Angiogenic response following renal ischemia reperfusion injury: new players

In Vivo Imaging of Acute Hindlimb Ischaemia in Rat Model: A Pre-Clinical PET Study

BACKGROUND

To better understand ischaemia-related molecular alterations, temporal changes in angiogenic Aminopeptidase N (APN/CD13) expression and glucose metabolism were assessed with PET using a rat model of peripheral arterial disease (PAD).

METHODS

The mechanical occlusion of the base of the left hindlimb triggered using a tourniquet was applied to establish the ischaemia/reperfusion injury model in Fischer-344 rats. 2-[18F]FDG and [68Ga]Ga-NOTA-c(NGR) PET imaging performed 1, 3, 5, 7, and 10 days post-ischaemia induction was followed by Western blotting and immunohistochemical staining for APN/CD13 in ischaemic and control muscle tissue extracts.

RESULTS

Due to a cellular adaptation to hypoxia, a gradual increase in [68Ga]Ga-NOTA-c(NGR) and 2-[18F]FDG uptake was observed from post-intervention day 1 to 7 in the ischaemic hindlimbs, which was followed by a drop on day 10. Conforming pronounced angiogenic recovery, the NGR accretion of the ischaemic extremities differed significantly from the controls 5, 7, and 10 days after ischaemia induction (p ≤ 0.05), which correlated with the Western blot and immunohistochemical results. No remarkable radioactivity was depicted between the normally perfused hindlimbs of either the ischaemic or the control groups.

CONCLUSIONS

The PET-based longitudinal assessment of angiogenesis-associated APN/CD13 expression and glucose metabolism during ischaemia may continue to broaden our knowledge on the pathophysiology of PAD.

Kidney-targeted irradiation triggers renal ischaemic preconditioning in mice

Renal ischemia/reperfusion (I/R) causes acute kidney injury (AKI). Ischemic preconditioning (IPC) attenuates I/R-associated AKI. Whole-body irradiation induces renal IPC in mice. Still, the mechanisms remain largely unknown. Furthermore, the impact of kidney-centered irradiation on renal resistance against I/R has not been studied. Renal irradiation (8.5Gy) was done in male 8-12-week-old C57bl/6 mice using Small Animal Radiation Therapy (SmART) device. Left renal I/R was performed by clamping the renal pedicles for 30 minutes, with simultaneous right nephrectomy, at 7, 14, and 28 days post-irradiation. The renal reperfusion lasted 48 hours. Following I/R, blood urea nitrogen (BUN) and creatinine (SCr) levels were lower in pre-irradiated mice compared to controls, so was the histological Jablonski score of AKI. The metabolomics signature of renal I/R was attenuated in pre-irradiated mice. The numbers of PCNA-, CD11b-, and F4-80-positive cells in the renal parenchyma post-I/R were reduced in pre-irradiated versus control groups. Such an IPC was significantly observed as early as D14 post-irradiation. RNA-Seq showed an up-regulation of angiogenesis- and stress response-related signaling pathways in irradiated non-ischemic kidneys at D28. RT-qPCR confirmed the increased expression of VEGF, ALK5, HO1, PECAM1, NOX2, HSP70, and HSP27 in irradiated kidneys compared to controls. In addition, irradiated kidneys showed an increased CD31-positive vascular area compared to controls. A 14-day gavage of irradiated mice with the anti-angiogenic drug Sunitinib before I/R abrogated the irradiation-induced IPC at both functional and structural levels. Our observations suggest that kidney-centered irradiation activates pro-angiogenic pathways and induces IPC, with preserved renal function and attenuated inflammation post-I/R.

The genetic deletion of the Dual Specificity Phosphatase 3 (DUSP3) attenuates kidney damage and inflammation following ischaemia/reperfusion injury in mouse

AIM

Dual Specificity Phosphatase 3 (DUSP3) regulates the innate immune response, with a putative role in angiogenesis. Modulating inflammation and perfusion contributes to renal conditioning against ischaemia/reperfusion (I/R). We postulate that the functional loss of DUSP3 is associated with kidney resistance to I/R.

METHODS

Ten C57BL/6 male WT and Dusp3^-/- mice underwent right nephrectomy and left renal I/R (30 min/48 hours). Renal injury was assessed based on serum levels of urea (BUN) and Jablonski score. The expression of CD31 and VEGF vascular markers was quantified by RT-qPCR and immuno-staining. Renal resistivity index (RRI) was measured in vivo by Doppler ultrasound. Comparative phosphoproteomics was conducted using IMAC enrichment of phosphopeptides. Inflammatory markers were quantified at both mRNA and protein levels in ischaemic vs non-ischaemic kidneys in WT vs Dusp3^-/- .

RESULTS

At baseline, we located DUSP3 in renal glomeruli and endothelial cells. CD31-positive vascular network was significantly larger in Dusp3^-/- kidneys compared to WT, with a lower RRI in Dusp3^-/- mice. Following I/R, BUN and Jablonski score were significantly lower in Dusp3^-/- vs WT mice. Phosphoproteomics highlighted a down-regulation of inflammatory pathways and up-regulation of phospho-sites involved in cell metabolism and VEGF-related angiogenesis in Dusp3^-/- vs WT ischaemic kidneys. Dusp3^-/- ischaemic kidneys showed decreased mRNA levels of CD11b, TNF-α, KIM-1, IL-6, IL-1β and caspase-3 compared to controls. The numbers of PCNA-, F4-80- and CD11b-positive cells were reduced in Dusp3^-/- vs WT kidneys post-I/R.

CONCLUSION

Genetic inactivation of Dusp3 is associated with kidney conditioning against I/R, possibly due to attenuated inflammation and improved perfusion.

The Protective Role of Prolyl Oligopeptidase (POP) Inhibition in Kidney Injury Induced by Renal Ischemia-Reperfusion

Ischemia/reperfusion injury (IRI) is a complex pathophysiological process characterized by blood circulation disorder caused by various factors, such as traumatic shock, surgery, organ transplantation, and thrombus. Severe metabolic dysregulation and tissue structure destruction are observed upon restoration of blood flow to the ischemic tissue. The kidney is a highly perfused organ, sensitive to ischemia and reperfusion injury, and the incidence of renal IRI has high morbidity and mortality. Several studies showed that infiltration of inflammatory cells, apoptosis, and angiogenesis are important mechanisms involved in renal IRI. Despite advances in research, effective therapies for renal IRI are lacking. Recently it has been demonstrated the role of KYP2047, a selective inhibitor of prolyl oligopeptidase (POP), in the regulation of inflammation, apoptosis, and angiogenesis. Thus, this research focused on the role of POP in kidney ischemia/reperfusion (KI/R). An in vivo model of KI/R was performed and mice were subjected to KYP2047 treatment (intraperitoneal, 0.5, 1 and 5 mg/kg). Histological analysis, Masson's trichrome and periodic acid shift (PAS) staining, immunohistochemical and Western blots analysis, real-time PCR (RT-PCR) and ELISA were performed on kidney samples. Moreover, serum creatinine and blood urea nitrogen (BUN) were quantified. POP-inhibition by KYP2047 treatment, only at the doses of 1 and 5 mg/kg, significantly reduced renal injury and collagen amount, regulated inflammation through canonical and non-canonical NF-κB pathway, and restored renal function. Moreover, KYP2047 modulated angiogenesis markers, such as TGF-β and VEGF, also slowing down apoptosis. Interestingly, treatment with KYP2047 modulated PP2A activity. Thus, these findings clarified the role of POP inhibition in AKI, also offering novel therapeutic target for renal injury after KI/R.

Quantitative 3-dimensional imaging and tissue cytometry reveals lymphatic expansion in acute kidney injury

The lymphatic system plays an integral role in physiology and has recently been identified as a key player in disease progression. Tissue injury stimulates lymphatic expansion, or lymphangiogenesis (LA), though its precise role in disease processes remains unclear. LA is associated with inflammation, which is a key component of acute kidney injury (AKI), for which there are no approved therapies. While LA research has gained traction in the last decade, there exists a significant lack of understanding of this process in the kidney. Though innovative studies have elucidated markers and models with which to study LA, the field is still evolving with ways to visualize lymphatics in vivo. Prospero-related homeobox-1 (Prox-1) is the master regulator of LA and determines lymphatic cell fate through its action on vascular endothelial growth factor receptor expression. Here, we investigate the consequences of AKI on the abundance and distribution of lymphatic endothelial cells using Prox1-tdTomato reporter mice (ProxTom) coupled with large-scale three-dimensional quantitative imaging and tissue cytometry (3DTC). Using these technologies, we describe the spatial dynamics of lymphatic vasculature in quiescence and post-AKI. We also describe the use of lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) as a marker of lymphatic vessels using 3DTC in the absence of the ProxTom reporter mice as an alternative approach. The use of 3DTC for lymphatic research presents a new avenue with which to study the origin and distribution of renal lymphatic vessels. These findings will enhance our understanding of renal lymphatic function during injury and could inform the development of novel therapeutics for intervention in AKI.

Intermedin Alleviates Renal Ischemia-Reperfusion Injury and Enhances Neovascularization in Wistar Rats

Background

Ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury (AKI) and increases the risk of subsequently developing chronic kidney disease. Angiogenesis has been shown to play an important role in reducing renal injury after ischemia reperfusion. In this study, we investigated whether IMD could reduce renal IRI by promoting angiogenesis.

Methods

The kidneys of Wistar rats were subjected to 45 min of warm ischemia followed by 24 h of reperfusion. IMD was overexpressed in vivo using the vector pcDNA3.1-IMD transfected by an ultrasound-mediated system. The renal injury after ischemia reperfusion was assessed by detection of the serum creatinine concentration and histologic examinations of renal tissues stained by PAS and H&E. Real-time PCR and Western blotting were used to determine the mRNA and protein levels, respectively. Histological examinations were used to assess the expression of CD31, MMP2, MMP9, ET-1, VEGF and VEGFR2 in tissues.

Results

Renal function and renal histological damage were significantly ameliorated in IMD-transfected rats after ischemia reperfusion. Compared to the IRI, IMD significantly promoted angiogenesis. IMD also upregulated the protein and mRNA expression levels of VEGF and VEGFR2 and downregulated the expression level of MMP2, MMP9 and ET-1.

Conclusion

IMD could protect the kidney after renal ischemia-reperfusion injury by promoting angiogenesis and reducing the destruction of the perivascular matrix.

Sex-dependent mechanisms involved in renal tolerance to ischemia-reperfusion: Role of inflammation and histone H3 citrullination

Ischemia-reperfusion (I/R) injury, an inevitable result of kidney transplantation, triggers early inflammatory events that affect graft viability. Evidence from human transplantation and preclinical models of I/R suggests that a female hormonal environment positively influences the ability to recover from ischemic injury. However, the mechanisms behind these effects remain mostly unexplored. Here, we studied the influence of sex on pro-inflammatory mediators involved in the pathophysiology of acute I/R injury in male, female, and female ovariectomized (OVX) Wistar rats that underwent unilateral renal ischemia for 45 min, followed by 24 h of reperfusion. We found improved renal function, reduced cytokine expression, and decreased infiltration of myeloperoxidase-positive cells in females after I/R, when compared to their male and female OVX counterparts. Remarkably, citrullination of histone H3 was exacerbated in serum and renal tubules of females after I/R. In contrast, we observed lower levels of citrullinated histone H3 in male and female OVX rats in response to I/R, mostly in neutrophil extracellular traps. Our results demonstrate that female sex promotes renal I/R tolerance by attenuating pro-inflammatory mediators involved in I/R-induced damage.

A novel role of HIF-1α/PROX-1/LYVE-1 axis on tissue regeneration after renal ischaemia/reperfusion in mice

Context: Renal ischaemia reperfusion (I/R) is a common clinical condition with a high morbidity and mortality rate. To date, I/R-induced renal injury remains an ineffective treatment. Objective: We hypothesis that angiogenesis and lymphangiogenesis markers, prospero homeobox-1 (PROX-1) and lymphatic endothelial hyaluronan receptor-1 (LYVE-1), are critical during I/R. Material and methods: Kunming mice were subjected to I/R and observed for the following eight consecutive days. Pathology analysis and protein distribution were detected by H&E staining, immunohistochemistry and immunofluorescence confocal analysis. Results: After I/R treatment, renal pathology was changed. HIF-1α was induced in the early stage and colocalisation with PROX-1 mainly in the renal tubular region, whereas PROX-1 and LYVE-1 were colocalised in the glomerulus of the endothelial region. Conclusions: In this study, we revealed HIF-1α/PROX-1/LVYE-1 axis dynamic changes in different regions after I/R and demonstrated for the first time it activates during I/R repair.

Snapshot: Implications for mTOR in Aging-related Ischemia/Reperfusion Injury

Aging may aggravate the damage and dysfunction of different components of multiorgan and thus increasing multiorgan ischemia/reperfusion (IR) injury. IR injury occurs in many organs and tissues, which is a major cause of morbidity and mortality worldwide. The kinase mammalian target of rapamycin (mTOR), an atypical serine/threonine protein kinase, involves in the pathophysiological process of IR injury. In this review, we first briefly introduce the molecular features of mTOR, the association between mTOR and aging, and especially its role on autophagy. Special focus is placed on the roles of mTOR during ischemic and IR injury. We then clarify the association between mTOR and conditioning phenomena. Following this background, we expand our discussion to potential future directions of research in this area. Collectively, information reviewed herein will serve as a comprehensive reference for the actions of mTOR in IR injury and may be significant for the design of future research and increase the potential of mTOR as a therapeutic target.

Molecular Pharmacology of VEGF-A Isoforms: Binding and Signalling at VEGFR2

Vascular endothelial growth factor-A (VEGF-A) is a key mediator of angiogenesis, signalling via the class IV tyrosine kinase receptor family of VEGF Receptors (VEGFRs). Although VEGF-A ligands bind to both VEGFR1 and VEGFR2, they primarily signal via VEGFR2 leading to endothelial cell proliferation, survival, migration and vascular permeability. Distinct VEGF-A isoforms result from alternative splicing of the Vegfa gene at exon 8, resulting in VEGFxxxa or VEGFxxxb isoforms. Alternative splicing events at exons 5⁻7, in addition to recently identified posttranslational read-through events, produce VEGF-A isoforms that differ in their bioavailability and interaction with the co-receptor Neuropilin-1. This review explores the molecular pharmacology of VEGF-A isoforms at VEGFR2 in respect to ligand binding and downstream signalling. To understand how VEGF-A isoforms have distinct signalling despite similar affinities for VEGFR2, this review re-evaluates the typical classification of these isoforms relative to the prototypical, “pro-angiogenic” VEGF165a. We also examine the molecular mechanisms underpinning the regulation of VEGF-A isoform signalling and the importance of interactions with other membrane and extracellular matrix proteins. As approved therapeutics targeting the VEGF-A/VEGFR signalling axis largely lack long-term efficacy, understanding these isoform-specific mechanisms could aid future drug discovery efforts targeting VEGF receptor pharmacology.

Downregulation of ERRα inhibits angiogenesis in human umbilical vein endothelial cells through regulating VEGF production and PI3K/Akt/STAT3 signaling pathway

The human estrogen related receptor α (ERRα) is a pivotal regulator involved in energy homeostasis and mitochondrial biogenesis. It has been demonstrated that activation of ERRα in various breast cancer cells results in a significant increase of vascular endothelial growth factor (VEGF) mRNA and protein secretion. However, little is known about the relationship between ERRα and angiogenesis. Thus, the present study is aimed to investigate the effects and mechanism of ERRα suppression on the angiogenesis in human umbilical vein endothelial cells (HUVECs). Here we show that ERRα suppression powerfully inhibits proliferation, migration and capillary-like structures formation of HUVECs. Importantly, we demonstrate that these inhibitory effects are associated with the significantly reduced expression and production of VEGF. Results from further experiments using western blot and luciferase reporter assay exhibit that ERRα suppression inhibits hypoxia-inducible factor 1α (HIF-1α) expression, and phosphorylation of protein kinase B (Akt) and signal transducer and activator of transcription (STAT3) which up-regulated VEGF expression. In summary, we show that ERRα suppression inhibits angiogenesis in HUVECs and deserves further studies for application of rationale therapeutic target for patient with diseases related with aberrant angiogenesis.