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Midkine is a heparin-binding growth factor, originally reported as the product of a retinoic acid-responsive gene during embryogenesis, but currently viewed as a multifaceted factor contributing to both normal tissue homeostasis and disease development. Midkine is abnormally expressed at high levels in various human malignancies and acts as a mediator for the acquisition of critical hallmarks of cancer, including cell growth, survival, metastasis, migration, and angiogenesis. Several studies have investigated the role of midkine as a cancer biomarker for the detection, prognosis, and management of cancer, as well as for monitoring the response to cancer treatment. Moreover, several efforts are also being made to elucidate its underlying mechanisms in therapeutic resistance and immunomodulation within the tumor microenvironment. We hereby summarize the current knowledge on midkine expression and function in cancer development and progression, and highlight its promising potential as a cancer biomarker and as a future therapeutic target in personalized cancer medicine.

An open question in aggressive cancers such as melanoma is how malignant cells can shift the immune system to pro-tumorigenic functions. Here we identify midkine (MDK) as a melanoma-secreted driver of an inflamed, but immune evasive, microenvironment that defines poor patient prognosis and resistance to immune checkpoint blockade. Mechanistically, MDK was found to control the transcriptome of melanoma cells, allowing for coordinated activation of nuclear factor-κB and downregulation of interferon-associated pathways. The resulting MDK-modulated secretome educated macrophages towards tolerant phenotypes that promoted CD8 + T cell dysfunction. In contrast, genetic targeting of MDK sensitized melanoma cells to anti-PD-1/anti-PD-L1 treatment. Emphasizing the translational relevance of these findings, the expression profile of MDK-depleted tumors was enriched in key indicators of a good response to immune checkpoint blockers in independent patient cohorts. Together, these data reveal that MDK acts as an internal modulator of autocrine and paracrine signals that maintain immune suppression in aggressive melanomas. Tumor-secreted midkine modulates immune tolerance in the melanoma tumor microenvironment and determines resistance to immune checkpoint blockade.

Lung adenocarcinomas (LUAD) arise from precancerous lesions such as atypical adenomatous hyperplasia, which progress into adenocarcinoma in situ and minimally invasive adenocarcinoma, then finally into invasive adenocarcinoma. The cellular heterogeneity and molecular events underlying this stepwise progression remain unclear. In this study, we perform single-cell RNA sequencing of 268,471 cells collected from 25 patients in four histologic stages of LUAD and compare them to normal cell types. We detect a group of cells closely resembling alveolar type 2 cells (AT2) that emerged during atypical adenomatous hyperplasia and whose transcriptional profile began to diverge from that of AT2 cells as LUAD progressed, taking on feature characteristic of stem-like cells. We identify genes related to energy metabolism and ribosome synthesis that are upregulated in early stages of LUAD and may promote progression. MDK and TIMP1 could be potential biomarkers for understanding LUAD pathogenesis. Our work shed light on the underlying transcriptional signatures of distinct histologic stages of LUAD progression and our findings may facilitate early diagnosis. The origin and progression of lung adenocarcinoma (LUAD) are still poorly understood. Here, the authors analyse LUAD composition and progression in patient samples using single-cell RNA-seq and multiplex imaging, revealing a potential transcriptional divergence from alveolar type 2 cells.

Objective Traumatic spinal cord injury (SCI) induces neuronal apoptosis and neuroinflammation, which exacerbate secondary damage and hinder functional recovery. Efficient clearance of apoptotic cells and modulation of the inflammatory microenvironment of spinal cord are essential for promoting tissue repair. This study aimed to investigate whether Midkine (MDK), a heparin‐binding growth factor, facilitates functional recovery after SCI and explores the underlying mechanisms. Methods A rat model of moderate SCI was established using Allen's impact method. Lentiviral vectors were used to overexpress MDK in the spinal cord. Behavioral assessments, including BBB score and gait analysis, were performed to evaluate motor function recovery. Motor evoked potentials (MEPs) serve as a neurophysiological tool for evaluating the functional integrity of the corticospinal tract. In vivo and in vitro experiments were conducted to assess microglial efferocytosis and elucidate the underlying molecular mechanisms. Results Transcriptomic bioinformatic analysis suggests that SCI is characterized by pronounced accumulation of apoptotic cells and robust neuroinflammatory responses, whereas single‐cell analysis implicates MDK as a key contributor to neurorepair after SCI. MDK expression is dynamically regulated following SCI, with an early upregulation followed by a gradual decline over time, its location predominantly observed around microglial cells. Functionally, MDK overexpression significantly enhances motor recovery after SCI, accompanied by reduced neuroinflammation, decreased neuronal apoptosis, and improved neuroprotection. Mechanistically, MDK promotes microglial efferocytosis both in vivo and in vitro, activates the AKT/mTOR signaling pathway, upregulates BDNF and LRP‐1 expression, and facilitates microglial polarization toward an anti‐inflammatory M2 phenotype. Notably, inhibition of LRP‐1 with receptor‐associated protein (RAP) abolished the efferocytic and neuroprotective effects of recombinant MDK, highlighting LRP‐1 as a key mediator of MDK's actions in microglia. Conclusion Our study unveils the MDK/LRP‐1/efferocytosis axis as a previously unrecognized therapeutic target for SCI. By orchestrating apoptotic cell clearance, dampening neuroinflammation, and fostering neuroprotection, this axis critically shapes the post‐injury microenvironment to facilitate recovery. These findings suggest that MDK‐centered therapy may represent a strategy for spinal cord repair, with LRP‐1 modulation offering precise control over microglial responses. Midkine (MDK) promotes functional recovery after spinal cord injury by enhancing microglial efferocytosis, reducing neuroinflammation, and decreasing neuronal apoptosis. Overexpression of MDK activates the AKT/mTOR pathway, upregulates LRP‐1 and BDNF, and drives microglia toward an anti‐inflammatory phenotype. Meanwhile, blocking LRP‐1 abolishes MDK‐mediated neuroprotection, highlighting the MDK/LRP‐1 axis as a promising therapeutic target.

Midkine (MDK), a multifunctional growth factor, has been implicated in promoting tumor progression, yet its role in glioblastoma (GBM) remains insufficiently characterized. To investigate MDK’s function in glioma, we integrated four RNA-Seq datasets into a harmonized cohort of 1,017 adult gliomas, including 256 GBM samples. We complemented this with freshly collected human GBM tissues and matched primary cell cultures to evaluate MDK expression and secretion patterns, further contextualized using single-cell RNA-Seq. Finally, we tested the impact of GBM-derived MDK on macrophage secretome composition to validate our in silico observations. We found that MDK expression increases with tumor grade in IDH wildtype gliomas, accompanied by a shift in isoform proportions favoring the canonical MDK transcript. High MDK expression was associated with poor prognosis specifically in GBM, where the MDK high subgroup comprised 75% of cases. MDK high GBMs exhibited a distinctive multiomic signature, including elevated chemokine and cytokine expression. Functionally, GBM-derived MDK induced macrophages to secrete multiple cytokines and chemokines, suggesting its role in reshaping the tumor microenvironment. Our findings reveal MDK’s previously underappreciated role in GBM aggressiveness and immune modulation, underscoring its potential as a biomarker and actionable therapeutic target for most GBM patients.

Midkine (MDK) is a multifunctional heparin-binding growth factor, and has been shown to regulate cell growth, survival, and migration. It also plays important roles in several inflammatory diseases such as sepsis. However, the role of MDK in the lungs has not yet been elucidated. In the present study, we investigated the role of MDK in pulmonary inflammation experiments using a mouse lipopolysaccharide (LPS)-induced pulmonary inflammation model and human bronchial cells. Wild-type and MDK-deficient mice were administered intratracheally with LPS, and several inflammatory parameters were analyzed. In the wild-type mice, MDK mRNA and protein in lung tissues were significantly increased after intratracheal LPS administration. The MDK-deficient mice showed significantly lower counts of total cells and neutrophils, as well as lower concentrations of total protein and neutrophil chemokines, KC and MIP-2 in bronchoalveolar lavage fluid, compared to wild-type mice. Moreover, mRNA expressions of TNF-α, keratinocyte chemoattractant (KC), and macrophage inflammatory protein (MIP)-2 in lung tissues, as well as the histopathological lung inflammation score, were significantly lower in the MDK-deficient mice. Furthermore, in in vitro experiments using bronchial epithelial cells, LPS stimulation increased mRNA expression of MDK, and MDK knockdown by siRNA decreased LPS-induced TNF-α and CXCL8 upregulation. These findings suggest that deficiency of MDK attenuates LPS-induced pulmonary inflammation, at least in part, through inhibiting inflammatory cytokine and chemokine upregulation in the lungs.

Metastasis accounts for most cancer-related deaths and hepatocellular carcinoma (HCC) is no exception. Midkine (MDK) is a multifunctional secreted protein elevated in HCC with a vague role in HCC. In this study, we used bioinformatics to verify MDK expression in HCC tumors, and next, we inhibited the MDK protein in invasive Hep3B cells using an MDK inhibitor (iMDK) both in vitro and in vivo. Our results showed that iMDK promoted cell migration and enhanced lamellipodia formation while at the same time downregulating the expression of cell–matrix adhesion genes. In order to also consider forces exerted by the surrounding matrix, we performed cell adhesion, transwell invasion, and 3D tumor spheroid invasion assays in two different stiffness conditions. Adhesion and invasion always exhibited opposite patterns, with adhesion being inhibited in soft matrix environments, accompanied by increased invasion, and a reverse effect in stiff environments. In vivo experiments where cells pre-treated with iMDK were implanted to zebrafish embryos showed overall reduced metastasis, verifying that MDK is a central mechanotransduction regulator that enables HCC cells to adapt their metastatic strategies to ECM stiffness. Thus, MDK inhibition effectively disrupts mechanosensitive coordination during metastasis, highlighting its potential as a therapeutic target.

Brain tumors (gliomas) are heterogeneous cellular ecosystems, where non-neoplastic monocytic cells have emerged as key regulators of tumor maintenance and progression. However, relative to macrophages/microglia, comparatively less is known about the roles of neurons and T cells in glioma pathobiology. Herein, we leverage genetically engineered mouse models and human biospecimens to define the axis in which neurons, T cells, and microglia interact to govern Neurofibromatosis-1 (NF1) low-grade glioma (LGG) growth. NF1 -mutant human and mouse brain neurons elaborate midkine to activate naïve CD8 +  T cells to produce Ccl4, which induces microglia to produce a key LGG growth factor (Ccl5) critical for LGG stem cell survival. Importantly, increased CCL5 expression is associated with reduced survival in patients with LGG. The elucidation of the critical intercellular dependencies that constitute the LGG neuroimmune axis provides insights into the role of neurons and immune cells in controlling glioma growth, relevant to future therapeutic targeting. The role of neurons and T cells in glioma progression remains poorly understood. Here the authors show that midkine-dependent activation of a neuron-T cell-microglia axis promotes the growth of optic pathway gliomas.

Pulmonary arterial hypertension (PAH) is a progressive fatal disease caused by pulmonary arterial remodeling. Midkine regulates cell proliferation and migration, and it is induced by hypoxia, but its roles in pulmonary arterial remodeling remain unclear. Serum midkine levels were significantly increased in PAH patients compared with control patients. Midkine expression was increased in lungs and sera of hypoxia-induced PAH mice. Hypoxia-induced pulmonary arterial remodeling and right ventricular hypertrophy were attenuated in midkine-knockout mice. Midkine-induced proliferation and migration of pulmonary arterial smooth muscle cells (PASMC) and epidermal growth factor receptor (EGFR) signaling were significantly increased under hypoxia, which also induced cell-surface translocation of nucleolin. Nucleolin siRNA treatment suppressed midkine-induced EGFR activation in vitro , and nucleolin inhibitor AS1411 suppressed proliferation and migration of PASMC induced by midkine. Furthermore, AS1411 significantly prevented the development of PAH in Sugen hypoxia rat model. Midkine plays a crucial role in PAH development through interaction with surface nucleolin. These data define a role for midkine in PAH development and suggest midkine-nucleolin-EGFR axis as a novel therapeutic target for PAH.

mTORC1 is hyperactive in multiple cancer types 1 , 2 . Here, we performed integrative analysis of single cell transcriptomic profiling, paired T cell receptor (TCR) sequencing, and spatial transcriptomic profiling on Tuberous Sclerosis Complex (TSC) associated tumors with mTORC1 hyperactivity, and identified a stem-like tumor cell state (SLS) linked to T cell dysfunction via tumor-modulated immunosuppressive macrophages. Rapamycin and its derivatives (rapalogs) are the primary treatments for TSC tumors, and the stem-like tumor cells showed rapamycin resistance in vitro, reminiscent of the cytostatic effects of these drugs in patients. The pro-angiogenic factor midkine (MDK) was highly expressed by the SLS population, and associated with enrichment of endothelial cells in SLS-dominant samples. Inhibition of MDK showed synergistic benefit with rapamycin in reducing the growth of TSC cell lines in vitro and in vivo. In aggregate, this study suggests an autocrine rapamycin resistance mechanism and a paracrine tumor survival mechanism via immune suppression adopted by the stem-like state tumor cells with mTORC1 hyperactivity. The tumour microenvironment in mTORC1 hyperactive cancers remains poorly characterised. Here, integrative analysis in tuberous sclerosis complex tumours with mTORC1 hyperactivity suggests distinct cell states associated with rapamycin resistance and immune modulation.