ISOLATION AND MOLECULAR CHARACTERIZATION OF A MOUSE RENAL MICROVASCULAR ENDOTHELIAL CELL LINE

Dexmedetomidine attenuates renal ischemia-reperfusion injury through activating PI3K/Akt-eNOS signaling via α2 adrenoreceptors in renal microvascular endothelial cells

Renal microvascular endothelial cells (RMECs), which are closely related to regulation of vascular reactivity and modulation of inflammation, play a crucial role in the process of renal ischemia and reperfusion (I/R) injury. Previous studies have reported the protective effects of dexmedetomidine (DEX) against renal I/R injury, but little is known about the role of DEX on RMECs. This study aimed to investigate whether DEX alleviated renal I/R injury via acting on the RMECs. Mice underwent bilateral renal artery clamping for 45 min followed by reperfusion for 48 h, and the cultured neonatal mice RMECs were subjected to hypoxia for 1 h followed by reoxygenation (H/R) for 24 h. The results suggest that DEX alleviated renal I/R injury in vivo and improved cell viability of RMECs during H/R injury in vitro. Gene sequencing revealed that the PI3K/Akt was the top enriched signaling pathway and the endothelial cells were widely involved in renal I/R injury. DEX activated phosphorylation of PI3K and Akt, increased eNOS expression, and attenuated inflammatory responses. In addition, the results confirmed the distribution of α₂ adrenoreceptor (α₂ -AR) in RMECs. Furthermore, the protective effects of DEX against renal I/R injury were abolished by α₂ -AR antagonist (atipamezole), which was partly reversed by the PI3K agonist (740 Y-P). These findings indicated that DEX protects against renal I/R injury by activating the PI3K/Akt-eNOS pathway and inhibiting inflammation responses via α₂ -AR in RMECs.

Akt suppression of TGFβ signaling contributes to the maintenance of vascular identity in embryonic stem cell-derived endothelial cells

The ability to generate and maintain stable in vitro cultures of mouse endothelial cells (ECs) has great potential for genetic dissection of the numerous pathologies involving vascular dysfunction as well as therapeutic applications. However, previous efforts at achieving sustained cultures of primary stable murine vascular cells have fallen short, and the cellular requirements for EC maintenance in vitro remain undefined. In this study, we have generated vascular ECs from mouse embryonic stem (ES) cells and show that active Akt is essential to their survival and propagation as homogeneous monolayers in vitro. These cells harbor the phenotypical, biochemical, and functional characteristics of ECs and expand throughout long-term cultures, while maintaining their angiogenic capacity. Moreover, Akt-transduced embryonic ECs form functional perfused vessels in vivo that anastomose with host blood vessels. We provide evidence for a novel function of Akt in stabilizing EC identity, whereby the activated form of the protein protects mouse ES cell-derived ECs from TGFβ-mediated transdifferentiation by downregulating SMAD3. These findings identify a role for Akt in regulating the developmental potential of ES cell-derived ECs and demonstrate that active Akt maintains endothelial identity in embryonic ECs by interfering with active TGFβ-mediated processes that would ordinarily usher these cells to alternate fates.

Low proliferative potential and impaired angiogenesis of cultured rat kidney endothelial cells

OBJECTIVE

CKD is histologically characterized by interstitial fibrosis, which may be driven by peritubular capillary dropout and hypoxia. Surprisingly, peritubular capillaries have little repair capacity. We sought to establish long-term cultures of rat kidney endothelial cells to investigate their growth regulatory properties.

METHODS

AKEC or YKEC were isolated using CD31-based isolation techniques and sustained in long-term cultures.

RESULTS

Although YKEC grew slightly better than AKEC, both performed poorly compared with endothelial cells of the rat adult PMVEC, PAEC, or HUVEC cells. PMVEC and PAEC contained a large percentage of cells with high colony-forming potential. In contrast, KECs were incapable of forming large colonies and most remained as single nondividing cells. KEC expressed high levels of mRNA for VEGF receptors, but were surprisingly insensitive to VEGF stimulation. KEC did not form branching structures on Matrigel when cultured alone, but in mixed cultures, KEC incorporated into branching structures with PMVEC.

CONCLUSIONS

These data suggest that the intrinsic growth of rat kidney endothelial cells is limited by unknown mechanisms. The low growth rate may be related to the minimal intrinsic regenerative capacity of renal capillaries.

TNF induces caspase-dependent inflammation in renal endothelial cells through a Rho- and myosin light chain kinase-dependent mechanism

The pathogenesis of LPS-induced acute kidney injury (AKI) requires signaling through tumor necrosis factor-alpha (TNF) receptor 1 (TNFR1), which within the kidney is primarily located in the endothelium. We showed previously that caspase inhibition protected mice against LPS-induced AKI and in parallel significantly inhibited LPS-induced renal inflammation. Therefore we hypothesized that caspase activation amplifies TNF-induced inflammation in renal endothelial cells (ECs). In cultured renal ECs, TNF induced apoptosis through a caspase-8-dependent pathway. TNF caused translocation of the p65 subunit of NF-kappaB to the nucleus, resulting in upregulation of inflammatory markers such as adhesion molecules ICAM-1 and VCAM-1. However, the broad-spectrum caspase inhibitor Boc-d-fmk reduced NF-kB activation as assessed by gel shift assay, reduced phosphorylation of subunit IkappaBalpha, and significantly inhibited TNF-induced expression of ICAM-1 and VCAM-1 as assessed by both real-time PCR and flow cytometry. Broad-spectrum caspase inhibition markedly inhibited neutrophil adherence to the TNF-activated endothelial monolayer, supporting the functional significance of this effect. Specific inhibitors of caspases-8 and -3, but not of caspase-1, reduced TNF-induced NF-kappaB activation. Caspase inhibition also reduced TNF-induced myosin light chain (MLC)-2 phosphorylation, and activation of upstream regulator RhoA. Consistent with this, MLC kinase (MLCK) inhibitor ML-7 reduced TNF-induced NF-kappaB activation. Thus caspase activation influences NF-kappaB signaling via its affect on cytoskeletal changes occurring through RhoA and MLCK pathways. These cell culture experiments support a role for caspase activation in TNF-induced inflammation in the renal endothelium, a key event in LPS-induced AKI.

Endothelial function of von Hippel-Lindau tumor suppressor gene: control of fibroblast growth factor receptor signaling

von Hippel-Lindau (VHL) disease results from germline and somatic mutations in the VHL tumor suppressor gene and is characterized by highly vascularized tumors. VHL mutations lead to stabilization of hypoxia-inducible factor (HIF), which up-regulates proangiogenic factors such as vascular endothelial growth factor (VEGF). This pathway is therefore believed to underlie the hypervascular phenotypes of the VHL tumors. However, recent studies have identified novel VHL functions that are independent of the HIF-VEGF pathway. In addition, a potential role of VHL in the tumor microenvironment, which carries heterozygous VHL mutations in VHL patients, has been overlooked. Here, we report a novel HIF-independent VHL function in the endothelium. VHL knockdown in primary human microvascular endothelial cells caused defective turnover of surface fibroblast growth factor (FGF) receptor, increased extracellular signal-regulated kinase signaling, and ETS1 activation, leading to increased cell motility in response to FGF and three-dimensional cord formation in vitro. HIF-alpha knockdown in VHL loss-of-function endothelial cells does not impede their elevated in vitro angiogenic activity. Importantly, the elevated angiogenic response to FGF is recapitulated in Vhl-heterozygous mice. Thus, partial loss of function of VHL in endothelium may be a contributing factor in tumor angiogenesis through a HIF-VEGF-independent mechanism.

The establishment of murine blood outgrowth endothelial cells and observations relevant to gene therapy

Endothelial cells are an attractive vehicle for gene therapy because they may be used in an autologous fashion and may allow for direct exposure of the gene product into the intravascular space. To explore this future potential, a reproducible system was developed for the culture of murine blood outgrowth endothelial cells. These cells demonstrated acetylated low-density lipoprotein (LDL) incorporation, matrigel tube formation, and specific endothelial staining characteristics, namely P1H12, VeCAD, vascular cell adhesion molecule (VCAM), vWF, platelet endothelial cell adhesion molecule (PECAM-1), and vascular endothelial growth factor receptor-2 (VEGFR2). They were also negative for smooth muscle actin and monocytic markers CD11b, CD14, and CD16. Moreover, these cells were amendable to gene transfer with red fluorescent and green fluorescent expression vectors as well as human Factor VIII (hFVIII) while maintaining endothelial characteristics. Both source- and gene-introduced cells also manifested excellent proliferative potential. Furthermore, murine blood outgrowth endothelial cells (BOECs) demonstrated persistent in vivo seeding in the liver, lung, spleen, and bone morrow of recipient mice.

Targeting tumor-associated macrophages and inhibition of MCP-1 reduce angiogenesis and tumor growth in a human melanoma xenograft

Chemokines such as monocyte chemoattractant protein (MCP)-1 are key agonists that attract macrophages to tumors. In melanoma, it has been previously shown that variable levels of MCP-1/CCL2 appear to correlate with infiltrating macrophages and tumor fate, with low to intermediate levels of the chemokine contributing to melanoma development. To work under such conditions, a poorly tumorigenic human melanoma cell line was transfected with an expression vector encoding MCP-1. We found that M2 macrophages are associated to MCP-1+ tumors, triggering a profuse vascular network. To target the protumoral macrophages recruitment and reverting tumor growth promotion, clodronate-laden liposomes (Clod-Lip) or bindarit were administered to melanoma-bearing mice. Macrophage depletion after Clod-Lip treatment induced development of smaller tumors than in untreated mice. Immunohistochemical analysis with an anti-CD31 antibody revealed scarce vascular structures mainly characterized by narrow vascular lights. Pharmacological inhibition of MCP-1 with bindarit also reduced tumor growth and macrophage recruitment, rendering necrotic tumor masses. We suggest that bindarit or Clod-Lip abrogates protumoral-associated macrophages in human melanoma xenografts and could be considered as complementary approaches to antiangiogenic therapy.