The COVID-19 pandemic had an unprecedented impact on all aspects of human activity worldwide, frequently resulting in post-acute sequelae and affecting multiple organ systems. The underlying mechanisms driving both acute and post-acute manifestations of COVID-19 are still poorly understood, warranting further investigation for new targets. The study represents the first attempt to explore the role of T-cadherin in COVID-19 pathogenesis as well as its implications in pulmonary fibrosis and endothelial dysfunction. First, we revealed a significant decrease in T-cadherin expression in post-mortem lung samples from COVID-19 patients. This downregulated T-cadherin expression correlated with the elevated levels of VE-cadherin and reduced levels of β-catenin, suggesting a disruption in endothelial cell-cell contact integrity and function. Second, the reciprocal relation of T-cadherin and VE-cadherin expression was further confirmed using cultured human endothelial Ea.hy926 cells. T-cadherin overexpression caused a decrease in VE-cadherin mRNA expression in cultured endothelial cells providing additional evidence in favor of their interplay. Third, employing Cdh13 -/- mice, we unveiled the protective role of T-cadherin deficiency against bleomycin-induced lung fibrosis. Fourth, we demonstrated the mice lacking T-cadherin to have downregulated reactive oxygen species production and Nox2 mRNA expression in an angiotensin II-mediated endothelial dysfunction model. Our findings provide rationale for further studies into T-cadherin-mediated mechanisms in these processes.

IntroductionImpaired function of brain morphogenic genes is considered one of the predisposing factors for the manifestation of psychiatric and cognitive disorders, such as paranoid schizophrenia (SCZ) and major depressive disorder (MDD). Identification of such genes (genes of neurotrophic factors and guidance molecules among them) and their deleterious genetic variants serves as a key to diagnosis, prevention, and possibly treatment of such disorders. In this study, we have examined the prevalence of genomic variants in brain morphogenic genes in individuals with SCZ and MDD within a Russian population.MethodsWe have performed whole-exome sequencing of 21 DNA samples: 11 from individuals with SCZ and 10 with MDD, followed by ARMS (Amplification-Refractory Mutation System) based screening of detected single nucleotide variants (SNVs) in larger groups: 102 for individuals with SCZ, 79 for those with MDD and 103 for healthy donors.ResultsWhole-exome sequencing has revealed 226 missense mutations in 79 genes (out of 140 studied), some of which occur in patients with psychiatric disorders significantly more frequently than in healthy donors. We have identified previously undescribed genomic variants in brain morphogenic genes: CDH2 (rs1944294-T and rs17445840-T), DCHS2 (rs11935573-G and rs12500437-G/T) and CDH23 (rs1227051-G/A), significantly associated with the incidence of SCZ and MDD in the Russian population. For some SNVs (rs6265-T, rs1944294-T, rs11935573-G, rs4760-G) sex-biased differences in their prevalence between SCZ/MDD patients and healthy donors was detected.DiscussionHowever, the functional significance of the SNVs identified has still to be confirmed in cellular and animal models. Once it is fulfilled, these SNVs have the potential to complement the diagnostic toolbox for assessing susceptibility to mental disorders. The data obtained indirectly confirm the importance of adequate brain structure formation for its correct functioning and preservation of mental health.

Angiogenesis plays a crucial role in tissue and organ regeneration by supplying essential nutrients and oxygen through the development of new blood vessels. Mesenchymal stem/stromal cells release extracellular vesicles that actively contribute to angiogenesis by carrying pro-angiogenic growth factors and microRNAs. MicroRNAs, small non-coding RNA molecules, are central players in angiogenesis, affecting endothelial cell proliferation, specialization, migration, apoptosis, and post-transcriptional gene expression. In the present study, we investigated the impact of extracellular vesicles containing Plaur-miR1- 5p microRNAs on angiogenesis, specifically focusing on its initial stages: vascular cell migration and the formation of capillary-like structures. Recently we discovered Plaur-miR1-5p, which is encoded within the urokinase receptor gene (Plaur). However, the functions of this microRNA remain largely unexplored. Using a vascular ring model embedded in Matrigel, we demonstrate that Plaur-miR1-5p is encapsulated within extracellular vesicles and plays a regulatory role in capillary-like structure formation. Moreover, applying bioinformatic analysis, we have identified potential target genes of Plaur-miR1-5p that participate in the regulation of angiogenesis. This study advances our comprehension of the fundamental processes governing angiogenesis, particularly the involvement of extracellular vesicles and microRNAs. Moreover, it sheds light on the functional aspects ofthe Plaur gene, contributing to a more profound understanding of its role in regulation of angiogenesis.

Recent research indicates that some types of mental illnesses (schizophrenia, autism, depressive disorders) may be associated with impaired functioning of a number of genes, including those involved in brain morphogenesis. To assess the possible contribution of brain morphogenesis genes in the formation of predisposition to depressive disorders in Russian population, we performed whole-exome sequencing of genomic DNA of such patients. We identified 166 missense genomic variants in 66 genes (out of 140 studied) involved in the formation of brain tissue. The prevalence of some of them was estimated by allele-specific PCR. For the first time, a significantly higher frequency of occurrence of genomic variants rs17445840‑T (CDH2 gene), rs12923655‑C (CDH3 gene), rs1227051‑G/A (CDH23 gene), and rs12500437‑G/T (DCHS2 gene) was shown in a group of patients suffering from endogenous depressive disorder, and an association of some of the identified genomic variants with gender was established. The data obtained confirm the previously stated assumption that genes of brain tissue morphogenesis may be associated with a predisposition to the development of mental and cognitive disorders. The functional significance of the identified genetic variants remains to be established. The identification of pathogenic genomic variants with the confirmation of their functional significance allows better understanding of the pathogenesis of mental disorders and opens prospects for the development of approaches to objective diagnosis of such diseases, their early prevention, and pathogenetic therapy.

Pulmonary fibrosis, a debilitating lung disorder characterised by excessive fibrous tissue accumulation in lung parenchyma, compromises respiratory function leading to a life-threatening respiratory failure. While its origins are multifaceted and poorly understood, the urokinase system, including urokinase-type plasminogen activator (uPA) and its receptor (uPAR), plays a significant role in regulating fibrotic response, extracellular matrix remodelling, and tissue repair. Mesenchymal stem/stromal cells (MSCs) hold promise in regenerative medicine for treating pulmonary fibrosis. Our study aimed to investigate the potential of MSCs to inhibit pulmonary fibrosis as well as the contribution of uPAR expression to this effect. We found that intravenous MSC administration significantly reduced lung fibrosis in the bleomycin-induced pulmonary fibrosis model in mice as revealed by MRI and histological evaluations. Notably, administering the MSCs isolated from adipose tissue of uPAR knockout mice (Plaur-/- MSCs) attenuated lung fibrosis to a lesser extent as compared to WT MSCs. Collagen deposition, a hallmark of fibrosis, was markedly reduced in lungs treated with WT MSCs versus Plaur-/- MSCs. Along with that, endogenous uPA levels were affected differently; after Plaur-/- MSCs were administered, the uPA content was specifically decreased within the blood vessels. Our findings support the potential of MSC treatment in attenuating pulmonary fibrosis. We provide evidence that the observed anti-fibrotic effect depends on uPAR expression in MSCs, suggesting that uPAR might counteract the uPA accumulation in lungs.

IntroductionT-cadherin, a non-canonical member of the cadherin superfamily, was initially identified for its involvement in homophilic recognition within the nervous and vascular systems. Apart from its adhesive function, T-cadherin acts as a receptor for two ligands: LDL, contributing to atherogenic processes, and HMW adiponectin, a hormone with well-known cardiovascular protective properties. However, the precise role of T-cadherin in adipose tissue remains elusive. Previously, we generated Cdh13∆Exon3 mice lacking exon 3 in the Cdh13 gene, which encodes the T-cadherin protein, and characterized their phenotype.MethodsUsing wild-type (WT) and T-cadherin-deficient mice (Cdh13ΔExon3), we isolated and cultured mesenchymal stem cells to explore the role of T-cadherin in adipogenic differentiation. The experimental approaches employed include culturing cells under standard or adipogenic conditions, performing Oil Red O and Nile Red staining followed by quantitative analysis, conducting rescue experiments to reintroduce T-cadherin using lentiviral constructs in T-cadherin-deficient cells combined with automated adipocyte differentiation quantification via a neural network. Additionally, Western blotting, ELISA assays, and statistical analysis were utilized to verify the results.ResultsIn this study, we demonstrate for the first time that T-cadherin influences the adipogenic differentiation of MSCs. The presence of T-cadherin dictates distinct morphological characteristics in MSCs. Lack of T-cadherin leads to spontaneous differentiation into adipocytes with the formation of large lipid droplets. T-cadherin-deficient cells (T−/− MSCs) exhibit an enhanced adipogenic potential upon induction with differentiating factors. Western Blot, ELISA assays, and rescue experiments collectively corroborate the conclusion that T−/− MSCs are predisposed toward adipogenic differentiation. We carried out an original comparative analysis to explore the effects of T-cadherin ligands on lipid droplet accumulation. LDL stimulate adipogenic differentiation, while T-cadherin expression mitigates the impact of LDL on lipid droplet accumulation. We also examined the effects of both low molecular weight (LMW) and high molecular weight (HMW) adiponectin on lipid droplet accumulation relative to T-cadherin. LMW adiponectin suppressed lipid droplet accumulation independently of T-cadherin, while the absence of T-cadherin enhanced susceptibility to the suppressive effects of HMW adiponectin on adipogenesis.DiscussionThese findings shed light on the role of T-cadherin in adipogenic differentiation and suggest an interplay with other receptors, such as LDLR and AdipoRs, wherein downstream signaling may be modulated through lateral interactions with T-cadherin.

Traumatic nerve injury is one of the most common cause of permanent disability. The problem of nerve regeneration is based on the slow growth of nerve fibers and short-term production of neutrophic factors (NGF, BDNF, NT-3, GDNF, etc.), which stimulate the survival of damaged neurons and growth of nerve fibers. In most cases, the intrinsic regenerative potential is insufficient to restore innervation, which requires the replacement therapy with neurotrophins. One of the most promising therapeutic approaches for regenerative medicine is gene therapy that allows to prolong the local production of neurotrophic factors. Previously, we created a bicistronic gene therapy construct pNCure (a plasmid for the treatment of nerves), based on the modified pVax1 plasmid construct approved by the FDA (U.S. Food and Drug Administration), and encoding the cDNA sequences of brain-derived neurotrophic factor (BDNF) and urokinase-type plasminogen activator (uPA). It revealed a prominent therapeutic activity in a model of traumatic nerve injury in mice. Gene therapy products is a particular class of drugs that need particular approaches to production, purification and standartization. There is practically no information on the purification and standardization of gene therapy drugs in Russian, and this is the topic of our manuscript. Here, we have elucidat-ed the issues of plasmid production in E. coli cells with subsequent multistage purification, as well as the issues of evaluation the identity and quantity of the plasmid (using PCR and UV spectrometry methods), and determination of pH and quantity of related and secondary impurities within the sub-stance. The results of the study have demonstrated that the proposed approach to plasmid production, purification and standartization allows to obtain the desired high-quality gene therapy drug that meets all the requirements of the XIV State Pharmacopia.

T-cadherin is a regulator of blood vessel remodeling and angiogenesis, involved in adiponectin-mediated protective effects in the cardiovascular system and in skeletal muscles. GWAS study has previously demonstrated a SNP in the Cdh13 gene to be associated with hypertension. However, the role of T-cadherin in regulating blood pressure has not been experimentally elucidated. Herein, we generated Cdh13∆Exon3 mice lacking exon 3 in the Cdh13 gene and described their phenotype. Cdh13∆Exon3 mice exhibited normal gross morphology, life expectancy, and breeding capacity. Meanwhile, their body weight was considerably lower than of WT mice. When running on a treadmill, the time spent running and the distance covered by Cdh13∆Exon3 mice was similar to that of WT. The resting blood pressure in Cdh13∆Exon3 mice was slightly higher than in WT, however, upon intensive physical training their systolic blood pressure was significantly elevated. While adiponectin content in the myocardium of Cdh13∆Exon3 and WT mice was within the same range, adiponectin plasma level was 4.37-fold higher in Cdh13∆Exon3 mice. Moreover, intensive physical training augmented the AMPK phosphorylation in the skeletal muscles and myocardium of Cdh13∆Exon3 mice as compared to WT. Our data highlight a critically important role of T-cadherin in regulation of blood pressure and stamina in mice, and may shed light on the pathogenesis of hypertension.

Pulmonary fibrosis is a common and threatening post-COVID-19 complication with poorly resolved molecular mechanisms and no established treatment. The plasminogen activator system, including urokinase (uPA) and urokinase receptor (uPAR), is involved in the pathogenesis of COVID-19 and contributes to the development of lung injury and post-COVID-19 pulmonary fibrosis, although their cellular and molecular underpinnings still remain obscure. The aim of the current study was to assess the role of uPA and uPAR in the pathogenesis of pulmonary fibrosis. We analyzed uPA and uPAR expression in human lung tissues from COVID-19 patients with pulmonary fibrosis using single-cell RNA-seq and immunohistochemistry. We modeled lung fibrosis in Plau-/- and Plaur-/- mice upon bleomycin instillation and explored the effect of uPAR downregulation in A549 and BEAS-2B lung epithelial cells. We found that uPAR expression drastically decreased in the epithelial airway basal cells and monocyte/macrophage cells, whereas uPA accumulation significantly increased in tissue samples of COVID-19 patients. Lung injury and fibrosis in Plaur-/- vs. WT mice upon bleomycin instillation revealed that uPAR deficiency resulted in pro-fibrogenic uPA accumulation, IL-6 and ACE2 upregulation in lung tissues and was associated with severe fibrosis, weight loss and poor survival. uPAR downregulation in A549 and BEAS-2B was linked to an increased N-cadherin expression, indicating the onset of epithelial–mesenchymal transition and potentially contributing to pulmonary fibrosis. Here for the first time, we demonstrate that plasminogen treatment reversed lung fibrosis in Plaur-/- mice: the intravenous injection of 1 mg of plasminogen on the 21st day of bleomycin-induced fibrosis resulted in a more than a two-fold decrease in the area of lung fibrosis as compared to non-treated mice as evaluated by the 42nd day. The expression and function of the plasminogen activator system are dysregulated upon COVID-19 infection, leading to excessive pulmonary fibrosis and worsening the prognosis. The potential of plasminogen as a life-saving treatment for non-resolving post-COVID-19 pulmonary fibrosis warrants further investigation.

uPAR is a membrane receptor that binds extracellular protease urokinase, contributes to matrix remodeling and plays a crucial role in cellular adhesion, proliferation, survival, and migration. uPAR overexpression in tumor cells promotes mitogenesis, opening a prospective avenue for targeted therapy. However, uPAR targeting in cancer has potential risks. We have recently shown that uPAR downregulation in neuroblastoma promotes epithelial-mesenchymal transition (EMT), potentially associated with metastasis and chemoresistance. We used data mining to evaluate the role of uPAR expression in primary and relapsed human neuroblastomas. To model the decreased uPAR expression, we targeted uPAR using CRISPR/Cas9 and shRNA in neuroblastoma Neuro2a cells and evaluated their chemosensitivity in vitro as well as tumor growth and metastasis in vivo. We demonstrate that the initially high PLAUR expression predicts poor survival in human neuroblastoma. However, relapsed neuroblastomas have a significantly decreased PLAUR expression. uPAR targeting in neuroblastoma Neuro2a cells leads to p38 activation and an increased p21 expression (suggesting a dormant phenotype). The dormancy in neuroblastoma cells can be triggered by the disruption of uPAR-integrin interaction. uPAR-deficient cells are less sensitive to cisplatin and doxorubicin treatment and exhibit lower p53 activation. Finally, low uPAR-expressing Neuro2a cells formed smaller primary tumors, but more frequent metastasis in mice. To the best of our knowledge, this is the first study revealing the pathological role of dormant uPAR-deficient cancer cells having a chemoresistant and motile phenotype.

Urokinase receptor (uPAR) is a glycosylphosphatidylinositol (GPI)-anchored receptor of urokinase (uPA), which is involved in brain development, nerve regeneration, wound healing and tissue remodeling. We have recently shown that Plaur, which encodes uPAR, is an early response gene in murine brain. Assumingly, diverse functions of Plaur might be attributed to hypothetical, unidentified microRNAs encoded within introns of the Plaur gene. Using a bioinformatic approach we identified novel small RNAs within the Plaur gene and named them Plaur-miR1-3p and Plaur-miR1-5p. We confirmed Plaur-dependent expression of Plaur-miR1-3p and Plaur-miR1-5p in the mouse brain and mouse neuroblastoma Neuro2a cells. Utilizing an in silico MR-microT algorithm in DianaTools we selected two target genes - Mef2d and Emx2 with the highest binding scores to small RNAs selected from identified Plaur-Pre-miR1. Furthermore, sequencing of mouse brain samples for Plaur-miR1-5p target genes revealed two more genes-Nrip3 and Snrnp200. The expression of Emx2, Mef2d, and Snrnp200 in the mouse brain and Mef2d and Snrnp200 in Neuro2a cells correlated with expression of Plaur and small RNAs-Plaur-miR1-3p and Plaur-miR1-5p. Finally, we demonstrated elevated MEF2D protein expression in the mouse brain after Plaur induction and displayed activating effects of Plaur-miR1-5p on Mef2d expression in Neuro2a cells using Luciferase reporter assay. In conclusion, we have identified Plaur-miR1-3p and Plaur-miR1-5p as novel small RNAs encoded in the Plaur gene. This finding expands the current understanding of Plaur function in brain development and functioning.

Background. Lack of universal diagnostic parameters that can accurately and reliably diagnose presence of a malignant neoplasm, anticancer drug effectiveness or metastasis development including dormant ones and also to detect the progression or relapse of the disease at an early stage put on the first place studies related to the identification of such markers. Increased secretion and activity of the urokinase type plasminogen activator (uPA), its receptor (uPAR) accompany many types of malignant neoplasms, contributing their progression and metastasis, as well as the emergence of chemoresistance. So today these proteins are promising diagnostic targets in oncology. Aim. To evaluate the diagnostic significance of the expression levels of uPA and uPAR in blood serum of patients with colorectal and gastric adenocarcinoma and uPA/uPAR distribution in samples obtained from the primary tumor node, to assess the possibility of their use as universal diagnostic indicators in cancer patients at the stage of primary treatment. Materials and methods. The study included patients with colorectal and gastric adenocarcinoma in the amount of 50 people and 25 healthy volunteers. The content of uPA and uPAR in blood serum was assessed by enzyme-linked immunosorbent assay, the level of expression of the studied proteins in tumor tissue was assessed using immunohistochemical staining with antibodies to uPA and uPAR. Results. It was found that in comparison with healthy donors uPA serum concentration was significantly higher in all patients with adenocarcinoma, regardless of gender, and the uPAR content in the blood serum was significantly higher in women. Immunohistochemical staining data showed that the expression of these two proteins in tumor tissue significantly exceeds their expression in normal tissue. Conclusion. Based on the obtained data the possibility of using uPA in blood serum as a universal diagnostic criterion in patients with colorectal and gastric adenocarcinoma regardless of gender was shown and uPAR in female patients.

Gene therapy is one of the promising approaches for regenerative medicine. Local and long-term expression of essential growth factors allows to achieve the desired therapeutic effect. However, some aspects of prolonged usage of genetic constructs encoding growth factors, such as toxicity, mutagenicity, genotoxicity, and ability to disseminate from the injection site and mediate ectopic expression of therapeutic proteins, are poorly investigated. These aspects of gene therapy drugs' usage became the subject of this study. To study plasmid biodistribution, toxicity, mutagenicity, and genotoxicity, we used previously described bicistronic genetic construct encoding human brain-derived neurotrophic factor (hBDNF) and human urokinase plasminogen activator (huPA) for nerve repair. Biodistribution studies were conducted in mice: a course of intramuscular plasmid injections was followed by the study of the content of the plasmid (real-time polymerase chain reaction) and recombinant proteins (enzyme-linked immunosorbent assay) in murine organs and tissues. The study of the plasmid chronic toxicity was carried out on rats with registration of their weight dynamics, neurological status, emotional state, and blood test parameters. The mutagenicity of the plasmid was studied in an in vivo DNA comet test in mice. Plasmid genotoxicity was investigated in the model of somatic recombination in Drosophila females. We have shown that plasmids can disseminate from the injection site, but do not mediate ectopic expression of growth factors upon repeated intramuscular injections. The studied plasmid also does not reveal toxic, mutagenic, or genotoxic effects. During the toxicological study on rats, we have shown that daily injections of this genetic construct, despite its ability to disseminate from the injection site, do not affect the physical, cognitive, and emotional state of experimental animals. We have demonstrated the safety of the bicistronic plasmid, encoding hBDNF and huPA, upon its repeated administration. The properties of genetic constructs strongly depend on their sequence and delivery approach, which requires conducting of their safety studies in each specific case. Impact statement Gene therapy is one of the promising approaches for regenerative medicine. Local and long-term expression of essential growth factors allows to achieve the desired therapeutic effect. However, some aspects of prolonged usage of genetic constructs encoding growth factors, such as toxicity, mutagenicity, genotoxicity, and ability to disseminate from the injection site and mediate ectopic expression of therapeutic proteins, are poorly investigated. These aspects of gene therapy became the subject of this study. To our knowledge, this is a unique study that provides a thorough safety investigation of a bicistronic plasmid after its readministration.

Topical advances in studying molecular and cellular mechanisms responsible for regeneration in the peripheral nervous system have highlighted the ability of the nervous system to repair itself. Still, serious injuries represent a challenge for the morphological and functional regeneration of peripheral nerves, calling for new treatment strategies that maximize nerve regeneration and recovery. This review presents the canonical view of the basic mechanisms of nerve regeneration and novel data on the role of exosomes and their transferred microRNAs in intracellular communication, regulation of axonal growth, Schwann cell migration and proliferation, and stromal cell functioning. An integrated comprehensive understanding of the current mechanistic underpinnings will open the venue for developing new clinical strategies to ensure full regeneration in the peripheral nervous system.

Neurotrophic factors play a key role in the development, differentiation, and survival of neurons and nerve regeneration. In the present study, we evaluated the effect of certain neurotrophic factors (NGF, BDNF, and GDNF) on axon growth and migration of Nestin-green fluorescent protein (GFP)-positive cells using a 3D model of dorsal root ganglion (DRG) explant culture in Matrigel. Our method generally represents a convenient model for assessing the effects of soluble factors and therapeutic agents on axon growth and nerve regeneration in R&D studies. By analyzing the DRG explants in ex vivo culture for 21 days, one can evaluate the parameters of neurite outgrowth and the rate of cell migration from the DRG explants into the Matrigel. For the current study, we used Nestin-GFP-expressing mice in which neural precursors express Nestin and the green fluorescent protein (GFP) under the same promoter. We revealed that GDNF significantly (two fold) stimulated axon outgrowth (p < 0.05), but not BDNF or NGF. It is well-known that axon growth can be stimulated by activated glial cells that fulfill a trophic function for regenerating nerves. For this reason, we evaluated the number of Nestin-GFP-positive cells that migrated from the DRG into the Matrigel in our 3D ex vivo explant model. We found that NGF and GDNF, but not BDNF, stimulated the migration of Nestin-GFP cells compared to the control (p < 0.05). On the basis of the aforementioned finding, we concluded that GDNF had the greatest stimulating potential for axon regeneration, as it stimulated not only the axon outgrowth, but also glial cell migration. Although NGF significantly stimulated glial cell migration, its effect on axon growth was insufficient for axon regeneration.

The urokinase system is involved in a variety of physiological processes, such as fibrinolysis, matrix remodeling, wound healing, and regeneration. Upon binding to its cognate receptor urokinase‐type plasminogen activator receptor (uPAR), urokinase‐type plasminogen activator (uPA) catalyzes the conversion of plasminogen to plasmin and the activation of matrix metalloproteases. Apart from this, uPA–uPAR interaction can lead to the activation of transcription factors, mitogen‐activated protein kinase signaling pathways and RTK cascades. Elevated expression of uPA and uPAR is markedly associated with cancer progression and metastasis and correlates with a poor prognosis in clinics. Targeting the urokinase system has proved to be effective in experimental models in vitro and in vivo, however, in clinics the inhibition of the uPA/uPAR system has fallen short of expectations, suggesting that the question of the functional relevance of uPA/uPAR system is far from being moot. Recently, using CRISPR/Cas9 technology, we have shown that uPAR knockout decreases the proliferation of neuroblastoma Neuro2a cells in vitro. In the present study we demonstrate that uPAR expression is essential for maintaining the epithelial phenotype in Neuro2a cells and that uPAR silencing promotes epithelial‐mesenchymal transition (EMT) and increased cell migration. Accordingly, uPAR knockout results in the downregulation of epithelial markers (E‐cadherin, occludin, and claudin‐5) and in the increase of mesenchymal markers (N‐cadherin, α‐smooth muscle actin, and interleukin‐6). In search of the molecular mechanism underlying these changes, we identified uPA as a key component. Two key insights emerged as a result of this work: in the absence of uPAR, uPA is translocated into the nucleus where it is presumably involved in the activation of transcription factors (nuclear factor κB and Snail) resulting in EMT. In uPAR‐expressing cells, uPAR functions as a uPA “trap” that binds uPA on the cell surface and promotes controlled uPA internalization and degradation in lysosomes.

PURPOSE:Urokinase receptor (uPAR) promotes extracellular matrix proteolysis, regulates adhesion and cell migration, transduces intracellular signals through interactions with the lateral partners. The expression of uPAR and urokinase (uPA) is significantly upregulated in peripheral nerves after injury, however, little is known about uPAR function in nerve regeneration or the molecular mechanisms involved. The purpose of this study is to investigate the role of uPAR in nerve regeneration after traumatic injury of n. Peroneus communis in uPA-/-, uPAR-/- or control mice (WT) and in neuritogenesis in an in vitro Neuro 2A cell model.RESULTS:Electrophysiological analysis indicates that nerve recovery is significantly impaired in uPAR-/- mice, but not in uPA-/- mice. These data correlate with the reduced amount of NF200-positive axons in regenerating nerves from uPAR-/- mice compared to uPA-/- or control mice. There is an increase in uPAR expression and remarkable colocalization of uPAR with α5 and β1 integrin in uPA-/- mice in recovering nerves, pointing to a potential link between uPAR and its lateral partner α5β1-integrin. Using an in vitro model of neuritogenesis and α325 blocking peptide, which abrogates uPAR-α5β1 interaction in Neuro 2A cells but has no effect on their function, we have further confirmed the significance of uPAR-α5β1 interaction.CONCLUSION:Taken together, we report evidence pointing to an important role of uPAR, rather than uPA, in peripheral nerve recovery and neuritogenesis.