Therapeutic potential of midkine in cardiovascular disease

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.

Evaluation of serum midkine levels and metabolic parameters in patients with hidradenitis suppurativa

The exact pathogenesis of Hidradenitis suppurativa (HS) has not been known yet. Midkine (MK) is a heparin-binding protein that has crucial roles in many processes such as cell proliferation, cell survival, cell migration, anti-apoptotic activity, and also inflammation and angiogenesis. No data exists in the literature on the evaluation of MK in patients with HS. The present study aimed to determine the serum levels of MK and metabolic parameters in patients with HS and to compare them with healthy subjects. Forty-five patients with HS and 45 healthy controls were included. The severity of the disease was assessed with Hurley staging system in the patient group. Levels of MK, C-reactive protein (CRP), lipids, and fasting glucose were measured with the enzyme-linked immunosorbent assay (ELISA) method. MK levels were significantly higher in the patient group (p < 0.05). Moreover, smoking habit, total cholesterol, triglyceride (TG), low-density lipoprotein (LDL) and CRP were significantly higher in the patient group (for all p < 0.05). Correlation analyses revealed that MK value was correlated positively with waist circumference, TG, total cholesterol level and diastolic blood pressure (for all p < 0.05), while negatively correlated with high-density lipoprotein (HDL) level (p = 0.046, r = - 0.219). There was no difference in the MK levels according to the severity of the disease among patients. This is the first preliminary study showing that these patients with HS have higher serum MK levels, which may also be related to autoinflammation, angiogenesis, atherosclerosis and metabolic syndrome risk.

Small Molecule BRD4 Inhibitors Apabetalone and JQ1 Rescues Endothelial Cells Dysfunction, Protects Monolayer Integrity and Reduces Midkine Expression

NF-κB signaling is a key regulator of inflammation and atherosclerosis. NF-κB cooperates with bromodomain-containing protein 4 (BRD4), a transcriptional and epigenetic regulator, in endothelial inflammation. This study aimed to investigate whether BRD4 inhibition would prevent the proinflammatory response towards TNF-α in endothelial cells. We used TNF-α treatment of human umbilical cord-derived vascular endothelial cells to create an in vitro inflammatory model system. Two small molecule inhibitors of BRD4—namely, RVX208 (Apabetalone), which is in clinical trials for the treatment of atherosclerosis, and JQ1—were used to analyze the effect of BRD4 inhibition on endothelial inflammation and barrier integrity. BRD4 inhibition reduced the expression of proinflammatory markers such as SELE, VCAM-I, and IL6 in endothelial cells and prevented TNF-α-induced endothelial tight junction hyperpermeability. Endothelial inflammation was associated with increased expression of the heparin-binding growth factor midkine. BRD4 inhibition reduced midkine expression and normalized endothelial permeability upon TNF-α treatment. In conclusion, we identified that TNF-α increased midkine expression and compromised tight junction integrity in endothelial cells, which was preventable by pharmacological BRD4 inhibition.

Targeting of midkine alleviates cardiac hypertrophy via attenuation of oxidative stress and autophagy

Midkine levels are related to various diseases, including cardiovascular disease, renal disease and autoimmune disease. The research aimed to investigate the mitigation influence of downregulation of intermediate factors on myocardial hypertrophy induced by angiotensin Ⅱ (Ang), and whether downregulation of midkine could attenuate oxidative stress and autophagy. Induced myocardial hypertrophy of the mice model and treated HL-1 cells with Ang Ⅱ in vitro. The expressions of midkine were increased in the model and HL-1 cells with Ang II treatment. Midkine silence alleviated cardiac hypertrophy induced by Ang II, and inhibited the increases of atrial natriuretic peptide (ANP), Brain natriuretic peptide (BNP) and beta-myosin heavy chain (β-MHC) in the heart of mice. The raises of ANP, BNP and β-MHC in Ang II-induced HL-1 cells were also suppressed after midkine downregulation. Downregulating of midkine inhibited the increases of oxidative stress markers 8-OHdG, superoxide anions and MDA in the heart of mice or in the Ang II-treated HL-1 cells. The raises of LC3B, Atg3, Atg5 and Beclin1 in mice heart and in the Ang II.-induced HL-1 cells were attenuated after midkine silence. These outcomes showed that midkine was upregulated in myocardial hypertrophy mice. Targeting of midkine could alleviate cardiac hypertrophy via attenuation of oxidative stress and autophagy.

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.

Midkine noncanonically suppresses AMPK activation through disrupting the LKB1-STRAD-Mo25 complex

Midkine (MDK), a secreted growth factor, regulates signal transduction and cancer progression by interacting with receptors, and it can be internalized into the cytoplasm by endocytosis. However, its intracellular function and signaling regulation remain unclear. Here, we show that intracellular MDK interacts with LKB1 and STRAD to disrupt the LKB1-STRAD-Mo25 complex. Consequently, MDK decreases the activity of LKB1 to dampen both the basal and stress-induced activation of AMPK by glucose starvation or treatment of 2-DG. We also found that MDK accelerates cancer cell proliferation by inhibiting the activation of the LKB1-AMPK axis. In human cancers, compared to other well-known growth factors, MDK expression is most significantly upregulated in cancers, especially in liver, kidney and breast cancers, correlating with clinical outcomes and inversely correlating with phosphorylated AMPK levels. Our study elucidates an inhibitory mechanism for AMPK activation, which is mediated by the intracellular MDK through disrupting the LKB1-STRAD-Mo25 complex.

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.

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.

HDGF enhances VEGF‑dependent angiogenesis and FGF‑2 is a VEGF‑independent angiogenic factor in non‑small cell lung cancer

Non-small cell lung cancer (NSCLC) accounts for over 80% of all diagnosed lung cancer cases. Lung cancer is the leading cause of cancer-related deaths worldwide. Most NSCLC cells overexpress vascular endothelial growth factor-A (VEGF-A) which plays a pivotal role in tumour angiogenesis. Anti-angiogenic therapies including VEGF-A neutralisation have significantly improved the response rates, progression-free survival and overall survival of patients with NSCLC. However, the median survival of these patients is shorter than 18 months, suggesting that NSCLC cells secrete VEGF-independent angiogenic factors, which remain unknown. We aimed to explore these factors in human NSCLC cell lines, A549, Lu99 and EBC-1 using serum-free culture, to which only EBC-1 cells could adapt. By mass spectrometry, we identified 1,007 proteins in the culture supernatant derived from EBC-1 cells. Among the identified proteins, interleukin-8 (IL-8), macrophage migration inhibitory factor (MIF), galectin-1, midkine (MK), IL-18, galectin-3, VEGF-A, hepatoma-derived growth factor (HDGF), osteopontin (OPN), connective tissue growth factor (CTGF) and granulin (GRN) are known to be involved in angiogenesis. Tube formation, neutralisation and RNA interference assays revealed that VEGF-A and HDGF function as angiogenic factors in EBC-1 cells. To confirm whether VEGF-A and HDGF also regulate angiogenesis in the other NSCLC cell lines, we established a novel culture method. NSCLC cells were embedded in collagen gel and cultured three-dimensionally. Tube formation, neutralisation and RNA interference assays using the three-dimensional (3D) culture supernatant showed that VEGF-A and HDGF were not angiogenic factors in Lu99 cells. By gene microarray in EBC-1 and Lu99 cells, we identified 61 mRNAs expressed only in Lu99 cells. Among these mRNAs, brain-derived neurotrophic factor (BDNF), fibroblast growth factor-2 (FGF-2) and FGF-5 are known to be involved in angiogenesis. Tube formation and neutralisation assays clarified that FGF-2 functions as an angiogenic factor in Lu99 cells. These results indicate that HDGF enhances VEGF-dependent angiogenesis and that FGF-2 is a VEGF-independent angiogenic factor in human NSCLC cells.

Heparin Administration, but Not Myocardial Ischemia or Necrosis, Leads to Midkine Elevation

Midkine (MK) is a heparin-binding growth factor, whose role as a biomarker of coronary artery disease, myocardial ischaemia and necrosis has not been well measured. This study quantified serial MK levels in patients undergoing coronary angiography (CA) and identified factors associated with MK. In this single-centre, parallel cohort study, forty patients undergoing CA had arterial samples collected prior, 10 and 20 min after heparin administration. Four groups were examined: 1-stable coronary artery disease (CAD) without percutaneous coronary intervention (PCI); 2-stable CAD for elective PCI; 3-non-ST elevation myocardial infarction (NSTEMI) with or without PCI; 4-ST elevation myocardial infarction (STEMI) with primary PCI. Groups 1, 2 and 4 were heparin naïve, allowing assessment of the effects of myocardial necrosis between baseline levels; group 3 had received low-molecular-weight heparin. MK levels were analysed by ELISA. Median MK at baseline did not differ between groups, demonstrating that myocardial ischaemia or necrosis does not affect MK levels. Heparin administration had an immediate effect on median MK at 10 min, showing an average 500-fold increase that is dose-dependent (R² = 0.35, p = 0.001). Median MK levels remained elevated at 20 min following heparin administration. Multivariate analysis showed that the estimated glomerular filtration rate (eGFR) was the only predictor of elevated baseline MK (p = 0.02). Baseline MK did not correlate with high-sensitivity troponin-I (HsTnI) taken just before CA (p = 0.97), or peak HsTnI during admission (p = 0.74). MK is not a reliable marker of myocardial ischaemia or necrosis. MK increased significantly in all patients following heparin administration in a dose-dependent manner.

Inhibiting nucleolin reduces inflammation induced by mitochondrial DNA in cardiomyocytes exposed to hypoxia and reoxygenation

BACKGROUND AND PURPOSE

Cellular debris causes sterile inflammation after myocardial infarction. Mitochondria constitute about 30 percent of the human heart. Mitochondrial DNA (mtDNA) is a damage-associated-molecular-pattern that induce injurious sterile inflammation. Little is known about mtDNA's inflammatory signalling pathways in cardiomyocytes and how mtDNA is internalized to associate with its putative receptor, toll-like receptor 9 (TLR9).

EXPERIMENTAL APPROACH

We hypothesized that mtDNA can be internalized in cardiomyocytes and induce an inflammatory response. Adult mouse cardiomyocytes were exposed to hypoxia-reoxygenation and extracellular DNA. Microscale thermophoresis was used to demonstrate binding between nucleolin and DNA.

KEY RESULTS

Expression of the pro-inflammatory cytokines IL-1β and TNFα were upregulated by mtDNA, but not by nuclear DNA (nDNA), in cardiomyocytes exposed to hypoxia-reoxygenation. Blocking the RNA/DNA binding protein nucleolin with midkine reduced expression of IL-1β/TNFα and the nucleolin inhibitor AS1411 reduced interleukin-6 release in adult mouse cardiomyocytes. mtDNA bound 10-fold stronger than nDNA to nucleolin. In HEK293-NF-κB reporter cells, mtDNA induced NF-κB activity in normoxia, while CpG-DNA and hypoxia-reoxygenation, synergistically induced TLR9-dependent NF-κB activity. Protein expression of nucleolin was found in the plasma membrane of cardiomyocytes and inhibition of nucleolin with midkine inhibited cellular uptake of CpG-DNA. Inhibition of endocytosis did not reduce CpG-DNA uptake in cardiomyocytes.

CONCLUSION AND IMPLICATIONS

mtDNA, but not nDNA, induce an inflammatory response in mouse cardiomyocytes during hypoxia-reoxygenation. In cardiomyocytes, nucleolin is expressed on the membrane and blocking nucleolin reduce inflammation. Nucleolin might be a therapeutic target to prevent uptake of immunogenic DNA and reduce inflammation.

LINKED ARTICLES

This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Midkine Is Elevated After Multiple Trauma and Acts Directly on Human Cardiomyocytes by Altering Their Functionality and Metabolism

Background and Purpose: Post-traumatic cardiac dysfunction often occurs in multiply injured patients (ISS ≥ 16). Next to direct cardiac injury, post-traumatic cardiac dysfunction is mostly induced by the release of inflammatory biomarkers. One of these is the heparin-binding factor Midkine, which is elevated in humans after fracture, burn injury and traumatic spinal cord injury. Midkine is associated with cardiac pathologies but the exact role of Midkine in the development of those diseases is ambiguous. The systemic profile of Midkine after multiple trauma, its effects on cardiomyocytes and the association with post-traumatic cardiac dysfunction, remain unknown.

Experimental Approach: Midkine levels were investigated in blood plasma of multiply injured humans and pigs. Furthermore, human cardiomyocytes (iPS) were cultured in presence/absence of Midkine and analyzed regarding viability, apoptosis, calcium handling, metabolic alterations, and oxidative stress. Finally, the Midkine filtration capacity of the therapeutic blood absorption column CytoSorb ®300 was tested with recombinant Midkine or plasma from multiply injured patients.

Key Results: Midkine levels were significantly increased in blood plasma of multiply injured humans and pigs. Midkine acts on human cardiomyocytes, altering their mitochondrial respiration and calcium handling in vitro. CytoSorb®300 filtration reduced Midkine concentration ex vivo and in vitro depending on the dosage.

Conclusion and Implications: Midkine is elevated in human and porcine plasma after multiple trauma, affecting the functionality and metabolism of human cardiomyocytes in vitro. Further examinations are required to determine whether the application of CytoSorb®300 filtration in patients after multiple trauma is a promising therapeutic approach to prevent post-traumatic cardiac disfunction.

Connecting Metainflammation and Neuroinflammation Through the PTN-MK-RPTPβ/ζ Axis: Relevance in Therapeutic Development

Inflammation is a common factor of pathologies such as obesity, type 2 diabetes or neurodegenerative diseases. Chronic inflammation is considered part of the pathogenic mechanisms of different disorders associated with aging. Interestingly, peripheral inflammation and the associated metabolic alterations not only facilitate insulin resistance and diabetes but also neurodegenerative disorders. Therefore, the identification of novel pathways, common to the development of these diseases, which modulate the immune response and signaling is key. It will provide highly relevant information to advance our knowledge of the multifactorial process of aging, and to establish new biomarkers and/or therapeutic targets to counteract the underlying chronic inflammatory processes. One novel pathway that regulates peripheral and central immune responses is triggered by the cytokines pleiotrophin (PTN) and midkine (MK), which bind its receptor, Receptor Protein Tyrosine Phosphatase (RPTP) β/ζ, and inactivate its phosphatase activity. In this review, we compile a growing body of knowledge suggesting that PTN and MK modulate the immune response and/or inflammation in different pathologies characterized by peripheral inflammation associated with insulin resistance, such as aging, and in central disorders characterized by overt neuroinflammation, such as neurodegenerative diseases and endotoxemia. Evidence strongly suggests that regulation of the PTN and MK signaling pathways may provide new therapeutic opportunities particularly in those neurological disorders characterized by increased PTN and/or MK cerebral levels and neuroinflammation. Importantly, we discuss existing therapeutics, and others being developed, that modulate these signaling pathways, and their potential use in pathologies characterized by overt neuroinflammation.

Ciliary neurotrophic factor stimulates cardioprotection and the proliferative activity in the adult zebrafish heart

Unlike mammals, adult zebrafish can regenerate their hearts after injury via proliferation of cardiomyocytes. The cell-cycle entry of zebrafish cardiac cells can also be stimulated through preconditioning by thoracotomy, a chest incision without myocardial damage. To identify effector genes of heart preconditioning, we performed transcriptome analysis of ventricles from thoracotomized zebrafish. This intervention led to enrichment of cardioprotective factors, epithelial-to-mesenchymal transition genes, matrix proteins and components of LIFR/gp130 signaling. We identified that inhibition of the downstream signal transducer of the LIFR/gp130 pathway through treatment with Ruxolitinib, a specific JAK1/2 antagonist, suppressed the cellular effects of preconditioning. Activation of LIFR/gp130 signaling by a single injection of the ligand Cilliary Neurotrophic Factor, CNTF, was sufficient to trigger cardiomyocyte proliferation in the intact heart. In addition, CNTF induced other pro-regenerative processes, including expression of cardioprotective genes, activation of the epicardium, enhanced intramyocardial Collagen XII deposition and leucocyte recruitment. These effects were abrogated by the concomitant inhibition of the JAK/STAT activity. Mutation of the cntf gene suppressed the proliferative response of cardiomyocytes after thoracotomy. In the regenerating zebrafish heart, CNTF injection prior to ventricular cryoinjury improved the initiation of regeneration via reduced cell apoptosis and boosted cardiomyocyte proliferation. Our findings reveal the molecular effectors of preconditioning and demonstrate that exogenous CNTF exerts beneficial regenerative effects by rendering the heart more resilient to injury and efficient in activation of the proliferative programs.

Electroacupuncture Alleviated Neuronal Apoptosis Following Ischemic Stroke in Rats via Midkine and ERK/JNK/p38 Signaling Pathway

This study aimed to evaluate the effects of electroacupuncture (EA) intervention administered at rats of middle cerebral artery occlusion (MCAO)/reperfusion. Fifty-four male Sprague-Dawley rats were divided into three groups, consisting of sham group, MCAO/R group, and EA group. EA treatment at Quchi and Zusanli acupoints was applied in rats of EA group at 24 h after MCAO once per day for 3 days. Our results indicated that EA treatment reduced infarct volumes and neurological deficits, as well alleviated the apoptotic cells in peri-infarct cortex, indicating that EA exerted neuroprotective effect in cerebral ischemic rats. Moreover, EA treatment may effectively reverse the upregulation of caspase-3 and Bim and alleviate the inhibition of Bcl-2 following 72-h ischemic stroke. EA may significantly reverse the promoted relative density level of p-ERK1/2, p-JNK, and p-p38 in the EA group compared with the MCAO/R group. In addition, the growth factor midkine (MK) was upregulated at 72 h after MCAO/R, and EA treatment may significantly prompt expression of MK. Our study demonstrated that EA exerted neuroprotective effect against neuronal apoptosis and the mechanism might involve in upregulation of MK and mediation of ERK/JNK/p38 signal pathway.

Cardiac Remodeling: Endothelial Cells Have More to Say Than Just NO

The heart is a highly structured organ consisting of different cell types, including myocytes, endothelial cells, fibroblasts, stem cells, and inflammatory cells. This pluricellularity provides the opportunity of intercellular communication within the organ, with subsequent optimization of its function. Intercellular cross-talk is indispensable during cardiac development, but also plays a substantial modulatory role in the normal and failing heart of adults. More specifically, factors secreted by cardiac microvascular endothelial cells modulate cardiac performance and either positively or negatively affect cardiac remodeling. The role of endothelium-derived small molecules and peptides—for instance NO or endothelin-1—has been extensively studied and is relatively well defined. However, endothelial cells also secrete numerous larger proteins. Information on the role of these proteins in the heart is scattered throughout the literature. In this review, we will link specific proteins that modulate cardiac contractility or cardiac remodeling to their expression by cardiac microvascular endothelial cells. The following proteins will be discussed: IL-6, periostin, tenascin-C, thrombospondin, follistatin-like 1, frizzled-related protein 3, IGF-1, CTGF, dickkopf-3, BMP-2 and−4, apelin, IL-1β, placental growth factor, LIF, WISP-1, midkine, and adrenomedullin. In the future, it is likely that some of these proteins can serve as markers of cardiac remodeling and that the concept of endothelial function and dysfunction might have to be redefined as we learn more about other factors secreted by ECs besides NO.

Signalling mechanisms underlying doxorubicin and Nox2 NADPH oxidase-induced cardiomyopathy: involvement of mitofusin-2

BACKGROUND AND PURPOSE

The anthracycline doxorubicin (DOX), although successful as a first-line cancer treatment, induces cardiotoxicity linked with increased production of myocardial ROS, with Nox2 NADPH oxidase-derived superoxide reported to play a key role. The aim of this study was to identify novel mechanisms underlying development of cardiac remodelling/dysfunction further to DOX-stimulated Nox2 activation.

EXPERIMENTAL APPROACH

Nox2-/- and wild-type (WT) littermate mice were administered DOX (12 mg·kg-1 over 3 weeks) prior to study at 4 weeks. Detailed mechanisms were investigated in murine HL-1 cardiomyocytes, employing a robust model of oxidative stress, gene silencing and pharmacological tools.

KEY RESULTS

DOX-induced cardiac dysfunction, cardiomyocyte remodelling, superoxide production and apoptosis in WT mice were attenuated in Nox2-/- mice. Transcriptional analysis of left ventricular tissue identified 152 differentially regulated genes (using adjusted P < 0.1) in DOX-treated Nox2-/- versus WT mice, and network analysis highlighted 'Cell death and survival' as the biological function most significant to the dataset. The mitochondrial membrane protein, mitofusin-2 (Mfn2), appeared as a strong candidate, with increased expression (1.5-fold), confirmed by qPCR (1.3-fold), matching clear published evidence of promotion of cardiomyocyte cell death. In HL-1 cardiomyocytes, targeted siRNA knockdown of Nox2 decreased Mfn2 protein expression, but not vice versa. While inhibition of Nox2 activity along with DOX treatment attenuated its apoptotic and cytotoxic effects, reduced apoptosis after Mfn2 silencing reflected a sustained cytotoxic response and reduced cell viability.

CONCLUSIONS AND IMPLICATIONS

DOX-induced and Nox2-mediated up-regulation of Mfn2, rather than contributing to cardiomyocyte dysfunction through apoptotic pathways, appears to promote a protective mechanism.

LINKED ARTICLES

This article is part of a themed section on New Insights into Cardiotoxicity Caused by Chemotherapeutic Agents. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.21/issuetoc.

Midkine's Role in Cardiac Pathology

Midkine (MDK) is a heparin-binding growth factor that is normally expressed in mid-gestational development mediating mesenchymal and epithelial interactions. As organisms age, expression of MDK diminishes; however, in adults, MDK expression is associated with acute and chronic pathologic conditions such as myocardial infarction and heart failure (HF). The role of MDK is not clear in cardiovascular disease and currently there is no consensus if it plays a beneficial or detrimental role in HF. The lack of clarity in the literature is exacerbated by differing roles that circulating and myocardial MDK play in signaling pathways in cardiomyocytes (some of which have yet to be elucidated). Of particular interest, serum MDK is elevated in adults with chronic heart failure and higher circulating MDK is associated with worse cardiac function. In addition, pediatric HF patients have higher levels of myocardial MDK. This review focuses on what is known about the effect of exogenous versus myocardial MDK in various cardiac disease models in an effort to better clarify the role of midkine in HF.

Limited effects of preterm birth and the first enteral nutrition on cerebellum morphology and gene expression in piglets

Preterm pigs show many signs of immaturity that are characteristic of preterm infants. In preterm infants, the cerebellum grows particularly rapid and hypoplasia and cellular lesions are associated with motor dysfunction and cognitive deficits. We hypothesized that functional brain delays observed in preterm pigs would be paralleled by both structural and molecular differences in the cerebellum relative to term born piglets. Cerebella were collected from term (n = 56) and preterm (90% gestation, n = 112) pigs at 0, 5, and 26 days after birth for stereological volume estimations, large‐scale qPCR gene expression analyses (selected neurodevelopmental genes) and western blot protein expression analysis (Sonic Hedgehog pathway). Memory and learning was tested using a T‐maze, documenting that preterm pigs showed delayed learning. Preterm pigs also showed reduced volume of both white and gray matter at all three ages but the proportion of white matter increased postnatally, relative to term pigs. Early initiation of enteral nutrition had limited structural or molecular effects. The Sonic Hedgehog pathway was unaffected by preterm birth. Few differences in expression of the selected genes were found, except consistently higher mRNA levels of Midkine, p75, and Neurotrophic factor 3 in the preterm cerebellum postnatally, probably reflecting an adaptive response to preterm birth. Pig cerebellar development appears more affected by postconceptional age than by environmental factors at birth or postnatally. Compensatory mechanisms following preterm birth may include faster white matter growth and increased expression of selected genes for neurotrophic factors and regulation of angiogenesis. While the pig cerebellum is immature in 90% gestation preterm pigs, it appears relatively mature and resilient toward environmental factors.

The effect of midkine on growth factors and oxidative status in an experimental wound model in diabetic and healthy rats

Wound healing is important for longevity. Midkine is a cytokine involved in controlling tissue repair and new tissue development, and in regulating inflammation. We investigated the effect of midkine on wound healing in rats. In total, 108 Wistar albino rats were used: 12 as healthy and diabetic controls; 96 were split into 4 groups: healthy, saline treated; healthy, midkine (10 ng/kg, 48 h intervals) treated; diabetic, saline treated; and diabetic, midkine treated. Following wound creation, 6 rats per group were euthanized on days 3, 7, 14, and 28; the wounded skin was removed. Levels of epidermal growth factor (EGF), matrix metalloproteinase-8 (MMP-8), transforming growth factor beta (TGF-β), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), and thiobarbituric acid reactive substances (TBARS) were measured. MMP-8 and PDGF levels fluctuated in all groups; TGF-β fluctuated in the diabetic groups and was significantly higher in the HM group than other groups after 14 days. EGF and VEGF levels were increased in the HM group after 3 days. TBARS levels were highest in the diabetic groups. Macroscopically, the midkine-treated groups healed better. Midkine can accelerate wound healing by influencing growth factors and oxidative status in wound tissues.

Progranulin and granulin-like protein as novel VEGF-independent angiogenic factors derived from human mesothelioma cells

Malignant mesothelioma is an aggressive tumor arising from the mesothelial cells of serous membranes and is associated with tumor angiogenesis, which is a prerequisite for tumor progression. Vascular endothelial growth factors (VEGFs) including VEGF-A have a crucial role in tumor angiogenesis. However, bevacizumab, a monoclonal antibody to VEGF-A, has recently been reported not to improve the progression-free survival of patients with malignant mesothelioma. Cell culture supernatant contains extracellular components such as serum, which can mask the existence of unknown cell-derived factors in the supernatant and make it difficult to detect the factors by subsequent protein analysis. We tried using serum-free culture for human mesothelioma cell lines, NCI-H28, NCI-H2452 and NCI-H2052, and only NCI-H2052 cells adapted to serum-free culture. We found that serum-free culture supernatant derived from NCI-H2052 cells induces the formation of capillary-like tube structures (tube formation) in three-dimensional culture, in which endothelial cells sandwiched between two layers of collagen or embedded in collagen are incubated with various angiogenic inducers. However, neither neutralization of VEGF-A nor RNA interference of VEGF receptor 2 (VEGFR2) suppressed the supernatant-induced tube formation. Using mass spectrometry, we identified a total of 399 proteins in the supernatant, among which interleukin-8 (IL-8), growth-regulated α-protein, midkine, IL-18, IL-6, hepatoma-derived growth factor, clusterin and granulin (GRN), also known as progranulin (PGRN), were included as a candidate protein inducing angiogenesis. Neutralizing assays and RNA interference showed that PGRN, but not the above seven candidate proteins, caused the supernatant-induced tube formation. We also found that NCI-H28 and NCI-H2452 cells express PGRN. Furthermore, we demonstrate that not only PGRN but also GRN-like protein have an important role in the supernatant-induced tube formation. Thus, mesothelioma-derived GRNs induce VEGF-independent angiogenesis.

Midkine Increases Diagnostic Yield in AFP Negative and NASH-Related Hepatocellular Carcinoma

Robust biomarkers for population-level hepatocellular carcinoma (HCC) surveillance are lacking. We compared serum midkine (MDK), dickkopf-1 (DKK1), osteopontin (OPN) and AFP for HCC diagnosis in 86 HCC patients matched to 86 cirrhotics, 86 with chronic liver disease (CLD) and 86 healthy controls (HC). Based on the performance of each biomarker, we assessed a separate longitudinal cohort of 28 HCC patients, at and before cancer diagnosis. Serum levels of MDK and OPN were higher in HCC patients compared to cirrhosis, CLD and HC groups. DKK1 was not different between cases and controls. More than half of HCC patients had normal AFP. In this AFP-negative HCC cohort, 59.18% (n = 29/49) had elevated MDK, applying the optimal cut-off of 0.44 ng/ml. Using AFP ≥ 20 IU/ml or MDK ≥ 0.44 ng/ml, a significantly greater number (76.7%; n = 66/86) of HCC cases were detected. The area under the receiver operating curve for MDK was superior to AFP and OPN in NASH-HCC diagnosis. In the longitudinal cohort, MDK was elevated in 15/28 (54%) of HCC patients at diagnosis, of whom 67% had elevated MDK 6 months prior.

CONCLUSION

AFP and MDK have a complementary role in HCC detection. MDK increases the diagnostic yield in AFP-negative HCC and has greater diagnostic performance than AFP, OPN and DKK-1 in the diagnosis of NASH-HCC. Additionally, MDK has a promising role in the pre-clinical diagnosis of HCC.

Effect of genetic and environmental factors on protein biomarkers for common non-communicable disease and use of personally normalized plasma protein profiles (PNPPP)

OBJECTIVE

To study the impact of genetic and lifestyle factors on protein biomarkers and develop personally normalized plasma protein profiles (PNPPP) controlling for non-disease-related variance.

MATERIALS AND METHODS

Proximity extension assays were used to measure 145 proteins in 632 controls and 344 cases with non-communicable diseases.

RESULTS

Genetic and lifestyle factors explained 20-88% of the variation in healthy controls. Adjusting for these factors reduced the number of candidate biomarkers by 63%.

CONCLUSION

PNPPP efficiently controls for non-disease-related variance, allowing both for efficient discovery of novel biomarkers and for covariate-independent linear cut-offs suitable for clinical use.

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.

Conditioned medium from human amniotic mesenchymal stromal cells limits infarct size and enhances angiogenesis

The paracrine properties of human amniotic membrane-derived mesenchymal stromal cells (hAMCs) have not been fully elucidated. The goal of the present study was to elucidate whether hAMCs can exert beneficial paracrine effects on infarcted rat hearts, in particular through cardioprotection and angiogenesis. Moreover, we aimed to identify the putative active paracrine mediators. hAMCs were isolated, expanded, and characterized. In vitro, conditioned medium from hAMC (hAMC-CM) exhibited cytoprotective and proangiogenic properties. In vivo, injection of hAMC-CM into infarcted rat hearts limited the infarct size, reduced cardiomyocyte apoptosis and ventricular remodeling, and strongly promoted capillary formation at the infarct border zone. Gene array analysis led to the identification of 32 genes encoding for the secreted factors overexpressed by hAMCs. Among these, midkine and secreted protein acidic and rich in cysteine were also upregulated at the protein level. Furthermore, high amounts of several proangiogenic factors were detected in hAMC-CM by cytokine array. Our results strongly support the concept that the administration of hAMC-CM favors the repair process after acute myocardial infarction.

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.