More Like this

1. MitoBK Ca channel is functionally associated with its regulatory β1 subunit in cardiac mitochondria

   https://doi.org/10.1113/JP277769  

   Balderas, Enrique ; Torres, Natalia S. ; Rosa‐Garrido, Manuel ; Chaudhuri, Dipayan ; Toro, Ligia ; Stefani, Enrico ; Olcese, Riccardo ( July 2019 , The Journal of Physiology)

   Association of plasma membrane BK_Cachannels with BK‐β subunits shapes their biophysical properties and physiological roles; however, functional modulation of the mitochondrial BK_Cachannel (mitoBK_Ca) by BK‐β subunits is not established.

   MitoBK_Ca‐α and the regulatory BK‐β1 subunit associate in mouse cardiac mitochondria.

   A large fraction of mitoBK_Cadisplay properties similar to that of plasma membrane BK_Cawhen associated with BK‐β1 (left‐shifted voltage dependence of activation,V_1/2 = −55 mV, 12 µmmatrix Ca²⁺).

   In BK‐β1 knockout mice, cardiac mitoBK_Cadisplayed a lowP_oand a depolarizedV_1/2of activation (+47 mV at 12 µmmatrix Ca²⁺)

   Co‐expression of BK_Cawith the BK‐β1 subunit in HeLa cells doubled the density of BK_Cain mitochondria.

   The present study supports the view that the cardiac mitoBK_Cachannel is functionally modulated by the BK‐β1 subunit; proper targeting and activation of mitoBK_Cashapes mitochondrial Ca²⁺handling.

   Association of the plasma membrane BK_Cachannel with auxiliary BK‐β1–4 subunits profoundly affects the regulatory mechanisms and physiological processes in which this channel participates. However, functional association of mitochondrial BK (mitoBK_Ca) with regulatory subunits is unknown. We report that mitoBK_Cafunctionally associates with its regulatory subunit BK‐β1 in adult rodent cardiomyocytes. Cardiac mitoBK_Cais a calcium‐ and voltage‐activated channel that is sensitive to paxilline with a large conductance for K⁺of 300 pS. Additionally, mitoBK_Cadisplays a high open probability (P_o) and voltage half‐activation (V_1/2 = −55 mV,n = 7) resembling that of plasma membrane BK_Cawhen associated with its regulatory BK‐β1 subunit. Immunochemistry assays demonstrated an interaction between mitochondrial BK_Ca‐α and its BK‐β1 subunit. Mitochondria from the BK‐β1 knockout (KO) mice showed sparse mitoBK_Cacurrents (five patches with mitoBK_Caactivity out of 28 total patches fromn = 5 different hearts), displaying a depolarizedV_1/2of activation (+47 mV in 12 µmmatrix Ca²⁺). The reduced activity of mitoBK_Cawas accompanied by a high expression of BK_Catranscript in the BK‐β1 KO, suggesting a lower abundance of mitoBK_Cachannels in this genotype. Accordingly, BK‐β1subunit increased the localization of BKDEC (i.e. the splice variant of BK_Cathat specifically targets mitochondria) into mitochondria by two‐fold. Importantly, both paxilline‐treated and BK‐β1 KO mitochondria displayed a more rapid Ca²⁺overload, featuring an early opening of the mitochondrial transition pore. We provide strong evidence that mitoBK_Caassociates with its regulatory BK‐β1 subunit in cardiac mitochondria, ensuring proper targeting and activation of the mitoBK_Cachannel that helps to maintain mitochondrial Ca²⁺homeostasis.

    

   more » « less
2. Diet alters age-related remodeling of aortic collagen in mice susceptible to atherosclerosis

   https://doi.org/10.1152/ajpheart.00420.2020  

   Watson, Shana R. ; Cooper, Kara M. ; Liu, Piaomu ; Gharraee, Nazli ; Du, Liya ; Han, Savannah M. ; Peña, Edsel A. ; Sutton, Michael A. ; Eberth, John F. ; Lessner, Susan M. ( January 2021 , American Journal of Physiology-Heart and Circulatory Physiology)

   null (Ed.)

   Vascular cells restructure extracellular matrix in response to aging or changes in mechanical loading. Here, we characterized collagen architecture during age-related aortic remodeling in atherosclerosis-prone mice. We hypothesized that changes in collagen fiber orientation reflect an altered balance between passive and active forces acting on the arterial wall. We examined two factors that can alter this balance, endothelial dysfunction and reduced smooth muscle cell (SMC) contractility. Collagen fiber organization was visualized by second-harmonic generation microscopy in aortic adventitia of apolipoprotein E (apoE) knockout (KO) mice at 6 wk and 6 mo of age on a chow diet and at 7.5 mo of age on a Western diet (WD), using image analysis to yield mean fiber orientation. Adventitial collagen fibers became significantly more longitudinally oriented with aging in apoE knockout mice on chow diet. Conversely, fibers became more circumferentially oriented with aging in mice on WD. Total collagen content increased significantly with age in mice fed WD. We compared expression of endothelial nitric oxide synthase and acetylcholine-mediated nitric oxide release but found no evidence of endothelial dysfunction in older mice. Time-averaged volumetric blood flow in all groups showed no significant changes. Wire myography of aortic rings revealed decreases in active stress generation with age that were significantly exacerbated in WD mice. We conclude that the aorta displays a distinct remodeling response to atherogenic stimuli, indicated by altered collagen organization. Collagen reorganization can occur in the absence of altered hemodynamics and may represent an adaptive response to reduced active stress generation by vascular SMCs. NEW & NOTEWORTHY The following major observations were made in this study: 1) aortic adventitial collagen fibers become more longitudinally oriented with aging in apolipoprotein E knockout mice fed a chow diet; 2) conversely, adventitial collagen fibers become more circumferentially oriented with aging in apoE knockout mice fed a high-fat diet; 3) adventitial collagen content increases significantly with age in mice on a high-fat diet; 4) these alterations in collagen organization occur largely in the absence of hemodynamic changes; and 5) circumferential reorientation of collagen is associated with decreased active force generation (contractility) in aged mice on a high-fat diet. 

   more » « less
3. Chronic statin therapy is associated with enhanced cutaneous vascular responsiveness to sympathetic outflow during passive heat stress

   https://doi.org/10.1113/JP278237  

   Greaney, Jody L. ; Stanhewicz, Anna E. ; Kenney, W. Larry ( August 2019 , The Journal of Physiology)

   Impairments in both central sympathetic and peripheral microvascular function contribute to blunted reflex cutaneous vasodilatation during heat stress in healthy older adults.

   Hypercholesterolaemia is associated with decrements in neurovascular function; however, little is known about the impact of hypercholesterolaemia on the integrated responses to heat stress. Further, whether chronic statin therapy alters skin sympathetic outflow or its relation to cutaneous vascular conductance during heat stress is unknown.

   We demonstrate that reflex cutaneous vasodilatation is impaired in older hypercholesterolaemic adults but not in formerly hypercholesterolaemic adults currently treated with a statin compared to age‐matched controls.

   Additionally, chronic statin treatment‐induced improvements in reflex vasodilatation are mediated, in part, by increases in end‐organ responsiveness to efferent sympathetic outflow during whole‐body heating.

   These data add to the growing body of literature substantiating the beneficial pleiotropic neurovascular effects of chronic statin treatment and provide further support for the use of statins to confer additional cardioprotective benefits in older adults.

   Attenuated reflex cutaneous vasodilatation in healthy human ageing is mediated by alterations in both central (sympathetic outflow) and peripheral (microvascular endothelial) function. Hypercholesterolaemia is associated with further impairments in neurovascular function. HMG‐CoA reductase inhibitors (statins) improve cutaneous endothelium‐dependent dilatation; however, whether statin therapy alters skin sympathetic nervous system activity (SSNA) or its relation to cutaneous vascular conductance (CVC) during passive heat stress is unknown. We hypothesized that (1) hypercholesterolaemic older adults would demonstrate blunted increases in both SSNA and CVC during passive heating and (2) chronic statin treatment would improve the response range and sensitivity of the SSNA:CVC relation. Reflex vasodilatation in response to a 1.0°C rise in oral temperature (T_or; water perfused suit) was induced in 13 healthy normocholesterolaemic adults (62 ± 2 years; LDL = 113 ± 7 mg/dl), 10 hypercholesterolaemic adults (60 ± 1 years; LDL = 183 ± 2 mg/dl), and 10 previously hypercholesterolaemic adults (64 ± 1 years; LDL = 102 ± 2 mg/dl) treated with lipophilic statin (10–40 mg daily). SSNA (peroneal microneurography) and red cell flux (laser‐Doppler flowmetry) in the innervated dermatome (dorsum of foot) were continuously measured. Reflex vasodilatation was blunted in hypercholesterolaemic adults, but not in statin‐treated adults, compared to normocholesterolaemic adults (at ∆T_or = 1.0°C: normal = 36 ± 1%CVC_max, high = 32 ± 1%CVC_max, statin = 38 ± 1%CVC_max;P < 0.01). ∆SSNA was not different (at ∆T_or = 1.0°C: normal: ∆ = 393 ± 96%, high: ∆ = 311 ± 120%, statin: ∆ = 256 ± 90%;P = 0.11). The slope of the SSNA:CVC relation was blunted in hypercholesterolaemic adults (0.02 ± 0.03%CVC_max/%_baseline) compared to both normocholesterolaemic (0.09 ± 0.02%CVC_max/%_baseline;P = 0.024) and statin‐treated (0.12 ± 0.05%CVC_max/%_baseline;P = 0.03) adults. Chronic statin treatment improves reflex cutaneous vasodilatation in formerly hypercholesterolaemic older adults by increasing end‐organ responsiveness to sympathetic outflow during passive heat stress.

    

   more » « less
4. A chloride channel blocker prevents the suppression by inorganic phosphate of the cytosolic calcium signals that control muscle contraction

   https://doi.org/10.1113/JP279917  

   Ferreira, Juan J. ; Pequera, Germán ; Launikonis, Bradley S. ; Ríos, Eduardo ; Brum, Gustavo ( October 2020 , The Journal of Physiology)

    Accumulation of inorganic phosphate (P_i) may contribute to muscle fatigue by precipitating calcium salts inside the sarcoplasmic reticulum (SR). Neither direct demonstration of this process nor definition of the entry pathway of P_iinto SR are fully established.

    We showed that P_ipromoted Ca²⁺release at concentrations below 10 mmand decreased it at higher concentrations. This decrease correlated well with that of [Ca²⁺]_SR.

    Pre‐treatment of permeabilized myofibres with 2 mmCl⁻channel blocker 9‐anthracenecarboxylic acid (9AC) inhibited both effects of P_i.

    The biphasic dependence of Ca²⁺release on [P_i] is explained by a direct effect of P_iacting on the SR Ca²⁺release channel, combined with the intra‐SR precipitation of Ca²⁺salts. The effects of 9AC demonstrate that P_ienters the SR via a Cl⁻pathway of an as‐yet‐undefined molecular nature.

   Fatiguing exercise causes hydrolysis of phosphocreatine, increasing the intracellular concentration of inorganic phosphate (P_i). P_idiffuses into the sarcoplasmic reticulum (SR) where it is believed to form insoluble Ca²⁺salts, thus contributing to the impairment of Ca²⁺release. Information on the P_ientrance pathway is still lacking. In amphibian muscles endowed with isoform 3 of the RyR channel, Ca²⁺spark frequency is correlated with the Ca²⁺load of the SR and can be used to monitor this variable. We studied the effects of P_ion Ca²⁺sparks in permeabilized fibres of the frog. Relative event frequency (f/f_ref) rose with increasing [P_i], reaching 2.54 ± 1.6 at 5 mm,and then decreased monotonically, reaching 0.09 ± 0.03 at [P_i] = 80 mm. Measurement of [Ca²⁺]_SRconfirmed a decrease correlated with spark frequency at high [P_i]. A large [Ca²⁺]_SRsurge was observed upon P_iremoval. Anion channels are a putative path for P_iinto the SR. We tested the effect of the chloride channel blocker 9‐anthracenecarboxylic acid (9AC) on P_ientrance. 9AC (400 µm)applied to the cytoplasm produced a non‐significant increase in spark frequency and reduced the P_ieffects on this parameter. Fibre treatment with 2 mm9AC in the presence of high cytoplasmic Mg²⁺suppressed the effects of P_ion [Ca²⁺]_SRand spark frequency up to 55 mm[P_i]. These results suggest that chloride channels (or transporters) provide the main pathway of inorganic phosphate into the SR and confirm that P_iimpairs Ca²⁺release by accumulating and precipitating with Ca²⁺inside the SR, thus contributing to myogenic fatigue.

    

   more » « less
5. The effects of bone morphogenetic protein 2 and thrombopoietin treatment on angiogenic properties of endothelial cells derived from the lung and bone marrow of young and aged, male and female mice

   https://doi.org/10.1096/fj.202001616RR  

   Dadwal, Ushashi C. ; Bhatti, Fazal Ur Rehman ; Awosanya, Olatundun D. ; Nagaraj, Rohit U. ; Perugini, III, Anthony J. ; Sun, Seungyup ; Valuch, Conner R. ; de Andrade Staut, Caio ; Mendenhall, Stephen K. ; Tewari, Nikhil P. ; et al ( August 2021 , The FASEB Journal)

   With an aging world population, there is an increased risk of fracture and impaired healing. One contributing factor may be aging‐associated decreases in vascular function; thus, enhancing angiogenesis could improve fracture healing. Both bone morphogenetic protein 2 (BMP‐2) and thrombopoietin (TPO) have pro‐angiogenic effects. The aim of this study was to investigate the effects of treatment with BMP‐2 or TPO on the in vitro angiogenic and proliferative potential of endothelial cells (ECs) isolated from lungs (LECs) or bone marrow (BMECs) of young (3‐4 months) and old (22‐24 months), male and female, C57BL/6J mice. Cell proliferation, vessel‐like structure formation, migration, and gene expression were used to evaluate angiogenic properties. In vitro characterization of ECs generally showed impaired vessel‐like structure formation and proliferation in old ECs compared to young ECs, but improved migration characteristics in old BMECs. Differential sex‐based angiogenic responses were observed, especially with respect to drug treatments and gene expression. Importantly, these studies suggest that NTN1, ROBO2, and SLIT3, along with angiogenic markers (CD31, FLT‐1, ANGPT1, and ANGP2) differentially regulate EC proliferation and functional outcomes based on treatment, sex, and age. Furthermore, treatment of old ECs with TPO typically improved vessel‐like structure parameters, but impaired migration. Thus, TPO may serve as an alternative treatment to BMP‐2 for fracture healing in aging owing to improved angiogenesis and fracture healing, and the lack of side effects associated with BMP‐2.

    

   more » « less