Valproic Acid Induces Endothelial-to-Mesenchymal Transition-Like Phenotypic Switching

Protein Disulfide Isomerase 4 Is an Essential Regulator of Endothelial Function and Survival

Endothelial autophagy plays an important role in the regulation of endothelial function. The inhibition of endothelial autophagy is associated with the reduced expression of protein disulfide isomerase 4 (PDIA-4); however, its role in endothelial cells is not known. Here, we report that endothelial cell-specific loss of PDIA-4 leads to impaired autophagic flux accompanied by loss of endothelial function and apoptosis. Endothelial cell-specific loss of PDIA-4 also induced marked changes in endothelial cell architecture, accompanied by the loss of endothelial markers and the gain of mesenchymal markers consistent with endothelial-to-mesenchymal transition (EndMT). The loss of PDIA-4 activated TGFβ-signaling, and inhibition of TGFβ-signaling suppressed EndMT in PDIA-4-silenced endothelial cells in vitro. Our findings help elucidate the role of PDIA-4 in endothelial autophagy and endothelial function and provide a potential target to modulate endothelial function and/or limit autophagy and EndMT in (patho-)physiological conditions.

SUMOylation of Smad2 mediates TGF-β-regulated endothelial-mesenchymal transition

Endothelial-mesenchymal transition (EndoMT) is a complex biological process in which endothelial cells are transformed into mesenchymal cells, and dysregulated EndoMT causes a variety of pathological processes. Transforming growth factor beta (TGF-β) signaling effectively induces the EndoMT process in endothelial cells, and Smad2 is the critical protein of the TGF-β signaling pathway. However, whether small ubiquitin-like modifier modification (SUMOylation) is involved in EndoMT remains unclear. Here, we show that Smad2 is predominantly modified by SUMO1 at two major SUMOylation sites with PIAS2α as the primary E3 ligase, whereas SENP1 (sentrin/SUMO-specific protease 1) mediates the deSUMOylation of Smad2. In addition, we identified that SUMOylation significantly enhances the transcriptional activity and protein stability of Smad2, regulating the expression of downstream target genes. SUMOylation increases the phosphorylation of Smad2 and the formation of the Smad2-Smad4 complex, thus promoting the nuclear translocation of Smad2. Ultimately, the wildtype, but not SUMOylation site mutant Smad2 facilitated the EndoMT process. More importantly, TGF-β enhances the nuclear translocation of Smad2 by enhancing its SUMOylation and promoting the EndoMT process. These results demonstrate that SUMOylation of Smad2 plays a critical role in the TGF-β-mediated EndoMT process, providing a new theoretical basis for the treatment and potential drug targets of EndoMT-related clinical diseases.

Roles of TGF-β signals in tumor microenvironment via regulation of the formation and plasticity of vascular system

Tumor cells evolve in tumor microenvironment composed of multiple cell types. Among these, endothelial cells (ECs) are the major players in tumor angiogenesis, which is a driver of tumor progression and metastasis. Increasing evidence suggests that ECs also contribute to tumor progression and metastasis as they modify their phenotypes to differentiate into mesenchymal cells through a process known as endothelial-mesenchymal transition (EndoMT). This plasticity of ECs is mediated by various cytokines, including transforming growth factor-β (TGF-β), and modulated by other stimuli depending on the cellular contexts. Recent lines of evidence have shown that EndoMT is involved in various steps of tumor progression, including tumor angiogenesis, intravasation and extravasation of cancer cells, formation of cancer-associated fibroblasts, and cancer therapy resistance. In this review, we summarize current updates on EndoMT, highlight the roles of EndoMT in tumor progression and metastasis, and underline targeting EndoMT as a potential therapeutic strategy.

Loss of fatty acid binding protein 3 ameliorates lipopolysaccharide-induced inflammation and endothelial dysfunction

Circulating fatty acid-binding protein 3 (FABP3) is an effective biomarker of myocardial injury and peripheral artery disease (PAD). The endothelium, which forms the inner most layer of every blood vessel, is exposed to higher levels of FABP3 in PAD or following myocardial injury, but the pathophysiological role of endothelial FABP3, the effect of FABP3 exposure on endothelial cells, and related mechanisms are unknown. Here, we aimed to evaluate the pathophysiological role of endothelial FABP3 and related mechanisms in vitro. Our molecular and functional in vitro analyses show that (1) FABP3 is basally expressed in endothelial cells; (2) inflammatory stress in the form of lipopolysaccharide (LPS) upregulated endothelial FABP3 expression; (3) loss of endogenous FABP3 protected endothelial cells against LPS-induced endothelial dysfunction; however, exogenous FABP3 exposure exacerbated LPS-induced inflammation; (4) loss of endogenous FABP3 protected against LPS-induced endothelial dysfunction by promoting cell survival and anti-inflammatory and pro-angiogenic signaling pathways. Together, these findings suggest that gain-of endothelial FABP3 exacerbates, whereas loss-of endothelial FABP3 inhibits LPS-induced endothelial dysfunction by promoting cell survival and anti-inflammatory and pro-angiogenic signaling. We propose that an increased circulating FABP3 in myocardial injury or PAD patients may be detrimental to endothelial function, and therefore, therapies aimed at inhibiting FABP3 may improve endothelial function in diseased states.

Tumors derived from lung cancer cells respond differently to treatment with sodium valproate (a HDAC inhibitor) in a chicken embryo chorioallantoic membrane model

Lung cancer is the most frequent cause of cancer death. Some human lung malignant tumors have a combined small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC) histology, with tumor cell phenotype changing during tumor progression. Valproic acid is used as an anti-seizure medication to treat migraine, and bipolar mood disorders. Recently, its efficacy as an adjuvant therapy was shown in cancer due to its histone deacetylase (HDAC) inhibitory property. HDACs are upregulated in lung tumors, and HDAC inhibitors, including valproic acid, inhibit endothelial cell proliferation in vitro and in vivo and have antiproliferative and antimigratory properties. We tested valproic acid for possible antiangiogenic and antimigratory effects on experimental lung tumors grafted onto the chicken embryo chorioallantoic membrane (CAM). Tumors were formed from two NSCLC cell lines and a single SCLC cell line. To investigate tumor and CAM interactions, in vivo biomicroscopy, visualization of blood vessels with injected fluorescent dextran, histological, immunohistochemical and histomorphometric methods were applied. Our results showed that a sodium valproate (NaVP) treatment-induced a dose-dependent decrease of experimental tumor invasion into the CAM mesenchyme and a reduction in angiogenesis. Both the invasion and the angiogenic response were dependent on the type of cell line used: invasion and angiogenesis of tumors derived from A549 and NCI-H146 cell lines responded to increasing doses of NaVP from 4 to 8 mM, whereas Sk_Lu_1 cells response were antimigratory and antiangiogenic when NaVP was used up to 6 mM. When 8mM NaVP was used, stimulated invasion and angiogenesis in tumors from Sk_Lu_1 cells were observed.

[Valproic Acid Could Help in the Fight Against COVID-19: a case-control study]

OBJECTIVE

There is early evidence about Valproic acid (VPA) antiviral effect. Our aim was to investigate the incidence and severity of SARS-CoV-2 infection in VPA users as compared with the general population.

MATERIAL AND METHODS

A case-control study nested within a cohort, carried out between March 1 and December 17, 2020. Retrospectively, we identified confirmed SARS-CoV-2 infection patients exposed to VPA in our health department (defined as case). We ascertained VPA regimen (all the time (AT)(292 days) or at least 20% of the study period (notAT)(≥58 days) and if VPA levels were in therapeutic range (ATR) (50-100 mcg/mL) in the last 24 months. We calculated the cumulative incidence of SARS-CoV-2 infection and hospital admission in the cases, comparing it with the general unexposed VPA population (controls).

RESULTS

During the study period, 6183 PCR+ were detected among 281035 inhabitants, of these, 746 were hospitalized. 691 patients were on VPA notAT and 628 (90.1%) AT. The indication for VPA use was epilepsy in 54.9%. The incidence of PCR+ was 1.736 % (OR 0.785 (95%CI 0.443-1.390) and 1.910 % (OR 0.865 (95%CI 0.488-1.533), on VPA notAT and VPA AT patients, respectively vs. 2.201% in people without VPA regimen. Those patients with VPA ATR had a lower risk of PCR + (OR 0.233 (95%CI 0.057-0.951) notAT; OR 0.218 (95%CI 0.053-0.890) AT). Hospital admission incidence was lower in patient on VPA (OR was 0.543 (95% CI 0.076 to 3.871).

CONCLUSION

Patients with VPA within the therapeutic range had a reduction of SARS-Cov-2 infection incidence greater than 75%. There is a downward trend in the risk of COVID-19 admission by SARS-CoV-2 in patients on VPA therapy. These findings warrant further investigation.

Epigenetic Regulation of Angiogenesis in Development and Tumors Progression: Potential Implications for Cancer Treatment

Angiogenesis is a multi-stage process of new blood vessel development from pre-existing vessels toward an angiogenic stimulus. The process is essential for tissue maintenance and homeostasis during embryonic development and adult life as well as tumor growth. Under normal conditions, angiogenesis is involved in physiological processes, such as wound healing, cyclic regeneration of the endometrium, placental development and repairing certain cardiac damage, in pathological conditions, it is frequently associated with cancer development and metastasis. The control mechanisms of angiogenesis in carcinogenesis are tightly regulated at the genetic and epigenetic level. While genetic alterations are the critical part of gene silencing in cancer cells, epigenetic dysregulation can lead to repression of tumor suppressor genes or oncogene activation, becoming an important event in early development and the late stages of tumor development, as well. The global alteration of the epigenetic spectrum, which includes DNA methylation, histone modification, chromatin remodeling, microRNAs, and other chromatin components, is considered one of the hallmarks of cancer, and the efforts are concentrated on the discovery of molecular epigenetic markers that identify cancerous precursor lesions or early stage cancer. This review aims to highlight recent findings on the genetic and epigenetic changes that can occur in physiological and pathological angiogenesis and analyze current knowledge on how deregulation of epigenetic modifiers contributes to tumorigenesis and tumor maintenance. Also, we will evaluate the clinical relevance of epigenetic markers of angiogenesis and the potential use of "epi-drugs" in modulating the responsiveness of cancer cells to anticancer therapy through chemotherapy, radiotherapy, immunotherapy and hormone therapy as anti-angiogenic strategies in cancer.

Valproic Acid Decreases Endothelial Colony Forming Cells Differentiation and Induces Endothelial-to-Mesenchymal Transition-like Process

Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor is a widely used anticonvulsant drug. VPA is also under clinical evaluation to be employed in anticancer therapy, as an antithrombotic agent or a molecule to be used in the stem cells expansion protocols. Since endothelial colony forming cells (ECFC) has been identified as the human postnatal vasculogenic cells involved in thrombotic disorders and serve as a promising source of immature cell for vascular repair, objectives of the present study were to determine how VPA contributes to ECFC commitment and their angiogenic properties. We examined the effect of VPA on ECFC obtained from cord blood by evaluating colony number, proliferation, migration and their sprouting ability in vitro, as well as their in vivo vasculogenic properties. VPA inhibited endothelial differentiation potential from of cord blood derived stem cells associated with decreased proliferation and sprouting activity of cultured ECFC. VPA treatment significantly decreased the vessel-forming ability of ECFC transplanted together with mesenchymal stem cells (MSC) in Matrigel implants in nude mice model. Surprisingly, a microscopic evaluation revealed that VPA induces marked morphological changes from a cobblestone-like EC morphology to enlarged spindle shaped morphology of ECFC. RT-qPCR and a CD31/CD90 flow cytometry analysis confirmed a phenotypic switch of VPA-treated ECFC to mesenchymal-like phenotype. In conclusion, the pan-HDAC inhibitor VPA described for expansion of hematopoietic stem cells and very small embryonic like stem cells cannot be successfully employed for differentiation of endothelial lineage committed ECFC into functional endothelial cells. Our data also suggest that VPA based therapeutics may induce endothelial dysfunction associated with fibrosis that might induce thrombosis recurrence or venous insufficiency.

The Role of Histone Protein Acetylation in Regulating Endothelial Function

Endothelial cell (EC), consisting of the innermost cellular layer of all types of vessels, is not only a barrier composer but also performing multiple functions in physiological processes. It actively controls the vascular tone and the extravasation of water, solutes, and macromolecules; modulates circulating immune cells as well as platelet and leukocyte recruitment/adhesion and activation. In addition, EC also tightly keeps coagulation/fibrinolysis balance and plays a major role in angiogenesis. Therefore, endothelial dysfunction contributes to the pathogenesis of many diseases. Growing pieces of evidence suggest that histone protein acetylation, an epigenetic mark, is altered in ECs under different conditions, and the acetylation status change at different lysine sites on histone protein plays a key role in endothelial dysfunction and involved in hyperglycemia, hypertension, inflammatory disease, cancer and so on. In this review, we highlight the importance of histone acetylation in regulating endothelial functions and discuss the roles of histone acetylation across the transcriptional unit of protein-coding genes in ECs under different disease-related pathophysiological processes. Since histone acetylation changes are conserved and reversible, the knowledge of histone acetylation in endothelial function regulation could provide insights to develop epigenetic interventions in preventing or treating endothelial dysfunction-related diseases.

Pravastatin-induced changes in expression of long non-coding and coding RNAs in endothelial cells

OBJECTIVE

Atherosclerosis is the main cause of the cardiovascular disease (CVD). Elevated blood cholesterol and inflammation of the endothelium are two major mechanisms contributing to the establishment of atherosclerotic plaques. Statins, such as pravastatin, are blood-cholesterol lowering drugs commonly prescribed for patients with or at risk for CVDs. In addition to lowering blood cholesterols, statins have recently been shown to improve endothelial function in both hyper- and normocholesterolemic patients with atherosclerosis. To understand the molecular mechanisms underlying the endothelial function improvement by statins, we assessed the RNA profile of pravastatin-treated endothelial cells, particularly their mRNAs and long non-coding RNAs (lncRNAs).

METHODS

Human umbilical vein endothelial cells (HUVECs) treated with pravastatin (10 µM) for 24 hr were profiled for lncRNAs and mRNAs using the Arraystar Human lncRNA Expression Microarray V3.0.

RESULTS

Of the 30,584 different lncRNAs screened, 95 were significantly upregulated, while 86 were downregulated in HUVECs responding to pravastatin. LINC00281 and BC045663 were the most upregulated (~8-fold) and downregulated (~3.5-fold) lncRNAs, respectively. Of the 26,106 different mRNAs screened in the pravastatin-treated HUVEC samples, 190 were significantly upregulated, while 90 were downregulated. Assigning the differentially expressed genes by bioinformatics into functional groups revealed their molecular signaling involvement in the following physiological processes: osteoclast differentiation, Rap1 signaling pathway, hematopoiesis, immunity, and neurotrophin signaling pathway.

CONCLUSIONS

This is the first lncRNA and mRNA expression profiling of pravastatin-mediated changes in human endothelial cells. Our results reveal potential novel targets and mechanisms for pravastatin-mediated vascular protection in atherosclerosis.

Endothelial dysfunction in neuroprogressive disorders-causes and suggested treatments

BACKGROUND

Potential routes whereby systemic inflammation, oxidative stress and mitochondrial dysfunction may drive the development of endothelial dysfunction and atherosclerosis, even in an environment of low cholesterol, are examined.

MAIN TEXT

Key molecular players involved in the regulation of endothelial cell function are described, including PECAM-1, VE-cadherin, VEGFRs, SFK, Rho GEF TRIO, RAC-1, ITAM, SHP-2, MAPK/ERK, STAT-3, NF-κB, PI3K/AKT, eNOS, nitric oxide, miRNAs, KLF-4 and KLF-2. The key roles of platelet activation, xanthene oxidase and myeloperoxidase in the genesis of endothelial cell dysfunction and activation are detailed. The following roles of circulating reactive oxygen species (ROS), reactive nitrogen species and pro-inflammatory cytokines in the development of endothelial cell dysfunction are then described: paracrine signalling by circulating hydrogen peroxide, inhibition of eNOS and increased levels of mitochondrial ROS, including compromised mitochondrial dynamics, loss of calcium ion homeostasis and inactivation of SIRT-1-mediated signalling pathways. Next, loss of cellular redox homeostasis is considered, including further aspects of the roles of hydrogen peroxide signalling, the pathological consequences of elevated NF-κB, compromised S-nitrosylation and the development of hypernitrosylation and increased transcription of atherogenic miRNAs. These molecular aspects are then applied to neuroprogressive disorders by considering the following potential generators of endothelial dysfunction and activation in major depressive disorder, bipolar disorder and schizophrenia: NF-κB; platelet activation; atherogenic miRs; myeloperoxidase; xanthene oxidase and uric acid; and inflammation, oxidative stress, nitrosative stress and mitochondrial dysfunction.

CONCLUSIONS

Finally, on the basis of the above molecular mechanisms, details are given of potential treatment options for mitigating endothelial cell dysfunction and activation in neuroprogressive disorders.

Endothelial-to-Mesenchymal Transition in Cancer

Cancer is one of the most important causes of morbidity and mortality worldwide. Tumor cells grow in a complex microenvironment constituted of immune, stromal, and vascular cells that supports growth, angiogenesis, and metastasis. Endothelial cells (ECs) are major components of the vascular microenvironment. These cells have been described for their plasticity and potential to transdifferentiate into mesenchymal cells through a process known as endothelial-to-mesenchymal transition (EndMT). This complex process is controlled by various factors, by which ECs convert into a phenotype characterized by mesenchymal protein expression and motile, contractile morphology. Initially described in normal heart development, EndMT is now identified in several pathologies, and especially in cancer. In this review, we highlight the process of EndMT in the context of cancer and we discuss it as an important adaptive process of the tumor microenvironment that favors tumor growth and dissemination but also resistance to treatment. Thus, we underline targeting of EndMT as a potential therapeutic strategy.

BReast CAncer susceptibility gene 2 deficiency exacerbates oxidized LDL-induced DNA damage and endothelial apoptosis

Mutations in the tumor suppressor gene BRCA2 (BReast CAncer susceptibility gene 2) predispose carriers to breast, ovarian, and other cancers. In response to DNA damage, BRCA2 participates in homology-directed DNA damage repair to maintain genome stability. Genome-wide association studies have identified an association between BRCA2 single nucleotide polymorphisms and plasma-lipid levels and lipid deregulation in humans. To date, DNA damage, apoptosis, and lipid deregulation are recognized as central pathways for endothelial dysfunction and atherosclerosis; however, the role of BRCA2 in endothelial dysfunction remains to be elucidated. To determine the role of BRCA2 in endothelial dysfunction, BRCA2 was silenced in human umbilical vein endothelial cells (ECs) and assessed for markers of DNA damage, apoptosis, and endothelial function following oxidized low-density lipoprotein (oxLDL) treatment. OxLDL was found to induce significant reactive oxygen species (ROS) production in BRCA2-silenced ECs. This increase in ROS production was associated with exacerbated DNA damage evidenced by increased expression and activation of DNA double-stranded break (DSB) marker γH2AX and reduced RAD51-foci formation-an essential regulator of DSB repair. Increased DSBs were associated with enhanced expression and activation of pro-apoptotic p53 and significant apoptosis in oxLDL-treated BRCA2-silenced ECs. Loss of BRCA2 in ECs was further associated with oxLDL-induced impaired tube-forming potential and eNOS expression. Collectively, the data reveals, for the first time, a novel role of BRCA2 as a regulator of EC survival and function in the setting of oxLDL treatment in vitro. Additionally, the data provide important clues regarding the potential susceptibility of BRCA2 mutation carriers to endothelial dysfunction, atherosclerosis, and other cardiovascular diseases.

Anti-epileptic activity, toxicity and teratogenicity in CD1 mice of a novel valproic acid arylamide derivative, N-(2-hydroxyphenyl)-2-propylpentanamide

N-(2-hydroxyphenyl)-2-propylpentamide (HO-AAVPA) is a novel arylamide derivative of valproic acid (VPA) designed in silico, with better antioxidant and antiproliferative effect on cancer cell lines than VPA. This study was aimed to evaluate the anticonvulsant activity, the toxicity and teratogenicity produced in HO-AAVPA-treated CD1 mice using VPA as positive control. With the maximal electroshock (MES)- and pentylenetetrazole (PTZ)-induced seizure models, HO-AAVPA reduced the time of hind limb extension, stupor and recovery, the number of clonic and tonic seizures and the mortality rate in a dose-dependent manner, obtaining an ED₅₀ of 370 and 348 mg/kg for MES and PTZ, respectively. On the rotarod test, mice administered with 600 mg/kg HO-AAVPA manifested reduced locomotor activity (2.78%); while HO-AAVPA at 300 mg/kg and VPA at 500 mg/kg gave a similar outcome (∼60%). The LD₅₀ of 936.80 mg/kg herein found for HO-AAVPA reflects moderate toxicity. Concerning teratogenicity, the administration of HO-AAVPA to pregnant females at 300 and 600 mg/kg on gestation day (GD) 8.5 generated less visceral and skeletal alterations in the fetuses, as well as, minor rate of modifications in the expression pattern of the neuronal marker Tuj1 and endothelial marker PECAM1 in embryos, that those induced by VPA administration. Altered embryonic development occurred with less frequency and severity with HO-AAVPA at 600 mg/kg than VPA at 500 mg/kg. In conclusion, the protective effect against convulsions provided by HO-AAVPA was comparable to that of VPA in the MES and PZT seizure models, showed lower toxicity and less damage to embryonic and fetal development.

Endothelial-specific Loss of IFT88 Promotes Endothelial-to-Mesenchymal Transition and Exacerbates Bleomycin-induced Pulmonary Fibrosis

Intraflagellar transport protein 88 (Ift88) is required for ciliogenesis and shear stress-induced dissolution of cilia in embryonic endothelial cells coincides with endothelial-to-mesenchymal transition (EndMT) in the developing heart. EndMT is also suggested to underlie heart and lung fibrosis, however, the mechanism linking endothelial Ift88, its effect on EndMT and organ fibrosis remains mainly unexplored. We silenced Ift88 in endothelial cells (ECs) in vitro and generated endothelial cell-specific Ift88-knockout mice (Ift88^endo) in vivo to evaluate EndMT and its contribution towards organ fibrosis, respectively. Ift88-silencing in ECs led to mesenchymal cells-like changes in endothelial cells. The expression level of the endothelial markers (CD31, Tie-2 and VE-cadherin) were significantly reduced with a concomitant increase in the expression level of mesenchymal markers (αSMA, N-Cadherin and FSP-1) in Ift88-silenced ECs. Increased EndMT was associated with increased expression of profibrotic Collagen I expression and increased proliferation in Ift88-silenced ECs. Loss of Ift88 in ECs was further associated with increased expression of Sonic Hedgehog signaling effectors. In vivo, endothelial cells isolated from the heart and lung of Ift88^endo mice demonstrated loss of Ift88 expression in the endothelium. The Ift88^endo mice were born in expected Mendelian ratios without any adverse cardiac phenotypes at baseline. Cardiac and pulmonary endothelial cells isolated from the Ift88^endo mice demonstrated signs of EndMT and bleomycin treatment exacerbated pulmonary fibrosis in Ift88^endo mice. Pressure overload stress in the form of aortic banding did not reveal a significant difference in cardiac fibrosis between Ift88^endo mice and control mice. Our findings demonstrate a novel association between endothelial cilia with EndMT and cell proliferation and also show that loss of endothelial cilia-associated increase in EndMT contributes specifically towards pulmonary fibrosis.

Endothelial-to-Mesenchymal Transition (EndoMT): Roles in Tumorigenesis, Metastatic Extravasation and Therapy Resistance

Cancer cells evolve in a very complex tumor microenvironment, composed of several cell types, among which the endothelial cells are the major actors of the tumor angiogenesis. Today, these cells are also characterized for their plasticity, as endothelial cells have demonstrated their potential to modify their phenotype to differentiate into mesenchymal cells through the endothelial-to-mesenchymal transition (EndoMT). This cellular plasticity is mediated by various stimuli including transforming growth factor-β (TGF-β) and is modulated dependently of experimental conditions. Recently, emerging evidences have shown that EndoMT is involved in the development and dissemination of cancer and also in cancer cell to escape from therapeutic treatment. In this review, we summarize current updates on EndoMT and its main induction pathways. In addition, we discuss the role of EndoMT in tumorigenesis, metastasis, and its potential implication in cancer therapy resistance.

Strain-dependent effects on lung structure, matrix remodeling, and Stat3/Smad2 signaling in C57BL/6N and C57BL/6J mice after neonatal hyperoxia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of preterm infants, characterized by lung growth arrest and matrix remodeling. Various animal models provide mechanistic insights in the pathogenesis of BPD. Since there is increasing evidence that genetic susceptibility modifies the response to lung injury, we investigated strain-dependent effects in hyperoxia (HYX)-induced lung injury of newborn mice. To this end, we exposed newborn C57BL/6N and C57BL/6J mice to 85% O₂ (HYX) or normoxia (NOX; 21% O₂) for 28 days, followed by lung excision for histological and molecular measurements. BL/6J-NOX mice exhibited a lower body and lung weight than BL/6N-NOX mice; hyperoxia reduced body weight in both strains and increased lung weight only in BL/6J-HYX mice. Quantitative histomorphometric analyses revealed reduced alveolar formation in lungs of both strains after HYX, but the effect was greater in BL/6J-HYX mice than BL/6N-HYX mice. Septal thickness was lower in BL/6J-NOX mice than BL/6N-NOX mice but increased in both strains after HYX. Elastic fiber density was significantly greater in BL/6J-HYX mice than BL/6N-HYX mice. Lungs of BL/6J-HYX mice were protected from changes in gene expression of fibrillin-1, fibrillin-2, fibulin-4, fibulin-5, and surfactant proteins seen in BL/6N-HYX mice. Finally, Stat3 was activated by HYX in both strains; in contrast, activation of Smad2 was markedly greater in lungs of BL/6N mice than BL/6J mice after HYX. In summary, we demonstrate strain-dependent differences in lung structure and matrix, alveolar epithelial cell markers, and Smad2 (transforming growth factor β) signaling in neonatal HYX-induced lung injury. Strain-dependent effects and genetic susceptibility need be taken into consideration for reproducibility and reliability of results in animal models.

Endothelial to Mesenchymal Transition: Role in Physiology and in the Pathogenesis of Human Diseases

Numerous studies have demonstrated that endothelial cells are capable of undergoing endothelial to mesenchymal transition (EndMT), a newly recognized type of cellular transdifferentiation. EndMT is a complex biological process in which endothelial cells adopt a mesenchymal phenotype displaying typical mesenchymal cell morphology and functions, including the acquisition of cellular motility and contractile properties. Endothelial cells undergoing EndMT lose the expression of endothelial cell-specific proteins such as CD31/platelet-endothelial cell adhesion molecule, von Willebrand factor, and vascular-endothelial cadherin and initiate the expression of mesenchymal cell-specific genes and the production of their encoded proteins including α-smooth muscle actin, extra domain A fibronectin, N-cadherin, vimentin, fibroblast specific protein-1, also known as S100A4 protein, and fibrillar type I and type III collagens. Transforming growth factor-β1 is considered the main EndMT inducer. However, EndMT involves numerous molecular and signaling pathways that are triggered and modulated by multiple and often redundant mechanisms depending on the specific cellular context and on the physiological or pathological status of the cells. EndMT participates in highly important embryonic development processes, as well as in the pathogenesis of numerous genetically determined and acquired human diseases including malignant, vascular, inflammatory, and fibrotic disorders. Despite intensive investigation, many aspects of EndMT remain to be elucidated. The identification of molecules and regulatory pathways involved in EndMT and the discovery of specific EndMT inhibitors should provide novel therapeutic approaches for various human disorders mediated by EndMT.