Comparison between gentamycin and exon skipping treatments to restore ryanodine receptor subtype 2 functions in mdx mouse duodenum myocytes

Disrupted Calcium Homeostasis in Duchenne Muscular Dystrophy: A Common Mechanism behind Diverse Consequences

Duchenne muscular dystrophy (DMD) leads to disability and death in young men. This disease is caused by mutations in the DMD gene encoding diverse isoforms of dystrophin. Loss of full-length dystrophins is both necessary and sufficient for causing degeneration and wasting of striated muscles, neuropsychological impairment, and bone deformities. Among this spectrum of defects, abnormalities of calcium homeostasis are the common dystrophic feature. Given the fundamental role of Ca2+ in all cells, this biochemical alteration might be underlying all the DMD abnormalities. However, its mechanism is not completely understood. While abnormally elevated resting cytosolic Ca2+ concentration is found in all dystrophic cells, the aberrant mechanisms leading to that outcome have cell-specific components. We probe the diverse aspects of calcium response in various affected tissues. In skeletal muscles, cardiomyocytes, and neurons, dystrophin appears to serve as a scaffold for proteins engaged in calcium homeostasis, while its interactions with actin cytoskeleton influence endoplasmic reticulum organisation and motility. However, in myoblasts, lymphocytes, endotheliocytes, and mesenchymal and myogenic cells, calcium abnormalities cannot be clearly attributed to the loss of interaction between dystrophin and the calcium toolbox proteins. Nevertheless, DMD gene mutations in these cells lead to significant defects and the calcium anomalies are a symptom of the early developmental phase of this pathology. As the impaired calcium homeostasis appears to underpin multiple DMD abnormalities, understanding this alteration may lead to the development of new therapies. In fact, it appears possible to mitigate the impact of the abnormal calcium homeostasis and the dystrophic phenotype in the total absence of dystrophin. This opens new treatment avenues for this incurable disease.

Hydroxysafflor yellow A actives BKCa channels and inhibits L-type Ca channels to induce vascular relaxation

Hydroxy-safflor yellow A (HSYA) can exert a variety of effects upon the vascular system. However, the underlying mechanisms are not clear. The present study is to investigate its vasodilating effect and the mechanisms. Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were enrolled for studying effects of HSYA on blood pressure, vasodilation, intracellular Ca²⁺ transient and membrane ion channels. Vasodilation and intracellular Ca²⁺ transient were measured by using vasomotor assay and fluorescence imaging system, respectively. The effect of HSYA on the large conductance Ca²⁺ activated and voltage-gated potassium channel (BK_Ca channel) currents in rat mesentery artery and on L-type calcium channel (Ca-L) currents in HEK293cells expressed with Ca-L were investigated using patch clamp techniques. Blood pressure of SHR and WKY rats were concentration dependently reduced by HSYA with a larger effect of HSYA in SHR than that in WKY rats. The tension of mesenteric arteries induced by 3 μM phenylephrine was attenuated by HSYA (IC₅₀ = 90.8 μΜ). Patch clamp study showed that HSYA could activate BK_Ca channels and suppress Ca-L channels in a concentration dependent manner. The results of calcium signaling assays indicated that HSYA could reduce the intracellular free Ca²⁺ level. These findings demonstrate that HSYA could activate BK_Ca channels and inhibit Ca-L channels and reduce intracellular free Ca²⁺ level, which are probably important for its vasodilatory effect.

Blood brain barrier precludes the cerebral arteries to intravenously-injected antisense oligonucleotide

Alternative splicing of the ryanodine receptor subtype 3 (RyR3) produces a short isoform (RyR3S) able to negatively regulate the ryanodine receptor subtype 2 (RyR2), as shown in cultured smooth muscle cells from mice. The RyR2 subtype has a crucial role in the control of vascular reactivity via the fine tuning of Ca(2+) signaling to regulate cerebral vascular tone. In this study, we have shown that the inhibition of RyR3S expression by a specific antisense oligonucleotide (asRyR3S) was able to increase the Ca(2+) signals implicating RyR2 in cerebral arteries ex vivo. Moreover, we tried to inhibit the expression of RyR3S in vivo. The asRyR3S was complexed with JetPEI and injected intravenously coupled with several methods known to induce a blood brain barrier disruption. We tested solutions to induce osmotic choc (mannitol), inflammation (bacteria lipopolysaccharide and pertussis toxin), vasoconstriction or dilatation (sumatriptan, phenylephrine, histamine), CD73 activation (NECA) and lipid instability (Tween80). All tested technics failed to target asRyR3 in the cerebral arteries wall, whereas the molecule was included in hepatocytes or cardiomyocytes. Our results showed that the RyR3 alternative splicing could have a function in cerebral arteries ex vivo; however, the disruption of the blood brain barrier could not induce the internalization of antisense oligonucleotides in the cerebral arteries, in order to prove the function of RYR3 short isoform in vivo.

Ongoing therapeutic trials and outcome measures for Duchenne muscular dystrophy

Muscular dystrophy is a heterogeneous group of genetic disorders characterised by progressive muscle tissue degeneration. No effective treatment has been discovered for these diseases. Preclinical and clinical studies aimed at the development of new therapeutic approaches have been carried out, primarily in subjects affected with dystrophinopathies (Duchenne and Becker muscular dystrophy). In this review, we outline the current therapeutic approaches and past and ongoing clinical trials, highlighting both the advantages and limits of each one. The experimental designs of these trials were based on different rationales, including immunomodulation, readthrough strategies, exon skipping, gene therapy, and cell therapy. We also provide an overview of available outcome measures, focusing on their reliability in estimating meaningful clinical improvement in order to aid in the design of future trials. This perspective is extremely relevant to the field considering the recent development of novel therapeutic approaches that will result in an increasing number of clinical studies over the next few years.

Ryanodine receptors, calcium signaling, and regulation of vascular tone in the cerebral parenchymal microcirculation

The cerebral blood supply is delivered by a surface network of pial arteries and arterioles from which arise (parenchymal) arterioles that penetrate into the cortex and terminate in a rich capillary bed. The critical regulation of CBF, locally and globally, requires precise vasomotor regulation of the intracerebral microvasculature. This vascular region is anatomically unique as illustrated by the presence of astrocytic processes that envelope almost the entire basolateral surface of PAs. There are, moreover, notable functional differences between pial arteries and PAs. For example, in pial VSMCs, local calcium release events ("calcium sparks") through ryanodine receptor (RyR) channels in SR membrane activate large conductance, calcium-sensitive potassium channels to modulate vascular diameter. In contrast, VSMCs in PAs express functional RyR and BK channels, but under physiological conditions, these channels do not oppose pressure-induced vasoconstriction. Here, we summarize the roles of ryanodine receptors in the parenchymal microvasculature under physiologic and pathologic conditions, and discuss their importance in the control of CBF.

Spaceflight regulates ryanodine receptor subtype 1 in portal vein myocytes in the opposite way of hypertension

Gravity has a structural role for living systems. Tissue development, architecture, and organization are modified when the gravity vector is changed. In particular, microgravity induces a redistribution of blood volume and thus pressure in the astronaut body, abolishing an upright blood pressure gradient, inducing orthostatic hypotension. The present study was designed to investigate whether isolated vascular smooth muscle cells are directly sensitive to altered gravitational forces and, second, whether sustained blood pressure changes act on the same molecular target. Exposure to microgravity during 8 days in the International Space Station induced the decrease of ryanodine receptor subtype 1 expression in primary cultured myocytes from rat hepatic portal vein. Identical results were found in portal vein from mice exposed to microgravity during an 8-day shuttle spaceflight. To evaluate the functional consequences of this physiological adaptation, we have compared evoked calcium signals obtained in myocytes from hindlimb unloaded rats, in which the shift of blood pressure mimics the one produced by the microgravity, with those obtained in myocytes from rats injected with antisense oligonucleotide directed against ryanodine receptor subtype 1. In both conditions, calcium signals implicating calcium-induced calcium release were significantly decreased. In contrast, in spontaneous hypertensive rat, an increase in ryanodine receptor subtype 1 expression was observed as well as the calcium-induced calcium release mechanism. Taken together, our results shown that myocytes were directly sensitive to gravity level and that they adapt their calcium signaling pathways to pressure by the regulation of the ryanodine receptor subtype 1 expression.

Aminoglycoside modifying enzymes

Aminoglycosides have been an essential component of the armamentarium in the treatment of life-threatening infections. Unfortunately, their efficacy has been reduced by the surge and dissemination of resistance. In some cases the levels of resistance reached the point that rendered them virtually useless. Among many known mechanisms of resistance to aminoglycosides, enzymatic modification is the most prevalent in the clinical setting. Aminoglycoside modifying enzymes catalyze the modification at different -OH or -NH₂ groups of the 2-deoxystreptamine nucleus or the sugar moieties and can be nucleotidyltransferases, phosphotransferases, or acetyltransferases. The number of aminoglycoside modifying enzymes identified to date as well as the genetic environments where the coding genes are located is impressive and there is virtually no bacteria that is unable to support enzymatic resistance to aminoglycosides. Aside from the development of new aminoglycosides refractory to as many as possible modifying enzymes there are currently two main strategies being pursued to overcome the action of aminoglycoside modifying enzymes. Their successful development would extend the useful life of existing antibiotics that have proven effective in the treatment of infections. These strategies consist of the development of inhibitors of the enzymatic action or of the expression of the modifying enzymes.