Cobalt promotes angiogenesis via hypoxia-inducible factor and protects tubulointerstitium in the remnant kidney model

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.

The role of hypoxia-inducible factors 1 and 2 in the pathogenesis of diabetic kidney disease

According to the 10th edition of the IDF Diabetes Atlas, 537 million people suffered from diabetes in 2021, and this number will increase by 47% by 2045. It is estimated that even 30-40% of these individuals may develop diabetic kidney disease (DKD) in the course of diabetes. DKD is one of the most important complications of diabetes, both in terms of impact and magnitude. It leads to high morbidity and mortality, which subsequently impacts on quality of life, and it carries a high financial burden. Diabetic kidney disease is considered a complex and heterogeneous entity involving disturbances in vascular, glomerular, podocyte, and tubular function. It would appear that hypoxia-inducible factors (HIF)-1 and HIF-2 may be important players in the pathogenesis of this disease. However, their exact role is still not fully investigated. In this article, we summarize the current knowledge about HIF signaling and its role in DKD. In addition, we focus on the possible effects of nephroprotective drugs on HIF expression and activity in various tissues.

Promoting a Cobalt Complex of Qingzhuan Dark Tea Polysaccharides on Fracture Healing in Rats

Fractures occur commonly with multiple injuries, and their incidence has increased in recent years. Trace amounts of cobalt are necessary for many living organisms as it stimulates hematopoiesis and improves bone health. However, cobalt is also toxic, as it might cause allergic reactions and tissue destruction. These factors limit the application of cobalt in some medical fields. We studied the tea polysaccode-cobalt complex (TPS-Co) prepared from Qingzhuan Dark Tea polysaccharides. We used 6-week-old Sprague-Dawley rats to establish a femoral fracture model and evaluated the effects of CoCl2 and TPS-Co on the healing of femoral fractures. In this study, treatment with TPS-Co for the same content of cobalt intake decreased the side effects associated with CoCl2 treatment and accelerated the healing of femoral fractures in rats. This treatment method promoted angiogenesis by upregulating the expression of vascular endothelial growth factor and hypoxia-inducible factor. Bone formation was promoted via the upregulation of the expression of bone morphogenetic protein 2 and serum bone alkaline phosphatase. TPS-Co was found to actively regulate bone and vascular systems, resulting in significant bone regeneration effects. Therefore, the Qingzhuan Dark Tea polysaccharide cobalt complex might be used as an additive or drug to promote fracture healing, and thus, it might have a huge market value.

Pathogenesis of Reinke's Edema of the Vocal Fold

OBJECTIVES

The most frequent etiologic factor of Reinke's edema (RE) is considered to be smoking. However, the mechanism for the onset and development of the disease remains unclear. Hypoxia-inducible factor-1α (HIF-1α) is an oxygen-dependent transcriptional activator which plays crucial roles in angiogenesis in hypoxic microenvironments. HIF-1α induces the expression of vascular endothelial growth factor (VEGF) which involves angiogenesis and enhances vascular permeability. This study investigated the roles of HIF-1α in the pathogenesis of RE.

METHODS

Surgical specimens of RE from patients who underwent endolaryngeal microsurgery were used. Normal vocal folds were used as a control group. Expression of HIF-1α and VEGF was analyzed by immunohistochemistry. Three-dimensional fine structures of the vessels in RE were investigated using correlative light and electron microscopy (CLEM) technique.

RESULTS

HIF-1α and VEGF were broadly expressed in the stromal, inflammatory, and endothelial cells in the lamina propria of the vocal fold of RE. The expression of HIF-1α and VEGF of RE were significantly higher than in the lamina propria of the normal vocal fold mucosa. CLEM showed vascularization and telangiectasia and there were many dilated capillaries with thin endothelium not covered with pericytes indicating the vessels were fragile.

CONCLUSION

Transcription factor HIF-1α and induced VEGF likely play roles in the pathogenesis of RE. And increased vascular permeability with fragile vessels in angiogenesis is likely to be an etiology of RE. Transcription factor HIF-1α and induced VEGF are potential therapeutic targets for RE.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:1785-1791, 2024.

Hyperbaric Oxygen Reduces Oxidative Stress Impairment and DNA Damage and Simultaneously Increases HIF-1α in Ischemia-Reperfusion Acute Kidney Injury

The central exacerbating factor in the pathophysiology of ischemic-reperfusion acute kidney injury (AKI) is oxidative stress. Lipid peroxidation and DNA damage in ischemia are accompanied by the formation of 3-nitrotyrosine, a biomarker for oxidative damage. DNA double-strand breaks (DSBs) may also be a result of postischemic AKI. γH2AX(S139) histone has been identified as a potentially useful biomarker of DNA DSBs. On the other hand, hypoxia-inducible factor (HIF) is the "master switch" for hypoxic adaptation in cells and tissues. The aim of this research was to evaluate the influence of hyperbaric oxygen (HBO) preconditioning on antioxidant capacity estimated by FRAP (ferric reducing antioxidant power) and ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) assay, as well as on oxidative stress parameter 3-nitrotyrosine, and to assess its effects on γH2AX(S139), HIF-1α, and nuclear factor-κB (NF-κB) expression, in an experimental model of postischemic AKI induced in spontaneously hypertensive rats. The animals were divided randomly into three experimental groups: sham-operated rats (SHAM, n = 6), rats with induced postischemic AKI (AKI, n = 6), and group exposed to HBO preconditioning before AKI induction (AKI + HBO, n = 6). A significant improvement in the estimated glomerular filtration rate, eGFR, in AKI + HBO group (p < 0.05 vs. AKI group) was accompanied with a significant increase in plasma antioxidant capacity estimated by FRAP (p < 0.05 vs. SHAM group) and a reduced immunohistochemical expression of 3-nitrotyrosine and γH2AX(S139). Also, HBO pretreatment significantly increased HIF-1α expression (p < 0.001 vs. AKI group), estimated by Western blot and immunohistochemical analysis in kidney tissue, and decreased immunohistochemical NF-κB renal expression (p < 0.01). Taking all of these results together, we may conclude that HBO preconditioning has beneficial effects on acute kidney injury induced in spontaneously hypertensive rats.

Osteogenic-angiogenic coupled response of cobalt-containing mesoporous bioactive glasses in vivo

The incorporation of cobalt ions into the composition of bioactive glasses has emerged as a strategy of interest for bone regeneration purposes. In the present work, we have designed a set of bioactive mesoporous glasses SiO2-CaO-P2O5-CoO (Co-MBGs) with different amounts of cobalt. The physicochemical changes introduced by the Co2+ ion, the in vitro effects of Co-MBGs on preosteoblasts and endothelial cells and their in vivo behaviour using them as bone grafts in a sheep model were studied. The results show that Co2+ ions neither destroy mesoporous ordering nor inhibit in vitro bioactive behaviour, exerting a dual role as network former and modifier for CoO concentrations above 3 % mol. On the other hand, the activity of Co-MBGs on MC3T3-E1 preosteoblasts and HUVEC vascular endothelial cells is dependent on the concentration of CoO present in the glass. For low Co-MBGs concentrations (1mg/ml) cell viability is not affected, while the expression of osteogenic (ALP, RUNX2 and OC) and angiogenic (VEGF) genes is stimulated. For Co-MBGs concentration of 5 mg/ml, cell viability decreases as a function of the CoO content. In vivo studies show that the incorporation of Co2+ ions to the MBGs improves the bone regeneration activity of these materials, despite the deleterious effect that this ion has on bone-forming cells for any of the Co-MBG compositions studied. This contradictory effect is explained by the marked increase in angiogenesis that takes place inside the bone defect, leading to an angiogenesis-osteogenesis coupling that compensates for the partial decrease in osteoblast cells. STATEMENT OF SIGNIFICANCE: The development of new bone grafts implies to address the need for osteogenesis-angiogenesis coupling that allows bone regeneration with viable tissue in the long term. In this sense the incorporation of cobalt ions into the composition of bioactive glasses has emerged as a strategy of great interest in this field. Due to the potential cytotoxic effect of cobalt ions, there is an important controversy regarding the suitability of their incorporation in bone grafts. In this work, we address this controversy after the implantation of cobalt-doped mesoporous bioactive glasses in a sheep model. The incorporation of cobalt ions in bioactive glasses improves the bone regeneration ability of these bone grafts, due to enhancement of the angiogenesis-osteogenesis coupling.

Dysregulation of ferroptosis may participate in the mitigating effect of CoCl2 on contrast-induced nephropathy

BACKGROUND

Contrast agents can directly or indirectly induce renal tubular ischemia and hypoxic damage. Given that cobalt chloride (CoCl2) can protect renal tubules, the protective effect and potential mechanism of action of CoCl2 on contrast-induced nephropathy (CIN) warrant investigation.

METHODS

A CIN mouse model was established to determine the protective effect of CoCl2 on renal injury in vivo. Then, TMT-based proteomics was performed to determine the differentially expressed proteins (DEPs), following which, enrichment analyses of gene ontology and the KEGG pathway were performed. In vitro, a CIN model was constructed with renal tubular epithelial cells (HK-2) to determine the effect of CoCl2 on potential targets and the role of the key protein identified from the in vivo experiments.

RESULTS

CoCl2 treatment decreased the levels of BUN and serum creatinine (sCr), while increasing the levels of urea and creatinine (Cr) in the urine of mice after CIN injury. Damage to the renal tubules in the CoCl2 treatment group was significantly less than in the CIN model group. We identified 79 DEPs after treating the in vivo model with CoCl2, and frequently observed ferroptosis-related GO and KEGG pathway terms. Of these, Hp (haptoglobin) was selected and found to have a strong renoprotective effect, even though its expression level in kidney tissue decreased after CoCl2 treatment. In HK-2 cells, overexpression of Hp reduced the ferroptosis caused by erastin, while knocking down Hp negated the attenuation effect of CoCl2 on HK-2 cell ferroptosis.

CONCLUSION

CoCl2 attenuated kidney damage in the CIN model, and this effect was associated with the decrease in ferroptosis mediated by Hp.

Transition metals in angiogenesis - A narrative review

The aim of this paper is to offer a narrative review of the literature regarding the influence of transition metals on angiogenesis, excluding lanthanides and actinides. To our knowledge there are not any reviews up to date offering such a summary, which inclined us to write this paper. Angiogenesis describes the process of blood vessel formation, which is an essential requirement for human growth and development. When the complex interplay between pro- and antiangiogenic mediators falls out of balance, angiogenesis can quickly become harmful. As it is so fundamental, both its inhibition and enhancement take part in various diseases, making it a target for therapeutic treatments. Current methods come with limitations, therefore, novel agents are constantly being researched, with metal agents offering promising results. Various transition metals have already been investigated in-depth, with studies indicating both pro- and antiangiogenic properties, respectively. The transition metals are being applied in various formulations, such as nanoparticles, complexes, or scaffold materials. Albeit the increasing attention this field is receiving, there remain many unanswered questions, mostly regarding the molecular mechanisms behind the observed effects. Notably, approximately half of all the transition metals have not yet been investigated regarding potential angiogenic effects. Considering the promising results which have already been established, it should be of great interest to begin investigating the remaining elements whilst also further analyzing the established effects.

Hypoxia and renal fibrosis

Renal fibrosis is the final stage of most progressive kidney diseases. Chronic kidney disease (CKD) is associated with high comorbidity and mortality. Thus, preventing fibrosis and thereby preserving kidney function increases the quality of life and prolongs the survival of patients with CKD. Many processes such as inflammation or metabolic stress modulate the progression of kidney fibrosis. Hypoxia has also been implicated in the pathogenesis of renal fibrosis, and oxygen sensing in the kidney is of outstanding importance for the body. The dysregulation of oxygen sensing in the diseased kidney is best exemplified by the loss of stimulation of erythropoietin production from interstitial cells in the fibrotic kidney despite anemia. Furthermore, hypoxia is present in acute or chronic kidney diseases and may affect all cell types present in the kidney including tubular and glomerular cells as well as resident immune cells. Pro- and antifibrotic effects of the transcription factors hypoxia-inducible factors 1 and 2 have been described in a plethora of animal models of acute and chronic kidney diseases, but recent advances in sequencing technologies now allow for novel and deeper insights into the role of hypoxia and its cell type-specific effects on the progression of renal fibrosis, especially in humans. Here, we review existing literature on how hypoxia impacts the development and progression of renal fibrosis.

Dznep, a histone modification inhibitor, inhibits HIF1α binding to TIMP2 gene and suppresses TIMP2 expression under hypoxia

Epidemiological studies have shown that patients who recovered from acute kidney injury (AKI) may subsequently develop chronic kidney disease (CKD). AKI is primarily caused by renal hypoxia, and it causes epigenetic alterations, known as hypoxic memory. 3-Deazaneplanocin A (Dznep), an inhibitor of histone modification, suppresses renal fibrosis and the expression of tissue inhibitor of metalloproteinases-2 (TIMP2), a profibrotic factor, in mouse ischemia-reperfusion models. The current study investigated the epigenetic regulation of TIMP2 in human kidney 2 (HK-2) cells. The expression of TIMP2 was upregulated in HK-2 cells under hypoxic conditions and was suppressed by Dznep. ChIP-qPCR showed that Dznep reduced the amount of H3K4me3 at the promoter region of the TIMP2 gene under hypoxic condition. Formaldehyde-assisted isolation of regulatory elements-qPCR of the TIMP2 gene showed that Dznep reduced open chromatin area. In addition, based on ChIP-qPCR of hypoxia-inducible factor 1 alpha (HIF1α), Dznep inhibited the binding of HIF1α to the TIMP2 gene under hypoxic conditions. The reporter assays for the binding region of HIF1α showed enhanced transcriptional activity by hypoxia. Dznep suppresses the expression of TIMP2 under hypoxic conditions by inhibiting the binding of HIF1α to the TIMP2 gene.

Chronic environmental hypoxia attenuates innate immunity activation and renal injury in two CKD models

Tissue hypoxia has been pointed out as a major pathogenic factor in chronic kidney disease (CKD). However, epidemiological and experimental evidence inconsistent with this notion has been described. We have previously reported that chronic exposure to low ambient Po2 promoted no renal injury in normal rats and in rats with 5/6 renal ablation (Nx) unexpectedly attenuated renal injury. In the present study, we investigated whether chronic exposure to low ambient Po2 would also be renoprotective in two additional models of CKD: adenine (ADE) excess and chronic nitric oxide (NO) inhibition. In both models, normobaric ambient hypoxia attenuated the development of renal injury and inflammation. In addition, renal hypoxia limited the activation of NF-κB and NOD-like receptor family pyrin domain containing 3 inflammasome cascades as well as oxidative stress and intrarenal infiltration by angiotensin II-positive cells. Renal activation of hypoxia-inducible factor (HIF)-2α, along with other adaptive mechanisms to hypoxia, may have contributed to these renoprotective effects. The present findings may contribute to unravel the pathogenesis of CKD and to the development of innovative strategies to arrest its progression.NEW & NOTEWORTHY Hypoxia is regarded as a major pathogenic factor in chronic kidney disease (CKD). In disagreement with this view, we show here that sustained exposure to low ambient Po2 lessened kidney injury and inflammation in two CKD models: adenine (ADE) excess and chronic nitric oxide (NO) inhibition. Together with our previous findings in the remnant kidney, these observations indicate that local changes elicited by hypoxia may exert renoprotection in CKD, raising the prospect of novel therapeutic strategies for this disease.

Strategies for in situ tissue engineering of vascularized bone regeneration (Review)

Numerous physiological processes occur following bone fracture, including inflammatory cell recruitment, vascularization, and callus formation and remodeling. In particular circumstances, such as critical bone defects or osteonecrosis, the regenerative microenvironment is compromised, rendering endogenous stem/progenitor cells incapable of fully manifesting their reparative potential. Consequently, external interventions, such as grafting or augmentation, are frequently necessary. In situ bone tissue engineering (iBTE) employs cell-free scaffolds that possess microenvironmental cues, which, upon implantation, redirect the behavior of endogenous stem/progenitor cells towards a pro-regenerative inflammatory response and reestablish angiogenesis-osteogenesis coupling. This process ultimately results in vascularized bone regeneration (VBR). In this context, a comprehensive review of the current techniques and modalities in VBR-targeted iBTE technology is provided.

All-in-one smart dressing for simultaneous angiogenesis and neural regeneration

Wound repair, along with skin appendage regeneration, is challenged by insufficient angiogenesis and neural regeneration. Therefore, promoting both proangiogenic and neuro-regenerative therapeutic effects is essential for effective wound repair. However, most therapeutic systems apply these strategies separately or ineffectively. This study investigates the performance of an all-in-one smart dressing (ASD) that integrates angiogenic functional materials and multiple biological factors within a light crosslinked hydrogel, forming a multi-functional dressing capable of facilitating simultaneous micro-vascularization and neural regeneration. The ASD uses a zeolite-imidazolate framework 67 with anchored vanadium oxide (VO₂@ZIF-67) that allows for the on-demand release of Co²⁺ with fluctuations in pH at the wound site to stimulate angiogenesis. It can simultaneously release CXCL12, ligustroflavone, and ginsenoside Rg1 in a sustained manner to enhance the recruitment of endogenous mesenchymal stem cells, inhibit senescence, and induce neural differentiation to achieve in situ nerve regeneration. The ASD can stimulate rapid angiogenesis and nerve regeneration within 17 days through multiple angiogenic and neuro-regenerative cues within one dressing. This study provides a proof-of-concept for integrating functional nanomaterials and multiple complementary drugs within a smart dressing for simultaneous angiogenesis and neural regeneration.

Antibacterial, Adhesive, and Conductive Hydrogel for Diabetic Wound Healing

Diabetic mellitus is one of the leading causes of chronic wounds and remains a challenging issue to be resolved. Herein, a hydrogel with conformal tissue adhesivity, skin-like conductivity, robust mechanical characteristics, as well as active antibacterial function is developed. In this hydrogel, silver nanoparticles decorated polypyrrole nanotubes (AgPPy) and cobalt ions (Co²⁺ ) are introduced into an in situ polymerized poly(acrylic acid) (PAA) and branched poly(ethylenimine) (PEI) network (PPCA hydrogel). The PPCA hydrogel provides active antibacterial function through synergic effects from protonated PEI and AgPPy nanotubes, with a tissue-like mechanical property (≈16.8 ± 4.5 kPa) and skin-like electrical conductivity (≈0.048 S m^-1 ). The tensile and shear adhesive strength (≈15.88 and ≈12.76 kPa, respectively) of the PPCA hydrogel is about two- to threefold better than that of fibrin glue. In vitro studies show the PPCA hydrogel is highly effective against both gram-positive and gram-negative bacteria. In vivo results demonstrate that the PPCA hydrogel promotes diabetic wounds with accelerated healing, with notable inflammatory reduction and prominent angiogenesis regeneration. These results suggest the PPCA hydrogel provide a promising approach to promote diabetic wound healing.

ZIF@VO2 as an Intelligent Nano-Reactor for On-Demand Angiogenesis and Disinfection

Absent angiogenesis and bacterial infection are two major challenges that simultaneously delay the repair of injured tissues and organs. However, most current therapeutic systems deliver therapeutic cues in a separate and inaccurate manner which stimulates angiogenesis or inhibits infection leading to limited repair and side effects. Advanced therapeutic systems capable of providing accurate angiogenic stimulation and anti-infection signals in response to the changing microenvironment are urgently needed. Herein, a nano-reactor (ZFVO) involving zeolitic imidazolate framework-67 (ZIF-67)-deposited hollow vanadium oxide (VO₂ ) is developed to intelligently execute pro-angiogenesis and/or disinfection via the responsive release of cobalt ions and hydroxyl radicals to the injury and infection sites, respectively. ZFVO nano-reactor demonstrates a novel strategy for constructing drug-free nano-platforms with a hierarchical structure which has potential for the accurate treatment of trauma and orthopedic diseases.

Disturbance of Hypoxia Response and Its Implications in Kidney Diseases

Significance: The disturbance of the hypoxia response system is closely related to human diseases, because it is essential for the maintenance of homeostasis. Given the significant role of the hypoxia response system in human health, therapeutic applications targeting prolyl hydroxylase-hypoxia-inducible factor (HIF) signaling have been attempted. Thus, systemically reviewing the hypoxia response-based therapeutic strategies is of great significance. Recent Advances: Disturbance of the hypoxia response is a characteristic feature of various diseases. Targeting the hypoxia response system is, thus, a promising therapeutic strategy. Interestingly, several compounds and drugs are currently under clinical trials, and some have already been approved for use in the treatment of certain human diseases. Critical Issues: We summarize the molecular mechanisms of the hypoxia response system and address the potential therapeutic implications in kidney diseases. Given that the effects of hypoxia response in kidney diseases are likely to depend on the pathological context, specific cell types, and the differences in the activation pattern of HIF isoforms, the precise application is critical for the treatment of kidney diseases. Although HIF-PHIs (HIF-PHD inhibitors) have been proven to be effective and well tolerated in chronic kidney disease patients with anemia, the potential on-target consequence of HIF activation and some outstanding questions warrant further consideration. Future Direction: The mechanism of the hypoxia response system disturbance remains unclear. Elucidation of the molecular mechanism of hypoxia response and its precise effects on kidney diseases warrants clarification. Considering the complexity of the hypoxia response system and multiple biological processes controlled by HIF signaling, the development of more specific inhibitors is highly warranted. Antioxid. Redox Signal. 37, 936-955.

Fabrication of succinate-alginate xerogel films for in vitro coupling of osteogenesis and neovascularization

The osseointegration of metallic implants is reliant on a cascade of molecular interactions and the delivery of macromolecules to the implant environment that occurs before substantial bone formation. Early blood vessel formation is a requisite first step in the healing timeline for osteoid formation, where vascular development can be accelerated as a result of controlled hypoxic conditioning. In this study, alginate-derived xerogel films containing varied concentrations of disodium succinate salt which has been shown to induce pseudohypoxia (short-term hypoxic effects while maintaining an oxygenated environment) were developed. Xerogels were characterized for their morphology, succinate release over time and cellular response with osteoblast-mimicking Saos-2 and human umbilical vein endothelial cells (HUVEC). Scanning electron microscopy revealed a multiscale topography that may favour osseointegration and alamarBlue assays indicated no cytotoxic effects during in vitro proliferation of Saos-2 cells. pH measurements of eluted succinate reach 95 % of peak value after 7 h of immersion for all gels containing 10 mM of succinate or less, and 60 % within the first 40 min. In vitro exposure of HUVECs to succinate-conditioned media increased the net concentration of total proteins measured by bicinchoninic acid (BCA) assay and maintains stable vascular endothelial growth factor (VEGF) and extracellular platelet-derived growth factor (PDGF) for vessel formation through comparison of enzyme-linked immunosorbent assays (ELISAs) of the culture media and cell lysate. Tube formation assays also showed a sustained increase in tube diameter across the first 48 h of HUVEC culture when succinate concentrations of 1 and 10 μM in the xerogel. Overall, the succinate-alginate films serve as a prospective organic coating for bone-interfacing implant materials which may induce temporary pseudohypoxic conditions favourable for early angiogenesis and bone regeneration in vivo at succinate concentrations of 1 or 10 μM.

A Metal‐Ion‐Incorporated Mussel‐Inspired Poly(Vinyl Alcohol)‐Based Polymer Coating Offers Improved Antibacterial Activity and Cellular Mechanoresponse Manipulation

Cobalt (Co^II) ions have been an attractive candidate for the biomedical modification of orthopedic implants for decades. However, limited research has been performed into how immobilized Co^II ions affect the physical properties of implant devices and how these changes regulate cellular behavior. In this study we modified biocompatible poly(vinyl alcohol) with terpyridine and catechol groups (PVA‐TP‐CA) to create a stable surface coating in which bioactive metal ions could be anchored, endowing the coating with improved broad‐spectrum antibacterial activity against Escherichia coli and Staphylococcus aureus, as well as enhanced surface stiffness and cellular mechanoresponse manipulation. Strengthened by the addition of these metal ions, the coating elicited enhanced mechanosensing from adjacent cells, facilitating cell adhesion, spreading, proliferation, and osteogenic differentiation on the surface coating. This dual‐functional PVA‐TP‐CA/Co surface coating offers a promising approach for improving clinical implantation outcomes.

Renal hypoxia-HIF-PHD-EPO signaling in transition metal nephrotoxicity: friend or foe?

The kidney is the main organ that senses changes in systemic oxygen tension, but it is also the key detoxification, transit and excretion site of transition metals (TMs). Pivotal to oxygen sensing are prolyl-hydroxylases (PHDs), which hydroxylate specific residues in hypoxia-inducible factors (HIFs), key transcription factors that orchestrate responses to hypoxia, such as induction of erythropoietin (EPO). The essential TM ion Fe is a key component and regulator of the hypoxia–PHD–HIF–EPO (HPHE) signaling axis, which governs erythropoiesis, angiogenesis, anaerobic metabolism, adaptation, survival and proliferation, and hence cell and body homeostasis. However, inadequate concentrations of essential TMs or entry of non-essential TMs in organisms cause toxicity and disrupt health. Non-essential TMs are toxic because they enter cells and displace essential TMs by ionic and molecular mimicry, e. g. in metalloproteins. Here, we review the molecular mechanisms of HPHE interactions with TMs (Fe, Co, Ni, Cd, Cr, and Pt) as well as their implications in renal physiology, pathophysiology and toxicology. Some TMs, such as Fe and Co, may activate renal HPHE signaling, which may be beneficial under some circumstances, for example, by mitigating renal injuries from other causes, but may also promote pathologies, such as renal cancer development and metastasis. Yet some other TMs appear to disrupt renal HPHE signaling, contributing to the complex picture of TM (nephro-)toxicity. Strikingly, despite a wealth of literature on the topic, current knowledge lacks a deeper molecular understanding of TM interaction with HPHE signaling, in particular in the kidney. This precludes rationale preventive and therapeutic approaches to TM nephrotoxicity, although recently activators of HPHE signaling have become available for therapy.

Comparison of the Surgical Resection and Infarct 5/6 Nephrectomy Rat Models of Chronic Kidney Disease

The 5/6 nephrectomy rat remnant kidney model is commonly employed to study chronic kidney disease (CKD). This model requires removal of one whole kidney and two-thirds of the other. The two most common ways of producing the remnant kidney are surgical resection of poles, known as the polectomy (Pol) model, or ligation of upper and lower renal arterial branches, resulting in pole infarction (Inf). These models have much in common, but also major phenotypic differences, and thus respectively model unique aspects of human CKD. The purpose of this review is to summarize phenotypic similarities and differences between these two models and their relation to human CKD, while emphasizing their vascular phenotype. In this article we review studies that have evaluated arterial blood pressure, the renin-angiotensin-aldosterone-system (RAAS), autoregulation, nitric oxide, single nephron physiology, angiogenic and anti-angiogenic factors, and capillary rarefaction in these two models. Phenotypic similarities: both models spontaneously develop hallmarks of human CKD including uremia, fibrosis, capillary rarefaction, and progressive renal function decline. They both undergo whole-organ hypertrophy, hyperfiltration of functional nephrons, reduced renal expression of angiogenic factor VEGF, increased renal expression of the anti-angiogenic thrombospondin-1, impaired renal autoregulation, and abnormal vascular nitric oxide physiology. Key phenotypic differences: the Inf model develops rapid-onset, moderate-to-severe systemic hypertension, and the Pol model early normotension followed by mild-to-moderate hypertension. The Inf rat has a markedly more active renin-angiotensin-aldosterone-system. Comparison of these two models facilitates understanding of how they can be utilized for studying CKD pathophysiology (e.g., RAAS dependent or independent pathology).

BM-MSC-derived small extracellular vesicles (sEV) from trained animals presented nephroprotective potential in unilateralureteral obstruction model

Background:

The efficacy of bone marrow mesenchymal stromal cells (BM-MSC) and its extracellular vesicles has been demonstrated for a broad spectrum of indications, including kidney diseases. However, BM-MSC donor characteristics and their potential are not usually considered. Therefore, the present work aims to evaluate the nephroprotective capacity of sEV secreted by BM-MSC from trained rats inunilateral ureteral obstruction (UUO) model.

Methods:

BM-MSC was characterized by their differentiation potential and immunophenotypic markers. The sEV were isolated by ultracentrifugation and characterized by nanoparticle tracking analysis and western blot. Its miRNA cargo was examined by quantitative PCR analysis for miR-26a, 126a, and 296. Wistar rats were submitted to UUO procedure and concomitantly treated with sEV secreted by BM-MSC from the untrained andtrained rats. The kidney tissue from all groups was evaluated for fibrosis mediators (transforming growth factor beta1 and collagen), CD34-angiogenesis marker, and hypoxia-inducible factor 1 alpha (HIF-1α).

Results:

Treadmill training stimulated in BM-MSC the production of sEV loaded with pro-angiogenic miR-296. The treatment with this sEVin UUO-rats was able to attenuate collagen accumulation and increase CD34 and HIF-1α in the kidney tissue when compared to untrained ones. Tubular proximal cells under hypoxia and exposed to BM-MSC sEV demonstrate accumulation in HIF-1α and NFR-2 (nuclear factor erythroid 2-related factor 2), possibly to mediate the response to hypoxia and oxidative stress, under these conditions.

Conclusion:

The BM-MSC sEV from trained animals presented an increased nephroprotective potential compared to untrained vesicles by carrying 296-angiomiR and contributing to angiogenesis in UUO model.

A small-molecule inhibitor of hypoxia-inducible factor prolyl hydroxylase improves obesity, nephropathy and cardiomyopathy in obese ZSF1 rats

Prolyl hydroxylase (PH) enzymes control the degradation of hypoxia-inducible factor (HIF), a transcription factor known to regulate erythropoiesis, angiogenesis, glucose metabolism, cell proliferation, and apoptosis. HIF-PH inhibitors (HIF-PHIs) correct anemia in patients with renal disease and in animal models of anemia and kidney disease. However, the effects of HIF-PHIs on comorbidities associated with kidney disease remain largely unknown. We evaluated the effects of the HIF-PHI FG-2216 in obese ZSF1 (Ob-ZSF1) rats, an established model of kidney failure with metabolic syndrome. Following unilateral nephrectomy (Nx) at 8 weeks of age, rats were treated with 40 mg/kg FG-2216 or vehicle by oral gavage three times per week for up to 18 weeks. FG-2216 corrected blood hemoglobin levels and improved kidney function and histopathology in Nx-Ob-ZSF1 rats by increasing the glomerular filtration rate, decreasing proteinuria, and reducing peritubular fibrosis, tubular damage, glomerulosclerosis and mesangial expansion. FG-2216 increased renal glucose excretion and decreased body weight, fat pad weight, and serum cholesterol in Nx-Ob-ZSF1 rats. Additionally, FG-2216 corrected hypertension, improved diastolic and systolic heart function, and reduced cardiac hypertrophy and fibrosis. In conclusion, the HIF-PHI FG-2216 improved renal and cardiovascular outcomes, and reduced obesity in a rat model of kidney disease with metabolic syndrome. Thus, in addition to correcting anemia, HIF-PHIs may provide renal and cardiac protection to patients suffering from kidney disease with metabolic syndrome.

HIF-1α is transcriptionally regulated by NF-κB in acute kidney injury

Oxygen homeostasis disturbances play a critical role in the pathogenesis of acute kidney injury (AKI). The transcription factor hypoxia-inducible factor-1 (HIF-1) is a master regulator of adaptive responses to hypoxia. Aside from posttranslational hydroxylation, the mechanism of HIF-1 regulation in AKI remains largely unclear. In this study, the mechanism of HIF-α regulation in AKI was investigated. We found that tubular HIF-1α expression significantly increased at the transcriptional level in ischemia-reperfusion-, unilateral ureteral obstruction-, and sepsis-induced AKI models, which was closely associated with macrophage-dependent inflammation. Meanwhile, NF-κB, which plays a central role in the inflammation response, was involved in the increasing expression of HIF-1α in AKI, as evidenced by pharmacological modulation (NF-κB inhibitor BAY11-7082). Mechanistically, NF-κB directly bound to the HIF-1α promoter and enhanced its transcription, which occurred not only under hypoxic conditions but also under normoxic conditions. Moreover, the induced HIF-1α by inflammation protected against tubular injury in AKI. Thus, our findings not only provide novel insights into HIF-1 regulation in AKI but also offer to understand the pathophysiology of kidney diseases.NEW & NOTEWORTHY Here, the mechanism of hypoxia-inducible factor-α (HIF-α) regulation in acute kidney injury (AKI) was investigated. We found that tubular HIF-1α expression significantly increased at the transcriptional level, which was closely associated with macrophage-dependent inflammation. Meanwhile, NF-κB was involved in the increasing expression of HIF-1α in AKI. Mechanistically, NF-κB directly bound to the HIF-1α promoter and enhanced its transcription. Our findings not only provide novel insights into HIF-1 regulation in AKI but also offer to understand the pathophysiology of kidney diseases.

Bone cements for therapy and regeneration for minimally invasive treatment of neoplastic bone defects

Although calcium phosphate cements (CPCs) have been clinically used to repair bone defects caused by bone tumor resection, traditional CPCs cannot kill the remaining tumor cells after surgery and prevent cancer recurrence. In this study, a multifunctional injectable metal-organic framework (MOF) cobalt coordinated tetrakis(4-carboxyphenyl)porphyrin (Co-TCPP)-modified calcium phosphate cement (Co-TCPP/CPC) was prepared for the minimally invasive treatment of neoplastic bone defects. The incorporation of Co-TCPP not only retained the good injectability of bone cements, but also shortened the setting time, improved the compressive strength, and endowed them with excellent photothermal properties. The hyperthermia effect induced by the presence of Co-TCPP well induced the therapeutic effect against bone tumors both in vitro and in vivo. Moreover, Co-TCPP/CPC exhibited desirable osteogenesis and angiogenesis by promoting bone and vascular regeneration in vivo. Therefore, the Co-TCPP composite bone cement demonstrated its great potential for bone tumor therapy and tissue regeneration, representing a multifunctional biomaterial for the treatment of neoplastic bone defects.

Treatment of Diabetic Kidney Disease: Current and Future

Diabetic kidney disease (DKD) is the major cause of end-stage kidney disease. However, only renin-angiotensin system inhibitor with multidisciplinary treatments is effective for DKD. In 2019, sodium-glucose cotransporter 2 (SGLT2) inhibitor showed efficacy against DKD in Canagliflozin and Renal Events in Diabetes with Established Nephropathy Clinical Evaluation (CREDENCE) trial, adding a new treatment option. However, the progression of DKD has not been completely controlled. The patients with transient exposure to hyperglycemia develop diabetic complications, including DKD, even after normalization of their blood glucose. Temporary hyperglycemia causes advanced glycation end product (AGE) accumulations and epigenetic changes as metabolic memory. The drugs that improve metabolic memory are awaited, and AGE inhibitors and histone modification inhibitors are the focus of clinical and basic research. In addition, incretin-related drugs showed a renoprotective ability in many clinical trials, and these trials with renal outcome as their primary endpoint are currently ongoing. Hypoxia-inducible factor prolyl hydroxylase inhibitors recently approved for renal anemia may be renoprotective since they improve tubulointerstitial hypoxia. Furthermore, NF-E2-related factor 2 activators improved the glomerular filtration rate of DKD patients in Bardoxolone Methyl Treatment: Renal Function in chronic kidney disease/Type 2 Diabetes (BEAM) trial and Phase II Study of Bardoxolone Methyl in Patients with Chronic Kidney Disease and Type 2 Diabetes (TSUBAKI) trial. Thus, following SGLT2 inhibitor, numerous novel drugs could be utilized in treating DKD. Future studies are expected to provide new insights.

A pH-Responsive System Based on Fluorescence Enhanced Gold Nanoparticles for Renal Targeting Drug Delivery and Fibrosis Therapy

Background

Stimuli-responsive gold nano-assemblies have attracted attention as drug delivery systems in the biomedical field. However, there are challenges achieving targeted delivery and controllable drug release for specific diseases.

Materials and Methods

In this study, a glutathione (GSH)-modified fluorescent gold nanoparticle termed AuLA-GSH was prepared and a Co²⁺-induced self-assembly drug delivery platform termed AuLA-GSH-Co was constructed. Both the pH-responsive character and drug loading behavior of AuLA-GSH-Co were studied in vitro. Kidney-targeting capability was investigated in vitro and in vivo. Finally, the anti-fibrosis efficiency of AuLA-GSH-Co in a mouse model of unilateral ureteral obstruction (UUO) was explored.

Results

AuLA-GSH-Co was sensitive to pH changes and released Co²⁺ in acidic conditions, allowing it to have controllable drug release abilities. AuLA-GSH-Co was found to improve cellular uptake of Co²⁺ ions compared to CoCl₂ in vitro. AuLA-GSH exhibited specific renal targeting and prolonged renal retention time with low non-specific accumulation in vivo. Moreover, the anti-fibrosis efficiency of AuLA-GSH-Co was higher compared to CoCl₂ in a mouse model of unilateral ureteral obstruction (UUO).

Conclusion

AuLA-GSH-Co could greatly enhance drug delivery efficiency with renal targeting capability and obviously relieve renal fibrosis, providing a promising strategy for renal fibrosis therapy.

Mechanisms Leading to Differential Hypoxia-Inducible Factor Signaling in the Diabetic Kidney: Modulation by SGLT2 Inhibitors and Hypoxia Mimetics

Sodium/glucose cotransporter 2 (SGLT2) inhibitors exert important renoprotective effects in the diabetic kidney, which cannot be readily explained by their actions to lower blood glucose, blood pressure, or glomerular filtration pressures. Their effects to promote erythrocytosis suggest that these drugs act on hypoxia-inducible factors (HIFs; specifically, HIF-1α and HIF-2α), which may underlie their ability to reduce the progression of nephropathy. Type 2 diabetes is characterized by renal hypoxia, oxidative and endoplasmic reticulum stress, and defective nutrient deprivation signaling, which (acting in concert) are poised to cause both activation of HIF-1α and suppression of HIF-2α. This shift in the balance of HIF-1α/HIF-2α activities promotes proinflammatory and profibrotic pathways in glomerular and renal tubular cells. SGLT2 inhibitors alleviate renal hypoxia and cellular stress and enhance nutrient deprivation signaling, which collectively may explain their actions to suppress HIF-1α and activate HIF-2α and thereby augment erythropoiesis, while muting organellar dysfunction, inflammation, and fibrosis. Cobalt chloride, a drug conventionally classified as a hypoxia mimetic, has a profile of molecular and cellular actions in the kidney that is similar to those of SGLT2 inhibitors. Therefore, many renoprotective benefits of SGLT2 inhibitors may be related to their effect to promote oxygen deprivation signaling in the diabetic kidney.

Hypoxia-Inducible Factor and Oxygen Biology in the Kidney

Kidney tissue hypoxia is detected in various kidney diseases and is considered to play an important role in the pathophysiology of both AKI and CKD. Because of the characteristic vascular architecture and high energy demand to drive tubular solute transport, the renal medulla is especially prone to hypoxia. Injured kidneys often present capillary rarefaction, inflammation, and fibrosis, which contribute to sustained kidney hypoxia, forming a vicious cycle promoting progressive CKD. Hypoxia-inducible factor (HIF), a transcription factor responsible for cellular adaptation to hypoxia, is generally considered to protect against AKI. On the contrary, consequences of sustained HIF activation in CKD may be either protective, neutral, or detrimental. The kidney outcomes seem to be affected by various factors, such as cell types in which HIF is activated/inhibited, disease models, balance between two HIF isoforms, and time and methods of intervention. This suggests multifaceted functions of HIF and highlights the importance of understanding its role within each specific context. Prolyl-hydroxylase domain (PHD) inhibitors, which act as HIF stabilizers, have been developed to treat anemia of CKD. Although many preclinical studies demonstrated renoprotective effects of PHD inhibitors in CKD models, there may be some situations in which they lead to deleterious effects. Further studies are needed to identify patients who would gain additional benefits from PHD inhibitors and those who may need to avoid them.

Hypoxia in chronic kidney disease: towards a paradigm shift?

Chronic kidney disease (CKD) is defined as an alteration of kidney structure and/or function lasting for >3 months [1]. CKD affects 10% of the general adult population and is responsible for large healthcare costs [2]. Since the end of the last century, the role of hypoxia in CKD progression has controversially been discussed. To date, there is evidence of the presence of hypoxia in late-stage renal disease, but we lack time-course evidence, stage correlation and also spatial co-localization with fibrotic lesions to ensure its causative role. The classical view of hypoxia in CKD progression is that it is caused by peritubular capillary alterations, renal anaemia and increased oxygen consumption regardless of the primary injury. In this classical view, hypoxia is assumed to further induce pro-fibrotic and pro-inflammatory responses, as well as oxidative stress, leading to CKD worsening as part of a vicious circle. However, recent investigations tend to question this paradigm, and both the presence of hypoxia and its role in CKD progression are still not clearly demonstrated. Hypoxia-inducible factor (HIF) is the main transcriptional regulator of the hypoxia response. Genetic HIF modulation leads to variable effects on CKD progression in different murine models. In contrast, pharmacological modulation of the HIF pathway [i.e. by HIF hydroxylase inhibitors (HIs)] appears to be generally protective against fibrosis progression experimentally. We here review the existing literature on the role of hypoxia, the HIF pathway and HIF HIs in CKD progression and summarize the evidence that supports or rejects the hypoxia hypothesis, respectively.

Renal ischemia/reperfusion injury: An insight on in vitro and in vivo models

Optimal tissue oxygenation is essential for its normal function. Suboptimal oxygenation or ischemia contributes to increased mortalities during various pathological conditions such as stroke, acute kidney injury (AKI), cardiac failure. Despite the rapid progression of renal tissue injury, the mechanism underlying renal ischemia/reperfusion injury (IRI) remains highly unclear. Experimental in vitro and in vivo models epitomizing the fundamental process is critical to the research of the pathogenesis of IRI and the development of plausible therapeutics. In this review, we describe the in vitro and in vivo models of IRI, ranges from proximal tubular cell lines to surgery-based animal models like clamping of both renal pedicles (bilateral IRI), clamping of one renal pedicle (unilateral IRI), clamping of one/or both renal arteries/or vein, or unilateral IRI with contralateral nephrectomy (uIRIx). Also, advanced technologies like three-dimensional kidney organoids, kidney-on-a-chip are explained. This review provides thoughtful information for establishing reliable and pertinent models for studying IRI-associated acute renal pathologies.

Modulating the cobalt dose range to manipulate multisystem cooperation in bone environment: a strategy to resolve the controversies about cobalt use for orthopedic applications

The paradoxical effect of cobalt on biological processes has aroused controversy regarding the application of cobalt-based biomaterials in bone regeneration. Tuning the dose range of cobalt ions may be a valid strategy to resolve the controversies about cobalt use for orthopedic applications. Recent progress in bone biology has highlighted the effects of multisystem cooperation (especially of osteoimmune, skeletal, and vascular systems) on bone dynamics. Before the application of this dose-tuning strategy, a deeper understanding of its dose-dependent effect on the cooperation of osteoimmune, skeletal, and vascular systems is needed. However, due to the difficulties with investigating the interaction of multiple systems in vitro, the multimodal effects of cobalt on bone homeostasis were investigated here, in an in vivo scenario. Methods: In vitro CCK8 assay and cytoskeletal staining were preformed to detecte the cell cytotoxic reaction in response to 0.1-100 ppm cobalt stimulation. Blood clot containing 0.1 to 5 ppm of cobalt were implanted in the rat calvarium defect. The gene profile of osteoimmune, skeletal, and vascular system as well as the systemic toxicity were evaluated via RT-qPCR, histological analysis and inductively coupled plasma mass spectrometry. The bone regeneration, osteoclastogenesis and vascularization were assessed by micro-ct and histological analysis. Results: Cobalt concentration below 5 ppm did not cause cell toxicity in vitro. No systemic toxicity was observed in vivo at 0.1-5 ppm cobalt concentration. It was found that the early cytokine profiles of the multiple interacting systems were different in response to different cobalt doses. Most of the anti-inflammatory, osteogenic, and proangiogenic factors were upregulated in the 1 ppm cobalt group at the early stage. In the late stage, the 1ppm group was most superior in bone regenerative effect while the 5 ppm group displayed the strongest osteoclastogenesis activity. Conclusions: The 1 ppm concentration of cobalt yielded the most favorable cooperation of the osteoimmune, skeletal, and vascular systems and subsequently optimal bone regeneration outcomes. Tuning the cobalt dose range to manipulate the cooperation of osteoimmune, skeletal, and vascular systems could be a promising and valuable strategy to prevent paradoxical effects of cobalt while preserving its beneficial effects.

Effects of a prolyl hydroxylase inhibitor on kidney and cardiovascular complications in a rat model of chronic kidney disease

Cardiovascular disease (CVD) is the main cause of death in patients with kidney disease. Hypoxia plays a crucial role in the progression of chronic kidney disease (CKD) and cardiovascular disease, which is associated with fibrosis, inflammation, and oxidative injury. Previous studies have indicated that prolyl hydroxylase (PHD) inhibitors, stabilizers of hypoxia-inducible factors (HIFs), can be used to treat acute organ injuries such as renal ischemia-reperfusion, myocardial infarction, and, in some contexts, CKD. However, the effects of PHD inhibitors on cardiovascular complications in CKD remain unknown. In the present study, we investigated whether HIF activation has a beneficial effect on kidney and cardiovascular outcomes in the remnant kidney model. We used the 5/6 nephrectomy model with the nitric oxide synthase inhibitor N^ω-nitro-l-arginine (20 mg/L in the drinking water). Rats received diet with 0.005% enarodustat (PHD inhibitor) or vehicle for 8 wk starting 2 wk before 5/6 nephrectomy. Activation of HIF by the PHD inhibitor reduced cardiac hypertrophy and ameliorated myocardial fibrosis in association with restored capillary density and improvement in mitochondrial morphology. With regard to kidneys, enarodustat ameliorated fibrosis in association with reduced proinflammatory cytokine expression, reduced apoptosis, and restored capillary density, even though renal endpoints such as proteinuria and serum creatinine levels were not significantly affected by enarodustat, except for blood urea nitrogen levels at 4 wk. In addition, cardiac hypertrophy marker genes, including atrial natriuretic peptide, were suppressed in P19CL6 cells treated with enarodustat. These findings suggest that PHD inhibitors might show beneficial effects in cardiovascular complications caused by CKD.

Effects of orally active hypoxia inducible factor alpha prolyl hydroxylase inhibitor, FG4592 on renal fibrogenic potential in mouse unilateral ureteral obstruction model

Orally active hypoxia-inducible factor (HIF) prolyl hydroxylase inhibitors that stabilize HIF protein and stimulate the production of erythropoietin have been approved to treat renal anemia. Our previous report suggested that HIF-1α dependent fibrogenic mechanisms are operating at the early onset of renal fibrosis and its contribution declines with the progression in mouse unilateral ureteral obstruction (UUO) model. The aim of the study is to evaluate the renal fibrogenic potential of FG4592, a recently approved orally active HIF prolyl hydroxylase inhibitor in mouse UUO model. Male C57BL/6J mice orally given FG-4592 (12.5 mg/kg/day and 50 mg/kg/day) were subjected to UUO. Neither dose of FG-4592 affected renal fibrosis or macrophage infiltration. FG-4592 had no effects on increased mRNA of collagen I, collagen III or transforming growth factor-β1. At 3 days after UUO, higher dose of FG-4592 potentiated the increased mRNA expression of profibrogenic molecules, plasminogen activator inhibitor 1 (Pai-1) and connective tissue growth factor (Ctgf) but such potentiation disappeared at 7 days after UUO. It is suggested that FG-4592 used in the present study had little effects on renal fibrosis even though high dose of FG-4592 used in the present study transiently potentiated gene expression of Pai-1 and Ctgf in the UUO kidney.

JTZ-951, an HIF prolyl hydroxylase inhibitor, suppresses renal interstitial fibroblast transformation and expression of fibrosis-related factors

Some preceding studies have provided evidence that hypoxia-inducible factor (HIF)-prolyl hydroxylase (PH) inhibitors have therapeutic potential against tubular interstitial fibrosis (TIF). Recently, transformation of renal interstitial fibroblasts (RIFs) into α-smooth muscle actin-positive myofibroblasts with loss of their hypoxia-inducible erythropoietin (EPO) expression has been hypothesized as the central mechanism responsible for TIF with renal anemia (the RIF hypothesis). These reports have suggested that HIF-PH inhibitors may suppress TIF via suppressing transformation of RIFs. However, the direct effect of HIF-PH inhibitors on transformation of RIFs has not been demonstrated because there has been no appropriate assay system. Here, we established a novel in vitro model of the transformation of RIFs. This model expresses key phenotypic changes such as transformation of RIFs accompanied by loss of their hypoxia-inducible EPO expression, as proposed by the RIF hypothesis. Using this model, we demonstrated that JTZ-951, a newly developed HIF-PH inhibitor, stabilized HIF protein in RIFs, suppressed transformation of RIFs, and maintained their hypoxia-inducible EPO expression. JTZ-951 also suppressed the expression of FGF2, FGF7, and FGF18, which are upregulated during transformation of RIFs. Furthermore, expression of Fgf2, Fgf7, and Fgf18 was correlated with TIF in an animal model of TIF. We also demonstrated that not only FGF2, which is a well-known growth-promoting factor, but also FGF18 promoted proliferation of RIFs. These data suggest that JTZ-951 has therapeutic potential against TIF with renal anemia. Furthermore, FGF2, FGF7, and FGF18, which faithfully reflect the anti-TIF effects of JTZ-951, have potential as TIF biomarkers.

Mechanisms of hypoxia signalling: new implications for nephrology

Studies of the regulation of erythropoietin (EPO) production by the liver and kidneys, one of the classical physiological responses to hypoxia, led to the discovery of human oxygen-sensing mechanisms, which are now being targeted therapeutically. The oxygen-sensitive signal is generated by 2-oxoglutarate-dependent dioxygenases that deploy molecular oxygen as a co-substrate to catalyse the post-translational hydroxylation of specific prolyl and asparaginyl residues in hypoxia-inducible factor (HIF), a key transcription factor that regulates transcriptional responses to hypoxia. Hydroxylation of HIF at different sites promotes both its degradation and inactivation. Under hypoxic conditions, these processes are suppressed, enabling HIF to escape destruction and form active transcriptional complexes at thousands of loci across the human genome. Accordingly, HIF prolyl hydroxylase inhibitors stabilize HIF and stimulate expression of HIF target genes, including the EPO gene. These molecules activate endogenous EPO gene expression in diseased kidneys and are being developed, or are already in clinical use, for the treatment of renal anaemia. In this Review, we summarize information on the molecular circuitry of hypoxia signalling pathways underlying these new treatments and highlight some of the outstanding questions relevant to their clinical use.

Effects of structural distinction in neodymium nanoparticle for therapeutic application in aberrant angiogenesis

In the present study we analyzed the effect of structural distinction in neodymium nanostructures for modulating angiogenic process as the strategy for identifying biocompatible Nano therapeutics for biomedical applications. We observed structural dependence of Nd nanoparticles on biocompatibility, the spherical polymorphs showed better biocompatibility when compared with cuboidal and nanorod shaped polymorphs of neodymium. The Nd nanopolymorphs in spherical morphology exhibited least redox modulating effect compared to cuboidal shaped that was higher when compared to Nd nanorods. The efficacy of the Nd Nanopolymorphs to induce biological effect in particular on angiogenic process was observed to be directly related to the polymorphs ability to modulate redox signaling. The redox signaling was observed to be via PKM2-NOX4 signaling pathways. Further the results demonstrated that ROS generated by cuboid and rod shaped nanopolymorphs activated the pro-angiogenic factors namely VE-cadherin, HIF 1α, VEGF and VEGFR-2 to facilitate the angiogenic process. The manuscript highlights the importance of rare earth metal nanoparticles in modulating biological process for therapeutic interventions. The present study opens up a new domain in developing novel biocompatible therapeutics based on rare earth metal nanoparticles for regulating disease pathophysiology.

Tissue Engineering of the Microvasculature

The ability to generate new microvessels in desired numbers and at desired locations has been a long-sought goal in vascular medicine, engineering, and biology. Historically, the need to revascularize ischemic tissues nonsurgically (so-called therapeutic vascularization) served as the main driving force for the development of new methods of vascular growth. More recently, vascularization of engineered tissues and the generation of vascularized microphysiological systems have provided additional targets for these methods, and have required adaptation of therapeutic vascularization to biomaterial scaffolds and to microscale devices. Three complementary strategies have been investigated to engineer microvasculature: angiogenesis (the sprouting of existing vessels), vasculogenesis (the coalescence of adult or progenitor cells into vessels), and microfluidics (the vascularization of scaffolds that possess the open geometry of microvascular networks). Over the past several decades, vascularization techniques have grown tremendously in sophistication, from the crude implantation of arteries into myocardial tunnels by Vineberg in the 1940s, to the current use of micropatterning techniques to control the exact shape and placement of vessels within a scaffold. This review provides a broad historical view of methods to engineer the microvasculature, and offers a common framework for organizing and analyzing the numerous studies in this area of tissue engineering and regenerative medicine. © 2019 American Physiological Society. Compr Physiol 9:1155-1212, 2019.

Genetic Susceptibility to Chronic Kidney Disease - Some More Pieces for the Heritability Puzzle

Chronic kidney disease (CKD) is a major global health problem with an increasing prevalence partly driven by aging population structure. Both genomic and environmental factors contribute to this complex heterogeneous disease. CKD heritability is estimated to be high (30-75%). Genome-wide association studies (GWAS) and GWAS meta-analyses have identified several genetic loci associated with CKD, including variants in UMOD, SHROOM3, solute carriers, and E3 ubiquitin ligases. However, these genetic markers do not account for all the susceptibility to CKD, and the causal pathways remain incompletely understood; other factors must be contributing to the missing heritability. Less investigated biological factors such as telomere length; mitochondrial proteins, encoded by nuclear genes or specific mitochondrial DNA (mtDNA) encoded genes; structural variants, such as copy number variants (CNVs), insertions, deletions, inversions and translocations are poorly covered and may explain some of the missing heritability. The sex chromosomes, often excluded from GWAS studies, may also help explain gender imbalances in CKD. In this review, we outline recent findings on molecular biomarkers for CKD (telomeres, CNVs, mtDNA variants, sex chromosomes) that typically have received less attention than gene polymorphisms. Shorter telomere length has been associated with renal dysfunction and CKD progression, however, most publications report small numbers of subjects with conflicting findings. CNVs have been linked to congenital anomalies of the kidney and urinary tract, posterior urethral valves, nephronophthisis and immunoglobulin A nephropathy. Information on mtDNA biomarkers for CKD comes primarily from case reports, therefore the data are scarce and diverse. The most consistent finding is the A3243G mutation in the MT-TL1 gene, mainly associated with focal segmental glomerulosclerosis. Only one GWAS has found associations between X-chromosome and renal function (rs12845465 and rs5987107). No loci in the Y-chromosome have reached genome-wide significance. In conclusion, despite the efforts to find the genetic basis of CKD, it remains challenging to explain all of the heritability with currently available methods and datasets. Although additional biomarkers have been investigated in less common suspects such as telomeres, CNVs, mtDNA and sex chromosomes, hidden heritability in CKD remains elusive, and more comprehensive approaches, particularly through the integration of multiple -"omics" data, are needed.

A stimuli-responsive drug release nanoplatform for kidney-specific anti-fibrosis treatment

The renoprotective effects of hypoxia inducible-factor (HIF) activators have been demonstrated by improving renal hypoxia in chronic kidney disease. Cobalt chloride is one of the most widely used HIF activators in biomedicine; however, poor kidney targeting and undesirable side effects greatly limit its clinical applications. Here, we report a novel stimuli-responsive drug release nanoplatform in which glutathione (GSH)-modified Au nanoparticles (GLAuNPs) and Co2+ self-assemble into nanoassemblies (GLAuNPs-Co) through coordination interactions between empty orbitals of Co2+ and lone pairs of GSH. The GLAuNPs, when used as a drug carrier, demonstrated high drug loading capacity and pH-triggered drug release after assembling with Co2+. The acidic environment of lysosomes in renal fibrosis tissues could disassemble GLAuNPs-Co and release Co2+. Moreover, encapsulation of the Co2+ ions in the GLAuNPs greatly lowered the cytotoxicity of Co2+ in kidney tubule cells. Tissue fluorescence imaging showed that GLAuNPs-Co specifically accumulated in the kidneys, especially in the renal proximal tubules. After GLAuNPs-Co was intraperitoneally injected into ureter-obstructed mice, significant attenuation of interstitial fibrosis was exhibited. The beneficial effects can be mainly ascribed to miR-29c expression restored by HIF-α activation. These findings revealed that GLAuNPs-Co have pH-responsive drug release and renal targeting capabilities; thus, they are a promising drug delivery platform for treating kidney disease.

Long-term in vitro degradation behavior and biocompatibility of polycaprolactone/cobalt-substituted hydroxyapatite composite for bone tissue engineering

OBJECTIVE

Currently, infections due to foreign-body reactions caused by bacteria or implant materials at the wound site are one of the major reasons for the failure of guided tissue regeneration (GTR) and guided bone regeneration (GBR) in clinical applications. The purpose of this study was to develop regeneration membranes with localized cobalt ion release to reduce infection and inflammation by polycaprolactone (PCL)/cobalt-substituted hydroxyapatite (CoHA).

METHODS

The PCL composite membrane containing 20 wt% CoHA powders was prepared by solvent casting. The surface morphology, crystal structure, chemical composition and thermal properties of PCL composite membranes were characterized. The biocompatibility, osteogenic differentiation and antibacterial properties of composite membrane were also investigated. Then, in biodegradability was assessed by immersing phosphate buffer solution (PBS) for 6 months.

RESULTS

Physicochemical analyses revealed that CoHA is evenly mixed in the membranes and assistance reduce the crystallinity of PCL for getting more degradation amounts than PCL membrane. Osteoblast cells culture on the membrane showed that the CoHA significantly increases cell proliferation and found the calcium deposition production increased over 90% compared with PCL after 7 days of culture. A good antibacterial effect was achieved by the addition of CoHA powder. The results were confirmed by 2.4 times reduction of proliferation of Escherichia coli (E. coli) seeded on the composite membrane after 24 h. Immersing in PBS for 6 months indicated that PCL-CoHA composite membrane has improved biodegradation and can continuously remove free radicals to reduce the inflammatory response.

SIGNIFICANCE

The PCL-CoHA composite membrane with suitable releasing of cobalt ion can be considered as a potential choice for bone tissue regeneration.

Hypoxia and Hypoxia-Inducible Factors in Kidney Injury and Repair

Acute kidney injury (AKI) is a major kidney disease characterized by an abrupt loss of renal function. Accumulating evidence indicates that incomplete or maladaptive repair after AKI can result in kidney fibrosis and the development and progression of chronic kidney disease (CKD). Hypoxia, a condition of insufficient supply of oxygen to cells and tissues, occurs in both acute and chronic kidney diseases under a variety of clinical and experimental conditions. Hypoxia-inducible factors (HIFs) are the "master" transcription factors responsible for gene expression in hypoxia. Recent researches demonstrate that HIFs play an important role in kidney injury and repair by regulating HIF target genes, including microRNAs. However, there are controversies regarding the pathological roles of HIFs in kidney injury and repair. In this review, we describe the regulation, expression, and functions of HIFs, and their target genes and related functions. We also discuss the involvement of HIFs in AKI and kidney repair, presenting HIFs as effective therapeutic targets.