Midkine is involved in tubulointerstitial inflammation associated with diabetic nephropathy

Elevated Midkine Serum Levels Are Associated with Long-Term Survival in Critically Ill Patients

Midkine (Mdk) is a multifunctional protein involved in inflammatory processes. Hence, circulating Mdk is increased in sepsis and has been previously suggested as a potential biomarker in these patients. The aim of this study was to elucidate the role of Mdk serum concentrations in critical illness and sepsis and to verify its value as a prognostic biomarker. Thus, we analyzed the Mdk serum concentrations of 192 critically ill patients on admission to the medical intensive care unit (ICU). While the serum levels of Mdk at admission were similar in septic and nonseptic critical illness (362 vs. 337 ng/L, p = 0.727), we found several interesting correlations of Mdk to laboratory and clinical markers associated with ischemia or hypoxia, e.g., to renal failure and hepatic injury. Mdk serum concentrations at admission did not differ between various causes of sepsis or other critical illness. Most noticeable, we observed upregulated Mdk serum concentrations at admission in patients surviving in the long-term, which was only seen in nonseptic critical illness but not in sepsis. Our study suggests a relevant role of Mdk in critically ill patients in general and highlights the possible protective features of Mdk in critical illness.

Nasopharynx Battlefield: Cellular Immune Responses Mediated by Midkine in Nasopharyngeal Carcinoma and COVID-19

Clinical evidence suggests that the severe respiratory illness coronavirus disease 2019 (COVID-19) is often associated with a cytokine storm that results in dysregulated immune responses. Prolonged COVID-19 positivity is thought to disproportionately affect cancer patients. With COVID-19 disrupting the delivery of cancer care, it is crucial to gain momentum and awareness of the mechanistic intersection between these two diseases. This review discusses the role of the cytokine midkine (MK) as an immunomodulator in patients with COVID-19 and nasopharyngeal carcinoma (NPC), both of which affect the nasal cavity. We conducted a review and analysis of immunocellular similarities and differences based on clinical studies, research articles, and published transcriptomic datasets. We specifically focused on ligand-receptor pairs that could be used to infer intercellular communication, as well as the current medications used for each disease, including NPC patients who have contracted COVID-19. Based on our findings, we recommend close monitoring of the MK axis to maintain the desirable effects of therapeutic regimens in fighting both NPC and COVID-19 infections.

Midkine—A novel player in cardiovascular diseases

Midkine (MK) is a 13-kDa heparin-binding cytokine and growth factor with anti-apoptotic, pro-angiogenic, pro-inflammatory and anti-infective functions, that enable it to partake in a series of physiological and pathophysiological processes. In the past, research revolving around MK has concentrated on its roles in reproduction and development, tissue protection and repair as well as inflammatory and malignant processes. In the recent few years, MK's implication in a wide scope of cardiovascular diseases has been rigorously investigated. Nonetheless, there is still no broadly accepted consensus on whether MK exerts generally detrimental or favorable effects in cardiovascular diseases. The truth probably resides somewhere in-between and depends on the underlying physiological or pathophysiological condition. It is therefore crucial to thoroughly examine and appraise MK's participation in cardiovascular diseases. In this review, we introduce the MK gene and protein, its multiple receptors and signaling pathways along with its expression in the vascular system and its most substantial functions in cardiovascular biology. Further, we recapitulate the current evidence of MK's expression in cardiovascular diseases, addressing the various sources and modes of MK expression. Moreover, we summarize the most significant implications of MK in cardiovascular diseases with particular emphasis on MK's advantageous and injurious functions, highlighting its ample diagnostic and therapeutic potential. Also, we focus on conflicting roles of MK in a number of cardiovascular diseases and try to provide some clarity and guidance to MK's multifaceted roles. In summary, we aim to pave the way for MK-based diagnostics and therapies that could present promising tools in the diagnosis and treatment of cardiovascular diseases.

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.

Novel Biomarkers of Atherosclerotic Vascular Disease-Latest Insights in the Research Field

The atherosclerotic vascular disease is a cardiovascular continuum in which the main role is attributed to atherosclerosis, from its appearance to its associated complications. The increasing prevalence of cardiovascular risk factors, population ageing, and burden on both the economy and the healthcare system have led to the development of new diagnostic and therapeutic strategies in the field. The better understanding or discovery of new pathophysiological mechanisms and molecules modulating various signaling pathways involved in atherosclerosis have led to the development of potential new biomarkers, with key role in early, subclinical diagnosis. The evolution of technological processes in medicine has shifted the attention of researchers from the profiling of classical risk factors to the identification of new biomarkers such as midregional pro-adrenomedullin, midkine, stromelysin-2, pentraxin 3, inflammasomes, or endothelial cell-derived extracellular vesicles. These molecules are seen as future therapeutic targets associated with decreased morbidity and mortality through early diagnosis of atherosclerotic lesions and future research directions.

Human macrophages and monocyte-derived dendritic cells stimulate the proliferation of endothelial cells through midkine production

The cytokine midkine (MK) is a growth factor that is involved in different physiological processes including tissue repair, inflammation, the development of different types of cancer and the proliferation of endothelial cells. The production of MK by primary human macrophages and monocyte-derived dendritic cells (MDDCs) was never described. We investigated whether MK is produced by primary human monocytes, macrophages and MDDCs and the capacity of macrophages and MDDCs to modulate the proliferation of endothelial cells through MK production. The TLR stimulation of human monocytes, macrophages and MDDCs induced an average of ≈200-fold increase in MK mRNA and the production of an average of 78.2, 62, 179 pg/ml MK by monocytes, macrophages and MDDCs respectively (p < 0.05). MK production was supported by its detection in CD11c+ cells, CLEC4C+ cells and CD68+ cells in biopsies of human tonsils showing reactive lymphoid follicular hyperplasia. JSH-23, which selectively inhibits NF-κB activity, decreased the TLR-induced production of MK in PMBCs, macrophages and MDDCs compared to the control (p < 0.05). The inhibition of MK production by macrophages and MDDCs using anti-MK siRNA decreased the capacity of their supernatants to stimulate the proliferation of endothelial cells (p = 0.01 and 0.04 respectively). This is the first study demonstrating that the cytokine MK is produced by primary human macrophages and MDDCs upon TLR triggering, and that these cells can stimulate endothelial cell proliferation through MK production. Our results also suggest that NF-κB plays a potential role in the production of MK in macrophages and MDDCs upon TLR stimulation. The production of MK by macrophages and MDDCs and the fact that these cells can enhance the proliferation of endothelial cells by producing MK are novel immunological phenomena that have potentially important therapeutic implications.

Integrated bioinformatics analysis reveals novel key biomarkers in diabetic nephropathy

Objectives:

The underlying molecular mechanisms of diabetic nephropathy have yet not been investigated clearly. In this investigation, we aimed to identify key genes involved in the pathogenesis and prognosis of diabetic nephropathy.

Methods:

We downloaded next-generation sequencing data set GSE142025 from Gene Expression Omnibus database having 28 diabetic nephropathy samples and nine normal control samples. The differentially expressed genes between diabetic nephropathy and normal control samples were analyzed. Biological function analysis of the differentially expressed genes was enriched by Gene Ontology and REACTOME pathways. Then, we established the protein–protein interaction network, modules, miRNA-differentially expressed gene regulatory network and transcription factor-differentially expressed gene regulatory network. Hub genes were validated by using receiver operating characteristic curve analysis.

Results:

A total of 549 differentially expressed genes were detected including 275 upregulated and 274 downregulated genes. The biological process analysis of functional enrichment showed that these differentially expressed genes were mainly enriched in cell activation, integral component of plasma membrane, lipid binding, and biological oxidations. Analyzing the protein–protein interaction network, miRNA-differentially expressed gene regulatory network and transcription factor-differentially expressed gene regulatory network, we screened hub genes MDFI, LCK, BTK, IRF4, PRKCB, EGR1, JUN, FOS, ALB, and NR4A1 by the Cytoscape software. The receiver operating characteristic curve analysis confirmed that hub genes were of diagnostic value.

Conclusions:

Taken above, using integrated bioinformatics analysis, we have identified key genes and pathways in diabetic nephropathy, which could improve our understanding of the cause and underlying molecular events, and these key genes and pathways might be therapeutic targets for diabetic nephropathy.

The Serum Level of Midkine in Patients With Multiple Sclerosis and Neuromyelitis Optica

Introduction

Midkine (MK), a heparin-binding growth factor, is involved in neurological diseases by mediating the inflammatory responses through enhancing the leukocyte migration. The present study assesses the serum concentration of this growth factor among newly developed Multiple Sclerosis (MS) and Neuromyelitis Optica (NMO) patients.

Methods

The present research, as a cross-sectional study, was performed at Isfahan University of Medical Sciences, Isfahan City, Iran. All samples were selected from patients who visited Kashani and Alzahra hospitals for two years (2014 to 2016). The MK level was assessed in 80 new MS cases, 80 NMO patients, and 80 healthy subjects. After collecting blood sera samples, MK serum level was measured using the ELISA. The obtained data were analyzed in SPSS.

Results

The Mean±SD MK level was 1038.58±44.73 pg/mL in the MS group, which was significantly higher than the Mean±SD MK level in the NMO (872.62±55.42 pg/mL) and control groups (605.02±9.42 pg/mL).

Conclusion

Overall, these results demonstrated that MK plays a prominent role in inflammatory reactions and neuroautoimmune diseases, especially in MS. So, the MK level may be used for earlier diagnosis and also prevention of disease progression by using a special inhibitor.

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.

Midkine: A multifaceted driver of atherosclerosis

Atherosclerosis constitutes the pathological basis of life-threatening events, including heart attack and stroke. Midkine is a heparin-binding growth factor and forms a small protein family with pleiotrophin. Under inflammatory or hypoxic conditions, midkine expression is up-regulated. Upon binding to its receptors, midkine can activate multiple signal pathways to regulate cell survival and migration, epithelial-to-mesenchymal transition, and oncogenesis. Circulating midkine levels are significantly increased in patients with essential hypertension, obesity or severe peripheral artery disease. Importantly, midkine exerts a proatherogenic effect by altering multiple pathophysiological processes involving atherogenesis, including macrophage lipid accumulation, vascular inflammation, neointima formation, insulin resistance and macrophage apoptosis. Midkine represents a potential therapeutic target for atherosclerosis-associated diseases. This review described the structure characteristics, expression patterns and signal transduction pathways of midkine with an emphasis on its role in atherosclerosis.

Serum Midkine, estimated glomerular filtration rate and chronic kidney disease-related events in elderly women: Perth Longitudinal Study of Aging Women

Midkine (MDK), a heparin-binding growth factor cytokine, is involved in the pathogenesis of kidney diseases by augmenting leukocyte trafficking and activation. Animal models and small case control studies have implicated MDK as a pathological biomarker in chronic kidney diseases (CKD), however this is yet to be confirmed in prospective human studies. In a prospective study of 499 elderly, predominantly Caucasian women aged over 70 years the association between serum MDK collected in 1998, and renal function change and the risk of CKD-related hospitalisations and deaths at 5 and 14.5 years, respectively, was examined. Baseline serum MDK was not associated with 5-year change in estimated glomerular filtration rate using the CKD Epidemiology Collaboration creatinine and cystatin C equation (Standardised β = - 0.09, 95% confidence interval - 3.76-0.48, p = 0.129), 5-year rapid decline in renal function (odds ratio = 0.97, 95% confidence interval 0.46-2.02, p = 0.927) or the risk of 14.5-year CKD-related hospitalisations and deaths (hazard ratio = 1.27, 95% confidence interval .66-2.46, p = 0.470) before or after adjusting for major risk factors. In conclusion, in this cohort of elderly women with normal or mildly impaired renal function, serum MDK was not associated with renal function change or future CKD-related hospitalisations and deaths, suggesting that MDK may not be an early biomarker for progression of CKD.

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.

Biomarkers of Contrast-Induced Nephropathy:: Which Ones are Clinically Important?

Contrast-induced acute kidney injury (CI-AKI) is a common complication after intravascular injection of iodinated contrast media, and it is associated with a prolonged in-hospital stay and unfavorable outcome. CI-AKI occurs in 5% to 20% among hospitalized patients. Its diagnosis relies on the increase in serum creatinine levels, which is a late biomarker of kidney injury. Novel and early serum and urinary biomarkers have been identified to detect kidney damage before the expected serum creatinine increase.

Pleiotrophin: Activity and mechanism

Pleiotrophin (PTN) is a potent mitogenic cytokine with a high affinity for the polysaccharide glycosaminoglycan (GAG). Although it is most strongly associated with neural development during embryogenesis and the neonatal period, its expression has also been linked to a plethora of other physiological events including cancer metastasis, angiogenesis, bone development, and inflammation. A considerable amount of research has been carried out to understand the mechanisms by which PTN regulates these events. In particular, PTN has now been shown to bind a diverse collection of receptors including many GAG-containing proteoglycans. These interactions lead to the activation of many intracellular kinases and, ultimately, activation and transformation of cells. Structural studies of PTN in complex with both GAG and domains from its non-proteoglycan receptors reveal a binding mechanism that relies on electrostatic interactions and points to PTN-induced receptor oligomerization as one of the possible ways PTN uses to control cellular functions.

The Role of Midkine in Arteriogenesis, Involving Mechanosensing, Endothelial Cell Proliferation, and Vasodilation

Mechanical forces in blood circulation such as shear stress play a predominant role in many physiological and pathophysiological processes related to vascular responses or vessel remodeling. Arteriogenesis, defined as the growth of pre-existing arterioles into functional collateral arteries compensating for stenosed or occluded arteries, is such a process. Midkine, a pleiotropic protein and growth factor, has originally been identified to orchestrate embryonic development. In the adult organism its expression is restricted to distinct tissues (including tumors), whereby midkine is strongly expressed in inflamed tissue and has been shown to promote inflammation. Recent investigations conferred midkine an important function in vascular remodeling and growth. In this review, we introduce the midkine gene and protein along with its cognate receptors, and highlight its role in inflammation and the vascular system with special emphasis on arteriogenesis, particularly focusing on shear stress-mediated vascular cell proliferation and vasodilatation.

Influence of Menopause on Inflammatory Cytokines during Murine and Human Bone Fracture Healing

Postmenopausal females display a chronic inflammatory phenotype with higher levels of circulating pro-inflammatory cytokines. Furthermore, the inflammatory response to injury may be altered under estrogen-deficiency, because it was shown previously that estrogen-deficient mice displayed increased levels of the inflammatory cytokines Midkine (Mdk) and Interleukin-6 (IL-6) in the early fracture hematoma. Because a balanced immune response to fracture is required for successful bone regeneration, this might contribute to the delayed fracture healing frequently observed in osteoporotic, postmenopausal fracture patients. In this study, we aimed to investigate whether further cytokines in addition to Mdk and IL-6 might be affected by estrogen-deficiency after fracture in mice and whether these cytokines are also relevant during human fracture healing. Additionally, we aimed to investigate whether serum from male vs. female fracture patients affects osteogenic differentiation of human mesenchymal stem cells (MSCs). To address these questions, female mice were either sham-operated or ovariectomized (OVX) and subjected to standardized femur osteotomy. A broad panel of pro- and anti-inflammatory cytokines was determined systemically and locally in the fracture hematoma. In a translational approach, serum was collected from healthy controls and patients with an isolated fracture. Mdk and IL-6 serum levels were determined at day 0, day 14 and day 42 after fracture. Subgroup analysis was performed to investigate differences between male and female fracture patients after menopause. In an in vitro approach, human MSCs were cultured with the collected patient serum and osteogenic differentiation was assessed by qPCR and alkaline-phosphatase staining. Our results suggest an important role for the pro-inflammatory cytokines Mdk and IL-6 in the response to fracture in estrogen-deficient mice among all of the measured inflammatory mediators. Notably, both cytokines were also significantly increased in the serum of patients after fracture. However, only Mdk serum levels differed significantly between male and female fracture patients after menopause. MSCs cultivated with serum from female fracture patients displayed significantly reduced osteogenic differentiation, which was attenuated by Mdk-antibody treatment. In conclusion, our study demonstrated increased Mdk levels after fracture in OVX mice and female fracture patients after menopause. Because Mdk is a negative regulator of bone formation, this might contribute to impaired osteoporotic fracture healing.

Involvement of midkine in the development of pulmonary fibrosis

Midkine is a low‐molecular‐weight heparin‐binding protein that is strongly expressed mainly in the midgestation period and has various physiological activities such as in development and cell migration. Midkine has been reported to be strongly expressed in cancer cells and in inflammation and repair processes, and to be involved in the pathogenesis of various diseases. However, its role in the lung is poorly understood. In this study, we analyzed the clinical characteristics of idiopathic pulmonary fibrosis patients in relation to midkine expression and used a mouse bleomycin‐induced pulmonary fibrosis model to investigate the role of midkine in pulmonary fibrosis. In the idiopathic pulmonary fibrosis patients, the serum midkine level was significantly higher than in healthy subjects, and midkine levels in the serum and bronchoalveolar lavage (BAL) fluid correlated positively with the percentage of inflammatory cells in the BAL fluid. In wild‐type mice, intratracheal bleomycin administration increased midkine expression in lung tissue. Additionally, compared with wild‐type mice, midkine‐deficient mice showed low expression of both collagen and α‐smooth muscle actin, as well as a low value for the pathological lung fibrosis score after bleomycin administration. Furthermore, the total cell count and lymphocyte percentage in the BAL fluid, as well as TNF‐α and transforming growth factor‐β expression in lung tissue, were significantly lower in the midkine‐deficient mice compared with wild‐type mice. These results suggest that midkine is involved in the development of pulmonary fibrosis by regulating inflammatory cell migration into the lung, and TNF‐α and transforming growth factor‐β expression.

Urine and serum midkine levels in an Australian chronic kidney disease clinic population: an observational study

BACKGROUND AND OBJECTIVES

The cytokine midkine (MK) is pathologically implicated in progressive chronic kidney disease (CKD) and its systemic consequences and has potential as both a biomarker and therapeutic target. To date, there are no published data on MK levels in patients with different stages of CKD. This study aims to quantify MK levels in patients with CKD and to identify any correlation with CKD stage, cause, progression, comorbid disease or prescribed medication.

METHODS

In this observational, single-centre study, demographic data were collected, and serum and urine assayed from 197 patients with CKD and 19 healthy volunteers in an outpatient setting.

RESULTS

The median serum and urine MK level in volunteers was 754 pg/mL (IQR: 554-1025) and 239 pg/mL (IQR: 154-568), respectively. Compared with serum MK in stage 1 CKD (660 pg/mL, IQR: 417-893), serum MK increased in stage 3 (1878 pg/mL, IQR: 1188-2756; p<0.001), 4 (2768 pg/mL, IQR: 2065-4735; p<0.001) and 5 (4816 pg/mL, IQ: 37477807; p<0.001). Urine MK levels increased from stage 1 CKD (343 pg/mL, IQR: 147-437) to stage 3 (1007 pg/mL, IQR: 465-2766; p=0.07), 4 (2961 pg/mL, IQR: 1368-5686; p=0.005) and 5 (6722 pg/mL, IQR: 3796-10 060; p=0.001). Fractional MK excretion (FeMK) increased from stage 1 CKD (0.159, IQR: 0.145-0.299) to stage 3 (1.024, IQR: 0.451-1.886, p=0.047), 4 (3.39, IQR: 2.10-5.82, p=0.004) and 5 (11.95, IQR: 5.36-24.41, p<0.001). When adjusted for estimated glomerular filtration rate, neither serum nor urine MK correlated with primary CKD diagnosis or CKD progression (small sample). There was a positive correlation between protein:creatinine ratio and FeMK (p=0.003). Angiotensin blockade (adjusted for proteinuria) was associated with lower urine MK (p=0.018) and FeMK (p=0.025).

CONCLUSION

MK levels sequentially rise with CKD stage beyond stage 2, and our data support existing animal evidence for an MK/renin angiotensin-system/proteinuria relationship. To what extent this is related to renal clearance versus pathology, or the consequences of chronically elevated MK levels requires further exploration.

Murine glomerular transcriptome links endothelial cell-specific molecule-1 deficiency with susceptibility to diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of kidney disease; however, there are no early biomarkers and no cure. Thus, there is a large unmet need to predict which individuals will develop nephropathy and to understand the molecular mechanisms that govern this susceptibility. We compared the glomerular transcriptome from mice with distinct susceptibilities to DN at four weeks after induction of diabetes, but before histologic injury, and identified differential regulation of genes that modulate inflammation. From these genes, we identified endothelial cell specific molecule-1 (Esm-1), as a glomerular-enriched determinant of resistance to DN. Glomerular Esm-1 mRNA and protein were lower in DN-susceptible, DBA/2, compared to DN-resistant, C57BL/6, mice. We demonstrated higher Esm-1 secretion from primary glomerular cultures of diabetic mice, and high glucose was sufficient to increase Esm-1 mRNA and protein secretion in both strains of mice. However, induction was significantly attenuated in DN-susceptible mice. Urine Esm-1 was also significantly higher only in DN-resistant mice. Moreover, using intravital microscopy and a biomimetic microfluidic assay, we showed that Esm-1 inhibited rolling and transmigration in a dose-dependent manner. For the first time we have uncovered glomerular-derived Esm-1 as a potential non-invasive biomarker of DN. Esm-1 inversely correlates with disease susceptibility and inhibits leukocyte infiltration, a critical factor in protecting the kidney from DN.

From top to bottom: midkine and pleiotrophin as emerging players in immune regulation

Cytokines are pivotal in the generation and resolution of the inflammatory response. The midkine/pleiotrophin (MK/PTN) family of cytokines, composed of just two members, was discovered as heparin-binding neurite outgrowth-promoting factors. Since their discovery, expression of this cytokine family has been reported in a wide array of inflammatory diseases and cancer. In this minireview, we will discuss the emerging appreciation of the functions of the MK/PTN family in the immune system, which include promoting lymphocyte survival, sculpting myeloid cell phenotype, driving immune cell chemotaxis, and maintaining hematopoiesis.

The potential use of biomarkers in predicting contrast-induced acute kidney injury

Contrast-induced acute kidney injury (CI-AKI) is a problem associated with the use of iodinated contrast media, causing kidney dysfunction in patients with preexisting renal failure. It accounts for 12% of all hospital-acquired kidney failure and increases the length of hospitalization, a situation that is worsening with increasing numbers of patients with comorbidities, including those requiring cardiovascular interventional procedures. So far, its diagnosis has relied upon the rise in creatinine levels, which is a late marker of kidney damage and is believed to be inadequate. Therefore, there is an urgent need for biomarkers that can detect CI-AKI sooner and more reliably. In recent years, many new biomarkers have been characterized for AKI, and these are discussed particularly with their use in known CI-AKI models and studies and include neutrophil gelatinase-associated lipocalin, cystatin C (Cys-C), kidney injury molecule-1, interleukin-18, N-acetyl-β-d-glucosaminidase, and L-type fatty acid-binding protein (L-FABP). The potential of miRNA and metabolomic technology is also mentioned. Early detection of CI-AKI may lead to early intervention and therefore improve patient outcome, and in future any one or a combination of several of these markers together with development in technology for their analysis may prove effective in this respect.

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.

Efficacy of urinary midkine as a biomarker in patients with acute kidney injury

BACKGROUND

The mortality and morbidity associated with acute kidney injury (AKI) remains high, despite advances in interventions. A multifunctional heparin-binding growth factor, midkine (MK), is involved in the pathogenesis of ischemic kidney injury. However, the clinical relevance of MK has not yet been elucidated. The present study investigated whether urinary MK can serve as a novel biomarker of AKI.

METHODS

We initially compared the predictive value of MK with other urinary biomarkers, including N-acetyl-β-D-glucosaminidase (NAG), interleukin (IL)-18, and neutrophil gelatinase-associated lipocalin (NGAL), for the detection and differential diagnosis of established AKI (549 patients). Subsequently, the reliability of MK for the early detection of AKI was prospectively evaluated in 40 patients undergoing elective abdominal aortic aneurysm surgery. Urine samples were obtained at baseline, the period of aortic cross-clamping and declamping, the end of the surgery, and on post-operative day 1.

RESULTS

The areas under the receiver operating characteristic curves for the diagnosis of AKI in various kidney diseases were 0.88, 0.70, 0.72, and 0.84 for MK, NAG, IL-18, and NGAL, respectively. When the optimal cutoff value of urinary MK was set at 11.5 pg/mL, the sensitivity and specificity were 0.87 and 0.85, respectively. In the second study, urinary MK peaked at the period of aortic declamping, about 1 h after cross-clamping in patients with AKI. Interestingly, the rise of MK in AKI patients was very precipitous compared with other biomarker candidates.

CONCLUSION

Urinary MK was prominent in its ability to detect AKI and may allow the start of preemptive medication.

Circulating midkine in children with Henoch-Schönlein purpura: Clinical implications

BACKGROUND

Midkine (MK) is a heparin-binding growth factor, which behaves like a cytokine, involved in various cellular processes such as cellular proliferation, differentiation, survival, adhesion, and migration. Studies provided evidence for a role of MK in acute and chronic inflammatory processes. The association between midkine and Henoch-Schönlein purpura (HSP) has not yet been explored. The aim of our study was to investigate the potential role of midkine in children with HSP.

METHODS

A total of 152 cases consisting of 92 children with HSP and 60 age- and sex-matched healthy control children were enrolled in this prospective study. Circulating midkine, IL-2, IL-4, IL-6, IL-10, TNF, IFN-γ, and IL-17A was measured in all of the 92 patients and 60 healthy controls. Midkine diagnostic value was evaluated by receiver operating characteristic (ROC) analysis.

RESULTS

Renal involvement occurred in 36 of the 92 patients. Circulating midkine level was elevated in children with HSPN than those of patients without renal involvement and of the controls (326.58 (266.58-459.25) pg/ml versus 280.72 (233.67-384.36) pg/ml and 217.3 (198.98-243.65) pg/ml, respectively; P<0.05). Midkine positively correlated with IL-4, IL-6, IL17A, IgA and IgE. The threshold MK concentration of HSPN was 295.58pg/ml, with the sensitivity and specificity of 80.6% and 88.3%, respectively. The area under the receiver operating characteristic (ROC) curve (AUCROC) of MK was 0.902.

CONCLUSIONS

MK seems to be involved in the development of HSP. Measurement of serum levels of MK is helpful in confirming the diagnosis of HSP and predicting HSPN.

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.

Mechanical Stress and the Induction of Lung Fibrosis via the Midkine Signaling Pathway

RATIONALE

Lung-protective ventilatory strategies have been widely used in patients with acute respiratory distress syndrome (ARDS), but the ARDS mortality rate remains unacceptably high and there is no proven pharmacologic therapy.

OBJECTIVES

Mechanical ventilation can induce oxidative stress and lung fibrosis, which may contribute to high dependency on ventilator support and increased ARDS mortality. We hypothesized that the novel cytokine, midkine (MK), which can be up-regulated in oxidative stress, plays a key role in the pathogenesis of ARDS-associated lung fibrosis.

METHODS

Blood samples were collected from 17 patients with ARDS and 10 healthy donors. Human lung epithelial cells were challenged with hydrogen chloride followed by mechanical stretch for 72 hours. Wild-type and MK gene-deficient (MK(-/-)) mice received two-hit injury of acid aspiration and mechanical ventilation, and were monitored for 14 days.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of MK were higher in patients with ARDS than in healthy volunteers. Exposure to mechanical stretch of lung epithelial cells led to an epithelial-mesenchymal transition profile associated with increased expression of angiotensin-converting enzyme, which was attenuated by silencing MK, its receptor Notch2, or NADP reduced oxidase 1. An increase in collagen deposition and hydroxyproline level and a decrease in lung tissue compliance seen in wild-type mice were largely attenuated in MK(-/-) mice.

CONCLUSIONS

Mechanical stretch can induce an epithelial-mesenchymal transition phenotype mediated by the MK-Notch2-angiotensin-converting enzyme signaling pathway, contributing to lung remodeling. The MK pathway is a potential therapeutic target in the context of ARDS-associated lung fibrosis.

CD147/basigin limits lupus nephritis and Th17 cell differentiation in mice by inhibiting the interleukin-6/STAT-3 pathway

OBJECTIVE

Interleukin-17 (IL-17)-producing T cells (Th17 cells) play critical roles in the pathogenesis of immune-related diseases, including systemic lupus erythematosus. However, the fundamental mechanism regulating Th17 cell differentiation is not fully understood. Recently, we demonstrated that plasma levels of CD147/basigin (Bsg) in patients with lupus nephritis (LN) were closely associated with disease activity. but the molecular mechanism involving Bsg has been elusive. Here, we addressed the role of Bsg in the pathogenesis of LN.

METHODS

Injections of pristane (2,6,10,14-tetramethylpentadecane [TMPD]) were administered to Bsg(-/-) or Bsg(+/+) mice to induce LN. The mice were killed 6 months after being injected, for histologic and biochemical analyses of the kidneys and spleens.

RESULTS

Pristane induced LN more strikingly in Bsg(-/-) mice than in Bsg(+/+) mice, even though humoral autoimmunity was similarly increased in both genotypes. The increased number of Th17, but not Th1, Treg cells, was augmented in Bsg(-/-) mice. The expression of IL-17 was also increased in the kidneys of Bsg(-/-) mice, in proportion to LN disease activity. Furthermore, treatment with anti-IL-17 antibody reduced LN disease activity in Bsg(-/-) mice. Complementary to these phenotypes of Bsg(-/-) mice, Bsg expression was enhanced in activated CD4+ T cells in vivo and in vitro. Bsg deficiency selectively augmented in vitro differentiation of naive CD4+ T cells to Th17 cells and STAT-3 phosphorylation during this differentiation. Moreover, STAT-3 phosphorylation was suppressed by crosslinking of Bsg with its antibody.

CONCLUSION

Bsg plays an indispensable role in Th17 cell differentiation as a negative regulator by suppressing the IL-6/STAT-3 pathway.

Synergistic Effects of Combining Anti-Midkine and Hepatocyte Growth Factor Therapies Against Diabetic Nephropathy in Rats

PURPOSE

This study aimed to assess whether synergism could be achieved when combining midkine (MK) antisense oligodeoxynucleotides (anti-MK ODN) and recombinant human hepatocyte growth factor (HGF) in diabetic nephropathy (DN) rat models.

METHODS

Rats were randomized into 6 groups: control, DN rats without treatment, DN rats treated with scrambled ODN, DN rats treated with anti-MK ODN, DN rats treated with HGF and DN rats treated with anti-MK ODN plus HGF. DN models were created by intraperitoneal injection of streptozotocin. Two weeks later, treatments commenced. ODN (1 mg/kg) was intravenously injected weekly for 4 weeks. HGF (500 μg/kg) was subcutaneously injected daily for 4 weeks. Eight weeks later, rats were euthanized. Serum and urine parameters, kidney histopathological injury scores, immunohistochemistry and protein expressions were measured.

RESULTS

Blood glucose, creatinine, blood urea nitrogen and urine albumin were significantly elevated in DN rats. Any single treatment markedly reduced their levels, yet combined treatment decreased them significantly further. Any monotherapy could decrease renal injury score and immunohistochemistry positive percentage, although the most prominent change was displayed in combinational therapy. Western blot showed the expression of MK was significantly elevated in DN rats. Anti-MK ODN suppressed MK significantly. The protein expressions and serum concentrations of transforming growth factor-β1 and connective tissue growth factor between monotherapy and the combined therapy were significant.

CONCLUSIONS

This study demonstrated that combining MK gene suppressing ODN and HGF protein synergistically attenuates renal injury in DN rats. This study may provide a novel avenue for designing future therapeutic regimens against DN.

Measuring midkine: the utility of midkine as a biomarker in cancer and other diseases

Midkine (MK) is a pleiotropic growth factor prominently expressed during embryogenesis but down-regulated to neglible levels in healthy adults. Many published studies have demonstrated striking MK overexpression compared with healthy controls in various pathologies, including ischaemia, inflammation, autoimmunity and, most notably, in many cancers. MK expression is detectable in biopsies of diseased, but not healthy, tissues. Significantly, because it is a soluble cytokine, elevated MK is readily apparent in the blood and other body fluids such as urine and CSF, making MK a relatively convenient, accessible, non-invasive and inexpensive biomarker for population screening and early disease detection. The first diagnostic tests that quantify MK are just now receiving regulatory clearance and entering the clinic. This review examines the current state of knowledge pertaining to MK as a biomarker and highlights promising indications and clinical settings where measuring MK could make a difference to patient treatment. I also raise outstanding questions about reported variants of MK as well as MK's bio-distribution in vivo. Answering these questions in future studies will enhance our understanding of the significance of measured MK levels in both patients and healthy subjects, and may reveal further opportunities for measuring MK to diagnose disease. MK has already proven to be a biomarker that can significantly improve detection, management and treatment of cancer, and there is significant promise for developing further MK-based diagnostics in the future.

Midkine: a novel and early biomarker of contrast-induced acute kidney injury in patients undergoing percutaneous coronary interventions

We tested the hypothesis whether midkine could represent an early biomarker of contrast-induced acute kidney injury (CIAKI) in 89 patients with normal serum creatinine undergoing PCI. Midkine, serum and urinary NGAL, and cystatin C were evaluated before and 2, 4, 8, 24, and 48 hours after PCI using commercially available kits. Serum creatinine was assessed before and 24 and 48 hours after PCI. We found a significant rise in serum midkine as early as after 2 hours (P < 0.001) when compared to the baseline values. It was also significantly higher 4 hours after PCI and then returned to the baseline values after 24 hours and started to decrease after 48 hours. When contrast nephropathy was defined as an increase in serum creatinine by >25% of the baseline level 48 hours after PCI, the prevalence of CIN was 10%. Patients with CIN received significantly more contrast agent (P < 0.05), but durations of PCI were similar. Midkine was significantly higher 2, 4, and 8 hours after PCI in patients with CIN. Since the “window of opportunity” is narrow in CIAKI and time is limited to introduce proper treatment after initiating insult, particularly when patients are discharged within 24 hours after the procedure, midkine needs to be investigated as a potential early marker for renal ischemia and/or nephrotoxicity.

Midkine-deficiency delays chondrogenesis during the early phase of fracture healing in mice

The growth and differentiation factor midkine (Mdk) plays an important role in bone development and remodeling. Mdk-deficient mice display a high bone mass phenotype when aged 12 and 18 months. Furthermore, Mdk has been identified as a negative regulator of mechanically induced bone formation and it induces pro-chondrogenic, pro-angiogenic and pro-inflammatory effects. Together with the finding that Mdk is expressed in chondrocytes during fracture healing, we hypothesized that Mdk could play a complex role in endochondral ossification during the bone healing process. Femoral osteotomies stabilized using an external fixator were created in wildtype and Mdk-deficient mice. Fracture healing was evaluated 4, 10, 21 and 28 days after surgery using 3-point-bending, micro-computed tomography, histology and immunohistology. We demonstrated that Mdk-deficient mice displayed delayed chondrogenesis during the early phase of fracture healing as well as significantly decreased flexural rigidity and moment of inertia of the fracture callus 21 days after fracture. Mdk-deficiency diminished beta-catenin expression in chondrocytes and delayed presence of macrophages during early fracture healing. We also investigated the impact of Mdk knockdown using siRNA on ATDC5 chondroprogenitor cells in vitro. Knockdown of Mdk expression resulted in a decrease of beta-catenin and chondrogenic differentiation-related matrix proteins, suggesting that delayed chondrogenesis during fracture healing in Mdk-deficient mice may be due to a cell-autonomous mechanism involving reduced beta-catenin signaling. Our results demonstrated that Mdk plays a crucial role in the early inflammation phase and during the development of cartilaginous callus in the fracture healing process.

Midkine in nephrogenesis, hypertension and kidney diseases

Midkine (MK; K; gene abbreviation, Mdk: mus musculus, MDK: homo sapiens) is a multifunctional heparin-binding growth factor that regulates cell growth, survival and migration as well as anti-apoptotic activity in nephrogenesis and development. Proximal tubular epithelial cells are the main sites of MK expression in the kidneys. The pathophysiological roles of MK are diverse, ranging from the development of acute kidney injury (AKI) to the progression of chronic kidney disease, often accompanied by hypertension, renal ischaemia and diabetic nephropathy. The obvious hypertension that develops in Mdk(+/+) mouse models of renal ablation compared with Mdk(-/-) mice eventually leads to progressive renal failure, such as glomerular sclerosis and tubulointerstitial damage associated with elevated plasma angiotensin (Ang) II levels. MK is also induced in the lung endothelium by oxidative stress and subsequently up-regulated by ACE, which hydrolyzes Ang II to induce further oxidative stress, thus accelerating MK generation; this leads to a vicious cycle of positive feedback in the MK-Ang II pathway. Kidney-lung interactions involving positive feedback between the renin-angiotensin system and MK might partly account for the pathogenesis of hypertension and kidney damage. MK is also involved in the pathogenesis of AKI and diabetic nephropathy through the recruitment of inflammatory cells. In contrast, MK plays a protective role against crescentic glomerulonephritis, by down-regulating plasminogen activator inhibitor-1. These diverse actions of MK might open up new avenues for targeted approaches to treating hypertension and various renal diseases.

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.

Biomarkers of Contrast-Induced Nephropathy: Which Ones and What Is Their Clinical Relevance?

Contrast-induced nephropathy, or contrast-induced acute kidney injury (AKI), is an acute impairment of renal function as manifested by an increase in serum creatinine. Different urinary and serum proteins have been intensively investigated as possible biomarkers for the early diagnosis of AKI. Promising candidate biomarkers have the ability to detect an early and graded increase in tubular epithelial cell injury and to distinguish prerenal causes of AKI from acute tubular necrosis. In this article new, emerging biomarkers of contrast-induced AKI are presented and described, of which serum neutrophil gelatinase-associated lipocalin appears to be the most promising.

Expression of midkine in normal human skin, dermatitis and neoplasms: association with differentiation of keratinocytes

Midkine is a 13-kDa heparin-binding growth factor. It promotes growth, survival, migration and gene expression of various target cells and play roles in many diseases. In normal adult tissues, midkine expression is highly restricted; however, midkine expression levels are high in various malignant tumors. The major biological roles of midkine can be categorized into three areas, namely, the nervous system, cancer and inflammation. Thus far, midkine has not been studied extensively in diseased human skin. We performed immunohistochemistry tests by using anti-midkine antibodies to study the expression of midkine in normal skin and skin samples of 26 different cutaneous diseases. In addition, we investigated the expression pattern of the midkine gene in cultured keratinocytes. In normal skin, midkine expression was observed in the secretory coils of the eccrine sweat glands, outer root sheath and inner root sheath. Among the cutaneous tumors, the majority of keratinocyte-derived neoplasms were positive for midkine. Tumors that were not derived from keratinocytes were negative for midkine. In cultured keratinocytes, the midkine gene was expressed earlier than the genes required for keratinization, for example, cytokeratin 10 and transglutaminase 1. Because midkine is expressed in the keratinized areas of normal skin, neoplasms and inflammation, it may play a role as a modulator of keratinization in the skin.

Midkine exacerbates pressure overload-induced cardiac remodeling

Midkine is a multifunctional growth factor, and its serum levels are increased with the functional severity of heart failure. This study aimed to examine the role of midkine in heart failure pathogenesis. Midkine expression levels were increased in the kidney and lung after transverse aortic constriction (TAC) surgery, but not sufficiently increased in the heart. After TAC, phosphorylation of extracellular signal-regulated kinase1/2 and AKT, and the expression levels of foetal genes in the heart were considerably increased in transgenic mice with cardiac-specific overexpression of midkine (MK-Tg) compared with wild-type (WT) mice. MK-Tg mice showed more severe cardiac hypertrophy and dysfunction, and showed lower survival rate after TAC than WT mice. We conclude that midkine plays a critical role in cardiac hypertrophy and remodelling.

The heparin-binding growth factor midkine: the biological activities and candidate receptors

The heparin-binding growth factor midkine (MK) comprises a family with pleiotrophin/heparin-binding growth-associated molecule. The biological phenomena in which MK is involved can be categorized into five areas: (i) cancer, (ii) inflammation/immunity, (iii) blood pressure, (iv) development and (v) tissue protection. The phenotypes are clear in vivo, but the mechanisms by which MK exerts these actions are not fully understood. Candidate receptors for MK include anaplastic lymphoma kinase, protein tyrosine phosphatase ζ, Notch2, LDL receptor-related protein 1, integrins and proteoglycans. Some physical associations between these candidate receptors are also known. Because of the striking in vivo phenotypes after manipulation of MK, MK could be an important molecular target for the treatment of various diseases. To this end, it will be important to pursue studies to fully understand the mechanisms of MK action.

Loss of heparin-binding protein prevents necrotizing glomerulonephritis: first clues hint at plasminogen activator inhibitor-1

The orchestration of acute inflammatory kidney injury is subject to widespread influences and involves cytokines as well as chemokines released by resident as well as infiltrating cells. Although intense research efforts have been made in the field, it still unravels yet novel key molecules involved in the pathogenesis of this kidney disease. A heparin-binding growth factor denoted midkine is expressed by various cell types following stress of tissue damage. Specific functions relate to orchestration of reparative and inflammatory processes by promoting migration of leucocytes and release of chemokines with ensuing angiogenesis. Midkine appears as a double-edged sword with beneficial or harmful effects in injured tissues. Here, we discuss a recent publication that provides evidence for the beneficial role of midkine in progressive glomerulonephritis, most likely due to blockade of plasminogen activator inhibitor-1 release.

Deficiency of growth factor midkine exacerbates necrotizing glomerular injuries in progressive glomerulonephritis

Inflammatory cell infiltration and fibrin deposition play important roles in the development of crescentic glomerulonephritis (GN). In particular, activation of coagulation is an indispensable factor in crescent formation. However, the mechanisms underlying the pathogenesis of crescent formation have not been completely elucidated. We identified the growth factor midkine (MK) as a novel key molecule in the progression of crescentic GN induced by anti-glomerular basement membrane antibody. Despite the lack of significant differences in autologous and heterologous reactions, MK-deficient (Mdk(-/-)) mice unexpectedly showed a greater number of necrotizing glomerular injuries than wild-type (Mdk(+/+)) mice. Likewise, more tubulointerstitial damage was observed in Mdk(-/-) mice, and this damage positively correlated with glomerular injury. Plasminogen activator inhibitor (PAI)-1 was strongly induced in the injured glomerulus of Mdk(-/-) mice, particularly in crescents and endothelial cells. This enhanced PAI-1 production was associated with an increase in inflammatory cell infiltration and matrix deposition in the glomerulus and the interstitium of Mdk(-/-) mice. In line with these in vivo data, primary cultured endothelial cells derived from Mdk(-/-) mice exhibited higher PAI-1 mRNA expression on fibrin challenge and less fibrinolysis than Mdk(+/+) mice. In contrast, the expression of plasminogen activators was not affected. Our combined data suggest that MK leads to a blockade of PAI-1, which is closely associated with the suppression of crescentic GN.

Cytokines as regulators of proliferation and survival of healthy and malignant peripheral B cells

Adaptive immunity depends on the production and maintenance of a pool of mature peripheral lymphocytes throughout life. The signals regulating the survival of mature splenic B cells have become a major focus in recent studies of B cell immunology. Lasting B cell persistence in the periphery is dependent on survival signals that are transduced by cell surface receptors. Cytokines have been shown to play a critical role in maintaining lymphocyte homeostasis. This review focuses on the role of cytokines and their receptors in the regulation of peripheral B cell survival, with an emphasis on those that have received relatively less attention in the literature.

Midkine in inflammation

The 13 kDa heparin-binding growth factor midkine (MK) was originally identified as a molecule involved in the orchestration of embryonic development. Recent studies provided evidence for a new role of MK in acute and chronic inflammatory processes. Accordingly, several inflammatory diseases including nephritis, arthritis, atherosclerosis, colitis, and autoimmune encephalitis have been shown to be alleviated in the absence of MK in animal models. Reduced leukocyte recruitment to the sites of inflammation was found to be one important mechanism attenuating chronic inflammation when MK was absent. Furthermore, MK was found to modulate expression of proinflammatory cytokines and the expansion of regulatory T-cells. Here, we review the current understanding of the role of MK in different inflammatory disorders and summarize the knowledge of MK biology.

Basigin/CD147 promotes renal fibrosis after unilateral ureteral obstruction

Regardless of their primary causes, progressive renal fibrosis and tubular atrophy are the main predictors of progression to end-stage renal disease. Basigin/CD147 is a multifunctional molecule-it induces matrix metalloproteinases and hyaluronan, for example-and has been implicated in organ fibrosis. However, the relationship between basigin and organ fibrosis has been poorly studied. We investigated basigin's role in renal fibrosis using a unilateral ureteral obstruction model. Basigin-deficient mice (Bsg(-/-)) demonstrated significantly less fibrosis after surgery than Bsg(+/+) mice. Fewer macrophages had infiltrated in Bsg(-/-) kidneys. Consistent with these in vivo data, primary cultured tubular epithelial cells from Bsg(-/-) mice produced less matrix metalloproteinase and exhibited less motility on stimulation with transforming growth factor β. Furthermore, Bsg(-/-) embryonic fibro blasts produced less hyaluronan and α-smooth muscle actin after transforming growth factor β stimulation. Together, these results demonstrate for the first time that basigin is a key regulator of renal fibrosis. Basigin could be a candidate target molecule for the prevention of organ fibrosis.

Growth factor Midkine is involved in the pathogenesis of renal injury induced by protein overload containing endotoxin

BACKGROUND

Growth factor Midkine (MK), which expresses on endothelial cells and renal proximal tubules, has been implicated in inflammation-related kidney diseases such as ischemic reperfusion-induced tubulointerstitial injury and diabetic nephropathy. The biological actions of MK are elicited through its chemotactic activity and chemokine-driven inflammatory pathway. Post-infectious glomerulonephritis is caused by the deposition of immune complexes into glomeruli by infiltrating a number of inflammatory cells. Therefore, we investigated whether MK might be involved in the pathogenesis of acute glomerulonephritis.

METHODS

We induced endocapillary proliferative glomerulonephritis in 129/SV mice using intraperitoneal injections of a large amount of protein.

RESULTS

In contrast to mice deficient in MK (Mdk (-/-)), Mdk (+/+) mice induced by protein overload demonstrated more diffuse cellular proliferation in the mesangial areas and capillary lumens, eventually leading to glomerular damage and tubulointerstitial injury. This pathological observation could be attributable to neutrophil infiltration through the chemotaxis and stimulation of the MK-macrophage inflammatory protein (MIP)-2 pathway, but appeared to be due to the MK-related immunoglobulin (Ig)G deposition and C3 activation. These findings are often seen in infectious-related glomerular injury. Furthermore, the profile of MK expression was strongly consistent with that of glomerular damage and tubulointersititial injury.

CONCLUSION

This study might provide a new insight into understanding the deleterious role of MK in endocapillary proliferative glomerulonephritis induced by protein overload.

Midkine, a heparin-binding protein, is increased in the diabetic mouse kidney postmenopause

Estrogen is thought to protect against the development of chronic kidney disease, and menopause increases the development and severity of diabetic kidney disease. In this study, we used streptozotocin (STZ) to induce diabetes in the 4-vinylcyclohexene diepoxide (VCD)-treated mouse model of menopause. DNA microarrays were used to identify gene expression changes in the diabetic kidney postmenopause. An ANOVA model, CARMA, was used to isolate the menopause effect between two groups of diabetic mice, diabetic menopausal (STZ/VCD) and diabetic cycling (STZ). In this diabetic study, 8,864 genes of the possible 15,600 genes on the array were included in the ANOVA; 99 genes were identified as demonstrating a >1.5-fold up- or downregulation between the STZ/VCD and STZ groups. We randomly selected genes for confirmation by real-time PCR; midkine (Mdk), immediate early response gene 3 (IEX-1), mitogen-inducible gene 6 (Mig6), and ubiquitin-specific protease 2 (USP2) were significantly increased in the kidneys of STZ/VCD compared with STZ mice. Western blot analysis confirmed that Mdk and IEX-1 protein abundance was significantly increased in the kidney cortex of STZ/VCD compared with STZ mice. In a separate study, DNA microarrays and CARMA analysis were used to identify the effect of menopause on the nondiabetic kidney; VCD-treated mice were compared with cycling mice. Of the possible 15,600 genes on the array, 9,142 genes were included in the ANOVA; 20 genes were identified as demonstrating a >1.5-fold up- or downregulation; histidine decarboxylase and vanin 1 were among the genes identified as differentially expressed in the postmenopausal nondiabetic kidney. These data expand our understanding of how hormone status correlates with the development of diabetic kidney disease and identify several target genes for further studies.

Serum midkine as a predictor of cardiac events in patients with chronic heart failure

BACKGROUND

Midkine, a heparin-binding growth factor, has various functions such as migration of inflammatory cell and anti-apoptotic effect. Invasion of inflammatory cell and cardiomyocyte apoptosis are involved in development and progression of heart failure (HF). However, the relationship between midkine and HF has not been previously examined. Therefore, we examined clinical significance of serum midkine levels to determine the prognosis of HF patients.

METHODS AND RESULTS

Serum levels of midkine were measured at admission in 216 consecutive patients hospitalized for HF and 60 control subjects. Patients were prospectively followed during a mean follow-up period of 653 +/- 375 days with the end points of cardiac death and progressive HF requiring rehospitalization. Serum concentrations of midkine were significantly higher in patients with HF than in controls. Patients with cardiac events had significantly higher concentrations of midkine than those without cardiac events. Kaplan-Meier analysis revealed that cardiac event rates increased markedly as midkine levels rose. Furthermore in the multivariate analysis, after adjustment for age, gender ,and complications, midkine was the independent predictor of cardiac events.

CONCLUSION

Serum midkine levels are increased in HF patients, and midkine is a novel marker for risk stratifying HF patients.