hESC Differentiation toward an Autonomic Neuronal Cell Fate Depends on Distinct Cues from the Co-Patterning Vasculature

To gain insight into the cellular and molecular cues that promote neurovascular co-patterning at the earliest stages of human embryogenesis, we developed a human embryonic stem cell model to mimic the developing epiblast. Contact of ectoderm-derived neural cells with mesoderm-derived vasculature is initiated via the neural crest (NC), not the neural tube (NT). Neurovascular co-patterning then ensues with specification of NC toward an autonomic fate requiring vascular endothelial cell (EC)-secreted nitric oxide (NO) and direct contact with vascular smooth muscle cells (VSMCs) via T-cadherin-mediated homotypic interactions. Once a neurovascular template has been established, NT-derived central neurons then align themselves with the vasculature. Our findings reveal that, in early human development, the autonomic nervous system forms in response to distinct molecular cues from VSMCs and ECs, providing a model for how other developing lineages might coordinate their co-patterning.

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Neural crest (NC) cells drive neurovascular co-patterning, as modeled by hESC

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Autonomic differentiation of NC cells depends on contact with perivascular cells

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This requires endothelial-derived NO and T-cadherin-mediated interaction with VSMCs

Multivalent proteoglycan modulation of FGF mitogenic responses in perivascular cells

Sprouting of angiogenic perivascular cells is thought to be highly dependent upon autocrine and paracrine growth factor stimulation. Accordingly, we report that corneal angiogenesis induced by ectopic FGF implantation is strongly impaired in NG2/CSPG4 proteoglycan (PG) null mice known to harbour a putative deficit in pericyte proliferation/mobilization. Conversely, no significant differences were seen between wild type and knockout corneas when VEGF was used as an angiocrine factor. Perturbed responsiveness of NG2-deficient pericytes to paracrine and autocrine stimulation by several FGFs could be confirmed in cells isolated from NG2 null mice, while proliferation induced by other growth factors was equivalent in wild type and knockout cells. Identical results were obtained after siRNA-mediated knock-down of NG2 in human smooth muscle-like cell lines, as also demonstrated by the decreased levels of FGF receptor phosphorylation detected in these NG2 deprived cells. Binding assays with recombinant proteins and molecular interactions examined on live cells asserted that FGF-2 bound to NG2 in a glycosaminoglycan-independent, core protein-mediated manner and that the PG was alone capable of retaining FGF-2 on the cell membrane for subsequent receptor presentation. The use of dominant-negative mutant cells, engineered by combined transduction of NG2 deletion constructs and siRNA knock-down of the endogenous PG, allowed us to establish that the FGF co-receptor activity of NG2 is entirely mediated by its extracellular portion. In fact, forced overexpression of the NG2 ectodomain in human smooth muscle-like cells increased their FGF-2-induced mitosis and compensated for low levels of FGF receptor surface expression, in a manner equivalent to that produced by overexpression of the full-length NG2. Upon FGF binding, the cytoplasmic domain of NG2 is phosphorylated, but there is no evidence that this event elicits signal transductions that could bypass the FGFR-mediated ones. Pull-down experiments, protein-protein binding assays and flow cytometry FRET coherently revealed an elective ligand-independent association of NG2 with FGFR1 and FGFR3. The NG2 cooperation with these receptors was also corroborated functionally by the outcome of FGF-2 treatments of cells engineered to express diverse NG2/FGFR combinations. Comprehensively, the findings suggest that perivascular NG2 may serve as a dual modulator of the availability/accessibility of FGF at the cell membrane, as well as the resulting FGFR transducing activity.

Adiponectin attenuates lipopolysaccharide-induced acute lung injury through suppression of endothelial cell activation

Adiponectin (APN) is an adipose tissue-derived factor with anti-inflammatory and vascular protective properties whose levels paradoxically decrease with increasing body fat. In this study, APN's role in the early development of ALI to LPS was investigated. Intratracheal LPS elicited an exaggerated systemic inflammatory response in APN-deficient (APN(-/-)) mice compared with wild-type (wt) littermates. Increased lung injury and inflammation were observed in APN(-/-) mice as early as 4 h after delivery of LPS. Targeted gene expression profiling performed on immune and endothelial cells isolated from lung digests 4 h after LPS administration showed increased proinflammatory gene expression (e.g., IL-6) only in endothelial cells of APN(-/-) mice when compared with wt mice. Direct effects on lung endothelium were demonstrated by APN's ability to inhibit LPS-induced IL-6 production in primary human endothelial cells in culture. Furthermore, T-cadherin-deficient mice that have significantly reduced lung airspace APN but high serum APN levels had pulmonary inflammatory responses after intratracheal LPS that were similar to those of wt mice. These findings indicate the importance of serum APN in modulating LPS-induced ALI and suggest that conditions leading to hypoadiponectinemia (e.g., obesity) predispose to development of ALI through exaggerated inflammatory response in pulmonary vascular endothelium.

The heme synthesis defect of mutants impaired in mitochondrial iron-sulfur protein biogenesis is caused by reversible inhibition of ferrochelatase

Mitochondria are responsible for the synthesis of both iron-sulfur clusters and heme, but the potential connection between the two major iron-consuming pathways is unknown. Here, we have shown that mutants in the yeast mitochondrial iron-sulfur cluster (ISC) assembly machinery displayed reduced cytochrome levels and diminished activity of the heme-containing cytochrome c oxidase, in addition to iron-sulfur protein defects. In contrast, mutants in components of the mitochondrial ISC export machinery, which are specifically required for maturation of cytosolic iron-sulfur proteins, were not decreased in heme synthesis or cytochrome levels. Heme synthesis does not involve the function of mitochondrial ISC components, because immunological depletion of various ISC proteins from mitochondrial extracts did not affect the formation and amounts of heme. The heme synthesis defects of ISC mutants were found in vivo in isolated mitochondria and in mitochondrial detergent extracts and were confined to an inhibition of ferrochelatase, the enzyme catalyzing the insertion of iron into protoporphyrin IX. In support of these findings, immunopurification of ferrochelatase from ISC mutants restored its activity to wild-type levels. We conclude that the reversible inhibition of ferrochelatase is the molecular reason for the heme deficiency in ISC assembly mutants. This inhibitory mechanism may be used for regulation of iron distribution between the two iron-consuming processes.