Vascular alterations in Fukuyama type congenital muscular dystrophy

The importance of dystrophin and the dystrophin associated proteins in vascular smooth muscle

This review details the role of dystrophin and the dystrophin associated proteins (DAPs) in the vascular smooth muscle. Dystrophin is most comprehensively studied in the skeletal muscle due to serious symptoms found related to the skeletal muscle of patients with muscular dystrophy. Mutations in the dystrophin gene, or DAPs genes, result in a wide range of muscular dystrophies. In skeletal muscle, dystrophin is known to act to as a cytoskeletal stabilization protein and protects cells against contraction-induced damage. In skeletal muscle, dystrophin stabilizes the plasma membrane by transmitting forces generated by sarcomeric contraction to the extracellular matrix (ECM). Dystrophin is a scaffold that binds the dystroglycan complex (DGC) and has many associated proteins (DAPs). These DAPs include sarcoglycans, syntrophins, dystroglycans, dystrobrevin, neuronal nitric oxide synthase, and caveolins. The DAPs provide biomechanical support to the skeletal or cardiac plasma membrane during contraction, and loss of one or several of these DAPs leads to plasma membrane fragility. Dystrophin is expressed near the plasma membrane of all muscles, including cardiac and vascular smooth muscle, and some neurons. Dystrophic mice have noted biomechanical irregularities in the carotid arteries and spontaneous motor activity in portal vein altered when compared to wild type mice. Additionally, some studies suggest the vasculature of patients and animal models with muscular dystrophy is abnormal. Although the function of dystrophin and the DAPs in vascular smooth muscle is not thoroughly established in the field, this review makes the point that these proteins are expressed, and important and further study is warranted.

Hypoxia and Hypoxia-Inducible Factor Signaling in Muscular Dystrophies: Cause and Consequences

Muscular dystrophies (MDs) are a group of inherited degenerative muscle disorders characterized by a progressive skeletal muscle wasting. Respiratory impairments and subsequent hypoxemia are encountered in a significant subgroup of patients in almost all MD forms. In response to hypoxic stress, compensatory mechanisms are activated especially through Hypoxia-Inducible Factor 1 α (HIF-1α). In healthy muscle, hypoxia and HIF-1α activation are known to affect oxidative stress balance and metabolism. Recent evidence has also highlighted HIF-1α as a regulator of myogenesis and satellite cell function. However, the impact of HIF-1α pathway modifications in MDs remains to be investigated. Multifactorial pathological mechanisms could lead to HIF-1α activation in patient skeletal muscles. In addition to the genetic defect per se, respiratory failure or blood vessel alterations could modify hypoxia response pathways. Here, we will discuss the current knowledge about the hypoxia response pathway alterations in MDs and address whether such changes could influence MD pathophysiology.

New MRI Findings in Fukuyama Congenital Muscular Dystrophy: Brain Stem and Venous System Anomalies

BACKGROUND AND PURPOSE

Leptomeningeal glioneuronal heterotopia of the brain stem and cerebral migration abnormality were pathologically reported in Fukuyama congenital muscular dystrophy, but the radiologic assessments of the brain stem and cerebral venous system (which may be involved in the development of the anomaly) were insufficient. Here, we evaluated the brain stem and cerebral veins on MR imaging in patients with Fukuyama congenital muscular dystrophy.

MATERIALS AND METHODS

We retrospectively reviewed the MR imaging findings of 27 patients with Fukuyama congenital muscular dystrophy. We visually assessed the hypoplasia, superficial structures, and signal intensity of the brain stem on T2WI, FLAIR, and double inversion recovery images and the cerebral, superficial, and deep veins with and without hemorrhage on T2WI and SWI.

RESULTS

Brain stem fluffy structures were seen in 96.3% of the cases on T2WI. Superficial high signal intensity on T2WI and FLAIR images was seen in 96.3% and 92.6%, respectively. Abnormally located superficial vessels beneath the cortex were seen in 11.1% on T2WI. Hypoplasia of the superficial cerebral veins was noted in all patients who underwent SWI. Dilated and tortuous subependymal veins were seen in 40.0% on SWI. Hemorrhages were seen in 11.1% on T2WI and in 60.0% on SWI.

CONCLUSIONS

Superficial brain stem structural and signal abnormalities would be useful MR imaging findings to diagnose Fukuyama congenital muscular dystrophy as well as venous system abnormalities. Clinicians must keep in mind that this disease has a high risk of hemorrhage.

Targeting angiogenesis in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) represents one of the most devastating types of muscular dystrophies which affect boys already at early childhood. Despite the fact that the primary cause of the disease, namely the lack of functional dystrophin is known already for more than 30 years, DMD still remains an incurable disease. Thus, an enormous effort has been made during recent years to reveal novel mechanisms that could provide therapeutic targets for DMD, especially because glucocorticoids treatment acts mostly symptomatic and exerts many side effects, whereas the effectiveness of genetic approaches aiming at the restoration of functional dystrophin is under the constant debate. Taking into account that dystrophin expression is not restricted to muscle cells, but is present also in, e.g., endothelial cells, alterations in angiogenesis process have been proposed to have a significant impact on DMD progression. Indeed, already before the discovery of dystrophin, several abnormalities in blood vessels structure and function have been revealed, suggesting that targeting angiogenesis could be beneficial in DMD. In this review, we will summarize current knowledge about the angiogenesis status both in animal models of DMD as well as in DMD patients, focusing on different organs as well as age- and sex-dependent effects. Moreover, we will critically discuss some approaches such as modulation of vascular endothelial growth factor or nitric oxide related pathways, to enhance angiogenesis and attenuate the dystrophic phenotype. Additionally, we will suggest the potential role of other mediators, such as heme oxygenase-1 or statins in those processes.

Abnormal vascular development in zebrafish models for fukutin and FKRP deficiency

Fukutin and fukutin-related protein (FKRP) are involved in the glycosylation of α-dystroglycan, a key receptor for basement membrane proteins. Aberrant α-dystroglycan glycosylation leads to a broad spectrum of disorders, ranging from limb girdle muscular dystrophy to Walker-Warburg syndrome. This is the first study investigating a role of fukutin and FKRP-mediated glycosylation in angiogenesis. Transgenic zebrafish expressing enhanced green fluorescent protein in blood vessels were treated with morpholino antisense oligonucleotides that blocked the expression of fukutin, FKRP and dystroglycan. All morphant fish showed muscle damage and vascular abnormalities at day 1 post-fertilization. Intersegmental vessels of somites failed to reach the dorsal longitudinal anastomosis and in more severe phenotypes retracted further or were in some cases even completely missing. In contrast, the eye vasculature was distorted in both fukutin and FKRP morphants, but not in dystroglycan morphants or control fish. The eye size was also smaller in the fukutin and FKRP morphants when compared with dystroglycan knockdown fish and controls. In general, the fukutin morphant fish had the most severe skeletal muscle and eye phenotype. Our findings suggest that fukutin and FKRP have functions that affect ocular development in zebrafish independently of dystroglycan. Despite anecdotal reports about vascular abnormalities in patients affected by dystroglycanopathies, the clinical relevance of such lesions remains unclear and should be subject to further review and investigations.

Serum levels of vascular endothelial growth factor elevated in patients with muscular dystrophy

In patients with muscular dystrophy, such as Duchenne muscular dystrophy (DMD), microcirculation abnormalities and hypoxic ischemic conditions in muscle tissues are suspected to be induced by non-symptomatic coagulation fibrinolysis abnormalities and vascular dysfunction. Vascular endothelial growth factor (VEGF) is a critical regulating factor in angiogenesis that is known to be induced by hypoxic and/or ischemic conditions. To examine whether VEGF is associated with muscular dystrophy, we measured serum levels of VEGF in 52 patients with DMD, 15 with Becker muscular dystrophy (BMD), 20 with Fukuyama congenital muscular dystrophy (FCMD), eight with myotonic dystrophy (DM), and four with spinal muscular atrophy (SMA), as well as in 15 healthy and eight disease controls. The serum level of VEGF in the DMD patients was 267.7+/-25.3 pg/ml (10.5-800.0), while it was 358.8+/-96.3 pg/ml (0.2-1320.0) in the BMD patients, 261.4+/-45.6 pg/ml (0.1-758.0) in the FCMD patients, 165.0+/-63.4 pg/ml (2.6-479.0) in the DM patients, 96.0+/-30.3 pg/ml (41.0-168.0) in the SMA patients, 148.3+/-20.1 pg/ml (46.5-298.0) in the healthy controls, and 154.1+/-54.0 pg/ml (7.2-343.0) in the disease controls. The level of VEGF in BMD was significantly elevated, as compared with DM, SMA, and control groups. Further, the level of VEGF in the bedridden sub-group of DMD patients was significantly elevated as compared with chair-bound DMD, DM, SMA, and control groups. We concluded that VEGF may reflect hypoxic and/or ischemic conditions in muscle tissue, and have a relationship with the process of disease progression in DMD and BMD patients.

A possible role of tryptase in angiogenesis in the brain of mdx mouse, a model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is characterized by muscle degeneration and affects the CNS. Dystrophin is absent in muscle and CNS of both DMD patients and mdx mouse, a model of DMD. While the involvement of vascular compartment in DMD was poorly investigated, some studies suggested a role for mast cells (MC). Tryptase, contained in the MC granules, stimulates angiogenesis in vitro and in vivo. We demonstrated for the first time a correlation between the extent of angiogenesis and the number of tryptase-positive neurons and microvessels and suggest that the tryptase contained in the neurons and in the endothelial cells of the mdx mouse brain may be involved in the regulation of angiogenesis taking place in mdx mouse.

Vascular endothelial growth factor and vascular endothelial growth factor receptor-2 expression in mdx mouse brain

Recent data have demonstrated that vascular endothelial growth factor (VEGF) is expressed by subsets of neurons, coincident with angiogenesis within its developing cerebral cortex. In this study, with the aim of elucidating the mechanisms of vascular involvement during brain impairment in Duchenne muscular distrophy (DMD), we have correlated the vascular density with VEGF and VEGF receptor-2 (VEGFR-2) expression in the brain cortex of normal and mdx mouse, an animal model with a genetic defect in a region homologous with the human DMD gene. Results showed that in mdx mouse, tissue area occupied by microvessels positive to factor VIII related antigen and VEGFR-2 increased in parallel to the tissue area occupied by neurons positive to VEGF. Our data suggest that increased vascularity in the brain of mdx mouse may be due, at least in part, to proliferation of endothelial cells in response to VEGF secreted by neuronal cells.

Coagulation and fibrinolysis disorder in muscular dystrophy

To investigate whether there are any basic abnormalities of coagulation and fibrinolysis in muscular dystrophy, we measured serum levels of the MM isozyme of creatine kinase (CK-MM), fibrin and fibrinogen degradation products (FDP), plasma levels of fibrinogen, antithrombin (AT), and D-dimer in 36 patients with Duchenne muscular dystrophy (DMD), 11 with Becker muscular dystrophy (BMD), 5 with Fukuyama congenital muscular dystrophy (FCMD), 5 with myotonic dystrophy (MyD), and 5 with spinal muscular atrophy (SMA) type 2. FDP levels were elevated in the patients with DMD, BMD, and FCMD (1.0 to 84.9 microg/ml), but not in the patients with MyD and SMA type 2. In DMD, BMD, and FCMD, FDP levels significantly correlated with CK-MM, but not with age, fibrinogen, AT, D-dimer, and type of dystrophy (multiple regression analysis; r(2) = 0.814, P < 0.0001). These findings suggested that enhanced coagulation and fibrinolysis are associated with muscle degeneration in patients with DMD, BMD, and FCMD.

Muscle and brain disease: an update

A number of syndromes included under this rubric are considered, and their main features discussed. The congenital muscular dystrophy of the Fukuyama type as it occurs in Japan and in the western world are almost certainly the same condition. The muscle disorder is associated with cerebral lesions which may be due to an arrest of neural migration or to demyelination. Muscle, eye and brain disease, or Santavuori's syndrome, shows ocular abnormalities, as well as those of the muscle and brain, as does the Walker-Warburg syndrome. In the latter disorder the cerebral lesions tend to be more severe, and it is more rapidly fatal. The manifestations of all these syndromes undoubtedly overlap, but there has been controversy on the question of their identity. Are they separate entities, or are they different expressions of a similar genetic disorder? The genes for all these conditions will have to be isolated to see if the different phenotypes are alleles of the same gene, or not. Some of the arguments, for and against, are presented.