Alexander Weidemann

Hypoxia, via stabilization of the hypoxia-inducible factor HIF-1α, is a direct and sufficient stimulus for brain-type natriuretic peptide induction

BNP (brain-type natriuretic peptide) is a cardiac hormone with systemic haemodynamic effects as well as local cytoprotective and antiproliferative properties. It is induced under a variety of pathophysiological conditions, including decompensated heart failure and myocardial infarction. Since regional hypoxia is a potential common denominator of increased wall stretch and myocardial hypoperfusion, we investigated the direct effects of hypoxia on BNP expression, and the role of the HIF (hypoxia-inducible transcription factor) in BNP regulation. Using an RNase protection assay we found a strong hypoxic induction of BNP mRNA expression in different cell lines and in cultured adult rat cardiomyocytes. Systemic hypoxia and exposure to 0.1% CO induced BNP expression in the rodent myocardium in vivo, although this was at a lower amplitude. BNP promoter-driven luciferase expression increased 10-fold after hypoxic stimulation in transient transfections. Inactivation of four putative HREs (hypoxia-response elements) in the promoter by site-directed mutagenesis revealed that the HRE at -466 nt was responsible for hypoxic promoter activation. A functional CACAG motif was identified upstream of this HRE. The HIF-1 complex bound specifically and inducibly only to the HRE at -466 nt, as shown by EMSA (electrophoretic mobility-shift assay) and ChIP (chromatin immunoprecipitation). siRNA (small interfering RNA)-mediated knockdown of HIF-1alpha, but not HIF-2alpha, interfered with hypoxic BNP mRNA induction and BNP promoter activation, confirming that BNP is a specific HIF-1alpha target gene. In conclusion, BNP appears to be part of the protective program steered by HIF-1 in response to oxygen deprivation. Induction of BNP may therefore contribute to the potential benefits of pharmacological HIF inducers in the treatment of ischaemic heart disease and heart failure.

Inactivation of tankyrases reduces experimental fibrosis by inhibiting canonical Wnt signalling

Objectives Canonical Wnt signalling has recently emerged as a key mediator of fibroblast activation and tissue fibrosis in systemic sclerosis. Here, we investigated tankyrases as novel molecular targets for inhibition of canonical Wnt signalling in fibrotic diseases. Methods The antifibrotic effects of the tankyrase inhibitor XAV-939 or of siRNA-mediated knockdown of tankyrases were evaluated in the mouse models of bleomycin-induced dermal fibrosis and in experimental fibrosis induced by adenoviral overexpression of a constitutively active TGF-β receptor I (Ad-TBRI). Results Inactivation of tankyrases prevented the activation of canonical Wnt signalling in experimental fibrosis and reduced the nuclear accumulation of β-catenin and the mRNA levels of the target gene c-myc. Treatment with XAV-939 or siRNA-mediated knockdown of tankyrases in the skin effectively reduced bleomycin-induced dermal thickening, differentiation of resting fibroblasts into myofibroblasts and accumulation of collagen. Potent antifibrotic effects were also observed in Ad-TBRI driven skin fibrosis. Inhibition of tankyrases was not limited by local or systemic toxicity. Conclusions Inactivation of tankyrases effectively abrogated the activation of canonical Wnt signalling and demonstrated potent antifibrotic effects in well-tolerated doses. Thus, tankyrases might be candidates for targeted therapies in fibrotic diseases.

Loss of epithelial hypoxia-inducible factor prolyl hydroxylase 2 accelerates skin wound healing in mice.

ABSTRACT Skin wound healing in mammals is a complex, multicellular process that depends on the precise supply of oxygen. Hypoxia-inducible factor (HIF) prolyl hydroxylase 2 (PHD2) serves as a crucial oxygen sensor and may therefore play an important role during reepithelialization. Hence, this study was aimed at understanding the role of PHD2 in cutaneous wound healing using different lines of conditionally deficient mice specifically lacking PHD2 in inflammatory, vascular, or epidermal cells. Interestingly, PHD2 deficiency only in keratinocytes and not in myeloid or endothelial cells was found to lead to faster wound closure, which involved enhanced migration of the hyperproliferating epithelium. We demonstrate that this effect relies on the unique expression of β3-integrin in the keratinocytes around the tip of the migrating tongue in an HIF1α-dependent manner. Furthermore, we show enhanced proliferation of these cells in the stratum basale, which is directly related to their attenuated transforming growth factor β signaling. Thus, loss of the central oxygen sensor PHD2 in keratinocytes stimulates wound closure by prompting skin epithelial cells to migrate and proliferate. Inhibition of PHD2 could therefore offer novel therapeutic opportunities for the local treatment of cutaneous wounds.

Loss of Fibroblast HIF-1α Accelerates Tumorigenesis

Solid tumors consist of malignant cells and associated stromal components, including fibroblastic cells that contribute to tumor growth and progression. Although tumor fibrosis and aberrant vascularization contribute to the hypoxia often found in advanced tumors, the contribution of hypoxic signaling within tumor-associated fibroblasts to tumorigenesis remains unknown. In this study, we used a fibroblast-specific promoter to create mice in which key hypoxia regulatory genes, including VHL, HIF-1α, HIF-2α, and VEGF-A, were knocked out specifically in tumor stromal fibroblasts. We found that loss of HIF-1α and its target gene VEGF-A accelerated tumor growth in murine model of mammary cancer. HIF-1α and VEGF-A loss also led to a reduction in vascular density and myeloid cell infiltration, which correlated with improved tumor perfusion. Together, our findings indicate that the fibroblast HIF-1α response is a critical component of tumor vascularization.

HIF-1α activation results in actin cytoskeleton reorganization and modulation of Rac-1 signaling in endothelial cells

BackgroundHypoxia is a major driving force in vascularization and vascular remodeling. Pharmacological inhibition of prolyl hydroxylases (PHDs) leads to an oxygen-independent and long-lasting activation of hypoxia-inducible factors (HIFs). Whereas effects of HIF-stabilization on transcriptional responses have been thoroughly investigated in endothelial cells, the molecular details of cytoskeletal changes elicited by PHD-inhibition remain largely unknown. To investigate this important aspect of PHD-inhibition, we used a spheroid-on-matrix cell culture model.ResultsMicrovascular endothelial cells (glEND.2) were organized into spheroids. Migration of cells from the spheroids was quantified and analyzed by immunocytochemistry. The PHD inhibitor dimethyloxalyl glycine (DMOG) induced F-actin stress fiber formation in migrating cells, but only weakly affected microvascular endothelial cells firmly attached in a monolayer. Compared to control spheroids, the residual spheroids were larger upon PHD inhibition and contained more cells with tight VE-cadherin positive cell-cell contacts. Morphological alterations were dependent on stabilization of HIF-1α and not HIF-2α as shown in cells with stable knockdown of HIF-α isoforms. DMOG-treated endothelial cells exhibited a reduction of immunoreactive Rac-1 at the migrating front, concomitant with a diminished Rac-1 activity, whereas total Rac-1 protein remained unchanged. Two chemically distinct Rac-1 inhibitors mimicked the effects of DMOG in terms of F-actin fiber formation and orientation, as well as stabilization of residual spheroids. Furthermore, phosphorylation of p21-activated kinase PAK downstream of Rac-1 was reduced by DMOG in a HIF-1α-dependent manner. Stabilization of cell-cell contacts associated with decreased Rac-1 activity was also confirmed in human umbilical vein endothelial cells.ConclusionsOur data demonstrates that PHD inhibition induces HIF-1α-dependent cytoskeletal remodeling in endothelial cells, which is mediated essentially by a reduction in Rac-1 signaling.

BK viremia and polyomavirus nephropathy in 352 kidney transplants; risk factors and potential role of mTOR inhibition.

BackgroundPolyomavirus BK nephropathy (PyVAN) remains an important cause of early graft dysfunction and graft loss in kidney transplantation.MethodsIn this retrospective, single centre cohort study we studied the incidence and outcome of BK viral infection in 352 patients transplanted in 2008–2011.ResultsDuring follow-up viral replication was detected in 48 patients (13.6%); 22 patients (6.2%) had biopsy proven PyVAN.In multivariate logistic regression analyses risk factors for BK-viremia were lack of enrolment into randomized controlled trials (RCTs), biopsy proven acute rejections, cytomegaly virus (CMV) serostatus of both donor and recipient and previous transplantation.In patients without PyVAN reduction or switch of immunosuppression was associated with rapid viral clearance and stable graft function. In contrast, in most patients with PyVAN graft function deteriorated and 5 patients prematurely lost their allograft. Switch of immunosuppression to a low dose cyclosporine plus mTOR inhibitor based regimen in patients with PyVAN was safe, well tolerated and tended to be associated with a better short-term outcome in terms of graft function compared to reduction of existing immunosuppression alone.ConclusionsWith the lack of licensed anti-polyoma viral drugs reduction or conversion of immunosuppression remains the mainstay of therapy in patients with PyVAN. The combination of low dose cyclosporine plus mTOR inhibition appears to be safe and warrants further investigation.

Inactivation of evenness interrupted (EVI) reduces experimental fibrosis by combined inhibition of canonical and non-canonical Wnt signalling

Objectives Canonical as well as non-canonical Wnt signalling pathways have emerged as core pathways of fibrosis. Their profibrotic effects are mediated via distinct intracellular cascades independently of each other. Thus, inhibition of both pathways may have additive antifibrotic effects. Here, we knocked down evenness interrupted (EVI) to simultaneously target for the first time canonical and non-canonical Wnt signalling in experimental fibrosis. Methods The antifibrotic effects of siRNA-mediated knockdown of EVI were evaluated in the mouse models of bleomycin-induced skin fibrosis and in fibrosis induced by adenoviral overexpression of a constitutively active TGF-β receptor I (AdTBRI). Results Knockdown of EVI decreased the release of canonical and non-canonical Wnt ligands by fibroblasts and reduced the activation of canonical and non-canonical Wnt cascades in experimental fibrosis with decreased accumulation of β-catenin and phosphorylated JNK and cJun. Inactivation of EVI exerted potent antifibrotic effects and reduced dermal thickening, myofibroblast differentiation and accumulation of collagen in the mouse models of bleomycin-induced and AdTBR-induced fibrosis. Conclusions Inhibition of Wnt secretion by knockdown of EVI inhibits canonical and non-canonical Wnt signalling and effectively reduces experimental fibrosis in different preclinical models. Inhibition of Wnt secretion may thus be an interesting approach for the treatment of fibrosis.

Kidney injury is independent of endothelial HIF-1α

Hypoxia-inducible transcription factors (HIFs) control cellular adaptation to low oxygen. In the kidney, activation of HIF is beneficial during injury; however, the specific contribution of HIF-1α in renal endothelial cells (EC) remains elusive. Since EC display tissue-specific heterogeneity, we investigated how HIF-1α affects key functions of glomerular EC in vitro and its contribution to renal development and pathophysiological adaptation to acute or chronic renal injury in vivo. Loss of HIF-1α in glomerular EC induces hypoxic cell death and reduces hypoxic adhesion of macrophages in vitro. In vivo, HIF-1α expression in EC in mouse kidneys is detectable but limited. Accordingly, EC-specific ablation of HIF-1α does not lead to developmental or phenotypical abnormalities in the kidney. Renal function and expression of adhesion molecules during acute ischemic kidney injury is independent of HIF-1α in EC. Likewise, inflammation and development of fibrosis after unilateral ureteric obstruction is not influenced by endothelial HIF-1α. Taken together, although HIF-1α exerts effects on glomerular EC in vitro, endothelial HIF-1α does not influence renal development and pathophysiological adaptation to kidney injury in vivo. This implies a profound difference of the hypoxic response of the renal vascular bed compared to other organs, such as the heart. This has implications for the development of pharmacological strategies targeting the endothelial hypoxic response pathways.Key messageHIF-1α controls hypoxic survival and adhesion on endothelial cells (EC) in vitro.In vivo, HIF-1α expression in renal EC is low.Deletion of HIF-1α in EC does not affect kidney development and function in mice.Renal function after acute and chronic kidney injury is independent of HIF-1α in EC.Data suggest organ-specific regulation of HIF-1α function in EC.

Hypoxia-inducible protein 2 Hig2/Hilpda mediates neutral lipid accumulation in macrophages and contributes to atherosclerosis in apolipoprotein E–deficient mice

Recently we identified hypoxia‐inducible protein 2 (HIG2)/hypoxia‐inducible lipid droplet–associated (HILPDA) as lipid droplet (LD) protein. Because HILPDA is highly expressed in atherosclerotic plaques, we examined its regulation and function in murine macrophages, compared it to the LD adipose differentiation‐related protein (Adrp)/perilipin 2 (Plin2), and investigated its effects on atherogenesis in apolipoprotein E–deficient (ApoE−/−) mice. Tie2‐Cre‐driven Hilpda conditional knockout (cKO) did not affect viability, proliferation, and ATP levels in macrophages. Hilpda proved to be a target of hypoxia‐inducible factor 1 (Hif‐1) and peroxisome proliferator‐activated receptors. In contrast, Adrp/Plin2 was not induced by Hif‐1. Hilpda localized to the endoplasmic reticulum–LD interface, the site of LD formation. Hypoxic lipid accumulation and storage of oxidized LDL, cholesteryl esters and triglycerides were abolished in Hilpda cKO macrophages, independent of the glycolytic switch, fatty acid or lipoprotein uptake. Hilpda depletion reduced resistance against lipid overload and increased production of reactive oxygen species after reoxygenation. LPS‐stimulated prostaglandin‐E2 production was dysregulated in macrophages, demonstrating the substrate buffer and reservoir function of LDs for eicosanoid production. In ApoE−/− Hilpda cKO mice, total aortic plaque area, plaque macrophages and vascular Vegf expression were reduced. Thus, macrophage Hilpda is crucial to foam‐cell formation and lipid deposition, and to controlled prostaglandin‐E2 production. By these means Hilpda promotes lesion formation and progression of atherosclerosis.—Maier, A., Wu, H., Cordasic, N., Oefner, P., Dietel, B., Thiele, C., Weidemann, A., Eckardt, K.‐U., Warnecke, C. Hypoxia‐inducible protein 2 Hig2/Hilpda mediates neutral lipid accumulation in macrophages and contributes to atherosclerosis in apolipoprotein E–deficient mice. FASEB J. 31, 4971–4984 (2017). www.fasebj.org

BANFF-Klassifikation der Histologie von Nierentransplantaten und therapeutische Konsequenzen

ZusammenfassungIn der Nachsorge nierentransplantierter Patienten kommt der nephropathologischen Begutachtung der Transplantatnierenbiopsie eine wesentliche Bedeutung zu. Die kontinuierliche Überarbeitung der diagnostischen Kriterien der Transplantatabstoßung durch die sog. BANFF-Konferenzen seit 1997 hat einen wesentlichen Anteil zur Systematisierung und damit zur Diagnosesicherheit beigetragen. Die letzte Überarbeitung 2013 mit dem Einschluss der C4d-negativen antikörpervermittelten Abstoßung schließt hier eine diagnostische Lücke, hat aber auch dazu beigetragen, dass mehr antikörpervermittelte Abstoßungen diagnostiziert werden. Die therapeutischen Optionen bei zellulären und antikörpervermittelten Abstoßungen sind multimodal, basieren jedoch auf geringer Evidenz. Zelluläre Rejektionen und akute/aktive humorale Rejektionen sind in der Regel dennoch gut behandelbar. Vor allem die chronisch, aktive humorale Rejektion stellt den Kliniker weiterhin vor große Herausforderungen, da viele der Therapieoptionen eingreifend und teuer sind und potenziell zu schweren Infektkomplikationen führen können. Der Artikel gibt eine Übersicht über die pathologischen Veränderungen entsprechend der BANFF-Klassifikation und erörtert spezifisch zu den unterschiedlichen Rejektionsformen die therapeutischen Optionen.AbstractEvaluation of renal transplant biopsies by a nephropathologist plays a pivotal role in the follow-up care of renal transplant patients. The diagnostic criteria from the original 1997 BANFF consensus conference have been revised and updated continuously which has contributed to a systematization of the diagnostic criteria and has ultimately led to an increased reliability of diagnoses. The latest BANFF update 2013 acknowledges C4d negative antibody-mediated rejection. This closes a diagnostic gap which, however, leads to an increased appreciation of antibody-mediated rejection, causing a therapeutic dilemma. Protocols of rejection therapy are mostly based on low-grade evidence; however, cellular and acute/active antibody-mediated rejections usually respond well to therapy. Chronic active antibody-mediated rejections pose a great challenge to clinicians as such rejections do not respond well to therapy, which is invasive, expensive and can potentially lead to serious infectious complications. This article outlines the histopathological changes associated with rejection according to the new BANFF 2013 classification and gives an overview of the different aspects of therapy.