Midkine in nephrogenesis, hypertension and kidney diseases

The role of midkine in health and disease

Midkine (MDK) is a neurotrophic growth factor highly expressed during embryogenesis with important functions related to growth, proliferation, survival, migration, angiogenesis, reproduction, and repair. Recent research has indicated that MDK functions as a key player in autoimmune disorders of the central nervous system (CNS), such as Multiple Sclerosis (MS) and is a promising therapeutic target for the treatment of brain tumors, acute injuries, and other CNS disorders. This review summarizes the modes of action and immunological functions of MDK both in the peripheral immune compartment and in the CNS, particularly in the context of traumatic brain injury, brain tumors, neuroinflammation, and neurodegeneration. Moreover, we discuss the role of MDK as a central mediator of neuro-immune crosstalk, focusing on the interactions between CNS-infiltrating and -resident cells such as astrocytes, microglia, and oligodendrocytes. Finally, we highlight the therapeutic potential of MDK and discuss potential therapeutic approaches for the treatment of neurological disorders.

Midkine-Notch2 Pathway Mediates Excessive Proliferation of Airway Smooth Muscle Cells in Chronic Obstructive Lung Disease

Inflammation-induced proliferation of airway smooth muscle cells (ASMCs) and subsequent airway remodeling is a hallmark of chronic obstructive lung disease (COPD). The role of midkine (MK) in COPD is unclear. In this work, we explored the role of MK-Notch2 signaling in COPD by inhibiting the expression of MK using lentivirus shRNA in ASMCs in vitro and instillation of AAV9-MK in the airway of a COPD rat model in vivo. The results demonstrated that LPS decreased ASMC migration and proliferation, increased apoptosis and induced the expression of MK and Notch2 signaling molecules. Inhibition of MK exacerbated the changes in migration and proliferation but decreased the expression of MK and Notch2 signaling molecules. Rats treated with smoke fumigation and LPS showed features of COPD. The small airways of COPD rats were remodeled and lung function was significantly reduced. The expressions of TGF-β, ICAM-1, HA, MMP-9, PC-III, and LN in BALF and the expression of MK and Notch2 signaling molecules were significantly increased in the COPD rats compared with controls. Inhibition of MK reversed these changes. In conclusion, the MK-Notch2 pathway plays a key role in airway remodeling induced by ASMC proliferation. Targeting the MK-Notch2 pathway may be a new strategy for improving airway remodeling and preventing progressive decline of pulmonary function in COPD.

Midkine promotes kidney injury in diabetic kidney disease by increasing neutrophil extracellular traps formation

Background

We sought to investigate the role of midkine (MK) on neutrophil extracellular trap formation (NETosis) and diabetic kidney disease (DKD) progression.

Methods

The expression of MK and NETosis in the renal tissue of DKD patients was examined by immunohistochemistry and immunofluorescence, respectively. Neutrophils extracted from mouse bone marrow by gradient centrifugation were treated with MK for this in-vitro study. A mouse diabetes model was induced by a high-fat diet combined with an intraperitoneal injection of streptozocin (STZ). Antisense oligodeoxynucleotide (ODN) for MK inhibition was administered via tail vein injection.

Results

We found that the expression of MK was increased in the kidney tissue of DKD patients. Additionally, a greater number of neutrophils were primed toward NETosis in the kidney tissue of DKD patients, which was manifested by the increased expression of NETosis biomarkers citrullinated histone H3 (H3Cit) and myeloperoxidase (MPO). In vitro, MK treatment concentration-dependently increased neutrophil proliferation (cell counting kit-8). Further, western blot and enzyme-linked immunosorbent assays showed that MK (100 ng/mL) significantly promoted NETosis and the expression of inflammatory factors interleukin (IL)-1 and IL-6 secretion in high-glucose treated neutrophils. In the mouse diabetes model, MK promoted the pathological damage and fibrosis of kidney tissue, as demonstrated by the reversion of the pathological damage and fibrosis by the MK antisense ODN [diabetes mellitus (DM) + MK – ODN] treatment. Additionally, the inhibition of MK reduced the formation of NETs.

Conclusions

MK promotes DKD progression by increasing NETosis.

Midkine release during hemodialysis is predictive of hypervolemia and associates with excess (cardiovascular) mortality in patients with end-stage renal disease: a prospective study

Background

In end-stage renal disease, a high cardiovascular risk profile and endothelial damage prevails. The heparin-binding growth factor midkine stimulates neo-angiogenesis in ischemic diseases, coordinates neutrophil influx, and raises blood pressure through stimulated angiotensin synthesis.

Methods

We determined changes of midkine serum levels during hemodialysis sessions under the assumption that endothelial cell-derived midkine is released. Periprocedural differences (∆midkine) were calculated and correlated with cardiovacular biomarkers and fluid status (clinical assessment, V. cava collapse, comet tail phenomenon), cardiovascular morbidities, mortality rates. Blood was collected before and after dialysis from hemodialysis patients (n = 171; diabetes: n = 70; hypervolemia: n = 83; both: n = 32).

Results

Baseline midkine levels were ~ fourfold elevated compared to healthy controls (n = 100). Further, on average a tenfold rise was detected during dialysis, the extent of which was partially related to non-fractionated heparin application (r² = 0.17). Inter-individual differences were highly reproducible. Hypervolemic patients responded with a less than average rise in midkine levels during dialysis (p < 0.02), this difference became more obvious with co-existing diabetes (p < 0.001 for long dialysis-free interval) and was confirmed in an independently enrolled dialysis cohort (n = 88). In Kaplan Meier survival curves, low delta midkine levels correlated with cardiovascular/overall mortality rates, similar to elevated uPAR levels, whereas other markers (NTproANP, galectin, tenascin-C) were less predictive. Following intervention with successful fluid removal in hypervolemic dialysis patients to optimize fluid homeostasis, midkine values increased (p < 0.002), which was not observed in patients that failed to decrease weight.

Conclusion

Thus, for dialysis patients inadequate periprocedural midkine upregulation is linked with hypervolemia and associates with cardiovascular events.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11255-022-03141-4.

Midkine and chronic kidney disease-associated multisystem organ dysfunctions

Chronic kidney disease (CKD) is a progressive multisystem condition with yet undefined mechanistic drivers and multiple implicated soluble factors. If identified, these factors could be targeted for therapeutic intervention for a disease that currently lacks specific treatment. There is increasing preclinical evidence that the heparin/endothelial glycocalyx-binding molecule midkine (MK) has a pathological role in multiple CKD-related, organ-specific disease processes, including CKD progression, hypertension, vascular and cardiac disease, bone disease and CKD-related cancers. Concurrent with this are studies documenting increases in circulating and urine MK proportional to glomerular filtration rate (GFR) loss in CKD patients and evidence that administering soluble MK reverses the protective effects of MK deficiency in experimental kidney disease. This review summarizes the growing body of evidence supporting MK's potential role in driving CKD-related multisystem disease, including MK's relationship with the endothelial glycocalyx, the deranged MK levels and glycocalyx profile in CKD patients and a proposed model of MK organ interplay in CKD disease processes and highlights the importance of ongoing research into MK's potential as a therapeutic target.

Midkine: Utility as a Predictor of Early Diabetic Nephropathy in Children with Type 1 Diabetes Mellitus

Objective

This study aimed to assess the role of serum midkine (MK) as a biomarker for early detection of diabetic nephropathy in children with type 1 diabetes mellitus (T1DM) before microalbuminuria emerges.

Methods

A total of 120 children with T1DM, comprising 60 microalbuminuric patients (Group 1), 60 normoalbuminuric patients (Group 2), and 60 healthy participants as a control group (Group 3) were included. Detailed medical history, clinical examination, and laboratory assessment of high-sensitivity C-reactive protein (hs-CRP), hemoglobin A1c percentage (HbA1c%), lipid profile, urinary albumin to creatinine ratio (ACR), serum MK and estimated glomerular filtration rate based on serum creatinine were performed in all participants.

Results

Both Group 1 and Group 2 had significantly higher serum MK compared to controls (p<0.001). Additionally, significantly higher MK concentrations were present in Group 1 compared with Group 2 (p<0.001). Receiver operating characteristic curve analysis revealed that the MK concentration cutoff value of 1512 pg/mL was able to predict microalbuminuria with a sensitivity of 96% and specificity of 92%. Stepwise regression analysis revealed that HbA1c%, hs-CRP, and ACR were independently related to MK levels (p<0.001 for each).

Conclusion

The results of this study suggest that serum MK is a useful, novel, practical marker for the evaluation of renal involvement in children with T1DM, especially in normoalbuminuric children.

Identification of candidate biomarkers and therapeutic agents for heart failure by bioinformatics analysis

INTRODUCTION

Heart failure (HF) is a heterogeneous clinical syndrome and affects millions of people all over the world. HF occurs when the cardiac overload and injury, which is a worldwide complaint. The aim of this study was to screen and verify hub genes involved in developmental HF as well as to explore active drug molecules.

METHODS

The expression profiling by high throughput sequencing of GSE141910 dataset was downloaded from the Gene Expression Omnibus (GEO) database, which contained 366 samples, including 200 heart failure samples and 166 non heart failure samples. The raw data was integrated to find differentially expressed genes (DEGs) and were further analyzed with bioinformatics analysis. Gene ontology (GO) and REACTOME enrichment analyses were performed via ToppGene; protein-protein interaction (PPI) networks of the DEGs was constructed based on data from the HiPPIE interactome database; modules analysis was performed; target gene-miRNA regulatory network and target gene-TF regulatory network were constructed and analyzed; hub genes were validated; molecular docking studies was performed.

RESULTS

A total of 881 DEGs, including 442 up regulated genes and 439 down regulated genes were observed. Most of the DEGs were significantly enriched in biological adhesion, extracellular matrix, signaling receptor binding, secretion, intrinsic component of plasma membrane, signaling receptor activity, extracellular matrix organization and neutrophil degranulation. The top hub genes ESR1, PYHIN1, PPP2R2B, LCK, TP63, PCLAF, CFTR, TK1, ECT2 and FKBP5 were identified from the PPI network. Module analysis revealed that HF was associated with adaptive immune system and neutrophil degranulation. The target genes, miRNAs and TFs were identified from the target gene-miRNA regulatory network and target gene-TF regulatory network. Furthermore, receiver operating characteristic (ROC) curve analysis and RT-PCR analysis revealed that ESR1, PYHIN1, PPP2R2B, LCK, TP63, PCLAF, CFTR, TK1, ECT2 and FKBP5 might serve as prognostic, diagnostic biomarkers and therapeutic target for HF. The predicted targets of these active molecules were then confirmed.

CONCLUSION

The current investigation identified a series of key genes and pathways that might be involved in the progression of HF, providing a new understanding of the underlying molecular mechanisms of HF.

Acute kidney injury risk in orthopaedic trauma patients pre and post surgery using a biomarker algorithm and clinical risk score

Acute kidney injury (AKI) after major trauma is associated with increased mortality. The aim of this study was to assess if measurement of blood biomarkers in combination with clinical characteristics could be used to develop a tool to assist clinicians in identifying which orthopaedic trauma patients are at risk of AKI. This is a prospective study of 237 orthopaedic trauma patients who were consecutively scheduled for open reduction and internal fixation of their fracture between May 2012 and August 2013. Clinical characteristics were recorded, and 28 biomarkers were analysed in patient blood samples. Post operatively a combination of H-FABP, sTNFR1 and MK had the highest predictive ability to identify patients at risk of developing AKI (AUROC 0.885). Three clinical characteristics; age, dementia and hypertension were identified in the orthopaedic trauma patients as potential risks for the development of AKI. Combining biomarker data with clinical characteristics allowed us to develop a proactive AKI clinical tool, which grouped patients into four risk categories that were associated with a clinical management regime that impacted patient care, management, length of hospital stay, and efficient use of hospital resources.

Multiple pathophysiological roles of midkine in human disease

Midkine (MK) is a low molecular-weight protein that was first identified as the product of a retinoic acid-responsive gene involved in embryonic development. Recent studies have indicated that MK levels are related to various diseases, including cardiovascular disease (CVD), renal disease and autoimmune disease. MK is a growth factor involved in multiple pathophysiological processes, such as inflammation, the repair of damaged tissues and cancer. The pathophysiological roles of MK are diverse. MK enhances the recruitment and migration of inflammatory cells upon inflammation directly and also through induction of chemokines, and contributes to tissue damage. In lung endothelial cells, oxidative stress increased the expression of MK, which induced angiotensin-converting enzyme (ACE) expression and the consequent conversion from Ang I to Ang II, leading to further oxidative stress. MK inhibited cholesterol efflux from macrophages by reducing ATP-binding cassette transporter A1 (ABCA1) expression, which is involved in lipid metabolism, suggesting that MK is an important positive factor involved in inflammation, oxidative stress and lipid metabolism. Furthermore, MK can regulate the expansion, differentiation and activation of T cells as well as B-cell survival; mediate angiogenic and antibacterial activity; and possess anti-apoptotic activity. In this paper, we summarize the pathophysiological roles of MK in human disease.

Stratifying risk of acute kidney injury in pre and post cardiac surgery patients using a novel biomarker-based algorithm and clinical risk score

Acute kidney injury (AKI) following cardiac surgery significantly increases morbidity and mortality risks. Improving existing clinical methods of identifying patients at risk of perioperative AKI may advance management and treatment options. This study investigated whether a combination of biomarkers and clinical factors pre and post cardiac surgery could stratify patients at risk of developing AKI. Patients (n = 401) consecutively scheduled for elective cardiac surgery were prospectively studied. Clinical data was recorded and blood samples were tested for 31 biomarkers. Areas under receiver operating characteristic (AUROCs) were generated for biomarkers pre and postoperatively to stratify patients at risk of AKI. Preoperatively sTNFR1 had the highest predictive ability to identify risk of developing AKI postoperatively (AUROC 0.748). Postoperatively a combination of H-FABP, midkine and sTNFR2 had the highest predictive ability to identify AKI risk (AUROC 0.836). Preoperative clinical risk factors included patient age, body mass index and diabetes. Perioperative factors included cardio pulmonary bypass, cross-clamp and operation times, intra-aortic balloon pump, blood products and resternotomy. Combining biomarker risk score (BRS) with clinical risk score (CRS) enabled pre and postoperative assignment of patients to AKI risk categories. Combining BRS with CRS will allow better management of cardiac patients at risk of developing AKI.

Plasma Midkine Is Associated With 28-Day Mortality and Organ Function in Sepsis

BACKGROUND

Midkine has been reported to play a crucial role in inflammatory, hypoxia, and tissue injury processes. We aimed to investigate plasma midkine in septic patients and its association with 28-day mortality and organ function.

METHODS

Septic patients admitted to the Department of Critical Care Medicine, Zhongda Hospital, a tertiary hospital, from November 2017 to March 2018 were enrolled in the study. The baseline characteristics of the septic patients were recorded at admission. A peripheral blood sample was obtained at admission, and plasma midkine levels were evaluated with an immunoassay. All patients were followed up with for 28 days, with all-cause mortality being recorded.

RESULTS

A total of 26 septic patients were enrolled, which included 18 survivors and 8 nonsurvivors at day 28. Plasma midkine levels were significantly elevated in the nonsurvivor group compared with the survivors (ng/L, 763.6 [404.7-1305], 268.5 [147.8-511.4]; P = .0387]. Plasma midkine levels were elevated in septic patients with moderate/severe acute respiratory distress syndrome (ARDS) compared with patients with non/mild ARDS (ng/L, 522.3 [336.6-960.1] vs 243.8 [110.3-478.9]; P = .0135) and in those with acute kidney injury compared with those without (ng/L, 489.8 [259.2-1058] vs 427.9 [129.6-510.3]; P = .0973). Changes in plasma midkine levels were also associated with extravascular lung water index (P = .063) and pulmonary vascular permeability index (P = .049).

CONCLUSIONS

Plasma midkine was associated with 28-day mortality, as well as pulmonary and kidney injury, in septic patients.

Serum biomarker for diagnostic evaluation of pulmonary arterial hypertension in systemic sclerosis

Background

Systemic sclerosis-associated pulmonary arterial hypertension (SSc-PAH) is one of the leading causes of death in SSc. Identification of a serum-based proteomic diagnostic biomarker for SSc-PAH would allow for rapid non-invasive screening and could positively impact patient survival. Identification and validation of novel proteins could potentially facilitate the identification of SSc-PAH, and might also point to important protein mediators in pathogenesis.

Methods

Thirteen treatment-naïve SSc-PAH patients had serum collected at time of diagnosis and were used as the discovery cohort for the protein-expression biomarker. Two proteins, Midkine and Follistatin-like 3 (FSTL3) were then validated by enzyme-linked immunosorbent assays. Midkine and FSTL3 were tested in combination to identify SSc-PAH and were validated in two independent cohorts of SSc-PAH (n = 23, n = 11).

Results

Eighty-two proteins were found to be differentially regulated in SSc-PAH sera. Two proteins (Midkine and FSTL3) were also shown to be elevated in publicly available data and their expression was evaluated in independent cohorts. In the validation cohorts, the combination of Midkine and FSTL3 had an area under the receiver operating characteristic curve (AUC) of 0.85 and 0.92 with respective corresponding measures of sensitivity of 76% and 91%, and specificity measures of 76% and 80%.

Conclusions

These findings indicate that there is a clear delineation between overall protein expression in sera from SSc patients and those with SSc-PAH. The combination of Midkine and FSTL3 can serve as an SSc-PAH biomarker and are potential drug targets for this rare disease population.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1679-8) contains supplementary material, which is available to authorized users.

Psychrophilic proteases dramatically reduce single-cell RNA-seq artifacts: a molecular atlas of kidney development

Single-cell RNA-seq is a powerful technique. Nevertheless, there are important limitations, including the technical challenges of breaking down an organ or tissue into a single-cell suspension. Invariably, this has required enzymatic incubation at 37°C, which can be expected to result in artifactual changes in gene expression patterns. Here, we describe a dissociation method that uses a protease with high activity in the cold, purified from a psychrophilic microorganism. The entire procedure is carried out at 6°C or colder, at which temperature mammalian transcriptional machinery is largely inactive, thereby effectively 'freezing in' the in vivo gene expression patterns. To test this method, we carried out RNA-seq on 20,424 single cells from postnatal day 1 mouse kidneys, comparing the results of the psychrophilic protease method with procedures using 37°C incubation. We show that the cold protease method provides a great reduction in gene expression artifacts. In addition, the results produce a single-cell resolution gene expression atlas of the newborn mouse kidney, an interesting time in development when mature nephrons are present yet nephrogenesis remains extremely active.

PEA3 protects against gentamicin nephrotoxicity: role of mitochondrial dysfunction

Toxin-induced nephrotoxicity is one of the major causes leading to the acute kidney injury (AKI). Among these nephrotoxic toxins, gentamicin can induce AKI with elusive mechanisms. Emerging evidence demonstrated that PEA3 (polyomavirus enhancer activator 3) contributed to the nephrogenesis, while its role in AKI remains unknown. Thus, this study was to investigate the role of PEA3 in gentamicin nephrotoxicity, as well as the underlying mechanisms. In rats, gentamicin treatment (200 mg/kg twice per day) for two days induced remarkable kidney injury with a peak damage on day 5 evaluated by the tubular injury score, proteinuria, and tubular injury markers of NGAL and KIM-1. In parallel with the tubular injury, PEA3 protein and mRNA expressions were significantly upregulated by gentamicin and peaked on day 5. To define the role of PEA3 in gentamicin nephrotoxicity, proximal tubule cells were transfected with PEA3 plasmid with or without gentamicin treatment (1 mg/ml). Notably, overexpression of PEA3 attenuated gentamicin-induced cell injury shown by the ameliorated cell apoptosis and NGAL and KIM-1 upregulation. Meantime, gentamicin caused severe mitochondrial dysfunction, which was largely normalized by PEA3 overexpression. In contrast, silencing PEA3 by a siRNA strategy further deteriorated gentamicin-induced cell apoptosis and mitochondrial dysfunction. In sum, PEA3 protected against gentamicin nephrotoxicity possibly via a mitochondrial mechanism.

Transcriptome Analysis of Human Reninomas as an Approach to Understanding Juxtaglomerular Cell Biology

Renin, a key component in the regulation of blood pressure in mammals, is produced by the rare and highly specialized juxtaglomerular cells of the kidney. Chronic stimulation of renin release results in a recruitment of new juxtaglomerular cells by the apparent conversion of adjacent smooth muscle cells along the afferent arterioles. Because juxtaglomerular cells rapidly dedifferentiate when removed from the kidney, their developmental origin and the mechanism that explains their phenotypic plasticity remain unclear. To overcome this limitation, we have performed RNA expression analysis on 4 human renin-producing tumors. The most highly expressed genes that were common between the reninomas were subsequently used for in situ hybridization in kidneys of 5-day-old mice, adult mice, and adult mice treated with captopril. From the top 100 genes, 10 encoding for ligands were selected for further analysis. Medium of human embryonic kidney 293 cells transfected with the mouse cDNA encoding these ligands was applied to (pro)renin-synthesizing As4.1 cells. Among the ligands, only platelet-derived growth factor B reduced the medium and cellular (pro)renin levels, as well as As4.1 renin gene expression. In addition, platelet-derived growth factor B-exposed As4.1 cells displayed a more elongated and aligned shape with no alteration in viability. This was accompanied by a downregulated expression of α-smooth muscle actin and an upregulated expression of interleukin-6, suggesting a phenotypic shift from myoendocrine to inflammatory. Our results add 36 new genes to the list that characterize renin-producing cells and reveal a novel role for platelet-derived growth factor B as a regulator of renin-synthesizing cells.

The role of midkine in the inflammatory process and its correlation with other inflammatory markers in renal transplant recipients

BACKGROUND

Midkine (MK), which is expressed in the proximal tubular epithelial cells of the kidney, is thought to have a role in the pathophysiology of inflammation-related renal diseases. Both immunological and nonimmunological mechanisms may affect renal functions negatively during the early and late post-transplantation periods. We aimed in our study to evaluate the relationship of MK with clinical findings and inflammatory markers, including high sensitivity C-reactive protein (hs-CRP), interleukin (IL-6) and tumor necrosis factor (TNF-α) in the pretransplant and post-transplant period.

METHODS

Forty-one consecutive patients transplanted from living related donors were included in this prospective observational study. All patients received the same immunosuppressive treatment protocol. MK, hsCRP, IL-6 and TNF-α levels were measured before and 2 months after renal transplantation.

RESULTS

Pretransplant MK levels correlated positively with hsCRP (r = 0.41, p = 0.004) and IL-6 (r = 0.58, p&lt;0.001). The mean post-transplant MK level was found to be higher than the pretransplant level (143 ± 350 pg/mL, 2792 ± 4235 pg/mL respectively, p = &lt;0.001), while the mean hsCRP, IL-6 and TNF-α levels did not change significantly. Post-transplant IL-6 correlated significantly with MK (r = 0.388, p = 0.012), hsCRP (r = 0.41, p = 0.007) and TNF-α (r = 0.348, p = 0.026). There was no significant correlation between clinical findings and inflammatory markers.

CONCLUSIONS

MK may be a good inflammatory marker in renal transplant recipients as in other inflammatory diseases. Moreover, it seems that it is not affected by factors other than inflammation during the post-transplantation period.

Midkine Deteriorates Cardiac Remodeling via Epidermal Growth Factor Receptor Signaling in Chronic Kidney Disease

In chronic kidney disease, activation of the epidermal growth factor receptor (EGFR) leads to cardiac hypertrophy, which affects morbidity and mortality. In patients with renal insufficiency and heart failure, the expression of midkine, a heparin-binding growth factor, is increased. Therefore, we investigated the association between midkine and EGFR in the induction of cardiac hypertrophy and dysfunction in chronic kidney disease. We performed subtotal nephrectomies in midkine-knockout mice and wild-type mice. We found that subtotal nephrectomy-induced cardiac hypertrophy and phosphorylation of extracellular signal-regulated kinase 1/2 and AKT were attenuated in midkine-knockout mice compared with wild-type mice. An antiphosphotyrosine receptor antibody array was used to demonstrate that EGFR phosphorylation in the heart was also lower in midkine-knockout mice than in wild-type mice. Midkine induced EGFR, extracellular signal-regulated kinase 1/2, and AKT phosphorylation and led to hypertrophy in neonatal rat cardiomyocytes. Pretreatment with EGFR inhibitors or EGFR silencing suppressed midkine-stimulated phosphorylation of extracellular signal-regulated kinase 1/2 and AKT, induction of fetal cardiac gene expression, and hypertrophy in cardiomyocytes. To confirm the association between midkine and EGFR in vivo, mice subjected to subtotal nephrectomy were treated with the EGFR inhibitor gefitinib. Gefitinib treatment attenuated subtotal nephrectomy-induced cardiac hypertrophy. These results indicate that midkine might be a key mediator of cardiorenal interactions through EGFR activation, which plays a crucial role in cardiac hypertrophy in chronic kidney disease.

Wnt/β-catenin up-regulates Midkine expression in glioma cells

Midkine, also known as neurite growth-promoting factor 2 (NEGF2), plays an important role in cell proliferation, apoptosis and differentiation. Recent studies have shown that Midkine is up-regulated in several types of human cancers. However, the molecular mechanism for its up-regulation remains poorly understood. Activation of Wnt/β-catenin signaling is viewed as crucial for multiple tumor growth and metastasis, including glioma. In the present study, we found that Wnt3a administration or transfection of a constitutively activated β-catenin promoted Midkine expression in glioma cells. We further identified a TCF/LEF binding site, with which beta-catenin interacts, on the proximal promoter region of Midkine gene, by luciferase reporter and chromatin immunoprecipitation assays. Thus, our results suggest a previously unknown Wnt/β-catenin/Midkine molecular network controlling glioma development.

Midkine proteins in cardio-vascular disease. Where do we come from and where are we heading to?

Midkine is a recently identified new growth factor/cytokine with pleiotropic functions in the human organism. First discovered in the late eighties, midkines have now become the subject of numerous studies in cardiovascular, neurologic, renal diseases and also various types of cancers. We summarize here the most important functions of midkine in cardiovascular diseases, emphasizing its role in inflammation and its antiapoptotic and proangiogenetic effects. Midkine has multiple roles in the organism, with the specific feature of being either beneficial or harmful depending on which tissue it acts on. Even though midkine has been shown to have cardiac protective effects against acute ischemia/reperfusion injury and to inhibit cardiac remodeling, it also promotes intimal hyperplasia and vascular stenosis. As such, different therapeutic strategies are currently being evaluated, consisting of administering either midkine proteins or midkine inhibitors depending on the desired outcome. More data is gathering to suggest that these novel therapies could become an adjunctive to standard cardiovascular therapy. Nonetheless, much is still to be learned about midkine. The encouraging results up till now require further studying in order to fully understand the complete profile of its mechanism of action and the clinical safety and efficacy of novel therapeutic opportunities offered by midkine molecular targeting.

Angiotensin II-induced hypertensive renal inflammation is mediated through HMGB1-TLR4 signaling in rat tubulo-epithelial cells

BACKGROUND AND PURPOSE

Angiotensin II is a vaso-constrictive peptide that regulates blood pressure homeostasis. Even though the inflammatory effects of AngII in renal pathophysiology have been studied, there still exists a paucity of data with regard to the mechanism of action of AngII-mediated kidney injury. The objective of this study was to elucidate the mechanistic role of HMGB1-TLR4 signaling in AngII-induced inflammation in the kidney.

EXPERIMENTAL APPROACH

Rat tubular epithelial cells (NRK52E) were treated with AngII over a preset time-course. In another set of experiments, HMGB1 was neutralized and TLR4 was knocked down using small interfering RNA targeting TLR4. Cell extracts were subjected to RT-PCR, immunoblotting, flow cytometry, and ELISA.

KEY RESULTS

AngII-induced inflammation in NRK52E cells increased gene and protein expression of TLR4, HMGB1 and key proinflammatory cytokines (TNFα and IL1β). Pretreatment with Losartan (an AT1 receptor blocker) attenuated the AngII-induced expression of TLR4 and inflammatory cytokines. TLR4 silencing was used to elucidate the specific role played by TLR4 in AngII-induced inflammation. TLR4siRNA treatment in these cells significantly decreased the AngII-induced inflammatory effect. Consistent observations were made when the Ang II treated cells were pretreated with anti-HMGB1. Downstream activation of NFκB and rate of generation of ROS was also decreased on gene silencing of TLR4 and exposure to anti-HMGB1.

CONCLUSIONS AND IMPLICATIONS

These results indicate a key role for HMGB1-TLR4 signaling in AngII-mediated inflammation in the renal epithelial cells. Our data also reveal that AngII-induced effects could be alleviated by HMGB1-TLR4 inhibition, suggesting this pathway as a potential therapeutic target for hypertensive renal dysfunctions.

Midkine: an emerging target of drug development for treatment of multiple diseases

Midkine is a multifunctional factor and has anti-apoptotic, migration-promoting, angiogenic, anti-microbial and other activities. Midkine ameliorates ischemic injury in the heart and brain, enhances oocyte maturation, and is involved in neurogenesis. On the other hand, midkine is an important factor in the etiology of various diseases, especially those with inflammatory backgrounds. Furthermore, midkine is overexpressed in most malignant tumors and plays roles in their invasive phenotypes as well as in their resistance to chemotherapeutics. Therefore, midkine itself is expected to be useful for the treatment of brain and heart diseases, while midkine inhibitors are promising for the treatment of malignant tumors, multiple sclerosis, restenosis, renal diseases, hypertension and osteoporosis. Blood levels of midkine are also expected to be helpful as disease markers, especially as cancer markers.

LINKED ARTICLES

This article is part of a themed section on Midkine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-4.