Ubiad1 is an antioxidant enzyme that regulates eNOS activity by CoQ10 synthesis.

Protection against oxidative damage caused by excessive reactive oxygen species (ROS) by an antioxidant network is essential for the health of tissues, especially in the cardiovascular system. Here, we identified a gene with important antioxidant features by analyzing a null allele of zebrafish ubiad1, called barolo (bar). bar mutants show specific cardiovascular failure due to oxidative stress and ROS-mediated cellular damage. Human UBIAD1 is a nonmitochondrial prenyltransferase that synthesizes CoQ10 in the Golgi membrane compartment. Loss of UBIAD1 reduces the cytosolic pool of the antioxidant CoQ10 and leads to ROS-mediated lipid peroxidation in vascular cells. Surprisingly, inhibition of eNOS prevents Ubiad1-dependent cardiovascular oxidative damage, suggesting a crucial role for this enzyme and nonmitochondrial CoQ10 in NO signaling. These findings identify UBIAD1 as a nonmitochondrial CoQ10-forming enzyme with specific cardiovascular protective function via the modulation of eNOS activity.

Nesprin-3 augments peripheral nuclear localization of intermediate filaments in zebrafish.

The outer nuclear membrane protein nesprin-3 binds the cytoskeletal linker protein plectin, which are proposed to anchor the intermediate filaments to the nuclear envelope. To investigate the function of nesprin-3 in vivo, we used the zebrafish as a vertebrate model system. Zebrafish nesprin-3 is expressed at the nuclear envelope of epidermal and skeletal muscle cells during development. Unexpectedly, loss of nesprin-3 did not affect embryonic development, viability or fertility. However, nesprin-3-deficient zebrafish embryos showed a reduced concentration of intermediate filaments around the nucleus. Additional analysis revealed the presence of two nesprin-3 isoforms in zebrafish, nesprin-3α and nesprin-3ß. Nesprin-3ß is only expressed during early development and lacks seven amino acids in its first spectrin repeat that are crucial for plectin binding and recruitment to the nuclear envelope. These seven amino acids are highly conserved and we showed that residues R43 and L44 within this motif are required for plectin binding. Furthermore, several residues in the actin-binding domain of plectin that are crucial for binding to the integrin ß4 subunit are also important for the binding to nesprin-3α, indicating partial overlapping binding sequences for nesprin-3α and integrin ß4. All this shows that nesprin-3 is dispensable for normal development in zebrafish, but important for mediating the association of the intermediate filament system with the nucleus in vivo.

Zebrafish integrin-linked kinase is required in skeletal muscles for strengthening the integrin-ECM adhesion complex.

Mechanical instability of skeletal muscle cells is the major cause of congenital muscular dystrophy. Here we show that the zebrafish lost-contact mutant, that lacks a functional integrin-linked kinase (ilk) gene, suffers from mechanical instability of skeletal muscle fibres. With genetic and morpholino knock-down experiments we demonstrate that: 1) laminin, itgalpha7, Ilk and beta-parvin are all critical for mechanical stability in skeletal muscles. 2) Ilk acts redundantly with the dystrophin/dystroglycan adhesion complex in maintaining mechanical stability of skeletal muscles. 3) Ilk protein is recruited to the myotendinous junctions, which requires the ECM component laminin and the presence of itgalpha7 in the sarcolemma. 4) Ilk, unexpectedly, is dispensable for formation of the adhesion complex. Ilk, however, is required for strengthening the adhesion of the muscle fibre with the ECM and this activity requires the presence of a functional kinase domain in Ilk. 5) We identified a novel interaction between Ilk and the mechanical stretch sensor protein MLP. Thus, Ilk is an essential intracellular component downstream of laminin and itgalpha7, providing strengthening of skeletal muscle fibre adhesion with the ECM and therefore qualified as a novel candidate gene for congenital muscular dystrophy.

Laminin-alpha4 and integrin-linked kinase mutations cause human cardiomyopathy via simultaneous defects in cardiomyocytes and endothelial cells.

BACKGROUND: Extracellular matrix proteins, such as laminins, and endothelial cells are known to influence cardiomyocyte performance; however, the underlying molecular mechanisms remain poorly understood. METHODS AND RESULTS: We used a forward genetic screen in zebrafish to identify novel genes required for myocardial function and were able to identify the lost-contact (loc) mutant, which encodes a nonsense mutation in the integrin-linked kinase (ilk) gene. This loc/ilk mutant is associated with a severe defect in cardiomyocytes and endothelial cells that leads to severe myocardial dysfunction. Additional experiments revealed the epistatic regulation between laminin-alpha4 (Lama4), integrin, and Ilk, which led us to screen for mutations in the human ILK and LAMA4 genes in patients with severe dilated cardiomyopathy. We identified 2 novel amino acid residue-altering mutations (2828C>T [Pro943Leu] and 3217C>T [Arg1073X]) in the integrin-interacting domain of the LAMA4 gene and 1 mutation (785C>T [Ala262Val]) in the ILK gene. Biacore quantitative protein/protein interaction data, which have been used to determine the equilibrium dissociation constants, point to the loss of integrin-binding capacity in case of the Pro943Leu (Kd=5+/-3 micromol/L) and Arg1073X LAMA4 (Kd=1+/-0.2 micromol/L) mutants compared with the wild-type LAMA4 protein (Kd=440+/-20 nmol/L). Additional functional data point to the loss of endothelial cells in affected patients as a direct consequence of the mutant genes, which ultimately leads to heart failure. CONCLUSIONS: This is the first report on mutations in the laminin, integrin, and ILK system in human cardiomyopathy, which has consequences for endothelial cells as well as for cardiomyocytes, thus providing a new genetic basis for dilated cardiomyopathy in humans.

Apelin: A putative novel predictive biomarker for bevacizumab response in colorectal cancer.

Bevacizumab (bvz) is currently employed as an anti-angiogenic therapy across several cancer indications. Bvz response heterogeneity has been well documented, with only 10-15% of colorectal cancer (CRC) patients benefitting in general. For other patients, clinical efficacy is limited and side effects are significant. This reinforces the need for a robust predictive biomarker of response. To identify such a biomarker, we performed a DNA microarray-based transcriptional profiling screen with primary endothelial cells (ECs) isolated from normal and tumour colon tissues. Thirteen separate populations of tumour-associated ECs and 10 of normal ECs were isolated using fluorescence-activated cell sorting. We hypothesised that VEGF-induced genes were overexpressed in tumour ECs; these genes could relate to bvz response and serve as potential predictive biomarkers. Transcriptional profiling revealed a total of 2,610 differentially expressed genes when tumour and normal ECs were compared. To explore their relation to bvz response, the mRNA expression levels of top-ranked genes were examined using quantitative PCR in 30 independent tumour tissues from CRC patients that received bvz in the adjuvant setting. These analyses revealed that the expression of MMP12 and APLN mRNA was significantly higher in bvz non-responders compared to responders. At the protein level, high APLN expression was correlated with poor progression-free survival in bvz-treated patients. Thus, high APLN expression may represent a novel predictive biomarker for bvz unresponsiveness.

Kindlin-1 mutant zebrafish as an in vivo model system to study adhesion mechanisms in the epidermis.

From a forward genetic screen for epidermal defects in zebrafish, we identified a loss-of-function mutation in Kindlin-1, an essential regulator of integrin function. The mutation generates a premature stop codon, deleting the integrin-binding site. The mutant zebrafish develops cell-matrix and cell-cell adhesion defects in the basal epidermis leading to progressive fin rupturing, and was therefore designated rupturing-of-fins (rof). Similar defects were observed in the epidermis of Kindler syndrome patients, carrying a loss-of-function mutation in kindlin-1. Mutational analysis and rescue experiments in zebrafish revealed that residues K610, W612, and I647 in the F3 domain are essential for Kindlin-1 function in vivo, and that Kindlin-2 can functionally compensate for the loss of Kindlin-1. The fin phenotype of rof/kindlin-1 mutants resembles that of badfin mutants, carrying a mutation in integrin α3. We show here that this mutation impairs the biosynthesis of integrin α3ß1 and causes cell-matrix and cell-cell defects in vivo. Whereas both Integrin-linked kinase (Ilk) and Kindlin-1 cooperate with Integrin α3ß1 to resist trauma-induced epidermal defects, Kindlin-1 and Ilk, surprisingly, do not act synergistically but in parallel. Thus, the rof/kindlin-1 mutant zebrafish provides a unique model system to study epidermal adhesion mechanisms in vivo.

Carbonic anhydrase 5 regulates acid-base homeostasis in zebrafish.

The regulation of the acid-base balance in cells is essential for proper cellular homeostasis. Disturbed acid-base balance directly affects cellular physiology, which often results in various pathological conditions. In every living organism, the protein family of carbonic anhydrases regulate a broad variety of homeostatic processes. Here we describe the identification, mapping and cloning of a zebrafish carbonic anhydrase 5 (ca5) mutation, collapse of fins (cof), which causes initially a collapse of the medial fins followed by necrosis and rapid degeneration of the embryo. These phenotypical characteristics can be mimicked in wild-type embryos by acetazolamide treatment, suggesting that CA5 activity in zebrafish is essential for a proper development. In addition we show that CA5 regulates acid-base balance during embryonic development, since lowering the pH can compensate for the loss of CA5 activity. Identification of selective modulators of CA5 activity could have a major impact on the development of new therapeutics involved in the treatment of a variety of disorders.

Galectin-1 is essential in tumor angiogenesis and is a target for antiangiogenesis therapy.

We describe that galectin-1 (gal-1) is a receptor for the angiogenesis inhibitor anginex, and that the protein is crucial for tumor angiogenesis. gal-1 is overexpressed in endothelial cells of different human tumors. Expression knockdown in cultured endothelial cells inhibits cell proliferation and migration. The importance of gal-1 in angiogenesis is illustrated in the zebrafish model, where expression knockdown results in impaired vascular guidance and growth of dysfunctional vessels. The role of gal-1 in tumor angiogenesis is demonstrated in gal-1-null mice, in which tumor growth is markedly impaired because of insufficient tumor angiogenesis. Furthermore, tumor growth in gal-1-null mice no longer responds to antiangiogenesis treatment by anginex. Thus, gal-1 regulates tumor angiogenesis and is a target for angiostatic cancer therapy.