Up-regulation of ryanodine receptor expression increases the calcium-induced calcium release and spontaneous calcium signals in cerebral arteries from hindlimb unloaded rats

Microgravity induces a redistribution of blood volume. Consequently, astronauts' body pressure is modified so that the upright blood pressure gradient is abolished, thereby inducing a modification in cerebral blood pressure. This effect is mimicked in the hindlimb unloaded rat model. After a duration of 8 days of unloading, Ca²⁺ signals activated by depolarization and inositol-1,4,5-trisphosphate intracellular release were increased in cerebral arteries. In the presence of ryanodine and thapsigargin, the depolarization-induced Ca²⁺ signals remained increased in hindlimb suspended animals, indicating that Ca²⁺ influx and Ca²⁺-induced Ca²⁺ release mechanism were both increased. Spontaneous Ca²⁺ waves and localized Ca²⁺ events were also investigated. Increases in both amplitude and frequency of spontaneous Ca²⁺ waves were measured in hindlimb suspension conditions. After pharmacological segregation of Ca²⁺ sparks and Ca²⁺ sparklets, their kinetic parameters were characterized. Hindlimb suspension induced an increase in the frequencies of both Ca²⁺ localized events, suggesting an increase of excitability. Labeling with bodipy compounds suggested that voltage-dependent Ca²⁺ channels and ryanodine receptor expressions were increased. Finally, the expression of the ryanodine receptor subtype 1 (RyR1) was increased in hindlimb unloading conditions. Taken together, these results suggest that RyR1 expression and voltage-dependent Ca²⁺ channels activity are the focal points of the regulation of Ca²⁺ signals activated by vasoconstriction in rat cerebral arteries with an increase of the voltage-dependent Ca²⁺ influx

Reducing Hypermuscularization of the Transitional Segment between Arterioles and Capillaries Protects Against Spontaneous Intracerebral Hemorrhage

International audienceBackground: Spontaneous deep intracerebral hemorrhage (ICH) is a devastating subtype of stroke without specific treatments. It has been thought that smooth muscle cell (SMC) degeneration at the site of arteriolar wall rupture may be sufficient to cause hemorrhage. However, deep ICHs are rare in some aggressive small vessel diseases that are characterized by significant arteriolar SMC degeneration. Here we hypothesized that a second cellular defect may be required for the occurrence of ICH. Methods: We studied a genetic model of spontaneous deep ICH using Col4a1+/G498V and Col4a1+/G1064D mouse lines that are mutated for the alpha1 chain of Collagen type IV. We analyzed cerebroretinal microvessels, performed genetic rescue experiments, vascular reactivity analysis and computational modeling. We examined post-mortem brain tissues from patients with sporadic deep ICH. Results: We identified in the normal cerebroretinal vasculature a novel segment between arterioles and capillaries, herein called the transitional segment (TS), that is covered by mural cells distinct from SMCs and pericytes. In Col4a1 mutant mice, this TS was hypermuscularized, with a hyperplasia of mural cells expressing more contractile proteins, whereas the upstream arteriole exhibited a loss of SMCs. Mechanistically, TS showed a transient increase in proliferation of mural cells during post-natal maturation. Mutant brain microvessels, unlike mutant arteries, displayed a significant upregulation of SM genes and Notch3 target genes, and genetic reduction of Notch3 in Col4a1+/G498V mice protected against ICH. Retina analysis showed that hypermuscularization of the TS was attenuated but arteriolar SMC loss unchanged in Col4a1+/G498V, Notch3+/- mice. Moreover, hypermuscularization of the retinal TS increased its contractility and tone and raised the intravascular pressure in the upstream feeding arteriole. We similarly found hypermuscularization of the TS and focal arteriolar SMC loss in brain tissues from patients with sporadic deep ICH. Conclusions: Our results suggest that hypermuscularization of the TS, via increased Notch3 activity, is involved in the occurrence of ICH in Col4a1 mutant mice, by raising the intravascular pressure in the upstream feeding arteriole and promoting its rupture at the site of SMC loss. Our human data indicate that these 2 mutually reinforcing vascular defects may represent a general mechanism of deep ICH

Identification et rôle fonctionnels de variants d'épissage du récepteur de la ryanodine de type 3 (RyR3)

La fonction du sous-type RYR 3 du récepteur de la ryanodine ne peut se comprendre qu'à travers l'étude de ses différents variants d'épissage. Dans les muscles lisses de souris, nous avons mis en évidence l'existence d'un variant court dominant négatif. En effet, dans le duodenum, celui-ci inhibe le sous-type RYR 2 responsable de la libération du calcium stocké dans le reticulum. L'isoforme complète de RYR3 n'interagit pas avec l'isoforme courte et code des oscillations calciques spontanées lors d'une surharge du contenu en calcium du reticulum. Enfin, cet épissage alternatif est modulé dans le myomètre lors de la gestation. A l'approche de la parturition, l'expression de l'isoforme complète domine ce qui permet aux voies de transduction aboutissant à la production d'ADP-ribose cyclique de produire la libération du calcium stocké, phénomène participant à la contraction utérine.The understanding of the function of ryanodine receptor subtype RYR3 needs the study of RYR3 alternative splicing. In mouse smooth muscles, we have shown the expression of short dominant negative variant. In fact, in duodenum, the short isoform inhibits the RYR2 subtype responsible for the release of stored calcium in reticulum. The complete isoform of RYR3 cannot interact with the short isoform but encodes spontaneous calcium oscillations only when the reticulum is calcium overloaded. This alternative splicing is also modulated in myometrium during pregnancy. Near the term, the expression of complete RYR3 isoform is dominant whch allows cyclic ADP-ribose-dependent transduction pathways to release stored calcium that participates to uterine contraction.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Isolation and Cannulation of Cerebral Parenchymal Arterioles

Intracerebral parenchymal arterioles (PAs), which include parenchymal arterioles, penetrating arterioles and pre-capillary arterioles, are high resistance blood vessels branching out from pial arteries and arterioles and diving into the brain parenchyma. Individual PA perfuse a discrete cylindrical territory of the parenchyma and the neurons contained within. These arterioles are a central player in the regulation of cerebral blood flow both globally (cerebrovascular autoregulation) and locally (functional hyperemia). PAs are part of the neurovascular unit, a structure that matches regional blood flow to metabolic activity within the brain and also includes neurons, interneurons, and astrocytes. Perfusion through PAs is directly linked to the activity of neurons in that particular territory and increases in neuronal metabolism lead to an augmentation in local perfusion caused by dilation of the feed PA. Regulation of PAs differs from that of better-characterized pial arteries. Pressure-induced vasoconstriction is greater in PAs and vasodilatory mechanisms vary. In addition, PAs do not receive extrinsic innervation from perivascular nerves — innervation is intrinsic and indirect in nature through contact with astrocytic endfeet. Thus, data regarding contractile regulation accumulated by studies using pial arteries does not directly translate to understanding PA function. Further, it remains undetermined how pathological states, such as hypertension and diabetes, affect PA structure and reactivity. This knowledge gap is in part a consequence of the technical difficulties pertaining to PA isolation and cannulation. In this manuscript we present a protocol for isolation and cannulation of rodent PAs. Further, we show examples of experiments that can be performed with these arterioles, including agonist-induced constriction and myogenic reactivity. Although the focus of this manuscript is on PA cannulation and pressure myography, isolated PAs can also be used for biochemical, biophysical, molecular, and imaging studies

Isolation and Cannulation of Cerebral Parenchymal Arterioles

Intracerebral parenchymal arterioles (PAs), which include parenchymal arterioles, penetrating arterioles and pre-capillary arterioles, are high resistance blood vessels branching out from pial arteries and arterioles and diving into the brain parenchyma. Individual PA perfuse a discrete cylindrical territory of the parenchyma and the neurons contained within. These arterioles are a central player in the regulation of cerebral blood flow both globally (cerebrovascular autoregulation) and locally (functional hyperemia). PAs are part of the neurovascular unit, a structure that matches regional blood flow to metabolic activity within the brain and also includes neurons, interneurons, and astrocytes. Perfusion through PAs is directly linked to the activity of neurons in that particular territory and increases in neuronal metabolism lead to an augmentation in local perfusion caused by dilation of the feed PA. Regulation of PAs differs from that of better-characterized pial arteries. Pressure-induced vasoconstriction is greater in PAs and vasodilatory mechanisms vary. In addition, PAs do not receive extrinsic innervation from perivascular nerves - innervation is intrinsic and indirect in nature through contact with astrocytic endfeet. Thus, data regarding contractile regulation accumulated by studies using pial arteries does not directly translate to understanding PA function. Further, it remains undetermined how pathological states, such as hypertension and diabetes, affect PA structure and reactivity. This knowledge gap is in part a consequence of the technical difficulties pertaining to PA isolation and cannulation. In this manuscript we present a protocol for isolation and cannulation of rodent PAs. Further, we show examples of experiments that can be performed with these arterioles, including agonist-induced constriction and myogenic reactivity. Although the focus of this manuscript is on PA cannulation and pressure myography, isolated PAs can also be used for biochemical, biophysical, molecular, and imaging studies

Chitosan as Reinforcement for Biopolymers - A Mini Review.

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

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Full length ryanodine receptor subtype 3 encodes spontaneous calcium oscillations in native duodenal smooth muscle cells

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Acidosis dilates brain parenchymal arterioles by conversion of calcium waves to sparks to activate BK channels

RATIONALE: Acidosis is a powerful vasodilator signal in the brain circulation. However, the mechanisms by which this response occurs are not well understood, particularly in the cerebral microcirculation. One important mechanism to dilate cerebral (pial) arteries is by activation of large-conductance, calcium-sensitive potassium (BK(Ca)) channels by local Ca(2+) signals (Ca(2+) sparks) through ryanodine receptors (RyRs). However, the role of this pathway in the brain microcirculation is not known. OBJECTIVE: The objectives of this study were to determine the mechanism by which acidosis dilates brain parenchymal arterioles (PAs) and to elucidate the roles of RyRs and BK(Ca) channels in this response. METHODS AND RESULTS: Internal diameter and vascular smooth muscle cell (VSMC) Ca(2+) signals were measured in isolated pressurized murine PAs, using imaging techniques. In physiological pH (7.4), VSMCs exhibited primarily RyR-dependent Ca(2+) waves. Reducing external pH from 7.4 to 7.0 in both normocapnic and hypercapnic conditions decreased Ca(2+) wave activity, and dramatically increased Ca(2+) spark activity. Acidic pH caused a dilation of PAs which was inhibited by about 60% by BK(Ca) channel or RyR blockers, in a non-additive manner. Similarly, dilator responses to acidosis were reduced by nearly 60% in arterioles from BK(Ca) channel knockout mice. Dilations induced by acidic pH were unaltered by inhibitors of K(ATP) channels or nitric oxide synthase. CONCLUSIONS: These results support the novel concept that acidification, by converting Ca(2+) waves to sparks, leads to the activation of BK(Ca) channels to induce dilation of cerebral parenchymal arterioles