Midkine is present in the early stage of cerebral infarct

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.

The role of midkine in health and disease

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

Transplantation of PSA-NCAM-Positive Neural Precursors from Human Embryonic Stem Cells Promotes Functional Recovery in an Animal Model of Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) results in permanent impairment of motor and sensory functions at and below the lesion site. There is no therapeutic option to the functional recovery of SCI involving diverse injury responses of different cell types in the lesion that limit endogenous nerve regeneration. In this regard, cell replacement therapy utilizing stem cells or their derivatives has become a highly promising approach to promote locomotor recovery. For this reason, the demand for a safe and efficient multipotent cell source that can differentiate into various neural cells is increasing. In this study, we evaluated the efficacy and safety of human polysialylated-neural cell adhesion molecule (PSA-NCAM)-positive neural precursor cells (hNPCsPSA-NCAM+) as a treatment for SCI.

METHODS

One hundred thousand hNPCsPSA-NCAM+ isolated from human embryonic stem cell-derived NPCs were transplanted into the lesion site by microinjection 7 days after contusive SCI at the thoracic level. We examined the histological characteristics of the graft and behavioral improvement in the SCI rats 10 weeks after transplantation.

RESULTS

Locomotor activity improvement was estimated by the Basso-Beattie-Bresnahan locomotor rating scale. Behavioral tests revealed that the transplantation of the hNPCsPSA-NCAM+ into the injured spinal cords of rats significantly improved locomotor function. Histological examination showed that hNPCsPSA-NCAM+ had differentiated into neural cells and successfully integrated into the host tissue with no evidence of tumor formation. We investigated cytokine expressions, which led to the early therapeutic effect of hNPCsPSA-NCAM+, and found that some undifferentiated NPCs still expressed midkine, a well-known neurotrophic factor involved in neural development and inflammatory responses, 10 weeks after transplantation.

CONCLUSION

Our results demonstrate that hNPCsPSA-NCAM+ serve as a safe and efficient cell source which has the potential to improve impaired motor function following SCI.

Environmental enrichment improves declined cognition induced by prenatal inflammatory exposure in aged CD-1 mice: Role of NGPF2 and PSD-95

INTRODUCTION

Research suggests that prenatal inflammatory exposure could accelerate age-related cognitive decline that may be resulted from neuroinflammation and synaptic dysfunction during aging. Environmental enrichment (EE) may mitigate the cognitive and synaptic deficits. Neurite growth-promoting factor 2 (NGPF2) and postsynaptic density protein 95 (PSD-95) play critical roles in neuroinflammation and synaptic function, respectively.

METHODS

We examined whether this adversity and EE exposure can cause alterations in Ngpf2 and Psd-95 expression. In this study, CD-1 mice received intraperitoneal injection of lipopolysaccharide (50 μg/kg) or normal saline from gestational days 15-17. After weaning, half of the male offspring under each treatment were exposed to EE. The Morris water maze was used to assess spatial learning and memory at 3 and 15 months of age, whereas quantitative real-time polymerase chain reaction and Western blotting were used to measure hippocampal mRNA and protein levels of NGPF2 and PSD-95, respectively. Meanwhile, serum levels of IL-6, IL-1β, and TNF-α were determined by enzyme-linked immunosorbent assay.

RESULTS

The results showed that aged mice exhibited poor spatial learning and memory ability, elevated NGPF2 mRNA and protein levels, and decreased PSD-95 mRNA and protein levels relative to their young counterparts during natural aging. Embryonic inflammatory exposure accelerated age-related changes in spatial cognition, and in Ngpf2 and Psd-95 expression. Additionally, the levels of Ngpf2 and Psd-95 products were significantly positively and negatively correlated with cognitive dysfunction, respectively, particularly in prenatal inflammation-exposed aged mice. Changes in serum levels of IL-6, IL-1β, and TNF-α reflective of systemic inflammation and their correlation with cognitive decline during accelerated aging were similar to those of hippocampal NGPF2. EE exposure could partially restore the accelerated decline in age-related cognitive function and in Psd-95 expression, especially in aged mice.

DISCUSSION

Overall, the aggravated cognitive disabilities in aged mice may be related to the alterations in Ngpf2 and Psd-95 expression and in systemic state of inflammation due to prenatal inflammatory exposure, and long-term EE exposure may ameliorate this cognitive impairment by upregulating Psd-95 expression.

Midkine: The Who, What, Where, and When of a Promising Neurotrophic Therapy for Perinatal Brain Injury

Midkine (MK) is a small secreted heparin-binding protein highly expressed during embryonic/fetal development which, through interactions with multiple cell surface receptors promotes growth through effects on cell proliferation, migration, and differentiation. MK is upregulated in the adult central nervous system (CNS) after multiple types of experimental injury and has neuroprotective and neuroregenerative properties. The potential for MK as a therapy for developmental brain injury is largely unknown. This review discusses what is known of MK's expression and actions in the developing brain, areas for future research, and the potential for using MK as a therapeutic agent to ameliorate the effects of brain damage caused by insults such as birth-related hypoxia and inflammation.

Disruption of Midkine gene reduces traumatic brain injury through the modulation of neuroinflammation

Background

Midkine (MK) is a multifunctional cytokine found upregulated in the brain in the presence of different disorders characterized by neuroinflammation, including neurodegenerative disorders and ischemia. The neuroinflammatory response to traumatic brain injury (TBI) represents a key secondary injury factor that can result in further neuronal injury. In the present study, we investigated the role of endogenous MK in secondary injury, including neuroinflammation, immune response, and neuronal apoptosis activity, after TBI.

Methods

Wild type (Mdk^+/+) and MK gene deficient (Mdk^−/−) mice were subjected to fluid percussion injury for TBI models and compared at 3, 7, and 14 days after TBI, in terms of the following: brain tissue loss, neurological deficits, microglia response, astrocytosis, expression of proinflammatory M1 and anti-inflammatory M2 microglia/macrophage phenotype markers, and apoptotic activity.

Results

As opposed to Mdk^+/+ mice, Mdk^−/− mice reported a significantly reduced area of brain tissue loss and an improvement in their neurological deficits. The ratios of the Iba1-immunoreactive microglia/macrophages in the perilesional site were significantly decreased in Mdk^−/− than in the Mdk^+/+ mice at 3 days after TBI. However, the ratios of the glial fibrillary acidic protein immunoreactive area were similar between the two groups. The M1 phenotype marker (CD16/32) immunoreactive areas were significantly reduced in Mdk^−/− than in the Mdk^+/+ mice. Likewise, the mRNA levels of the M1 phenotype markers (TNF-α, CD11b) were significantly decreased in Mdk^−/− mice than in Mdk^+/+ mice. Furthermore, flow cytometry analysis identified the M2 markers, i.e., CD163⁺ macrophages cells and arginase-1⁺ microglia cells, to be significantly higher in Mdk^−/− than in Mdk^+/+ mice. Finally, the ratios of apoptotic neurons were significantly decreased in the area surrounding the lesion in Mdk^−/− than in Mdk^+/+ mice following TBI.

Conclusion

Our findings suggest that MK-deficiency reduced tissue infiltration of microglia/macrophages and altered their polarization status thereby reducing neuroinflammation, neuronal apoptosis, and tissue loss and improving neurological outcomes after TBI. Therefore, targeting MK to modulate neuroinflammation may represent a potential therapeutic strategy for TBI management.

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.

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.

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.

Ethanol activates midkine and anaplastic lymphoma kinase signaling in neuroblastoma cells and in the brain

Alcohol engages signaling pathways in the brain. Midkine (MDK) is a neurotrophic factor that is over-expressed in the prefrontal cortex of alcoholics. MDK and one of its receptors, anaplastic lymphoma kinase (ALK), also regulate behavioral responses to ethanol in mice. The goal of this study was to determine whether MDK and ALK expression and signaling are activated by ethanol. We found that ethanol treatment of neuroblastoma cells increased MDK and ALK expression. We also assessed activation of ALK by ethanol in cells and found that ALK and ALK-dependent extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription 3 (STAT3) phosphorylation increased rapidly with ethanol exposure. Similarly, treatment of cells with recombinant MDK protein increased ALK, ERK and STAT3 phosphorylation, suggesting that ethanol may utilize MDK to activate ALK signaling. In support of this, transfection of cells with MDK siRNAs attenuated ALK signaling in response to ethanol. Ethanol also activates ERK signaling in the brain. We found that inhibition of ALK or knockout of MDK attenuated ethanol-induced ERK phosphorylation in mouse amygdala. These results demonstrate that ethanol engages MDK and ALK signaling, which has important consequences for alcohol-induced neurotoxicity and the regulation of behaviors related to alcohol abuse.

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 in repair of the injured nervous system

Midkine (MK) is a growth factor with neurotrophic and neurite outgrowth activities. It was expressed in the peri-ischaemic area in the acute phase of cerebral infarction in rat brains. Astrocytes were the origin of MK in this occasion. MK has been assessed in terms of its effects on neural injury. The administration of MK into the lateral ventricle immediately prior to ischaemia prevented cell death in the hippocampal CA1 neurons degenerated by transient forebrain ischaemia in gerbils. MK administration was also beneficial in rats with neural injury, especially after kainic acid-induced seizures. Gene therapy with mouse MK cDNA using an adenovirus was effective in reducing the cerebral infarction volume and in increasing the number of neuronal precursor cells in the subventricular zone of the rat brain. MK mRNA and MK protein were found in spinal cord motor neurons of the anterior horn in both the acute phase of sciatic nerve injury and 3 weeks later. MK immunoreactivity was also found in the proximal side of a sciatic nerve-injured site in sciatic nerve axons. MK receptors were expressed in Schwann cells after injury, suggesting crosstalk between axons and Schwann cells. MK was also present in nerve terminals and influenced ACh receptor clustering during neuromuscular development in Xenopus. Thus, MK may also be involved in reinforcing and maintaining the synapse. All these findings indicate the therapeutic potential of MK for promoting repair of the nervous system after injury.

Structure and function of midkine as the basis of its pharmacological effects

Midkine (MK) is a heparin-binding growth factor or cytokine and forms a small protein family, the other member of which is pleiotrophin. MK enhances survival, migration, cytokine expression, differentiation and other activities of target cells. MK is involved in various physiological processes, such as development, reproduction and repair, and also plays important roles in the pathogenesis of inflammatory and malignant diseases. MK is largely composed of two domains, namely a more N-terminally located N-domain and a more C-terminally located C-domain. Both domains are basically composed of three antiparallel β-sheets. In addition, there are short tails in the N-terminal and C-terminal sides and a hinge connecting the two domains. Several membrane proteins have been identified as MK receptors: receptor protein tyrosine phosphatase Z1 (PTPζ), low-density lipoprotein receptor-related protein, integrins, neuroglycan C, anaplastic lymphoma kinase and Notch-2. Among them, the most established one is PTPζ. It is a transmembrane tyrosine phophatase with chondroitin sulfate, which is essential for high-affinity binding with MK. PI3K and MAPK play important roles in the downstream signalling system of MK, while transcription factors affected by MK signalling include NF-κB, Hes-1 and STATs. Because of the involvement of MK in various physiological and pathological processes, MK itself as well as pharmaceuticals targeting MK and its signalling system are expected to be valuable for the treatment of numerous 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.

Midkine overcomes neurite outgrowth inhibition of chondroitin sulfate proteoglycan without glial activation and promotes functional recovery after spinal cord injury

Injuries in the mammalian central nervous system induce a variety of factors which promote or inhibit neuronal axon regeneration/sprouting. However, the inhibitory activities are much stronger, and indeed are the major obstacle to functional recovery. Chondroitin sulfate proteoglycans (CSPGs) are produced by activated glial cells, and are among the strongest inhibitors. Here, we investigated the role of the growth factor midkine (MK), which binds to CSPGs, in neuronal injury. MK expression was induced by spinal cord injury, and was mainly produced by activated astrocytes. A prolonged culture of neurons also produced MK. MK not only enhanced neurite outgrowth on the substratum coated with poly-l-lysine, but also overcame the neurite growth inhibition by the CSPG substratum. Moreover, we found that MK activated neither astrocytes nor microglia as evaluated by morphological changes and cell proliferation or nitric oxide production. These properties would be advantageous for the treatment of neuronal injuries in vivo. Therefore, we next explored the therapeutic effect of MK in a rat spinal cord injury model. MK or vehicle was administered intrathecally for 2 weeks using an osmotic pump after spinal cord contusion injury. Rats treated with MK showed significantly better functional recovery after 5 weeks. These results suggest that MK may offer a potent alternative for the treatment of neuronal injuries without activating glial cells.

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.

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.

Midkine in the pathology of cancer, neural disease, and inflammation

Midkine (MK) is a heparin-binding growth factor involved in various cellular processes such as cellular proliferation, survival, and migration. In addition to these typical growth factor activities, MK exhibits several other activities related to fibrinolysis, blood pressure, host defense and other processes. Many cell-surface receptors have been identified to account for the multiple biological activities of MK. The expression of MK is frequently upregulated in many types of human carcinoma. Moreover, blood MK levels are closely correlated with patient outcome. Knockdown and blockade of MK suppress tumorigenesis and tumor development. Thus, MK serves as a tumor marker and a molecular target for cancer therapy. Furthermore, there is growing evidence that MK plays pivotal roles in neural and inflammatory diseases. Understanding of the mechanisms of action of MK is expected to create new therapeutic options for several human diseases.

Recombinant human midkine stimulates proliferation and decreases dedifferentiation of auricular chondrocytes in vitro

Autologous chondrocyte implantation (ACI) is widely used for the repair of cartilage defects. However, due to the lack of chondrocyte growth factor and dedifferentiation of the cultured primary chondrocytes, cell source has limited the clinical potential of ACI. Auricular cartilage is an attractive potential source of cells for cartilage tissue engineering. Here we demonstrated that recombinant human midkine (rhMK) significantly promoted proliferation of rat primary auricular chondrocytes cultured and passaged in monolayer, which was mediated by the activation of mitogen-activated protein kinase and phosphoinositide 3-kinase pathways. Furthermore, rhMK attenuated the dedifferentiation of cultured chondrocytes by maintaining the expression of chondrocyte-specific matrix proteins during culture expansion and passage. Importantly, rhMK-expanded chondrocytes reserved their full chondrogenic potential and redifferentiated into elastic chondrocytes after being cultured in high density. The results suggest that rhMK may be used for the preparation of chondrocytes in cartilage tissue engineering.

Notch signaling activated by replication stress-induced expression of midkine drives epithelial-mesenchymal transition and chemoresistance in pancreatic cancer

The incidence of pancreatic ductal adenocarcinoma (PDAC) nearly equals its mortality rate, partly because most PDACs are intrinsically chemoresistant and thus largely untreatable. It was found recently that chemoresistant PDAC cells overexpress the Notch-2 receptor and have undergone epithelial-mesenchymal transition (EMT). In this study, we show that these two phenotypes are interrelated by expression of Midkine (MK), a heparin-binding growth factor that is widely overexpressed in chemoresistant PDAC. Gemcitabine, the front-line chemotherapy used in PDAC treatment, induced MK expression in a dose-dependent manner, and its RNAi-mediated depletion was associated with sensitization to gemcitabine treatment. We identified an interaction between the Notch-2 receptor and MK in PDAC cells. MK-Notch-2 interaction activated Notch signaling, induced EMT, upregulated NF-κB, and increased chemoresistance. Taken together, our findings define an important pathway of chemoresistance in PDAC and suggest novel strategies for its clinical attack.

The effects of early exercise on brain damage and recovery after focal cerebral infarction in rats

Aim

Exercise can be used to enhance neuroplasticity and facilitate motor recovery after a stroke in rats. We investigated whether treadmill running could reduce brain damage and enhance the expression of midkine (MK) and nerve growth factor (NGF), increase angiogenesis and decrease the expression of caspase-3.

Methods

Seventy-seven Wistar rats were split into three experimental groups (ischaemia-control: 36, ischaemia-exercise: 36, sham-exercise: 5). Stroke was induced by 90-min left middle cerebral artery occlusion using an intraluminal filament. Beginning on the following day, the rats were made to run on a treadmill for 20 min once a day for a maximum of 28 consecutive days. Functional recovery after ischaemia was assessed using the beam-walking test and a neurological evaluation scale in all rats. Infarct volume, and the expression of MK, NGF, anti-platelet-endothelial cell adhesion molecule (PECAM-1), and caspase-3 were evaluated at 1, 3, 5, 7, 14 and 28 days after the induction of ischaemia.

Results

Over time motor coordination and neurological deficits improved more in the exercised group than in the non-exercised group. The infarct volume in the exercised group (12.4 ± 0.8%) subjected to treadmill running for 28 days was significantly decreased compared with that in the control group (19.8 ± 4.2%, P < 0.01). The cellular expression levels of MK, NGF and PECAM-1 were significantly increased while that of caspase-3 was decreased in the peri-infarct area of the exercised rats.

Conclusions

Our findings show that treadmill exercise improves motor behaviour and reduces neurological deficits and infarct volume, suggesting that it may aid recovery from central nervous system injury.

The effects of early exercise on brain damage and recovery after focal cerebral infarction in rats

AIM

Exercise can be used to enhance neuroplasticity and facilitate motor recovery after a stroke in rats. We investigated whether treadmill running could reduce brain damage and enhance the expression of midkine (MK) and nerve growth factor (NGF), increase angiogenesis and decrease the expression of caspase-3.

METHODS

Seventy-seven Wistar rats were split into three experimental groups (ischaemia-control: 36, ischaemia-exercise: 36, sham-exercise: 5). Stroke was induced by 90-min left middle cerebral artery occlusion using an intraluminal filament. Beginning on the following day, the rats were made to run on a treadmill for 20 min once a day for a maximum of 28 consecutive days. Functional recovery after ischaemia was assessed using the beamwalking test and a neurological evaluation scale in all rats. Infarct volume, and the expression of MK, NGF, anti-platelet-endothelial cell adhesion molecule (PECAM-1), and caspase-3 were evaluated at 1, 3, 5, 7, 14 and 28 days after the induction of ischaemia.

RESULTS

Over time motor coordination and neurological deficits improved more in the exercised group than in the non-exercised group. The infarct volume in the exercised group (12.4 ± 0.8%) subjected to treadmill running for 28 days was significantly decreased compared with that in the control group (19.8 ± 4.2%, P < 0.01). The cellular expression levels of MK, NGF and PECAM-1 were significantly increased while that of caspase-3 was decreased in the peri-infarct area of the exercised rats.

CONCLUSIONS

Our findings show that treadmill exercise improves motor behaviour and reduces neurological deficits and infarct volume, suggesting that it may aid recovery from central nervous system injury.

Midkine: a promising molecule for drug development to treat diseases of the central nervous system

Midkine (MK) is a heparin-binding cytokine, and promotes growth, survival, migration and other activities of target cells. After describing the general properties of MK, this review focuses on MK and MK inhibitors as therapeutics for diseases in the central nervous system. MK is strongly expressed during embryogenesis especially at the midgestation period, but is expressed only at restricted sites in adults. MK expression is induced upon tissue injury such as ischemic brain damage. Since exogenously administered MK or the gene transfer of MK suppresses neuronal cell death in experimental systems, MK has the potential to treat cerebral infarction. MK might become important also in the treatment of neurodegenerative diseases such as Alzheimer's disease. MK is involved in inflammatory diseases by enhancing migration of leukocytes, inducing chemokine production and suppressing regulatory T cells. Since an aptamer to MK suppresses experimental autoimmune encephalitis, MK inhibitors are promising for the treatment of multiple sclerosis. MK is overexpressed in most malignant tumors including glioblastoma, and is involved in tumor invasion. MK inhibitors may be of value in the treatment of glioblastoma. Furthermore, an oncolytic adenovirus, whose replication is under the control of the MK promoter, inhibits the growth of glioblastoma xenografts. MK inhibitors under development include antibodies, aptamers, glycosaminoglycans, peptides and low molecular weight compounds. siRNA and antisense oligoDNA have proved effective against malignant tumors and inflammatory diseases in experimental systems. Practical information concerning the development of MK and MK inhibitors as therapeutics is described in the final part of the review.

Midkine expression in malignant salivary gland tumors and its role in tumor angiogenesis

The aims of this study were to investigate midkine (MK) expression patterns in salivary gland tumors (SGTs) and to evaluate the correlation between MK expression and the degree of malignancy. We performed immunohistochemistry to examine MK expression in specimens of adenoid cystic carcinoma (ACC), mucoepidermoid carcinoma (MEC), and pleomorphic adenoma (PA). In addition, we performed immunohistochemistry for CD31 and measured microvessel density (MVD), which is an indicator of angiogenesis. Immunohistochemistry showed that MK protein expression was significantly higher in specimens of malignant SGTs (ACC [P<0.01] and MEC [P<0.001]) than in benign SGT (PA) samples. Furthermore, MVD values tended to be higher in cases that exhibited high expression of MK, which indicated a significant correlation between the degree of MK expression and MVD (P<0.001). These results suggest that MK may play important roles in malignant transformation and tumor angiogenesis in SGTs.

Recombinant human midkine stimulates proliferation of articular chondrocytes

OBJECTIVES

Midkine, a heparin-binding growth factor, promotes population growth, survival and migration of several cell types, but its effect on articular chondrocytes remains unknown. The aim of this study was to investigate its role on proliferation of articular chondrocytes in vitro and in vivo.

MATERIALS AND METHODS

Bromodeoxyuridine incorporation and MTT assays were performed to examine the proliferative effect of recombinant human midkine (rhMK) on primary articular chondrocytes. Activation of extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3K) was analysed using western blot analysis. Systemic and local delivery of rhMK into mice and rats was preformed to investigate the proliferative effect of rhMK in vivo, respectively. Histological evaluation, including measurement of articular cartilage thickness, cell density, matrix staining and immunostaining of proliferating cell nuclear antigen was carried out.

RESULTS

rhMK promoted proliferation of articular chondrocytes cultured in a monolayer, which was mediated by activation of ERK and PI3K. The proliferative role of rhMK was not coupled to dedifferentiation of culture-expanded cells. Consistent with its action in vitro, rhMK stimulated proliferation of articular chondrocytes in vivo when it was administered subcutaneously and intra-articularly in mice and rats, respectively.

CONCLUSION

Our results demonstrate that rhMK stimulates proliferation of primary articular chondrocytes in vitro and in vivo. The results of this study warrant further examination of rhMK for treatment of animal models of articular cartilage defects.

Midkine: a novel prognostic biomarker for cancer

Since diagnosis at an early stage still remains a key issue for modern oncology and is crucial for successful cancer therapy, development of sensitive, specific, and non-invasive tumor markers, especially, in serum, is urgently needed. Midkine (MK), a plasma secreted protein, was initially identified in embryonal carcinoma cells at early stages of retinoic acid-induced differentiation. Multiple studies have reported that MK plays important roles in tumor progression, and is highly expressed in various malignant tumors. Because increased serum MK concentrations also have been reported in patients with various tumors, serum MK may have the potential to become a very useful tumor marker. Here, we review and discuss the possibility and usefulness of MK as a novel tumor marker.

Midkine, heparin-binding growth factor, blocks kainic acid-induced seizure and neuronal cell death in mouse hippocampus

BACKGROUND

Midkine (MK), a member of the heparin-binding growth factor family, which includes MK and pleiotrophin, is known to possess neurotrophic and neuroprotective properties in the central nervous system. Previous studies have shown that MK is an effective neuroprotective agent in reducing retinal degeneration caused by excessive light and decreasing hippocampal neuronal death in ischemic gerbil brain. The present study was undertaken to investigate whether MK acts as an anticonvulsant in kainic acid (KA)-induced seizure in mouse and blocks KA-mediated neuronal cell death in hippocampus.

RESULTS

Increased expression of MK was found in hippocampus of mouse following seizures induced by intracerebroventricular injection of KA, and MK expression was found in glial fibrillary acidic protein (GFAP)-positive astrocytes. Concurrent injection of MK and KA attenuated KA-induced seizure activity and cell death of hippocampal neurons including pyramidal cells and glutamic acid decarboxylase 67 (GAD67)-positive GABAergic interneurons in the CA3 and hilar area.

CONCLUSION

The results of the present study indicate that MK functions as an anticonvulsant and neuroprotective agent in hippocampus during KA-induced seizures.

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.

Midkine, a heparin-binding cytokine with multiple roles in development, repair and diseases

Midkine is a heparin-binding cytokine or a growth factor with a molecular weight of 13 kDa. Midkine binds to oversulfated structures in heparan sulfate and chondroitin sulfate. The midkine receptor is a molecular complex containing proteoglycans. Midkine promotes migration, survival and other activities of target cells. Midkine has about 50% sequence identity with pleiotrophin. Mice deficient in both factors exhibit severe abnormalities including female infertility. In adults, midkine is expressed in damaged tissues and involved in the reparative process. It is also involved in inflammatory reactions by promoting the migration of leukocytes, induction of chemokines and suppression of regulatory T cells. Midkine is expressed in a variety of malignant tumors and promotes their growth and invasion. Midkine appears to be helpful for the treatment of injuries in the heart, brain, spinal cord and retina. Midkine inhibitors are expected to be effective in the treatment of malignancies, rheumatoid arthritis, multiple sclerosis, renal diseases, restenosis, hypertension and adhesion after surgery.

Midkine gene transfer protects against focal brain ischemia and augments neurogenesis

BACKGROUND AND PURPOSE

Midkine is a heparin-binding growth factor having various biological activities including chemotaxis of inflammatory cells, angiogenesis and migration of neuronal cells. These biological activities are expected to have a great impact on the pathology of brain infarction in subacute phase. Therefore, we investigated the effect of post-ischemic gene transfer of midkine in the phase.

METHODS

Brain ischemia was produced by the photothrombotic distal middle cerebral artery occlusion in spontaneously hypertensive rats. We measured cerebral blood flow by laser Doppler flowmetry. At 90 min after induction of brain ischemia, adenovirus vectors encoding mouse midkine (AdMK) or enhanced green fluorescence protein (AdGFP) were injected into the lateral ventricle. At 7 days after brain ischemia, the infarct volume, angiogenesis, inflammation and neuronal regeneration were evaluated.

RESULTS

There were no differences in cerebral blood flow changes between AdMK and AdGFP groups. However, infarct volume of AdMK group was significantly smaller than AdGFP group by 33%. The vascular density, the numbers of leukocytes in blood vessels, infiltrated macrophages and proliferated neuronal precursor cells were not significantly different between both groups. Contrastingly the numbers of migrating neuronal precursor cells toward the brain infarction were significantly increased in AdMK group than AdGFP group.

CONCLUSIONS

Neuroprotective effect of midkine gene transfer persisted until the subacute phase of brain infarction. Midkine may contribute to neuronal regeneration. These results suggest the usefulness of midkine gene transfer for treatment of brain infarction.

Effects of human midkine on spontaneous resorption of herniated intervertebral discs

This study was performed in 36 rabbits to investigate the role of midkine (MK) in the resorption of herniated intervertebral discs. The L(1-2) disc was excised and immersed in one of three kinds of solution for two hours before relocation into the L4 epidural space. In the MK-treated group, the weight of relocated intervertebral discs decreased more over time than in the control group. Newly formed vessels and inflammatory cells were more frequently observed in the MK-treated group than in the control group two weeks after surgery. The degradation of matrix was more significant in the MK-treated group than in the control group four weeks after surgery. Larger areas were replaced by fibrous tissues in the MK-treated group eight weeks after surgery. Thus, MK can accelerate the resorption of the intervertebral disc relocation to the epidural space. Epidural injection of MK may contribute to the therapy of lumber disc herniation.

Expression and purification of bioactive high-purity human midkine in Escherichia coli

Midkine is a heparin-binding growth factor, which plays important roles in the regulation of cell growth and differentiation. The non-tagged recombinant human midkine (rhMK) is therefore required to facilitate its functional studies of this important growth factor. In the present work, rhMK was expressed in Escherichia coli (E. coli) BL21 (DE3). The expression of midkine was efficiently induced by isopropyl-beta-D-thiogalactopyranoside (IPTG). After sonication, midkine was recovered in an insoluble form, and was dissolved in guanidine hydrochloride buffer. Renaturation of the denatured protein was carried out in the defined protein refolding buffer, and the refolded protein was purified using S-Sepharose ion-exchange chromatography. The final preparation of the rhMK was greater than 98% pure as measured by sodium dodecylsulfate-polyacrylamid gel electrophoresis (SDS-PAGE) and reverse phase high performance liquid chromatography (RP-HPLC). The purified rhMK enhanced the proliferation of NIH3T3 cells.

Midkine as a prognostic biomarker in oral squamous cell carcinoma

The aim of this study was to evaluate serum midkine (S-MK) concentrations as a prognostic tumour marker in oral squamous cell carcinoma (OSCC). We measured S-MK concentrations in patients with OSCC and healthy volunteers. In addition, we performed real-time quantitative reverse transcription-PCR analysis and immunohistochemistry with fresh tumour samples. To determine whether S-MK concentrations have prognostic value, we performed survival analyses with clinical information by using the log-rank test. Serum midkine concentrations were significantly higher in patients with OSCC than in healthy controls (P<0.001). Serum midkine concentrations were also significantly increased in early-stage OSCC compared with those of healthy individuals (P<0.001). In addition, immunohistochemistry allowed identification of overexpressed MK protein in OSCC tissues. MK mRNA showed higher expression in OSCC samples compared with normal mucosal samples. Patients in high S-MK groups showed a significantly lower 5-year survival rate compared with patients in low S-MK groups (P<0.05). The increased S-MK concentrations in early-stage OSCC were strongly associated with poor survival. Serum midkine concentrations may thus be a useful marker not only for cancer screening but also for predicting prognosis of OSCC patients.

Impact of alcohol abuse on protein expression of midkine and excitatory amino acid transporter 1 in the human prefrontal cortex

BACKGROUND

Alcoholism is associated with shrinkage of brain tissue and reduction in the number of neurons and dendritic arbors particularly in the prefrontal cortex. These changes correlate with the cognitive defects common in alcoholics. A recent study investigated the mRNA expression of selected genes in the prefrontal cortex and found that the levels of mRNA encoding the neurotrophic factor, midkine (MDK), and the excitatory amino acid transporter 1 (EAAT1) were significantly higher in alcoholics compared with nonalcoholic controls. This study aimed to investigate, whether the transcriptional changes observed result in alterations to protein expression. Additionally, the study aimed to expand our understanding of MDK and EAAT1 action by localizing their expression within morphologically and functionally distinct layers of this brain region.

METHODS

Quantitative changes in protein levels of MDK and EAAT1 were investigated in alcoholic and control cases using Western blots. Immunohistochemistry was utilized to localize proteins expression in formalin-fixed sagittal sections of the prefrontal cortex.

RESULTS

A marked increase was revealed in protein expression of both genes in the prefrontal cortex of chronic alcoholics. MDK-like immunofluorescence in alcoholic and control cases was present in nuclei throughout the prefrontal cortex and was particularly apparent in cell bodies of astrocytes in cortical layer II. Immunolabeling of the EAAT1 was densest in cortical layer II in control cases and induced in deeper layers in alcoholic cases.

CONCLUSION

Midkine promotes neuronal outgrowth and survival. The up-regulation of MDK protein expression may indicate the induction of reparative processes. The amino acid transporter is vital for the removal of glutamate from the synaptic cleft. At alcohol withdrawal, extracellular glutamate is thought to reach excitotoxic concentrations. Up-regulation of EAAT1 throughout the cortical layers may indicate an attempt to combat elevated glutamate concentrations. The predominant expression of the two proteins in layer II of the cortex implies a region-specific role of astrocytes.

Midkine secretion protects Hep3B cells from cadmium induced cellular damage

AIM: To evaluate role of midkine secretion during Cadmium (Cd) exposure in the human hepatocyte cell line Hep3B cells.

METHODS: Different dosages of Cd (0.5-1-5-10 &mgr;g/mL) were applied to Hep3B cells and their effects to apoptosis, lactate dehydrogenase (LDH) leakage and midkine secretion were evaluated as time dependent manner. Same experiments were repeated with exogenously applied midkine (250-5000 pg/mL) and/or 5 &mgr;g/mL Cd.

RESULTS: Cd exposure induced prominent apoptosis and LDH leakage beginning from lower dosages at the 48^th h. Cd induced midkine secretion with higher dosages (P < 0.001), (control, Cd 0.5-1-5-10 &mgr;g/mL respectively: 1123 ± 73, 1157 ± 63, 1242 ± 90, 1886 ± 175, 1712 ± 166 pg/mL). Exogenous 500-5000 pg/mL midkine application during 5 &mgr;g/mL Cd toxicity prevented caspase-3 activation (control, Cd toxicity, 250, 500, 1000, 2500, 5000 pg/mL midkine+ Cd toxicity, respectively: 374 ± 64, 1786 ± 156, 1545 ± 179, 1203 ± 113, 974 ± 116, 646 ± 56, 556 ± 63 cfu) LDH leakage and cell death in Hep3B cells (P < 0.001).

CONCLUSION: Our results showed that midkine secretion from Hep3B cells during Cd exposure protects liver cells from Cd induced cellular damage. Midkine has anti-apoptotic and cytoprotective role during Cd toxicity. Further studies are needed to explain the mechanism of midkine secretion and cytoprotective role of midkine during Cd exposure. Midkine may be a promising therapeutic agent in different toxic hepatic diseases.

Expression of the heparin-binding growth factor midkine in the cerebrospinal fluid of patients with neurological disorders

OBJECTIVE

This study was to clarify the roles of midkine (MK) in the brain.

METHODS

We determined cerebrospinal fluid MK levels in patients with neurological disorders by enzyme-linked immunoassay and immunostained autopsied brain samples in patients with meningitis.

RESULTS

MK levels were 0.37+/-0.21 ng/ml in controls (n=46, mean +/- S.D.), 0.67+/-0.19 ng/ml in patients with cerebral infarction (n=8), 1.78+/-1.32 ng/ml in patients with meningitis (n=25; ANOVA and post-hoc Fisher's PLSD test, p<0.0001), 0.31+/-0.25 ng/ml in patients with human T-lymphotrophic virus type I-associated myelopathy/tropical spastic paraparesis (n=29), and 0.42+/-0.17 ng/ml in patients with amyotrophic lateral sclerosis (n=8). The regression equations were Y=0.005X+0.498 (Y, CSF MK level; X, cell number) and Y=0.007X+0.326 (Y, MK level; X, protein level) for all CSF samples. Autopsy brain samples from patients with meningitis expressed MK weakly in mononuclear cells on immunohistochemical examination. Western blot and polymerase chain reaction analyses showed that leukocytes were MK positive. CSF MK levels were not high in patients with cerebral infarction but were increased in patients with meningitis. CSF MK levels were high in normal controls, compared to those of other cytokines. MK was expressed in choroid plexus of normal brain and released there.

CONCLUSION

Our findings suggested that MK may maintain normal adult brain as a neurotrophic factor, and that MK may be released from leucocytes in brain of patients with meningitis as an immunological mediator.

Truncated midkine correlates with sensitivity to anticancer drugs and malignancy in human tumor cell line

Midkine (MK) is a heparin binding growth factor having functions of neurite-outgrowth, mitogenesis and tissue repair. This molecule is involved in tumor growth and metastasis. The MK molecule consists of five exons, but there is a truncated isoform, lacking exon 3. We established SW13 cells transfected with the human truncated MK cDNA. These cells were induced to undergo apoptosis by anticancer agents, cisplatin, etoposide (ETP), mitomycin C (MMC) and paclitaxel (PAX). Truncated midkine (tMK) suppressed cell death and helped the cells to be viable. When the cells were cultured on dishes coated with extracellular matrix molecules, spontaneous detachment occurred in the tMK expressing cells. Also tMK enhanced cell invasion. These results suggest that expression of tMK has cell-protective functions and plays important roles in carcinogenesis and malignancy. Furthermore, it is suggested that tMK has a greater ability of malignant transformation than full-length MK. Whether tMK is expressed or not will be useful information for improving cancer chemotherapy.

Midkine and its receptor in regenerating rat skeletal muscle after bupivacaine injection

Midkine (MK) is a multifunctional cytokine and heparin-binding growth factor with neurotrophic activity. MK and its receptor were examined for up to 14 days in a chemically injured rat muscle regeneration process caused by the injection of bupivacaine using immunohistochemical and Western blot analysis. Although MK immunoreactivity was not detectable in the mature uninjured skeletal muscle, MK was strongly detected in the regenerating muscle cells. MK immunoreactivity was observed in the myoblast-like cells and myotubes, which were desmin-positive cells, whereas it was not detectable in the surviving normal muscle fibers. Most myotubes labeling for desmin showed MK immunoreactivity 5-7days after the injury. However, MK immunoreactivity was not detected 14 days after the injury. Immunoreactivity of low-density lipoprotein receptor-related protein (LRP), a cell membrane receptor of MK, was detected in the regenerating muscle cells, whereas it was not detected in the normal adult skeletal muscle and surviving muscle. These findings suggested that MK was involved. MK may have a role for differentiation during skeletal muscle regeneration and may be taken up in an autocrine fashion with LRP.

Controlled release of small interfering RNA targeting midkine attenuates intimal hyperplasia in vein grafts

OBJECTIVE

Intimal hyperplasia is a major obstacle to patency after vein grafting. Despite of a diverse array of trials to prevent it, a satisfactory therapeutic strategy for clinical use has not been established. However, sufficient inhibition of early stages of intimal hyperplasia may prevent this long-term progressive disease. Midkine (MK) is a heparin-binding growth factor that was originally discovered as the product of a retinoic acid-responsive gene. We previously demonstrated that MK-deficient mice exhibit a striking reduction of neointima formation in a restenosis model, which is reversed on systemic MK administration. In this study, we evaluated a strategy of using small interfering RNA (siRNA) targeting MK as a therapy for vein graft failure.

METHODS

We first made a highly effective siRNA to rabbit MK. Jugular vein-to-carotid artery interposition vein grafts, which are applied to a low flow condition, were made in Japanese white rabbits. Small interfering RNA mixed with atelocollagen was administrated to the external wall of grafted veins. Cy3-conjugated stabilized siRNA was used to confirm its stability and successful transfer into the vein graft wall. Neointimal hyperplasia was evaluated 4 weeks after the operation. The proliferation index and leukocyte infiltration were determined.

RESULTS

MK expression was induced and reached the maximum level 7 days after operation. Fluorescence of Cy3-labeled siRNA could be detected in the graft wall even 7 days after operation. Knockdown of the gradually increasing expression was achieved by perivascular application of siRNA using atelocollagen. The intima-media ratio and the intima thickness at 28 days after grafting were both reduced >90% by this treatment compared with controls. This phenomenon was preceded by significant reductions of inflammatory cell recruitment to the vessel walls and subsequent cell proliferation in MK siRNA-treated grafts.

CONCLUSIONS

These results suggest that midkine is a candidate molecular target for preventing vein graft failure. Furthermore, for clinical applications of siRNA, a single intraoperative atelocollagen-based nonviral delivery method could be a reliable approach to achieve maximal function of siRNA in vivo. This strategy may be a useful and practical form of gene therapy against human vein graft failure.

Growth factor midkine is involved in the pathogenesis of diabetic nephropathy

Diabetic nephropathy is a life-threatening disease associated with diabetes mellitus. Longstanding hyperglycemia induces pathological reactions of glomerular mesangial cells, such as overproduction of extracellular matrix, which finally lead to nephropathy. However, the mechanisms underlying its pathogenesis have not been completely elucidated. Using the Streptozotocin-induced model of diabetes, we report that mice deficient in the growth factor midkine (Mdk-/-) exhibited strikingly milder nephropathy than Mdk+/+ mice, even though both mice showed similar extents of hyperglycemia after Streptozotocin injection. Midkine expression was induced in the glomerular mesangium of Mdk+/+ mice with diabetic nephropathy and in primary cultured mesangial cells exposed to high glucose. Mdk-/- mesangial cells exhibited reduced phosphorylation of protein kinase C and extracellular signal-regulated kinase as well as reduced production of transforming growth factor-beta(1) on high glucose loading. Addition of exogenous midkine restored extracellular signal-regulated kinase phosphorylation in Mdk-/- cells under high glucose conditions, whereas a midkine antisense oligodeoxynucleotide suppressed midkine in Mdk+/+ cells. Therefore, this study identifies midkine as a key molecule in diabetic nephropathy and suggests that midkine accelerates the intracellular signaling network evoked by hyperglycemia in nephropathy.

Transiently truncated and differentially regulated expression of midkine during mouse embryogenesis

Midkine (MK) is a retinoic acid response cytokine, mostly expressed in embryonic tissues. Aberrant expression of MK was found in numerous cancers. In human, a truncated MK was expressed specifically in tumor/cancer tissues. Here we report the discovery of a novel truncated form of MK transiently expressed during normal mouse embryonic development. In addition, MK is concentrated at the interface between developing epithelium and mesenchyme as well as highly proliferating cells. Its expression, which is closely coordinated with angiogenesis and vasculogenesis, is spatiotemporally regulated with peaks in extensive organogenesis period and undifferentiated cells tailing off in maturing cells, implying its role in nascent blood vessel (endothelial) signaling of tissue differentiation and stem cell renewal/differentiation. Cloning and sequencing analysis revealed that the embryonic truncated MK, in which the conserved domain is in-frame deleted, presumably producing a novel secreted small peptide, is different from the truncated form in human cancer tissues, whose deletion results in a frame-shift mutation. Our data suggest that MK may play a role in epithelium-mesenchyme interactions, blood vessel signaling, and the decision of proliferation vs differentiation. Detection of the transiently expressed truncated MK reveals its novel function in development and sheds light on its role in carcinogenesis.

Postischemic gene transfer of midkine, a neurotrophic factor, protects against focal brain ischemia

Gene therapy may be a promising approach for treatment of brain ischemia. In this study, we examined the effect of postischemic gene transfer of midkine, a heparin-binding neurotrophic factor, using a focal brain ischemia model with the photothrombotic occlusion method. At 90 min after induction of brain ischemia in spontaneously hypertensive rats, a replication-deficient recombinant adenovirus encoding mouse midkine (AdMK, n=7) or a control vector encoding beta-galactosidase (Adbetagal, n=7) was injected into the lateral ventricle ipsilateral to ischemia. At 2 days after ischemia, we determined infarct volume by 2,3,5-triphenyltetrazolium chloride staining. There were no significant differences in cerebral blood flow 1 h after ischemia between AdMK and Adbetagal groups. Infarct volume of AdMK group was 51+/-27 mm3, which was significantly smaller than that of Adbetagal group (86+/-27 mm3, P<0.05). TUNEL-positive and cleaved caspase-3-positive cells in the periischemic area of AdMK-treated rats were significantly fewer than those in Adbetagal-treated rats, suggesting that the reduction of infarct volume by midkine was partly mediated by its antiapoptotic action. Thus, gene transfer of midkine to the ischemic brain may be effective in the treatment of brain ischemia.

Alcohol-responsive genes in the frontal cortex and nucleus accumbens of human alcoholics

The molecular processes underlying alcohol dependence are not fully understood. Many characteristic behaviours result from neuroadaptations in the mesocorticolimbic system. In addition, alcoholism is associated with a distinct neuropathology. To elucidate the molecular basis of these features, we compared the RNA expression profile of the nucleus accumbens and prefrontal cortex of human brain from matched individual alcoholic and control cases using cDNA microarrays. Approximately 6% of genes with a marked alcohol response were common to the two brain regions. Alcohol-responsive genes were grouped into 11 functional categories. Predominant alcohol-responsive genes in the prefrontal cortex were those encoding DNA-binding proteins including transcription factors and repair proteins. There was also a down-regulation of genes encoding mitochondrial proteins, which could result in disrupted mitochondrial function and energy production leading to oxidative stress. Other alcohol-responsive genes in the prefrontal cortex were associated with neuroprotection/apoptosis. In contrast, in the nucleus accumbens, alcohol-responsive genes were associated with vesicle formation and regulation of cell architecture, which suggests a neuroadaptation to chronic alcohol exposure at the level of synaptic structure and function. Our data are in keeping with the previously reported alcoholism-related pathology characteristic of the prefrontal cortex, but suggest a persistent decrease in neurotransmission and changes in plasticity in the nucleus accumbens of the alcoholic.

Increased midkine levels in sera from patients with Alzheimer's disease

Midkine (MK) is a heparin binding growth factor and promotes growth, survival and migration of various cells including neurons. It is also known to accumulate in senile plaques of patients with Alzheimer's disease (AD). To investigate the involvement of serum MK in the pathophysiology of AD, serum MK levels were determined in patients with AD (n=36) and age- and sex-matched healthy controls (n=32), using an enzyme-linked immunosorbent assay (ELISA). The serum MK values of the patients with AD (median 560 and interquartile range (500-755) pg/ml) were significantly (U=278.5, P=0.0003, Mann-Whitney U-test) higher than those of the controls (median 500 and interquartile range (385-520) pg/ml). Moreover, 17 patients (47.2%) had abnormally high values of more than 600 pg/ml, but no controls (0%) did. There was no correlation between serum MK level and the mini mental state examination (MMSE) score in the patients. The demonstration of elevated MK levels in sera of patients with AD may contribute toward an understanding the pathophysiology of this disease, and provide a novel potential therapeutic strategy for decreasing neuronal damages in patients with AD. We found that serum MK levels in patients with AD were increased in comparison with those of normal controls.

Midkine expression in rat spinal motor neurons following sciatic nerve injury

Midkine (MK), a heparin-binding growth factor, is produced in the developing and damaged nervous system. However, the role of MK in peripheral nerve injury has not been clarified. Here, we investigated MK expression in lumbar spinal motor neurons after rat sciatic nerve injury by immunohistochemical, in situ hybridization, and Western blot analyses. The rat sciatic nerve showed complete degeneration after local freezing. Numerous regenerated myelinated and thin nerve fibers were observed 3 weeks after injury. Intense MK immunoreactivity was detected in the ipsilateral spinal motor neurons of the anterior horn of the lumbar spinal cord after 1 day and in ipsilateral and contralateral spinal motor neurons from 4 days to 1 week after injury. It decreased after 2 weeks and again transiently increased in spinal motor neurons after 3 weeks. MK was found in the motor neurons and axon of the sciatic nerve. However, it was not detected in normal neurons and axon. In situ hybridization showed the expression of MK mRNA in lumbar spinal motor neurons of the anterior horn, but it was not present in Schwann cells or non-neuronal cells. Low-density lipoprotein receptor-related protein (LRP) immunoreactivity, a cell membrane receptor of MK, was observed in anterior horn motor neurons, but receptor-type protein tyrosine phosphatase zeta (PTPzeta) immunoreactivity as a signaling receptor complex of MK was not observed. LRP and PTPzeta immunoreactivities were observed in Schwann cells of the injured and uninjured sciatic nerve. Our findings suggest that MK is synthesized, released, and taken up in anterior horn motor neurons in an autocrine fashion with LRP. MK may have a role in degeneration and regeneration after peripheral nerve injury.

Traumatic injury-induced midkine expression in the adult rat spinal cord during the early stage

Spinal cord injury is a debilitating condition. Midkine (MK) is involved in the generation of the central nervous system during development; however, the role of MK in the mature spinal cord has not been clarified. We examined the expression of MK, which has neurotrophic activity, before and after traumatic injury to the adult rat spinal cord. Following laminectomy, the rat spinal cord was injured at the T-9 level by applying extradural static weight-compression, in which a cylindrical compressor was used to induce complete and irreversible transverse spinal cord injury with paralysis of the lower extremities. The expression of MK was examined up to 14 days after the injury by immunohistochemical and Western blot analyses. Intense MK immunoreactivity was observed in the gray matter around the injury site but not in the necrotic lesion 1-7 days postinjury, although it was slightly positive 14 days after the injury. MK immunoreactivity was not detected in the normal spinal cord. The expression of MK was an early event, and its expression was compared to the increased production of glial fibrillary acidic protein (GFAP), a marker of reactive astrocytes, that was elevated at 2 days postinjury and continued over a 14 day period following the injury. Double immunostaining with anti-MK and anti-GFAP showed the existence of MK in the astrocytic cytoplasm. These findings suggest that MK was produced in astrocytes approximating the damaged region and may represent a reparative neurotrophic factor during the early phase of traumatic injury of the spinal cord.