Cavin4b/Murcb Is Required for Skeletal Muscle Development and Function in Zebrafish.

Skeletal muscles provide metazoans with the ability to feed, reproduce and avoid predators. In humans, a heterogeneous group of genetic diseases, termed muscular dystrophies (MD), lead to skeletal muscle dysfunction. Mutations in the gene encoding Caveolin-3, a principal component of the membrane micro-domains known as caveolae, cause defects in muscle maintenance and function; however it remains unclear how caveolae dysfunction underlies MD pathology. The Cavin family of caveolar proteins can form membrane remodeling oligomers and thus may also impact skeletal muscle function. Changes in the distribution and function of Cavin4/Murc, which is predominantly expressed in striated muscles, have been reported to alter caveolae structure through interaction with Caveolin-3. Here, we report the generation and phenotypic analysis of murcb mutant zebrafish, which display impaired swimming capacity, skeletal muscle fibrosis and T-tubule abnormalities during development. To understand the mechanistic importance of Murc loss of function, we assessed Caveolin-1 and 3 localization and found it to be abnormal. We further identified an in vivo function for Murc in Erk signaling. These data link Murc with developmental defects in T-tubule formation and progressive muscle dysfunction, thereby providing a new candidate for the etiology of muscular dystrophy.

Developmental alterations in centrosome integrity contribute to the post-mitotic state of mammalian cardiomyocytes.

Mammalian cardiomyocytes become post-mitotic shortly after birth. Understanding how this occurs is highly relevant to cardiac regenerative therapy. Yet, how cardiomyocytes achieve and maintain a post-mitotic state is unknown. Here, we show that cardiomyocyte centrosome integrity is lost shortly after birth. This is coupled with relocalization of various centrosome proteins to the nuclear envelope. Consequently, postnatal cardiomyocytes are unable to undergo ciliogenesis and the nuclear envelope adopts the function as cellular microtubule organizing center. Loss of centrosome integrity is associated with, and can promote, cardiomyocyte G0/G1 cell cycle arrest suggesting that centrosome disassembly is developmentally utilized to achieve the post-mitotic state in mammalian cardiomyocytes. Adult cardiomyocytes of zebrafish and newt, which are able to proliferate, maintain centrosome integrity. Collectively, our data provide a novel mechanism underlying the post-mitotic state of mammalian cardiomyocytes as well as a potential explanation for why zebrafish and newts, but not mammals, can regenerate their heart.

Organ-specific function of adhesion G protein-coupled receptor GPR126 is domain-dependent.

Despite their abundance and multiple functions in a variety of organ systems, the function and signaling mechanisms of adhesion G protein-coupled receptors (GPCRs) are poorly understood. Adhesion GPCRs possess large N termini containing various functional domains. In addition, many of them are autoproteolytically cleaved at their GPS sites into an N-terminal fragment (NTF) and C-terminal fragment. Here we demonstrate that Gpr126 is expressed in the endocardium during early mouse heart development. Gpr126 knockout in mice and knockdown in zebrafish caused hypotrabeculation and affected mitochondrial function. Ectopic expression of Gpr126-NTF that lacks the GPS motif (NTF(ΔGPS)) in zebrafish rescued the trabeculation but not the previously described myelination phenotype in the peripheral nervous system. These data support a model in which the NTF of Gpr126, in contrast to the C-terminal fragment, plays an important role in heart development. Collectively, our analysis provides a unique example of the versatile function and signaling properties of adhesion GPCRs in vertebrates.

The functional properties of nephronectin: an adhesion molecule for cardiac tissue engineering.

Despite significant advances in preventive cardiovascular medicine and therapy for acute and chronic heart failure, cardiovascular diseases remain among the leading causes of death worldwide. In recent years cardiac tissue engineering has been established as a possible future treatment option for cardiac disease. However, the quality of engineered myocardial tissues remains poor. In tissue engineering it is important that the scaffold allows cells to attach, spread, maintain their differentiation status or differentiate into functional cells in order to exhibit their physiological function. Here, we have investigated the suitability of the natural cardiac extracellular matrix component nephronectin as an adhesive material for cardiac tissue engineering. Primary neonatal rat cardiomyocytes were seeded on collagen-, fibronectin- or nephronectin-coated glass coverslips and analyzed for cell adhesion, cellular metabolic activity, response to extracellular stimuli, cell-to-cell communication, differentiation and contractility. Our data demonstrate that most neonatal cardiomyocytes attached in an RGD domain-dependent manner within 18 h to nephronectin. The cells exhibited high metabolic activity, responded to growth factor stimuli and maintained their differentiation status. Moreover, nephronectin promoted sarcomere maturation and alignment, cell-to-cell communication and synchronous contractions. In conclusion, our findings demonstrate that nephronectin has excellent properties for cardiomyocyte adhesion and function and thus has the potential to improve current cardiac tissue engineering approaches.

Genome-wide association study of intracranial aneurysm identifies three new risk loci.

Saccular intracranial aneurysms are balloon-like dilations of the intracranial arterial wall; their hemorrhage commonly results in severe neurologic impairment and death. We report a second genome-wide association study with discovery and replication cohorts from Europe and Japan comprising 5,891 cases and 14,181 controls with approximately 832,000 genotyped and imputed SNPs across discovery cohorts. We identified three new loci showing strong evidence for association with intracranial aneurysms in the combined dataset, including intervals near RBBP8 on 18q11.2 (odds ratio (OR) = 1.22, P = 1.1 x 10(-12)), STARD13-KL on 13q13.1 (OR = 1.20, P = 2.5 x 10(-9)) and a gene-rich region on 10q24.32 (OR = 1.29, P = 1.2 x 10(-9)). We also confirmed prior associations near SOX17 (8q11.23-q12.1; OR = 1.28, P = 1.3 x 10(-12)) and CDKN2A-CDKN2B (9p21.3; OR = 1.31, P = 1.5 x 10(-22)). It is noteworthy that several putative risk genes play a role in cell-cycle progression, potentially affecting the proliferation and senescence of progenitor-cell populations that are responsible for vascular formation and repair.

Modulation of the glyoxalase system in the aging model Podospora anserina: effects on growth and lifespan.

The eukaryotic glyoxalase system consists of two enzymatic components, glyoxalase I (lactoylglutathione lyase) and glyoxalase II (hydroxyacylglutathione hydrolase). These enzymes are dedicated to the removal of toxic α-oxoaldehydes like methylglyoxal (MG). MG is formed as a by-product of glycolysis and MG toxicity results from its damaging capability leading to modifications of proteins, lipids and nucleic acids. An efficient removal of MG appears to be essential to ensure cellular functionality and viability. Here we study the effects of the genetic modulation of genes encoding the components of the glyoxalase system in the filamentous ascomycete and aging modelPodospora anserina. Overexpression of PaGlo1 leads to a lifespan reduction on glucose rich medium, probably due to depletion of reduced glutathione. Deletion of PaGlo1 leads to hypersensitivity against MG added to the growth medium. A beneficial effect on lifespan is observed when both PaGlo1 and PaGlo2 are overexpressed and the corresponding strains are grown on media containing increased glucose concentrations. Notably, the double mutant has a 'healthy' phenotype without physiological impairments. Moreover, PaGlo1/PaGlo2_OEx strains are not long-lived on media containing standard glucose concentrations suggesting a tight correlation between the efficiency and capacity to remove MG within the cell, the level of available glucose and lifespan. Overall, our results identify the up-regulation of both components of the glyoxalase system as an effective intervention to increase lifespan in P. anserina.

The mitochondrial kinase PINK1, stress response and Parkinson's disease.

Mitochondrial dysfunction is well documented in presymptomatic brain tissue with Parkinson's disease (PD). Identification of the autosomal recessive variant PARK6 caused by loss-of-function mutations in the mitochondrial kinase PINK1 provides an opportunity to dissect pathogenesis. Although PARK6 shows clinical differences to PD, the induction of alpha-synuclein "Lewy" pathology by PINK1-deficiency proves that mitochondrial pathomechanisms are relevant for old-age PD. Mitochondrial dysfunction is induced by PINK1 deficiency even in peripheral tissues unaffected by disease, consistent with the ubiquitous expression of PINK1. It remains unclear whether this dysfunction is due to PINK1-mediated phosphorylation of proteins inside or outside mitochondria. Although PINK1 deficiency affects the mitochondrial fission/fusion balance, cell stress is required in mammals to alter mitochondrial dynamics and provoke apoptosis. Clearance of damaged mitochondria depends on pathways including PINK1 and Parkin and is critical for postmitotic neurons with high energy demand and cumulative stress, providing a mechanistic concept for the tissue specificity of disease.

Parkinson phenotype in aged PINK1-deficient mice is accompanied by progressive mitochondrial dysfunction in absence of neurodegeneration.

BACKGROUND: Parkinson's disease (PD) is an adult-onset movement disorder of largely unknown etiology. We have previously shown that loss-of-function mutations of the mitochondrial protein kinase PINK1 (PTEN induced putative kinase 1) cause the recessive PARK6 variant of PD. METHODOLOGY/PRINCIPAL FINDINGS: Now we generated a PINK1 deficient mouse and observed several novel phenotypes: A progressive reduction of weight and of locomotor activity selectively for spontaneous movements occurred at old age. As in PD, abnormal dopamine levels in the aged nigrostriatal projection accompanied the reduced movements. Possibly in line with the PARK6 syndrome but in contrast to sporadic PD, a reduced lifespan, dysfunction of brainstem and sympathetic nerves, visible aggregates of alpha-synuclein within Lewy bodies or nigrostriatal neurodegeneration were not present in aged PINK1-deficient mice. However, we demonstrate PINK1 mutant mice to exhibit a progressive reduction in mitochondrial preprotein import correlating with defects of core mitochondrial functions like ATP-generation and respiration. In contrast to the strong effect of PINK1 on mitochondrial dynamics in Drosophila melanogaster and in spite of reduced expression of fission factor Mtp18, we show reduced fission and increased aggregation of mitochondria only under stress in PINK1-deficient mouse neurons. CONCLUSION: Thus, aging Pink1(-/-) mice show increasing mitochondrial dysfunction resulting in impaired neural activity similar to PD, in absence of overt neuronal death.

Parkinson patient fibroblasts show increased alpha-synuclein expression.

Parkinson's disease (PD) is a neurodegenerative movement disorder of advanced age with largely unknown etiology, but well documented tissue damage from oxidative stress. Increased alpha-synuclein (SNCA) expression is known to cause a rare form of PD, early-onset autosomal dominant PARK4. We have previously shown that loss-of-function mutations of the mitochondrial kinase PINK1 which cause the early-onset recessive PARK6 variant result in oxidative damage in patient fibroblasts. We now investigated the molecular chain of events from mitochondrial dysfunction to cell death which is largely unknown. Primary skin fibroblast cultures from patients were analysed for gene expression anomalies. In G309D-PINK1 patient fibroblasts, mainly genes regulated by oxidative stress, as well as genes encoding synaptic proteins such as SNCA showed altered expression. The induction of SNCA was also observed in control fibroblasts with knock-down of PINK1. The induction of SNCA expression was found to constitute a specific disease biomarker in sporadic PD patient fibroblasts. To understand the mechanism of this induction, we exposed control fibroblasts to oxidative, proteasomal and endoplasmic reticulum stress and were able to trigger the SNCA expression upregulation. Our data indicate that loss-of-function of PINK1 leads to enhanced alpha-synuclein expression and altered cell-cell contact. Alpha-synuclein induction might represent a common event for different variants of PD as well as a PD-specific trigger of neurodegeneration. We propose that the expression changes described might potentially serve as biomarkers that allow objective PD patient diagnosis in an accessible, peripheral tissue.