Angiogenesis, the sprouting of new blood vessels from pre‐existing ones, and the permeability of blood vessels are regulated by vascular endothelial growth factor (VEGF) via its two known receptors Flt1 (VEGFR‐1) and KDR/Flk‐1 (VEGFR‐2). The Flt4 receptor tyrosine kinase is related to the VEGF receptors, but does not bind VEGF and its expression becomes restricted mainly to lymphatic endothelia during development. In this study, we have purified the Flt4 ligand, VEGF‐C, and cloned its cDNA from human prostatic carcinoma cells. While VEGF‐C is homologous to other members of the VEGF/platelet derived growth factor (PDGF) family, its C‐terminal half contains extra cysteine‐rich motifs characteristic of a protein component of silk produced by the larval salivary glands of the midge, Chironomus tentans. VEGF‐C is proteolytically processed, binds Flt4, which we rename as VEGFR‐3 and induces tyrosine autophosphorylation of VEGFR‐3 and VEGFR‐2. In addition, VEGF‐C stimulated the migration of bovine capillary endothelial cells in collagen gel. VEGF‐C is thus a novel regulator of endothelia, and its effects may extend beyond the lymphatic system, where Flt4 is expressed.

Antila et al. show that meningeal lymphatic vessels in mice develop postnatally. Interruption of VEGF-C/VEGFR3 signal transduction arrests their development. In adult mice, VEGFR3 deletion and VEGFR3 blockers, including a clinically available tyrosine kinase inhibitor, induce regression of meningeal lymphatic vessels.

Mitochondrial dysfunction affects cellular energy metabolism, but less is known about the consequences for cytoplasmic biosynthetic reactions. We report that mtDNA replication disorders caused by TWINKLE mutations-mitochondrial myopathy (MM) and infantile onset spinocerebellar ataxia (IOSCA)-remodel cellular dNTP pools in mice. MM muscle shows tissue-specific induction of the mitochondrial folate cycle, purine metabolism, and imbalanced and increased dNTP pools, consistent with progressive mtDNA mutagenesis. IOSCA-TWINKLE is predicted to hydrolyze dNTPs, consistent with low dNTP pools and mtDNA depletion in the disease. MM muscle also modifies the cytoplasmic one-carbon cycle, transsulfuration, and methylation, as well as increases glucose uptake and its utilization for de novo serine and glutathione biosynthesis. Our evidence indicates that the mitochondrial replication machinery communicates with cytoplasmic dNTP pools and that upregulation of glutathione synthesis through glucose-driven de novo serine biosynthesis contributes to the metabolic stress response. These results are important for disorders with primary or secondary mtDNA instability and offer targets for metabolic therapy.

We report here the cloning and characterization of human and mouse genes for vascular endothelial growth factor C (VEGF-C), a newly isolated member of the vascular endothelial growth factor/platelet-derived growth factor (VEGF/PDGF) family. Both VEGF-C genes comprise over 40 kilobase pairs of genomic DNA and consist of seven exons, all containing coding sequences. The VEGF homology domain of VEGF-C is encoded by exons 3 and 4. Exons 5 and 7 encode cysteine-rich motifs of the type C 6 C 10 CRC, and exon 6 encodes additional C 10 CXCXC motifs typical of a silk protein. A putative alternatively spliced rare RNA form lacking exon 4 was identified in human fibrosarcoma cells, and a major transcription start site was located in the human VEGF-C gene 523 base pairs upstream of the translation initiation codon. The upstream promoter sequences contain conserved putative binding sites for Sp-1, AP-2, and NF-B transcription factors but no TATA box, and they show promoter activity when transfected into cells. The VEGF-C gene structure is thus assembled from exons encoding propeptides and distinct cysteine-rich domains in addition to the VEGF homology domain, and it shows both similarities and distinct differences in comparison with other members of the VEGF/PDGF gene family.