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

Extracellular Lactate Dehydrogenase A Release From Damaged Neurons Drives Central Nervous System Angiogenesis

Angiogenesis, a prominent feature of pathology, is known to be guided by factors secreted by living cells around a lesion. Although many cells are disrupted in a response to injury, the relevance of degenerating cells in pathological angiogenesis is unclear. Here, we show that the release of lactate dehydrogenase A (LDHA) from degenerating neurons drives central nervous system (CNS) angiogenesis. Silencing neuronal LDHA expression suppressed angiogenesis around experimental autoimmune encephalomyelitis (EAE)- and controlled cortical impact-induced lesions. Extracellular LDHA-mediated angiogenesis was dependent on surface vimentin expression and vascular endothelial growth factor receptor (VEGFR) phosphorylation in vascular endothelial cells. Silencing vimentin expression in vascular endothelial cells prevented angiogenesis around EAE lesions and improved survival in a mouse model of glioblastoma. These results elucidate novel mechanisms that may mediate pathologic angiogenesis and identify a potential molecular target for the treatment of CNS diseases involving angiogenesis.

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Injury leads to the release of intracellular components including LDHA, which promotes angiogenesis in the CNS.

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Cell surface vimentin, which is expressed on vascular endothelial cells, is involved in LHDA-mediated angiogenesis.

Angiogenesis is a prominent feature of many central nervous system (CNS) diseases, and regulates both pathologic progression and wound healing in several diseases. Pathologic CNS is characterized by neuronal damage that leads to the release of intracellular components. However, the effect of damaged cells on angiogenesis has not been clarified. This study revealed that LDHA, which is a known damage marker, promotes CNS-specific angiogenesis. LDHA-mediated angiogenesis depends on vimentin on the surface of vascular endothelial cells. The work described here proposes a novel mechanism by which neurodegeneration drives angiogenesis in the CNS.

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.

Focal adhesion kinase-promoted tumor glucose metabolism is associated with a shift of mitochondrial respiration to glycolysis

Cancer cells often gains a growth advantage by taking up glucose at a high rate and undergoing aerobic glycolysis through intrinsic cellular factors that reprogram glucose metabolism. Focal adhesion kinase (FAK), a key transmitter of growth factor and anchorage stimulation, is aberrantly overexpressed or activated in most solid tumors, including pancreatic ductal adenocarcinomas (PDACs). We determined whether FAK can act as an intrinsic driver to promote aerobic glycolysis and tumorigenesis. FAK inhibition decreases and overexpression increases intracellular glucose levels during unfavorable conditions, including growth factor deficiency and cell detachment. Amplex glucose assay, fluorescence and carbon-13 tracing studies demonstrate that FAK promotes glucose consumption and glucose-to-lactate conversion. Extracellular flux analysis indicates that FAK enhances glycolysis and decreases mitochondrial respiration. FAK increases key glycolytic proteins, including enolase, pyruvate kinase M2 (PKM2), lactate dehydrogenase and monocarboxylate transporter. Furthermore, active/tyrosine-phosphorylated FAK directly binds to PKM2 and promotes PKM2-mediated glycolysis. On the other hand, FAK-decreased levels of mitochondrial complex I can result in reduced oxidative phosphorylation (OXPHOS). Attenuation of FAK-enhanced glycolysis re-sensitizes cancer cells to growth factor withdrawal, decreases cell viability and reduces growth of tumor xenografts. These observations, for the first time, establish a vital role of FAK in cancer glucose metabolism through alterations in the OXPHOS-to-glycolysis balance. Broadly targeting the common phenotype of aerobic glycolysis and more specifically FAK-reprogrammed glucose metabolism will disrupt the bioenergetic and biosynthetic supply for uncontrolled growth of tumors, particularly glycolytic PDAC.

Improvement in endothelial cell adhesion and retention under physiological shear stress using a laminin-apatite composite layer on titanium

Apatite (Ap), laminin-apatite composite (L5Ap, L10Ap, L20Ap and L40Ap) and albumin-apatite (AlbAp) composite layers were prepared on titanium (Ti) using a supersaturated calcium phosphate solution supplemented with laminin (0, 5, 10, 20 and 40 μg ml(-1)) or albumin (800 μg ml(-1)). With an increase in the concentrations of laminin in the supersaturated calcium phosphate solutions, the amounts of laminin immobilized on the Ti increased. The number of human umbilical vein endothelial cells (HUVECs) adhered to the laminin-apatite composite layers were remarkably higher than those to the untreated Ti, Ap layer and AlbAp composite layer. The number of cells adhered to the L40Ap was 4.3 times the untreated Ti. Moreover, cells adhered to the laminin-apatite composite layers showed significantly higher cell retention under the physiological shear stress for 1 h and 2 h than those to the untreated Ti, Ap layer and AlbAp composite layer. The number of cells remaining on the L40Ap under the physiological shear stress for 2 h was 9.5 times that of the untreated Ti. The laminin-apatite composite layer is a promising interfacial layer for endothelialization of blood-contacting materials.

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.

Proteomic characterization of HIV-modulated membrane receptors, kinases and signaling proteins involved in novel angiogenic pathways

Background

Kaposi's sarcoma (KS), hemangioma, and other angioproliferative diseases are highly prevalent in HIV-infected individuals. While KS is etiologically linked to the human herpesvirus-8 (HHV8) infection, HIV-patients without HHV-8 and those infected with unrelated viruses also develop angiopathies. Further, HIV-Tat can activate protein-tyrosine-kinase (PTK-activity) of the vascular endothelial growth factor receptor involved in stimulating angiogenic processes. However, Tat by itself or HHV8-genes alone cannot induce angiogenesis in vivo unless specific proteins/enzymes are produced synchronously by different cell-types. We therefore tested a hypothesis that chronic HIV-replication in non-endothelial cells may produce novel factors that provoke angiogenic pathways.

Methods

Genome-wide proteins from HIV-infected and uninfected T-lymphocytes were tested by subtractive proteomics analyses at various stages of virus and cell growth in vitro over a period of two years. Several thousand differentially regulated proteins were identified by mass spectrometry (MS) and >200 proteins were confirmed in multiple gels. Each protein was scrutinized extensively by protein-interaction-pathways, bioinformatics, and statistical analyses.

Results

By functional categorization, 31 proteins were identified to be associated with various signaling events involved in angiogenesis. 88% proteins were located in the plasma membrane or extracellular matrix and >90% were found to be essential for regeneration, neovascularization and angiogenic processes during embryonic development.

Conclusion

Chronic HIV-infection of T-cells produces membrane receptor-PTKs, serine-threonine kinases, growth factors, adhesion molecules and many diffusible signaling proteins that have not been previously reported in HIV-infected cells. Each protein has been associated with endothelial cell-growth, morphogenesis, sprouting, microvessel-formation and other biological processes involved in angiogenesis (p = 10^-4 to 10^-12). Bioinformatics analyses suggest that overproduction of PTKs and other kinases in HIV-infected cells has suppressed VEGF/VEGFR-PTK expression and promoted VEGFR-independent pathways. This unique mechanism is similar to that observed in neovascularization and angiogenesis during embryogenesis. Validation of clinically relevant proteins by gene-silencing and translational studies in vivo would identify specific targets that can be used for early diagnosis of angiogenic disorders and future development of inhibitors of angiopathies. This is the first comprehensive study to demonstrate that HIV-infection alone, without any co-infection or treatment, can induce numerous "embryonic" proteins and kinases capable of generating novel VEGF-independent angiogenic pathways.