Modulation of expression of LDH isoenzymes in endothelial cells by laminin: implications for angiogenesis

Phosphorylation of mammalian cytosolic and mitochondrial malate dehydrogenase: insights into regulation

Malate dehydrogenase (MDH) is a key enzyme in mammalian metabolic pathways in cytosolic and mitochondrial compartments. Regulation of MDH through phosphorylation remains an underexplored area. In this review we consolidate evidence supporting the potential role of phosphorylation in modulating the function of mammalian MDH. Parallels are drawn with the phosphorylation of lactate dehydrogenase, a homologous enzyme, to reveal its regulatory significance and to suggest a similar regulatory strategy for MDH. Comprehensive mining of phosphorylation databases, provides substantial experimental (primarily mass spectrometry) evidence of MDH phosphorylation in mammalian cells. Experimentally identified phosphorylation sites are overlaid with MDH's functional domains, offering perspective on how these modifications could influence enzyme activity. Preliminary results are presented from phosphomimetic mutations (serine/threonine residues changed to aspartate) generated in recombinant MDH proteins serving as a proof of concept for the regulatory impact of phosphorylation. We also examine and highlight several approaches to probe the structural and cellular impact of phosphorylation. This review highlights the need to explore the dynamic nature of MDH phosphorylation and calls for identifying the responsible kinases and the physiological conditions underpinning this modification. The synthesis of current evidence and experimental data aims to provide insights for future research on understanding MDH regulation, offering new avenues for therapeutic interventions in metabolic disorders and cancer.

Regulation of vascular endothelial growth factor by metabolic context of the cell

Expression of vascular endothelial growth factor, major endothelial specific glycoprotein growth factor that promotes angiogenesis is regulated at transcriptional, post transcriptional and posttranslational levels. One of the key posttranslational modifications involved in regulating the angiogenic potential of VEGF is covalent modification involving polyADP ribosylation. Major factors contributing to the regulation of VEGF include factors relating to hypoxia, growth factors and cytokines and hormones. Apart from these, the metabolite status of the cell as sensed by various metabolite regulators can influence the angiogenic potential. Changes in the metabolite status of the cell occur during different conditions associated with excessive or insufficient angiogenesis contributing to pathology. Effect of metabolites, as exemplified by certain metabolites such as lactate, citrate, sarcosine, metabolites of arachidonic acid on angiogenesis through the regulation of expression of VEGF as well as its angiogenic potential through polyADP ribosylation is discussed.

Preparation of chitosan films using different neutralizing solutions to improve endothelial cell compatibility

The development of chitosan-based constructs for application in large-size defects or highly vascularized tissues is still a challenging issue. The poor endothelial cell compatibility of chitosan hinders the colonization of vascular endothelial cells in the chitosan-based constructs, and retards the establishment of a functional microvascular network following implantation. The aim of the present study is to prepare chitosan films with different neutralization methods to improve their endothelial cell compatibility. Chitosan salt films were neutralized with either sodium hydroxide (NaOH) aqueous solution, NaOH ethanol solution, or ethanol solution without NaOH. The physicochemical properties and endothelial cell compatibility of the chitosan films were investigated. Results indicated that neutralization with different solutions affected the surface chemistry, swelling ratio, crystalline conformation, nanotopography, and mechanical properties of the chitosan films. The NaOH ethanol solution-neutralized chitosan film (Chi-NaOH/EtOH film) displayed a nanofiber-dominant surface, while the NaOH aqueous solution-neutralized film (Chi-NaOH/H(2)O film) and the ethanol solution-neutralized film (Chi-EtOH film) displayed nanoparticle-dominant surfaces. Moreover, the Chi-NaOH/EtOH films exhibited a higher stiffness as compared to the Chi-NaOH/H(2)O and Chi-EtOH films. Endothelial cell compatibility of the chitosan films was evaluated with a human microvascular endothelial cell line, HMEC-1. Compared with the Chi-NaOH/H(2)O and Chi-EtOH films, HMECs cultured on the Chi-NaOH/EtOH films fully spread and exhibited significantly higher levels of adhesion and proliferation, with retention of the endothelial phenotype and function. Our findings suggest that the surface nanotopography and mechanical properties contribute to determining the endothelial cell compatibility of chitosan films. The nature of the neutralizing solutions can affect the physicochemical properties and endothelial cell compatibility of chitosan films. Therefore, selection of suitable neutralization methods is highly important for the application of chitosan in tissue engineering.

Changes in expression of VE-cadherin and MMPs in endothelial cells: Implications for angiogenesis

The mechanism of cell-cell contact dependent regulation of pericellular proteolysis in angiogenesis was examined by studying the expression of MMPs using isolated HUVECs in culture. Zymography, Immunoblot and RT-PCR analysis showed that the production and secretion of matrixmetalloproteinase-2 and matrixmetalloproteinase-9 by HUVECs in culture were high when they remain as individual cells and significantly decreased during later stages of culture when cells developed cell-cell contact and tubular network-like structure. As MMPs decreased there was significant upregulation of VE-cadherin in cells undergoing angiogenic transition. Investigations to understand the signaling pathways downstream of VE-cadherin showed a relatively high level of β-catenin in the nucleus of endothelial cells in culture during initial stages and decrease in its levels in the nucleus, associated with an increase in the cytosol during later stages of culture. The distribution of β-catenin was found to be regulated by Tyr/Ser phosphorylation status of this protein. Cell-cell contact dependent downregulation of MMPs during angiogenesis was also observed in experiments using proangiogenic substances which caused a rapid rate of downregulation of MMP-2 and MMP-9 and absence of downregulation of MMPs when treated with anti-angiogenic agents.

Angiogenic effect of laminin involves modulation of cyclooxygenase-2 and prostaglandin levels

The molecular mechanism of the angiogenic effect of laminin (Ln) was studied using human umbilical vein endothelial cells (HUVECs) maintained in culture on Ln-1 substratum. High-pressure liquid chromatography analysis showed that in cells maintained on Ln, the levels of proangiogenic prostaglandin E(2) (PGE(2)) increased and that of antiangiogenic PGD(2) decreased. The angiogenic effect of PGE(2) and PGD(2) was confirmed by assessing the expression of CD31 and E-selectin in HUVECs. Immunoblot analysis, reverse transcription-polymerase chain reaction and cyclooxygenase (COX) assay showed increase in the expression and activity of COX-2 in cells maintained on Ln. Use of pharmacological inhibitors suggested that the modulation in the expression of COX-2 and thereby the levels of PGE(2) and PGD(2) in endothelial cells by Ln is mediated through the α(6)β(4) integrin-p38MAPK (mitogen-activated protein kinase)-NF-κB signaling pathway.

Inkjet printing of laminin gradient to investigate endothelial cellular alignment

To investigate the influence of the protein surface-density gradient on endothelial cell alignment, a novel approach for the fabrication of a laminin gradient on gold-coated substrates has been developed in this study. Our approach involves programmed inkjet printing of an alkanethiol (11-mercaptoundecanoic acid, C(10)COOH, MUA) gradient onto gold-coated substrates, followed by backfilling with 11-mercapto-1-undecanol (C(11)OH, MUD). The -COOH moieties were activated and then covalently linked with laminin. This treatment led to a surface-density gradient of laminin. Contact angle measurement, X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy were employed to characterize the self-assembled monolayers (SAMs) and protein gradient, respectively. Results proved the feasibility of the fabrication of a protein gradient by using the inkjet printing technique. The self-assembled monolayer gradients displayed a high packing density, as indicated by dynamic contact angle measurement. More importantly, the gradient slope was easily tunable over a significant distance from 20 to 30 mm. The laminin gradient was clearly visible by fluorescence microscopy observation. Endothelial cells cultured on the surface-density gradient of laminin demonstrated a strong alignment tendency in parallel to the gradient. The higher the laminin density the more cells were observed. The result indicates that cell attachment is dependent on the surface density of laminin. This work broadens our methodology to investigate chemical stimuli-induced cell directional alignment. It is potentially important for understanding cell alignment/ingrowth behavior for angiogenesis and implant technology including tissue-engineered structures.

Endothelial cell-laminin interaction: modulation of LDH expression involves alpha6beta4 integrin-FAK-p38MAPK pathway

One of the possible mechanisms of the angiogenic effect of laminin (Ln) involves modulation of the biological activity of VEGF by regulating poly ADP ribosylation (PAR). PAR modification of VEGF was found to be related with the changes in NAD(+) associated with a shift in LDH isoenzymes. Further investigations on LDH gene expression in HUVECs suggested that the effect of Ln was mediated through alpha(6)beta(4) integrin-FAK-src-p38 MAPK pathway. This was evidenced by (a) co-immunoprecipitation of beta(4) integrin with alpha(6) subunit, (b) activation by tyrosine phosphorylation of beta(4) integrin and FAK, (c) co-immunoprecipitation of FAK with beta(4) and with adapter protein, src, (d) increased phosphorylation of p38 MAPK in cells maintained on Ln and (e) blocking of effect of Ln on LDH-B gene expression by inhibition of p38 MAPK. Increase in serine phosphorylation of c-fos and c-jun and higher levels of heterodimers of AP-1 in the nucleus in cells maintained on Ln suggested activation of AP-1 transcription factor. These results provide evidence for modulation of endothelial cell function relevant to angiogenesis by Ln through alpha(6)beta(4) integrin.

Modulation of angiogenic factors by ursolic acid

Investigations were carried out to understand the molecular basis of the effect of ursolic acid on angiogenesis by analysing its effects on the expression of modulators of angiogenesis by HUVECs in culture. Treatment with ursolic acid increased the expression of adhesion molecules such as E-selectin, CD-31 and I-CAM, upregulated angiogenic growth factors such as VEGF and FGF-2 and their receptors and caused increase in the ratio of PGE(2) to PGD(2). Reversal of the effect of ursolic acid by inhibition of PI3K-Akt pathway and increase in the level of phospho Akt suggest that the ursolic acid effect is mediated through PI3K-Akt pathway.