT) is a key pathological factor in diabetic renal tubulointerstitial fibrosis (RIF). Our previous studies have shown that connexin 43 (Cx43) activation attenuated the development of diabetic renal fibrosis. However, whether Cx43 regulates the EMT of renal tubular epithelial cells (TECs) and the pathological process of RIF under the diabetic conditions remains to be elucidated. In the present study, we identified that Cx43 protein expression was down-regulated in the kidney tissues of db/db mice as well as in high glucose (HG)-induced NRK-52E cells. Overexpression of Cx43 improved renal function in db/db spontaneous diabetic model mice, increased SIRT1 levels, decreased hypoxia-inducible factor (HIF)-1α expression, and reduced production of EMT markers and extracellular matrix (ECM) components. Additionally, Cx43 overexpression inhibited the EMT process and reduced the expression of ECM components such as fibronectin (FN), Collagen I, and Collagen IV in HG-induced NRK-52E cells, whereas Cx43 deficiency had the opposite effects. Mechanistically, Cx43 in a carboxyl-terminal signal transduction-dependent manner could up-regulate SIRT1 expression and enhance SIRT1-dependent deacetylation of HIF-1α to reduce HIF-1α activity, which eventually ameliorated renal EMT and diabetic RIF. Our study indicates the essential role of Cx43 in regulating renal EMT and diabetic RIF via regulating the SIRT1-HIF-1α signaling pathway and provides an experimental basis for Cx43 as a potential target for diabetic nephropathy (DN).

miR‑212 promotes renal interstitial fibrosis by inhibiting hypoxia‑inducible factor 1‑α inhibitor

Renal interstitial fibrosis is one of the common causes, and a major pathological basis for the development of various types of chronic progressive renal to end-stage renal diseases. Therefore, it is important to clarify the underlying mechanisms of disease progression in order to develop effective strategies for the treatment and prevention of these pathologies. The aim of the present study was to investigate the association between microRNA (miR)-212 expression and the development of renal interstitial fibrosis, as well as analyzing the role of miR-212 in the disease. The expression of miR-212 was significantly increased in the peripheral blood of patients with renal interstitial fibrosis and in the kidney tissues of unilateral ureteral obstruction (UUO) mice. Angiotensin (Ang) II, TGF-β1 and hypoxia were found to increase the expression of miR-212 and α smooth muscle actin (α-SMA) in NRK49F cells. Ang II stimulation induced the expression of miR-212 and α-SMA in NRK49F cells, while transfection of miR-212 mimics further upregulated the expression of α-SMA. miR-212 was also revealed to target hypoxia-inducible factor 1α inhibitor (HIF1AN) and to upregulate the expression of hypoxia-inducible factor 1α, α-SMA, connective tissue growth factor, collagen α-1(I) chain and collagen α-1(III) chain, whereas HIF1AN overexpression reversed the regulatory effects of miR-212. In UUO mice, miR-212 overexpression promoted the progression of renal interstitial fibrosis, whereas inhibiting miR-212 resulted in the opposite effect. These results indicated that high expression of miR-212 was closely associated with the occurrence of renal interstitial fibrosis, and that miR-212 may promote its development by targeting HIF1AN.

The Epithelial-to-Mesenchymal Transition as a Possible Therapeutic Target in Fibrotic Disorders

Fibrosis is a chronic and progressive disorder characterized by excessive deposition of extracellular matrix, which leads to scarring and loss of function of the affected organ or tissue. Indeed, the fibrotic process affects a variety of organs and tissues, with specific molecular background. However, two common hallmarks are shared: the crucial role of the transforming growth factor-beta (TGF-β) and the involvement of the inflammation process, that is essential for initiating the fibrotic degeneration. TGF-β in particular but also other cytokines regulate the most common molecular mechanism at the basis of fibrosis, the Epithelial-to-Mesenchymal Transition (EMT). EMT has been extensively studied, but not yet fully explored as a possible therapeutic target for fibrosis. A deeper understanding of the crosstalk between fibrosis and EMT may represent an opportunity for the development of a broadly effective anti-fibrotic therapy. Here we report the evidences of the relationship between EMT and multi-organ fibrosis, and the possible therapeutic approaches that may be developed by exploiting this relationship.

Opioid Preconditioning Modulates Repair Responses to Prevent Renal Ischemia-Reperfusion Injury

Progression to renal damage by ischemia-reperfusion injury (IRI) is the result of the dysregulation of various tissue damage repair mechanisms. Anesthetic preconditioning with opioids has been shown to be beneficial in myocardial IRI models. Our main objective was to analyze the influence of pharmacological preconditioning with opioids in renal function and expression of molecules involved in tissue repair and angiogenesis. Experimental protocol includes male rats with 45 min ischemia occluding the left renal hilum followed by 24 h of reperfusion with or without 60 min preconditioning with morphine/fentanyl. We analyzed serum creatinine and renal KIM-1 expression. We measured circulating and intrarenal VEGF. Immunohistochemistry for HIF-1 and Cathepsin D (CTD) and real-time PCR for angiogenic genes HIF-1α, VEGF, VEGF Receptor 2 (VEGF-R2), CTD, CD31 and IL-6 were performed. These molecules are considered important effectors of tissue repair responses mediated by the development of new blood vessels. We observed a decrease in acute renal injury mediated by pharmacological preconditioning with opioids. Renal function in opioid preconditioning groups was like in the sham control group. Both anesthetics modulated the expression of HIF-1, VEGF, VEGF-R2 and CD31. Preconditioning negatively regulated CTD. Opioid preconditioning decreased injury through modulation of angiogenic molecule expression. These are factors to consider when establishing strategies in pathophysiological and surgical processes.

p53 upregulated by HIF-1α promotes hypoxia-induced G2/M arrest and renal fibrosis in vitro and in vivo

Hypoxia plays an important role in the genesis and progression of renal fibrosis. The underlying mechanisms, however, have not been sufficiently elucidated. We examined the role of p53 in hypoxia-induced renal fibrosis in cell culture (human and rat renal tubular epithelial cells) and a mouse unilateral ureteral obstruction (UUO) model. Cell cycle of tubular cells was determined by flow cytometry, and the expression of profibrogenic factors was determined by RT-PCR, immunohistochemistry, and western blotting. Chromatin immunoprecipitation and luciferase reporter experiments were performed to explore the effect of HIF-1α on p53 expression. We showed that, in hypoxic tubular cells, p53 upregulation suppressed the expression of CDK1 and cyclins B1 and D1, leading to cell cycle (G2/M) arrest (or delay) and higher expression of TGF-β, CTGF, collagens, and fibronectin. p53 suppression by siRNA or by a specific p53 inhibitor (PIF-α) triggered opposite effects preventing the G2/M arrest and profibrotic changes. In vivo experiments in the UUO model revealed similar antifibrotic results following intraperitoneal administration of PIF-α (2.2 mg/kg). Using gain-of-function, loss-of-function, and luciferase assays, we further identified an HRE3 region on the p53 promoter as the HIF-1α-binding site. The HIF-1α–HRE3 binding resulted in a sharp transcriptional activation of p53. Collectively, we show the presence of a hypoxia-activated, p53-responsive profibrogenic pathway in the kidney. During hypoxia, p53 upregulation induced by HIF-1α suppresses cell cycle progression, leading to the accumulation of G2/M cells, and activates profibrotic TGF-β and CTGF-mediated signaling pathways, causing extracellular matrix production and renal fibrosis.

Nicorandil ameliorates bleomycin-induced pulmonary fibrosis in rats through modulating eNOS, iNOS, TXNIP and HIF-1α levels

Bleomycin (BLM) is one of the most common anti-cancer drugs used to treat numerous types of tumors. However, pulmonary toxicity is considered the most dramatic effect of BLM. Therefore, BLM has been frequently used for induction of pulmonary fibrosis. This study aimed to evaluate the effect of nicorandil on BLM-induced pulmonary fibrosis and explore the possible mechanisms. BLM was instilled intratracheally into male Sprague-Dawley rats as a single dose (5 mg/kg) and oral nicorandil was given (30 mg/kg/day) for 6 weeks after BLM challenge. At the end of experimental period, rats were sacrificed, and lung histopathology and biochemical parameters were evaluated. Nicorandil therapy attenuated lung inflammation and fibrosis elicited by BLM. Nicorandil significantly reduced total protein content, lactate dehydrogenase (LDH) activity and total and differential cell counts. Moreover, nicorandil diminished lung levels of malondialdehyde and total nitrite/nitrate, in addition to increasing lung contents of reduced glutathione and superoxide dismutase activity. Nicorandil reduced lung and bronchoalveolar lavage fluid contents of hypoxia inducible factor-1α (HIF-1α) and lung content of thioredoxin-interacting protein (TXNIP). Besides, nicorandil significantly improved histological lesions and reduced collagen deposition as well as hydroxyproline content. Immunohistochemical examination revealed that nicorandil-treated rats exhibited significant diminutions in protein expression levels of transforming growth factor beta-1(TGF-β1) and inducible nitric oxide synthase (iNOS) and enhanced pulmonary protein expression of endothelial NOS (eNOS). In conclusion, these results illustrate the possible potential effects of nicorandil for managing pulmonary fibrosis caused by BLM.

Plasma Metabolomics Profiling in Maintenance Hemodialysis Patients Based on Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry

Background

Key pathogenetic mechanisms underlying renal disease progression are unaffected by current treatment. Metabolite profiling has significantly contributed to a deeper understanding of the biochemical metabolic networks and pathways in disease, but the biochemical details in maintenance hemodialysis (MHD) patients remain largely undefined.

Methods

The metabolic fingerprinting of plasma samples from 19 MHD patients and 12 healthy controls was characterized using liquid chromatography quadrupole time-of-flight mass spectrometry. Principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) were applied to analyze the metabolic data.

Results

The plasma metabolite profile distinguished the MHD patients from the healthy controls successfully by using both PCA and OPLS-DA models. Sixty-three metabolites were identified as the key metabolites to discriminate the MHD patients from healthy controls, involving several metabolic pathways (all p < 0.05). An increase in plasma levels of D-glucose, hippuric acid, androsterone glucuronide, indolelactic acid, and a reduction in plasma levels of glycerophosphocholine, serotonin, L-lactic acid, phytosphingosine, and several lysophosphatidylcholine were observed in MHD patients compared to healthy subjects. Metabolomics analysis combined with KEGG pathway enrichment analysis revealed that non-alcoholic fatty liver disease, choline metabolism in cancer, the forkhead box O signaling pathway, and the hypoxia-inducible factor-1 signaling pathway in MHD patients were significantly changed (p < 0.05).

Conclusion

The identification of a novel signaling pathway and key metabolite markers in MHD patients provides insights into potential pathogenesis and valuable pharmacological targets for end-stage renal disease.

Hypoxia-induced HE4 in tubular epithelial cells promotes extracellular matrix accumulation and renal fibrosis via NF-κB

Hypoxia-induced extracellular matrix (ECM) deposition is an important cause of renal fibrosis that is triggered by unknown mechanisms. Human epididymis secretory protein 4 (HE4) is a newly discovered key molecule that causes ECM deposition. We used the unilateral ureteral obstruction (UUO) mouse model to investigate the expression and mechanisms of HE4 in the pathogenesis of renal fibrosis. Results were confirmed in the HK2 cell line and in human donors of kidney tissue with chronic kidney disease. Hypoxia significantly increased HE4 in renal tubular epithelial cells. HE4 overexpression activated the NF-κB pathway through the NF-κB transcription-activating group P65 by phosphorylation and nuclear translocation. NF-κB upregulated tissue inhibitor metalloproteinases 1, which may inhibit ECM degradation through inhibition of matrix metallopeptidase 2 activity. Silencing HE4 inhibited hypoxia-induced ECM deposition and alleviated fibrosis in UUO mice in vivo and blocked NF-κB activation in vitro. Expression of HE4 in the tubulointerstitium was positively correlated with tubulointerstitial fibrosis in tissue samples from patients with chronic kidney disease. Our results suggest that hypoxia induces renal fibrosis by upregulating HE4 and activating the HIF-1α/HE4/NF-κB signaling pathway. Uncovering the molecular mechanisms and function of HE4 overexpression in hypoxia-induced renal fibrosis will provide important insights into understanding renal fibrosis and antifibrotic strategies.

Systemic Succinate, Hypoxia-Inducible Factor-1 Alpha, and IL-1β Gene Expression in Autosomal Dominant Polycystic Kidney Disease with and without Hypertension

BACKGROUND AND OBJECTIVES

Cyst pressure induces renin-angiotensin-aldosterone system activation and kidney hypoxia in autosomal dominant polycystic kidney disease (ADPKD). Lipopolysaccharide-induced Toll-like receptor activation causes metabolic disturbances that are triggered by increased succinate levels and hypoxia inducible factors, which results in inflammation via IL-1β activation. Since we aimed to investigate the role of both inflammation and hypoxia in the clinical course of ADPKD, via succinate levels from sera samples, HIF-1α gene expression from whole blood and urine samples and IL-1βgene expression from whole blood were measured.

METHODS

One hundred ADPKD patients and 100 matched healthy controls were enrolled to this cross-sectional study. Twenty-four-hour ambulatory blood pressure monitoring was conducted in all participants. Blood, serum, and urine samples were taken after 12-h fasting for the measurement of biochemical parameters and succinate levels. Whole blood and urine samples were used for HIF-1α and IL-1β geneexpression by using quantitative real-time PCR.

RESULTS

There were significant differences in whole blood HIF-1α, IL-1β geneexpression, and serumsuccinate levels between the ADPKD patients and the control subjects. Whole blood HIF-1αgene expression, IL-1β geneexpression, and serumsuccinate levels were also significantly different in ADPKD patients with hypertension in comparison with normotensive ones (p < 0.05). Serum succinate levels and blood IL-1β geneexpression were increased in ADPKD patients with high levels of HIF-1α geneexpression (p = 0.018 and p = 0.029, respectively).

CONCLUSIONS

Increased age,low eGFR, and HIF-1α and IL-1β geneexpressions were also independently associated with hypertension in ADPKD patients. Inflammation and hypoxia are both relevant factors that might be associated with hypertension in ADPKD.

Erythrocyte Adenosine A2B Receptor-Mediated AMPK Activation: A Missing Component Counteracting CKD by Promoting Oxygen Delivery

BACKGROUND

Oxygen deprivation or hypoxia in the kidney drives CKD and contributes to end organ damage. The erythrocyte's role in delivery of oxygen (O₂) is regulated by hypoxia, but the effects of CKD are unknown.

METHODS

We screened all of the metabolites in the whole blood of mice infused with angiotensin II (Ang II) at 140 ng/kg per minute up to 14 days to simulate CKD and compared their metabolites with those from untreated mice. Mice lacking a receptor on their erythrocytes called ADORA2B, which increases O₂ delivery, and patients with CKD were studied to assess the role of ADORA2B-mediated O₂ delivery in CKD.

RESULTS

Untargeted metabolomics showed increased production of 2,3-biphosphoglycerate (2,3-BPG), an erythrocyte-specific metabolite promoting O₂ delivery, in mice given Ang II to induce CKD. Genetic studies in mice revealed that erythrocyte ADORA2B signaling leads to AMPK-stimulated activation of BPG mutase, promoting 2,3-BPG production and O₂ delivery to counteract kidney hypoxia, tissue damage, and disease progression in Ang II-induced CKD. Enhancing AMPK activation in mice offset kidney hypoxia by triggering 2,3-BPG production and O₂ delivery. Patients with CKD had higher 2,3-BPG levels, AMPK activity, and O₂ delivery in their erythrocytes compared with controls. Changes were proportional to disease severity, suggesting a protective effect.

CONCLUSIONS

Mouse and human evidence reveals that ADORA2B-AMPK signaling cascade-induced 2,3-BPG production promotes O₂ delivery by erythrocytes to counteract kidney hypoxia and progression of CKD. These findings pave a way to novel therapeutic avenues in CKD targeting this pathway.

Ischaemia reperfusion injury: mechanisms of progression to chronic graft dysfunction

The increasing use of extended criteria organs to meet the demand for kidney transplantation raises an important question of how the severity of early ischaemic injury influences long-term outcomes. Significant acute ischaemic kidney injury is associated with delayed graft function, increased immune-associated events and, ultimately, earlier deterioration of graft function. A comprehensive understanding of immediate molecular events that ensue post-ischaemia and their potential long-term consequences are key to the discovery of novel therapeutic targets. Acute ischaemic injury primarily affects tubular structure and function. Depending on the severity and persistence of the insult, this may resolve completely, leading to restoration of normal function, or be sustained, resulting in persistent renal impairment and progressive functional loss. Long-term effects of acute renal ischaemia are mediated by several mechanisms including hypoxia, HIF-1 activation, endothelial dysfunction leading to vascular rarefaction, sustained pro-inflammatory stimuli involving innate and adaptive immune responses, failure of tubular cells to recover and epigenetic changes. This review describes the biological relevance and interaction of these mechanisms based on currently available evidence.

Hypoxia-Induced Epithelial-To-Mesenchymal Transition Mediates Fibroblast Abnormalities via ERK Activation in Cutaneous Wound Healing

Previous studies described the involvement of extracellular signal-related kinase (ERK) in systemic fibrotic diseases, but the role of ERK in cutaneous scarring is unknown. Although hypoxia drives tissue fibrosis by activating hypoxia-inducible factor-1α (HIF-1α), the specific roles of hypoxia and associated ERK phosphorylation in abnormal fibroblast activity during cutaneous scarring are unclear. Here, we investigated whether pathologic myofibroblast-like keloid fibroblast activity is promoted by hypoxia-induced epithelial-mesenchymal transition mediated by ERK activation. ERK phosphorylation was significantly increased in keloid tissue and fibroblasts. Human dermal fibroblasts cultured under hypoxia (1% O₂) expressed phosphorylated ERK and exhibited activation of p38 mitogen-activated protein kinase signaling. Hypoxic human dermal fibroblasts showed increased protein and mRNA levels of epithelial-mesenchymal transition markers. Furthermore, administration of an ERK inhibitor (SCH772984) reduced the hypoxia-induced elevation of collagen type I levels in human dermal fibroblasts. Therefore, ERK may be a promising therapeutic target in profibrogenic diseases.

Hypoxia causes important changes of extracellular matrix biomarkers and ADAMTS proteinases in the adriamycin-induced renal fibrosis model

AIM

Renal fibrosis is a common cause of renal dysfunction with chronic kidney diseases. This process is characterized by excessive production of extracellular matrix (ECM) or inhibition of ECM degradation. A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) proteinases, which are widely presented in mammals, have very critical roles in ECM remodelling. We aimed to study the role of ADAMTS proteinases and some of the ECM markers in the pathogenesis of renal fibrosis and to investigate the effects of hypoxia on these biomarkers.

METHODS

In addition to the control group, Adriamycin (ADR) treated rats were divided into four groups as ADR, sham and two hypoxia groups. Renal nephropathy was assessed biochemical assays, pathological and immunohistochemical staining methods. The expression of ADAMTSs and mRNA were determined using Western blotting and real-time PCR, respectively.

RESULTS

Renal dysfuntion and tissue damage in favour of ECM accumulation and renal fibrosis were observed in the ADR group. This was approved by remarkable changes in the expression of ADAMTS such as increased ADAMTS-1, -12 and -15. In addition, it was found that hypoxia and duration of hypoxia enhanced markers of tubulointerstitial fibrosis in the rat kidney tissues. Also, expression differences especially in ADAMTS-1, -6 and -15 were observed in the hypoxia groups. The variable and different expression patterns of ADAMTS proteinases in the ADR-induced renal fibrosis suggest that ADAMTS family members are involved in the development and progression of fibrosis.

CONCLUSION

The expression changes of ADAMTS proteinases in kidney and association with hypoxia have potential clues to contribute to the early diagnosis and treatment options of renal fibrosis.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

Morphology and Evaluation of Renal Fibrosis

With continuing damage, both the indigenous cells of the cortex and medulla, and inflammatory cells are involved in the formation and development of renal fibrosis. Furthermore, interactions among the glomerular, tubular, and interstitial cells contribute to the process by excessive synthesis and decreased degradation of extracellular matrix. The morphology of kidney is different from pathological stages of diseases and changes with various causes. At the end stage of the disease, the kidneys are symmetrically contracted with diffuse granules. Most glomeruli show diffuse fibrosis and hyaline degeneration, and intervening tubules become atrophied. Renal interstitium shows obvious hyperplasia of fibrous tissues with marked infiltration of lymphocytes, mononuclear cells, and plasma cells. The renal arterioles are wall thickening frequently because of hyaline degeneration. Morphologic analysis based on Masson staining of the kidney tissues has been regarded as the golden standard to evaluate the visual fibrosis. However, the present studies have found that the evaluation system has poor repeatability. Several computer-aided image analysis techniques have been used to assess interstitial fibrosis. It is possible that the evaluation of renal fibrosis is carried out by the artificial intelligence renal biopsy pathological diagnosis system in the near future.

A Unifying Hypothesis Linking Hepatic Adaptations for Ethanol Metabolism to the Proinflammatory and Profibrotic Events of Alcoholic Liver Disease

The pathogenesis of alcoholic liver disease (ALD) remains poorly understood but is likely a multihit pathophysiological process. Here, we propose a hypothesis of how early mitochondrial adaptations for alcohol metabolism lead to ALD pathogenesis. Acutely, ethanol (EtOH) feeding causes a near doubling of hepatic EtOH metabolism and oxygen consumption within 2 to 3 hours. This swift increase in alcohol metabolism (SIAM) is an adaptive response to hasten metabolic elimination of both EtOH and its more toxic metabolite, acetaldehyde (AcAld). In association with SIAM, EtOH causes widespread hepatic mitochondrial depolarization (mtDepo), which stimulates oxygen consumption. In parallel, voltage-dependent anion channels (VDAC) in the mitochondrial outer membrane close. Together, VDAC closure and respiratory stimulation promote selective and more rapid oxidation of EtOH first to AcAld in the cytosol and then to nontoxic acetate in mitochondria, since membrane-permeant AcAld does not require VDAC to enter mitochondria. VDAC closure also inhibits mitochondrial fatty acid oxidation and ATP release, promoting steatosis and a decrease in cytosolic ATP. After acute EtOH, these changes revert as EtOH is eliminated with little hepatocellular cytolethality. mtDepo also stimulates mitochondrial autophagy (mitophagy). After chronic high EtOH exposure, the capacity to process depolarized mitochondria by mitophagy becomes compromised, leading to intra- and extracellular release of damaged mitochondria, mitophagosomes, and/or autolysosomes containing mitochondrial damage-associated molecular pattern (mtDAMP) molecules. mtDAMPs cause inflammasome activation and promote inflammatory and profibrogenic responses, causing hepatitis and fibrosis. We propose that persistence of mitochondrial responses to EtOH metabolism becomes a tipping point, which links initial adaptive EtOH metabolism to maladaptive changes initiating onset and progression of ALD.

Localized hypoxia links ER stress to lung fibrosis through induction of C/EBP homologous protein

ER stress in type II alveolar epithelial cells (AECs) is common in idiopathic pulmonary fibrosis (IPF), but the contribution of ER stress to lung fibrosis is poorly understood. We found that mice deficient in C/EBP homologous protein (CHOP), an ER stress-regulated transcription factor, were protected from lung fibrosis and AEC apoptosis in 3 separate models where substantial ER stress was identified. In mice treated with repetitive intratracheal bleomycin, we identified localized hypoxia in type II AECs as a potential mechanism explaining ER stress. To test the role of hypoxia in lung fibrosis, we treated mice with bleomycin, followed by exposure to 14% O2, which exacerbated ER stress and lung fibrosis. Under these experimental conditions, CHOP-/- mice, but not mice with epithelial HIF (HIF1/HIF2) deletion, were protected from AEC apoptosis and fibrosis. In vitro studies revealed that CHOP regulates hypoxia-induced apoptosis in AECs via the inositol-requiring enzyme 1α (IRE1α) and the PKR-like ER kinase (PERK) pathways. In human IPF lungs, CHOP and hypoxia markers were both upregulated in type II AECs, supporting a conclusion that localized hypoxia results in ER stress-induced CHOP expression, thereby augmenting type II AEC apoptosis and potentiating lung fibrosis.

Long noncoding RNA TUG1 promotes cardiac fibroblast transformation to myofibroblasts via miR‑29c in chronic hypoxia

Cardiac fibroblast‑myofibroblast transformation (FMT) contributes to the fibrotic deterioration evoked by chronic hypoxia. Growing evidence implicates long noncoding RNAs (lncRNAs) in various types of cardiac physiological and pathological processes, especially in cardiac fibrosis. In the present study, the lncRNA Taurine Upregulated Gene 1 (TUG1), reported as a regulator of hypoxia fibrosis in the lungs, was found to also be an important regulator of cardiac FMT. Specifically, the possible role of TUG1 in cardiac FMT and fibrosis under chronic hypoxia was investigated. It was revealed that the degree of fibrosis in heart tissues collected from congenital heart surgery patients with low pulse oxygen saturation and mice housed under chronic hypoxic and atmospheric pressure conditions was negatively correlated with pulse oxygen saturation. Moreover, TUG1 expression was positively correlated with the degree of fibrosis but negatively correlated with pulse oxygen saturation. Cardiac fibroblasts showed increased myofibroblast marker, collagen I and α‑SMA expression levels as the hypoxia time increased. TUG1 knockdown ameliorated the hypoxia‑induced FMT. A bioinformatics analysis predicted that TUG1 had miR‑29c binding sites in its 3'‑UTR and miR‑29c is a key regulator of cardiac fibrosis. The present study demonstrated that TUG1, along with miR‑29c, may contribute to cardiac FMT activation and promote fibrosis in chronic hypoxia.

Effects of Post Ischemia-Reperfusion Treatment with Trimetazidine on Renal Injury in Rats: Insights on Delayed Renal Fibrosis Progression

Even after recovery from acute kidney injury, glomeruli remain vulnerable to further injury by way of interstitial fibrosis. This study is aimed at elucidating the effects of post ischemia-reperfusion (I/R) treatment with trimetazidine on the progression to renal fibrosis as well as short- and intermediate-term aspects. Trimetazidine 3 mg/kg or 0.9% saline was given intraperitoneally once upon reperfusion or daily thereafter for 5 d or 8 w. Renal histologic changes and related signaling proteins were assessed. After 24 h, post I/R treatment with trimetazidine significantly reduced serum blood urea nitrogen and creatinine levels and tubular injury accompanied with upregulation of hypoxia-inducible factor- (HIF-) 1α, vascular endothelial growth factor (VEGF), and Bcl-2 expression. After 5 d, post I/R treatment with trimetazidine reduced renal tubular cell necrosis and apoptosis with upregulation of HIF-1α-VEGF and tissue inhibitors of metalloproteinase activities, attenuation of matrix metalloproteinase activities, and alteration of the ratio of Bax to Bcl-2 levels. After 8 w, however, post I/R treatment with trimetazidine did not modify the progression of renal fibrosis. In conclusion, post I/R treatment with trimetazidine allows ischemic kidneys to regain renal function and structure more rapidly compared to nontreated kidneys, but not enough to resolute renal fibrosis in long-term aspect.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

BAMBI is a novel HIF1-dependent modulator of TGFβ-mediated disruption of cell polarity during hypoxia

Hypoxia and loss of cell polarity are common features of malignant carcinomas. Hypoxia-inducible factor 1 (HIF1) is the major regulator of cellular hypoxia response and mediates the activation of ∼300 genes. Increased HIF1 signaling is known to be associated with epithelial-mesenchymal transformation. Here, we report that hypoxia disrupts polarized epithelial morphogenesis of MDCK cells in a HIF1α-dependent manner by modulating the transforming growth factor-β (TGFβ) signaling pathway. Analysis of potential HIF1 targets in the TGFβ pathway identified the bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI), a transmembrane glycoprotein related to the type I receptors of the TGFβ family, whose expression was essentially lost in HIF1-depleted cells. Similar to what was observed in HIF1-deficient cells, BAMBI-depleted cells failed to efficiently activate TGFβ signaling and retained epithelial polarity during hypoxia. Taken together, we show that hypoxic conditions promote TGFβ signaling in a HIF1-dependent manner and BAMBI is identified in this pathway as a novel HIF1-regulated gene that contributes to hypoxia-induced loss of epithelial polarity.

Identifying intestinal fibrosis and inflammation by spectroscopic photoacoustic imaging: an animal study in vivo

Crohn's disease (CD) is a chronic autoimmune disease characterized by obstructing intestinal strictures. Conventional imaging modalities can identify the strictures but cannot characterize whether a stricture is predominantly inflammatory or fibrotic. The purpose of this study is to examine the capability of photoacoustic (PA) imaging to characterize intestinal fibrosis and inflammation in vivo. Intestinal strictures in a rat model of CD were imaged with a PA-ultrasound parallel imaging system. Internal and external illuminations were attempted, both with transcutaneous PA signal reception. The PA signal magnitudes acquired at wavelengths targeting individual molecular components and the derived functional information showed significant differences between the inflammatory and fibrotic strictures, consistent with histological inflammation and fibrosis.

Bisecting N-Acetylglucosamine Structures Inhibit Hypoxia-Induced Epithelial-Mesenchymal Transition in Breast Cancer Cells

The epithelial-mesenchymal transition (EMT) process plays a key role in many biological processes, including tissue fibrosis, metastatic diseases, and cancer progression. EMT can be induced by certain factors, notably hypoxia, in the tumor microenvironment. Aberrant levels of certain N-glycans is associated with cancer progression. We used an integrated strategy (mass spectrometry in combination with lectin microarray analysis) to elucidate aberrant glycosylation in a hypoxia-induced EMT model using breast cancer cell lines MCF7 and MDA-MB-231. The model showed reduced levels of bisecting GlcNAc structures, and downregulated expression of the corresponding glycosyltransferase MGAT3. MGAT3 overexpression in MCF7 suppressed cell migration, proliferation, colony formation, expression of EMT markers, and AKT signaling pathway, whereas MGAT3 knockdown (shRNA silencing) had opposite effects. Our findings clearly demonstrate the functional role (and effects of dysregulation) of bisecting GlcNAc structures in hypoxia-induced EMT, and provide a useful basis for further detailed studies of physiological functions of these structures in breast cancer.

Targeting Hypoxia-Inducible Factor-1α/Pyruvate Dehydrogenase Kinase 1 Axis by Dichloroacetate Suppresses Bleomycin-induced Pulmonary Fibrosis

Hypoxia has long been implicated in the pathogenesis of fibrotic diseases. Aberrantly activated myofibroblasts are the primary pathological driver of fibrotic progression, yet how various microenvironmental influences, such as hypoxia, contribute to their sustained activation and differentiation is poorly understood. As a defining feature of hypoxia is its impact on cellular metabolism, we sought to investigate how hypoxia-induced metabolic reprogramming affects myofibroblast differentiation and fibrotic progression, and to test the preclinical efficacy of targeting glycolytic metabolism for the treatment of pulmonary fibrosis. Bleomycin-induced pulmonary fibrotic progression was evaluated in two independent, fibroblast-specific, promoter-driven, hypoxia-inducible factor (Hif) 1A knockout mouse models and in glycolytic inhibitor, dichloroacetate-treated mice. Genetic and pharmacological approaches were used to explicate the role of metabolic reprogramming in myofibroblast differentiation. Hypoxia significantly enhanced transforming growth factor-β-induced myofibroblast differentiation through HIF-1α, whereas overexpression of the critical HIF-1α-mediated glycolytic switch, pyruvate dehydrogenase kinase 1 (PDK1) was sufficient to activate glycolysis and potentiate myofibroblast differentiation, even in the absence of HIF-1α. Inhibition of the HIF-1α/PDK1 axis by genomic deletion of Hif1A or pharmacological inhibition of PDK1 significantly attenuated bleomycin-induced pulmonary fibrosis. Our findings suggest that HIF-1α/PDK1-mediated glycolytic reprogramming is a critical metabolic alteration that acts to promote myofibroblast differentiation and fibrotic progression, and demonstrate that targeting glycolytic metabolism may prove to be a potential therapeutic strategy for the treatment of pulmonary fibrosis.

Effects of erythropoietin receptor activity on angiogenesis, tubular injury, and fibrosis in acute kidney injury: a "U-shaped" relationship

The erythropoietin receptor (EpoR) is widely expressed but its renoprotective action is unexplored. To examine the role of EpoR in vivo in the kidney, we induced acute kidney injury (AKI) by ischemia-reperfusion in mice with different EpoR bioactivities in the kidney. EpoR bioactivity was reduced by knockin of wild-type human EpoR, which is hypofunctional relative to murine EpoR, and a renal tubule-specific EpoR knockout. These mice had lower EPO/EpoR activity and lower autophagy flux in renal tubules. Upon AKI induction, they exhibited worse renal function and structural damage, more apoptosis at the acute stage (<7 days), and slower recovery with more tubulointerstitial fibrosis at the subacute stage (14 days). In contrast, mice with hyperactive EpoR signaling from knockin of a constitutively active human EpoR had higher autophagic flux, milder kidney damage, and better renal function at the acute stage but, surprisingly, worse tubulointerstitial fibrosis and renal function at the subacute stage. Either excess or deficient EpoR activity in the kidney was associated with abnormal peritubular capillaries and tubular hypoxia, creating a "U-shaped" relationship. The direct effects of EpoR on tubular cells were confirmed in vitro by a hydrogen peroxide model using primary cultured proximal tubule cells with different EpoR activities. In summary, normal erythropoietin (EPO)/EpoR signaling in renal tubules provides defense against renal tubular injury maintains the autophagy-apoptosis balance and peritubular capillary integrity. High and low EPO/EpoR bioactivities both lead to vascular defect, and high EpoR activity overides the tubular protective effects in AKI recovery.

Hypoxia inducible factor-1α mediates the profibrotic effect of albumin in renal tubular cells

Proteinuria is closely associated with the progression of chronic kidney diseases (CKD) by producing renal tubulointerstitial fibrosis. Over-activation of hypoxia inducible factor (HIF)-1α has been implicated in the progression of CKD. The present study tested the hypothesis that HIF-1α mediates albumin-induced profibrotic effect in cultured renal proximal tubular cells. Incubation of the cells with albumin (40 μg/ml) for 72 hrs significantly increased the protein levels of HIF-1α, tissue inhibitor of metalloproteinase (TIMP)-1 and collagen-I, which were blocked by HIF-1α shRNA. Albumin also stimulated an epithelial-mesenchymal transition (EMT) as indicated by the decrease in epithelial marker E-cadherin, and the increase in mesenchymal markers α-smooth muscle actin and fibroblast-specific protein 1. HIF-1α shRNA blocked albumin-induced changes in these EMT markers as well. Furthermore, albumin reduced the level of hydroxylated HIF-1α, indicating an inhibition of the activity of prolyl-hydroxylases, enzymes promoting the degradation of HIF-1α. An anti-oxidant ascorbate reversed albumin-induced inhibition of prolyl-hydroxylase activity. Overexpression of prolyl-hydroxylase 2 (PHD2) transgene, a predominant isoform of PHDs in renal tubules, to reduce HIF-1α level significantly attenuated albumin-induced increases in TIMP-1 and collagen-I levels. These results suggest that albumin-induced oxidative stress inhibits PHD activity to accumulate HIF-1α, which mediates albumin-induced profibrotic effects in renal tubular cells.

AKI on CKD: heightened injury, suppressed repair, and the underlying mechanisms

Acute kidney injury (AKI) and chronic kidney disease (CKD) are interconnected. Although AKI-to-CKD transition has been intensively studied, the information of AKI on CKD is very limited. Nonetheless, AKI, when occurring in patients with CKD, is known to be more severe and difficult to recover. CKD is associated with significant changes in cell signaling in kidney tissues, including the activation of transforming growth factor-β, p53, hypoxia-inducible factor, and major developmental pathways. At the cellular level, CKD is characterized by mitochondrial dysfunction, oxidative stress, and aberrant autophagy. At the tissue level, CKD is characterized by chronic inflammation and vascular dysfunction. These pathologic changes may contribute to the heightened sensitivity of, and nonrecovery from, AKI in patients with CKD.