Removal of FKBP12/12.6 from endothelial ryanodine receptors leads to an intracellular calcium leak and endothelial dysfunction

Immunosuppressant drug tacrolimus inhibits HUVEC angiogenesis and production of placental growth factor

BACKGROUND

Tacrolimus is a cornerstone of immunosuppression in solid organ transplants, but its use is linked with the development of endothelial dysfunction. Pregnant solid organ transplant recipients are four to six times more likely to develop preeclampsia, which is also associated with endothelial dysfunction. Therefore, this in vitro study investigated the acute effects of tacrolimus on the expression of common angiogenic factors related to preeclampsia, and effects on angiogeneis in primary human tissues.

METHODS

Primary human umbilical vein endothelial cells (HUVECs) were exposed to tacrolimus (0, 5, 20, 50 ng/mL) for 24h alone, or in combination with tumour necrosis factor (TNF, 10 ng/mL) and high dose glucose (25 mM). Cell culture concentrations of sFlt-1, PlGF and activin A were measured. In addition, the effect of tacrolimus on markers of endothelial dysfunction and permeability were assessed, as were the effect of tacrolimus on tube formation. Angiogenic factors and mRNA markers of oxidative stress and inflammation were also assessed in primary placental tissue after an acute 24 h exposure to tacrolimus.

RESULTS

Tacrolimus exposure significantly reduced HUVEC secretion of PlGF, increased production of activin A, andreduced tubular structure formation without impacting cell permeability or viability. There was no change in ICAM1 or VCAM1 expression in HUVECs treated with tacrolimus treatment alone, however co-culture with TNF significantly increased expression of ICAM1 and VCAM1. In placental explants tacrolimus did not change angiogenic factor production or markers of inflammation or oxidative stress.

CONCLUSION

An acute tacrolimus exposure reduced PlGF secretion and impaired angiogenesis in primary endothelial cells, without affecting. These findings provide a potential mechanistic basis for tacrolimus to contribute to the endothelial dysfunction contributing to preeclampsia.

An Immune-Independent Mode of Action of Tacrolimus in Promoting Human Extravillous Trophoblast Migration Involves Intracellular Calcium Release and F-Actin Cytoskeletal Reorganization

We have previously reported that the calcineurin inhibitor macrolide immunosuppressant Tacrolimus (TAC, FK506) can promote the migration and invasion of the human-derived extravillous trophoblast cells conducive to preventing implantation failure in immune-complicated gestations manifesting recurrent implantation failure. Although the exact mode of action of TAC in promoting implantation has yet to be elucidated, the integral association of its binding protein FKBP12 with the inositol triphosphate receptor (IP3R) regulated intracellular calcium [Ca2+]i channels in the endoplasmic reticulum (ER), suggesting that TAC can mediate its action through ER release of [Ca2+]i. Using the immortalized human-derived first-trimester extravillous trophoblast cells HTR8/SVneo, our data indicated that TAC can increase [Ca2+]I, as measured by fluorescent live-cell imaging using Fluo-4. Concomitantly, the treatment of HTR8/SVneo with TAC resulted in a major dynamic reorganization in the actin cytoskeleton, favoring a predominant distribution of cortical F-actin networks in these trophoblasts. Notably, the findings that TAC was unable to recover [Ca2+]i in the presence of the IP3R inhibitor 2-APB indicate that this receptor may play a crucial role in the mechanism of action of TAC. Taken together, our results suggest that TAC has the potential to influence trophoblast migration through downstream [Ca2+]i-mediated intracellular events and mechanisms involved in trophoblast migration, such as F-actin redistribution. Further research into the mono-therapeutic use of TAC in promoting trophoblast growth and differentiation in clinical settings of assisted reproduction is warranted.

Dantrolene and ryanodine receptors in COVID-19: The daunting task and neglected warden

Dantrolene (DTN) is a ryanodine receptor (RyR) antagonist that inhibits Ca²⁺ release from stores in the sarcoplasmic reticulum. DTN is mainly used in the management of malignant hyperthermia. RyRs are highly expressed in immune cells and are involved in different viral infections, including severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), because Ca²⁺ is necessary for viral replication, maturation and release. DTN can inhibit the proliferation of SARS-CoV-2, indicating its potential role in reducing entry and pathogenesis of SARS-CoV-2. DTN may increase clearance of SARS-CoV-2 and promote coronavirus disease 2019 (COVID-19) recovery by shortening the period of infection. DTN inhibits N-methyl-D-aspartate (NMDA) mediated platelets aggregations and thrombosis. Therefore, DTN may inhibit thrombosis and coagulopathy in COVID-19 through suppression of platelet NMDA receptors. Moreover, DTN has a neuroprotective effect against SARS-CoV-2 infection-induced brain injury through modulation of NMDA receptors, which are involved in excitotoxicity, neuronal injury and the development of neuropsychiatric disorders. In conclusion, DTN by inhibiting RyRs may attenuate inflammatory disorders in SARS-CoV-2 infection and associated cardio-pulmonary complications. Therefore, DNT could be a promising drug therapy against COVID-19. Preclinical and clinical studies are warranted in this regards.

Chronic Dantrolene Treatment Does Not Affect Hypertension, but Attenuates Sympathetic Stimulation Enhanced Atrial Fibrillation Inducibility in SHR

BACKGROUND

Ryanodine receptor (RyR) dysfunction in skeletal muscle (RyR1) leads to malignant hyperthermia, and in cardiac muscle (RyR2) triggers cardiac arrhythmias. We hypothesized that RyR dysfunction in vascular smooth muscle could increase vascular resistance and hypertension, and may contribute to increased atrial fibrillation (AF) in hypertension. Thus, stabilizing RyR function with chronic dantrolene treatment may attenuate hypertension and AF inducibility in spontaneously hypertensive rats (SHR).

METHODS

Male SHR (16 weeks old) were randomized into vehicle- (n = 10) and dantrolene-treated (10 mg/kg/day, n = 10) groups for 4 weeks. Wistar Kyoto (WKY, n = 11) rats served as controls. Blood pressures (BP) were monitored before and during the 4-week treatment. After 4-week treatment, direct BP, echocardiography, and hemodynamics were recorded. AF inducibility tests were performed in vivo at baseline and repeated under sympathetic stimulation (SS).

RESULTS

Compared with WKY, SHR had significantly higher BP throughout the experimental period. Dantrolene treatment had no effect on BP levels in SHR (final systolic BP 212 ± 9 mm Hg in vehicle group vs. 208 ± 16 mm Hg in dantrolene group, P > 0.05). AF inducibility was very low and not significantly different between 5-month-old WKY and SHR at baseline. However, under SS, AF inducibility and duration were significantly increased in SHR (20% in WKY vs. 60% in SHR-vehicle, P<0.05). Dantrolene treatment significantly attenuated AF inducibility under SS in SHR (60% in vehicle vs. 20% in dantrolene, P < 0.05).

CONCLUSIONS

Stabilizing RyR with chronic dantrolene treatment does not affect hypertension development in SHR. SHR has increased vulnerability to AF induction under SS, which can be attenuated with dantrolene treatment.

FK506 regulates Ca2+ release evoked by inositol 1,4,5-trisphosphate independently of FK-binding protein in endothelial cells

Background and Purpose

FK506 and rapamycin are modulators of FK‐binding proteins (FKBP) that are used to suppress immune function after organ and hematopoietic stem cell transplantations. The drugs share the unwanted side‐effect of evoking hypertension that is associated with reduced endothelial function and nitric oxide production. The underlying mechanisms are not understood. FKBP may regulate IP₃ receptors (IP₃R) and ryanodine receptors (RyR) to alter Ca²⁺ signalling in endothelial cells.

Experimental Approach

We investigated the effects of FK506 and rapamycin on Ca²⁺ release via IP₃R and RyR in hundreds of endothelial cells, using the indicator Cal‐520, in intact mesenteric arteries from male Sprague‐Dawley rats. IP₃Rs were activated by acetylcholine or localised photo‐uncaging of IP₃, and RyR by caffeine.

Key Results

While FKBPs were present, FKBP modulation with rapamycin did not alter IP₃‐evoked Ca²⁺ release. Conversely, FK506, which modulates FKBP and blocks calcineurin, increased IP₃‐evoked Ca²⁺ release. Inhibition of calcineurin (okadiac acid or cypermethrin) also increased IP₃‐evoked Ca²⁺ release and blocked FK506 effects. When calcineurin was inhibited, FK506 reduced IP₃‐evoked Ca²⁺ release. These findings suggest that IP₃‐evoked Ca²⁺ release is not modulated by FKBP, but by FK506‐mediated calcineurin inhibition. The RyR modulators caffeine and ryanodine failed to alter Ca²⁺ signalling suggesting that RyR is not functional in native endothelium.

Conclusion and Implications

The hypertensive effects of the immunosuppressant drugs FK506 and rapamycin, while mediated by endothelial cells, do not appear to be exerted at the documented cellular targets of Ca²⁺ release and altered FKBP binding to IP₃ and RyR.

Direct Targeting of the mTOR (Mammalian Target of Rapamycin) Kinase Improves Endothelial Permeability in Drug-Eluting Stents-Brief Report

Objective- Drug-eluting stents eluting canonical mTOR (mammalian target of rapamycin) inhibitors are widely used to treat coronary artery disease but accelerate the development of atherosclerosis within the stent (neoatherosclerosis)-a leading cause of late stent failure. We recently showed that canonical mTOR inhibitors bind FKBP12.6 (12.6-kDa FK506-binding protein 12), displace it from calcium release channels, resulting in activation of PKCα (protein kinase Cα) and dissociation of p-120-catenin (p120) from VE-CAD (vascular endothelial cadherin; promoting endothelial barrier dysfunction [EBD]). However, the relevance of these findings to drug-eluting stents remains unknown. Newer generation direct mTOR kinase inhibitors do not bind FKBP12.6 and offer the potential of improving endothelial barrier function while maintaining antirestenotic efficacy, but their actual effects are unknown. We examined the effects of 2 different pharmacological targeting strategies-canonical mTOR inhibitor everolimus and mTOR kinase inhibitors Torin-2-on EBD after stenting. Approach and Results- Using the rabbit model of stenting and a combination of Evans blue dye, confocal and scanning electron microscopy studies, everolimus-eluting stents resulted in long-term EBD compared with bare metal stents. EBD was mitigated by using stents that eluted mTOR kinase inhibitors (Torin-2-eluting stent). At 60 days after stent placement, everolimus-eluting stents demonstrated large areas of Evans blue dye staining and evidence of p120 VE-CAD dissociation consistent with EBD. These findings were absent in bare metal stents and significantly attenuated in Torin-2-eluting stent. As proof of concept of the role of EBD in neoatherosclerosis, 100 days after stenting, animals were fed an enriched cholesterol diet for an additional 30 days. Everolimus-eluting stents demonstrated significantly more macrophage infiltration (consistent with neoatherosclerosis) compared with both bare metal stents and Torin-2-eluting stent. Conclusions- Our results pinpoint interactions between FKBP12.6 and canonical mTOR inhibitors as a major cause of vascular permeability and neoatherosclerosis, which can be overcome by using mTOR kinase inhibitors. Our study suggests further refinement of molecular targeting of the mTOR complex may be a promising strategy (Graphic Abstract).

Lactobacillus fermentum Improves Tacrolimus-Induced Hypertension by Restoring Vascular Redox State and Improving eNOS Coupling

SCOPE

The aim is to analyze whether the probiotic Lactobacillus fermentum CECT5716 (LC40) can prevent endothelial dysfunction and hypertension induced by tacrolimus in mice.

METHODS AND RESULTS

Tacrolimus increases systolic blood pressure (SBP) and impairs endothelium-dependent relaxation to acetylcholine and these effects are partially prevented by LC40. Endothelial dysfunction induced by tacrolimus is related to both increased nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX2) and uncoupled endothelial nitric oxide synthase (eNOS)-driven superoxide production and Rho-kinase-mediated eNOS inhibition. LC40 treatment prevents all the aortic changes induced by tacrolimus. LC40 restores the imbalance between T-helper 17 (Th17)/regulatory T (Treg) cells induced by tacrolimus in mesenteric lymph nodes and the spleen. Tacrolimus-induced gut dysbiosis, that is, it decreases microbial diversity, increases the Firmicutes/Bacteroidetes (F/B) ratio and decreases acetate- and butyrate-producing bacteria, and these effects are prevented by LC40. Fecal microbiota transplantation (FMT) from LC40-treated mice to control mice prevents the increase in SBP and the impaired relaxation to acetylcholine induced by tacrolimus.

CONCLUSION

LC40 treatment prevents hypertension and endothelial dysfunction induced by tacrolimus by inhibiting gut dysbiosis. These effects are associated with a reduction in vascular oxidative stress, mainly through NOX2 downregulation and prevention of eNOS uncoupling, and inflammation possibly because of decreased Th17 and increased Treg cells polarization in mesenteric lymph nodes.

Interleukin 22 Promotes Blood Pressure Elevation and Endothelial Dysfunction in Angiotensin II-Treated Mice

BACKGROUND

CD4+ T helper (Th) cells, including Th1, Th2, and Th17 cells, play critical roles in angiotensin II-induced hypertension. Th22 cells, a novel subset of Th cells, take part in cardiovascular diseases by producing IL-22 (interleukin 22). This study aimed to investigate whether IL-22 is involved in hypertension.

METHODS AND RESULTS

Th22 cells and IL-22 levels were detected in angiotensin II-infused mice, and the results showed that Th22 cells and IL-22 levels significantly increased. To determine the effect of Th22/IL-22 on blood pressure regulation, angiotensin II-infused mice were treated with recombinant mouse IL-22, an anti-IL-22 neutralizing monoclonal antibody, or control. Treatment with recombinant IL-22 resulted in increased blood pressure, amplified inflammatory responses, and aggravated endothelial dysfunction, whereas the anti-IL-22 neutralizing monoclonal antibody decreased blood pressure, reduced inflammatory responses, and attenuated endothelial dysfunction. To determine whether the STAT3 (signal transducer and activator of transcription 3) pathway mediates the effect of IL-22 on blood pressure regulation, the special STAT3 pathway inhibitor S31-201 was administered to mice treated with recombinant IL-22. S31-201 treatment significantly ameliorated the IL-22 effects of increased blood pressure and endothelial dysfunction. In addition, serum IL-22 levels were significantly increased in hypertensive patients compared with healthy persons. Correlation analysis showed a positive correlation between IL-22 levels and blood pressure.

CONCLUSIONS

IL-22 amplifies the inflammatory response, induces endothelial dysfunction and promotes blood pressure elevation in angiotensin II-induced hypertensive mice. The STAT3 pathway mediates the effect of IL-22 on hypertension. Blocking IL-22 may be a novel therapeutic strategy to prevent and treat hypertension.

TRPC3-mediated Ca2+ signals as a promising strategy to boost therapeutic angiogenesis in failing hearts: The role of autologous endothelial colony forming cells

Endothelial progenitor cells (EPCs) are a sub-population of bone marrow-derived mononuclear cells that are released in circulation to restore damaged endothelium during its physiological turnover or rescue blood perfusion after an ischemic insult. Additionally, they may be mobilized from perivascular niches located within larger arteries' wall in response to hypoxic conditions. For this reason, EPCs have been regarded as an effective tool to promote revascularization and functional recovery of ischemic hearts, but clinical application failed to exploit the full potential of patients-derived cells. Indeed, the frequency and biological activity of EPCs are compromised in aging individuals or in subjects suffering from severe cardiovascular risk factors. Rejuvenating the reparative phenotype of autologous EPCs through a gene transfer approach has, therefore, been put forward as an alternative approach to enhance their therapeutic potential in cardiovascular patients. An increase in intracellular Ca²⁺ concentration constitutes a pivotal signal for the activation of the so-called endothelial colony forming cells (ECFCs), the only known truly endothelial EPC subset. Studies from our group showed that the Ca²⁺ toolkit differs between peripheral blood- and umbilical cord blood (UCB)-derived ECFCs. In the present article, we first discuss how VEGF uses repetitive Ca²⁺ spikes to regulate angiogenesis in ECFCs and outline how VEGF-induced intracellular Ca²⁺ oscillations differ between the two ECFC subtypes. We then hypothesize about the possibility to rejuvenate the biological activity of autologous ECFCs by transfecting the cell with the Ca²⁺ -permeable channel Transient Receptor Potential Canonical 3, which selectively drives the Ca²⁺ response to VEGF in UCB-derived ECFCs.

Nebivolol Effects on Nitric Oxide Levels, Blood Pressure, and Renal Function in Kidney Transplant Patients

In hypertensive kidney transplant recipients, the effects of nebivolol vs metoprolol on nitric oxide (NO) blood level, estimated glomerular filtration rate (eGFR), and blood pressure (BP) have not been previously reported. In a 12-month prospective, randomized, open-label, active-comparator trial, hypertensive kidney transplant recipients were treated with nebivolol (n=15) or metoprolol (n=15). Twenty-nine patients (nebivolol [n=14], metoprolol [n=15]) completed the trial. The primary endpoint was change in blood NO level after 12 months of treatment. Secondary endpoints were changes in eGFR, BP, and number of antihypertensive drug classes used. After 12 months of treatment, least squares mean change in plasma NO level in the nebivolol kidney transplant recipient group younger than 50 years was higher by 68.19% (99.17% confidence interval [CI], 13.02-123.36), 69.54% (99.17% CI, 12.71-126.37), and 66.80% (99.17% CI, 12.95-120.64) compared with the metoprolol group younger than 50 years, the metoprolol group 50 years and older, and the nebivolol group 50 years and older, respectively. The baseline to month 12 change in mean arterial BP, eGFR, and number of antihypertensive drug classes used was not significantly different between the treatment groups. In hypertensive kidney transplant recipients, nebivolol use in patients younger than 50 years increased blood NO.

Cotreatment with interleukin 4 and interleukin 10 modulates immune cells and prevents hypertension in pregnant mice

BACKGROUND

Excessive maternal immune system activation plays a central role in the development of the hypertensive disorder of pregnancy preeclampsia (PE). The immunomodulatory cytokines interleukin 4 (IL-4) and interleukin 10 (IL-10) are dysregulated during PE; therefore we hypothesized that treatment with both recombinant IL-4 and IL-10 during pregnancy could prevent the development of PE in mice.

METHODS

Using our mouse model of PE in which immune system activation is induced by the double-stranded RNA receptor agonist poly I:C, we gave daily injections of IL-4, IL-10, or both on days 13-17 of pregnancy. Mice were then killed on day 18.

RESULTS

Poly I:C caused a significant increase in systolic blood pressure in pregnant (P-PIC) mice compared with vehicle-treated pregnant (P) mice. All 3 treatments significantly decreased blood pressure in P-PIC mice to P levels, ameliorated the endothelial dysfunction, and decreased placental TLR3 levels in P-PIC mice. However, only IL-4/IL-10 cotreatment prevented the proteinuria and increased incidence of fetal demise in P-PIC mice; IL-4 or IL-10 alone had no effect. Additionally, only IL-4/IL-10 cotreatment prevented the significant increase in CD3(+)/γδ(+) T cells and CD11c(+) dendritic cells and significant decrease in CD11b(+)/CD14(-) suppressor monocytes, as well as completely prevented placental necrosis, in P-PIC mice. Importantly, IL-4/IL-10 cotreatment in P mice had no detrimental effects.

CONCLUSIONS

Taken together, these data demonstrate that exogenous IL-4 and IL-10 administration concurrently during pregnancy can normalize immune cell subsets and prevent PE induced by maternal immune system activation.

FKBP12.6 activates RyR1: investigating the amino acid residues critical for channel modulation

We have previously shown that FKBP12 associates with RyR2 in cardiac muscle and that it modulates RyR2 function differently to FKBP12.6. We now investigate how these proteins affect the single-channel behavior of RyR1 derived from rabbit skeletal muscle. Our results show that FKBP12.6 activates and FKBP12 inhibits RyR1. It is likely that both proteins compete for the same binding sites on RyR1 because channels that are preactivated by FKBP12.6 cannot be subsequently inhibited by FKBP12. We produced a mutant FKBP12 molecule (FKBP12E31Q/D32N/W59F) where the residues Glu(31), Asp(32), and Trp(59) were converted to the corresponding residues in FKBP12.6. With respect to the functional regulation of RyR1 and RyR2, the FKBP12E31Q/D32N/W59F mutant lost all ability to behave like FKBP12 and instead behaved like FKBP12.6. FKBP12E31Q/D32N/W59F activated RyR1 but was not capable of activating RyR2. In conclusion, FKBP12.6 activates RyR1, whereas FKBP12 activates RyR2 and this selective activator phenotype is determined within the amino acid residues Glu(31), Asp(32), and Trp(59) in FKBP12 and Gln(31), Asn(32), and Phe(59) in FKBP12.6. The opposing but different effects of FKBP12 and FKBP12.6 on RyR1 and RyR2 channel gating provide scope for diversity of regulation in different tissues.

Endoplasmic reticulum stress in insulin resistance and diabetes

The endoplasmic reticulum is the main intracellular Ca(2+) store for Ca(2+) release during cell signaling. There are different strategies to avoid ER Ca(2+) depletion. Release channels utilize first Ca(2+)-bound to proteins and this minimizes the reduction of the free luminal [Ca(2+)]. However, if release channels stay open after exhaustion of Ca(2+)-bound to proteins, then the reduction of the free luminal ER [Ca(2+)] (via STIM proteins) activates Ca(2+) entry at the plasma membrane to restore the ER Ca(2+) load, which will work provided that SERCA pump is active. Nevertheless, there are several noxious conditions that result in decreased activity of the SERCA pump such as oxidative stress, inflammatory cytokines, and saturated fatty acids, among others. These conditions result in a deficient restoration of the ER [Ca(2+)] and lead to the ER stress response that should facilitate recovery of the ER. However, if the stressful condition persists then ER stress ends up triggering cell death and the ensuing degenerative process leads to diverse pathologies; particularly insulin resistance, diabetes and several of the complications associated with diabetes. This scenario suggests that limiting ER stress should decrease the incidence of diabetes and the mobility and mortality associated with this illness.

Everolimus-eluting stents improve vascular response in a diabetic animal model

BACKGROUND

Preclinical evaluation of the vascular response of drug-eluting stents is limited especially in the setting of diabetes mellitus preventing the evaluation of changes in drug-eluting stent design and eluted drugs after clinical use.

METHODS AND RESULTS

Cultured human aortic endothelial cells were used to assess the differences between sirolimus and its analog, everolimus, in the setting of hyperglycemia on various cellular functions necessary for endothelial recovery. A diabetic rabbit model of iliac artery stenting was used to compare histological and morphometric characteristics of the vascular response to everolimus-eluting, sirolimus-eluting, and bare metal stent placement. Under hyperglycemic conditions, sirolimus impaired human aortic endothelial cell barrier function, migration, and proliferation to a greater degree compared with everolimus. In our in vivo model of diabetes mellitus, endothelialization at 28 days was significantly lower and endothelial integrity was impaired in sirolimus-eluting stent compared with both everolimus-eluting and bare metal stents. Neointimal area, uncovered struts, and fibrin deposition were significantly higher in sirolimus-eluting compared with everolimus-eluting and bare metal stents.

CONCLUSIONS

Use of everolimus-eluting stent results in improved vascular response in our preclinical models of diabetes mellitus.

FK506-binding protein 1b/12.6: a key to aging-related hippocampal Ca2+ dysregulation?

It has been recognized for some time that the Ca(2+)-dependent slow afterhyperpolarization (sAHP) is larger in hippocampal neurons of aged compared with young animals. In addition, extensive studies since have shown that other Ca(2+)-mediated electrophysiological responses are increased in hippocampus with aging, including Ca(2+) transients, L-type voltage-gated Ca(2+) channel activity, Ca(2+) spike duration and action potential accommodation. Elevated Ca(2+)-induced Ca(2+) release from ryanodine receptors (RyRs) appears to drive amplification of the Ca(2+) responses. Components of this Ca(2+) dysregulation phenotype correlate with deficits in cognitive function and plasticity, indicating they may play critical roles in aging-related impairment of brain function. However, the molecular mechanisms underlying aging-related Ca(2+) dysregulation are not well understood. FK506-binding proteins 1a and 1b (FKBP1a/1b, also known as FKBP12/12.6) are immunophilin proteins that bind the immunosuppressant drugs FK506 and rapamycin. In muscle cells, FKBP1a/1b also bind RyRs and inhibits Ca(2+)-induced Ca(2+) release, but it is not clear whether FKBPs act similarly in brain cells. Recently, we found that selectively disrupting hippocampal FKBP1b function in young rats, either by microinjecting adeno-associated viral vectors expressing siRNA, or by treatment with rapamycin, increases the sAHP and recapitulates much of the hippocampal Ca(2+) dysregulation phenotype. Moreover, in microarray studies, we found FKBP1b gene expression was downregulated in hippocampus of aging rats and early-stage Alzheimer's disease subjects. These results suggest the novel hypothesis that declining FKBP function is a key factor in aging-related Ca(2+) dysregulation in the brain and point to potential new therapeutic targets for counteracting unhealthy brain aging.

Sirolimus-FKBP12.6 impairs endothelial barrier function through protein kinase C-α activation and disruption of the p120-vascular endothelial cadherin interaction

OBJECTIVE

Sirolimus (SRL) is an immunosuppressant drug used to prevent rejection in organ transplantation and neointimal hyperplasia when delivered from drug-eluting stents. Major side effects of SRL include edema and local collection of intimal lipid deposits at drug-eluting stent sites, suggesting that SRL impairs endothelial barrier function (EBF). The aim of this study was to address the role of SRL on impaired EBF and the potential mechanisms involved.

APPROACH AND RESULTS

Cultured human aortic endothelial cells (HAECs) and intact human and mouse endothelium was examined to determine the effect of SRL, which binds FKBP12.6 to inhibit the mammalian target of rapamycin, on EBF. EBF, measured by transendothelial electrical resistance, was impaired in HAECs when treated with SRL or small interfering RNA for FKBP12.6 and reversed when pretreated with ryanodine, a stabilizer of ryanodine receptor 2 intracellular calcium release channels. Intracellular calcium increased in HAECs treated with SRL and normalized with ryanodine pretreatment. SRL-treated HAECs demonstrated increases in protein kinase C-α phosphorylation, a calcium sensitive serine/threonine kinase important in vascular endothelial (VE) cadherin barrier function through its interaction with p120-catenin (p120). Immunostaining of HAECs, human coronary and mouse aortic endothelium treated with SRL showed disruption of p120-VE cadherin interaction treated with SRL. SRL impairment of HAEC EBF was reduced with protein kinase C-α small interfering RNA. Mice treated with SRL demonstrated increased vascular permeability by Evans blue albumin extravasation in the lungs, heart, and aorta.

CONCLUSIONS

SRL-FKBP12.6 impairs EBF by activation of protein kinase C-α and downstream disruption of the p120-VE cadherin interaction in vascular endothelium. These data suggest this mechanism may be an important contributor of SRL side effects related to impaired EBF.

Interleukin-17 causes Rho-kinase-mediated endothelial dysfunction and hypertension

AIMS

Elevated levels of pro-inflammatory cytokine interleukin-17A (IL-17) are associated with hypertensive autoimmune diseases; however, the connection between IL-17 and hypertension is unknown. We hypothesized that IL-17 increases blood pressure by decreasing endothelial nitric oxide production.

METHODS AND RESULTS

Acute treatment of endothelial cells with IL-17 caused a significant increase in phosphorylation of the inhibitory endothelial nitric oxide (NO) synthase residue threonine 495 (eNOS Thr495). Of the kinases known to phosphorylate eNOS Thr495, only inhibition of Rho-kinase prevented the IL-17-induced increase. IL-17 caused a threefold increase in the Rho-kinase activator RhoA, and this was prevented by an IL-17 neutralizing antibody. In isolated mouse aortas, IL-17 significantly increased eNOS Thr495 phosphorylation, induced RhoA expression, and decreased NO-dependent relaxation responses, all of which were prevented by either an IL-17 neutralizing antibody or inhibition of Rho-kinase. In mice, IL-17 treatment for 1 week significantly increased systolic blood pressure and this was associated with decreased aortic NO-dependent relaxation responses, increased eNOS Thr495 phosphorylation, and increased RhoA expression. Inhibition of Rho-kinase prevented the hypertension caused by IL-17.

CONCLUSION

These data demonstrate that IL-17 activates RhoA/Rho-kinase leading to endothelial dysfunction and hypertension. Inhibitors of IL-17 or Rho-kinase may prove useful as anti-hypertensive drugs in IL-17-associated autoimmune diseases.

Update on vascular endothelial Ca2+ signalling: A tale of ion channels, pumps and transporters

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and forms a multifunctional transducing organ that mediates a plethora of cardiovascular processes. The activation of ECs from as state of quiescence is, therefore, regarded among the early events leading to the onset and progression of potentially lethal diseases, such as hypertension, myocardial infarction, brain stroke, and tumor. Intracellular Ca²⁺ signals have long been know to play a central role in the complex network of signaling pathways regulating the endothelial functions. Notably, recent work has outlined how any change in the pattern of expression of endothelial channels, transporters and pumps involved in the modulation of intracellular Ca²⁺ levels may dramatically affect whole body homeostasis. Vascular ECs may react to both mechanical and chemical stimuli by generating a variety of intracellular Ca²⁺ signals, ranging from brief, localized Ca²⁺ pulses to prolonged Ca²⁺ oscillations engulfing the whole cytoplasm. The well-defined spatiotemporal profile of the subcellular Ca²⁺ signals elicited in ECs by specific extracellular inputs depends on the interaction between Ca²⁺ releasing channels, which are located both on the plasma membrane and in a number of intracellular organelles, and Ca²⁺ removing systems. The present article aims to summarize both the past and recent literature in the field to provide a clear-cut picture of our current knowledge on the molecular nature and the role played by the components of the Ca²⁺ machinery in vascular ECs under both physiological and pathological conditions.

Endothelial cell transforming growth factor-β receptor activation causes tacrolimus-induced renal arteriolar hyalinosis

Arteriolar hyalinosis is a common histological finding in renal transplant recipients treated with the calcineurin inhibitor tacrolimus; however, the pathophysiologic mechanisms remain unknown. In addition to increasing transforming growth factor (TGF)-β levels, tacrolimus inhibits calcineurin by binding to FK506 binding protein 12 (FKBP12). FKBP12 alone also inhibits TGF-β receptor activation. Here we tested whether tacrolimus binding to FKBP12 removes an inhibition of the TGF-β receptor, allowing ligand binding, ultimately leading to receptor activation and arteriolar hyalinosis. We found that specific deletion of FKBP12 from endothelial cells was sufficient to activate endothelial TGF-β receptors and induce renal arteriolar hyalinosis in these knockout mice, similar to that induced by tacrolimus. Tacrolimus-treated and knockout mice exhibited significantly increased levels of aortic TGF-β receptor activation as evidenced by SMAD2/3 phosphorylation, along with increased collagen and fibronectin expression compared to controls. Treatment of isolated mouse aortas with tacrolimus increased TGF-β receptor activation, collagen and fibronectin expression. These effects were independent of calcineurin, absent in endothelial denuded aortic rings, and could be prevented by the small molecule TGF-β receptor inhibitor SB-505124. Thus endothelial cell TGF-β receptor activation is sufficient to cause vascular remodeling and renal arteriolar hyalinosis.

Pin1 deficiency causes endothelial dysfunction and hypertension

Pin1 is a peptidyl prolyl cis-trans isomerase that only binds to and isomerizes phosphorylated serine/threonine-proline motifs, inducing conformational changes that alter target protein function and phosphorylation. We have shown previously that deficiency of another peptidyl prolyl isomerase, FK506 binding protein 12/12.6, alters endothelial NO synthase phosphorylation and causes endothelial dysfunction and hypertension. Endothelial NO synthase contains the Pin1 binding sequence at (p)serine 116-proline 117 and phosphorylation of endothelial NO synthase serine 116 inhibits NO production; however, whether Pin1 deficiency alters vascular function and blood pressure is unknown. We hypothesized that Pin1 isomerizes p-endothelial NO synthase serine 116, which enables dephosphorylation and stimulates NO production. Immunoprecipitation of endothelial NO synthase and probing for Pin1 in rat aortic endothelial cells confirmed the interaction between the two. Pin1 knockdown via small interfering RNA or inhibition by juglone increased endothelial NO synthase serine 116 phosphorylation and prevented vascular endothelial growth factor-induced serine 116 dephosphorylation in endothelial cells. Acute treatment of isolated mouse aortas with juglone increased endothelial NO synthase serine 116 phosphorylation and decreased NO production and relaxation responses. Mice treated with juglone for 2 weeks, as well as Pin1 knockout mice, exhibited increased aortic endothelial NO synthase serine 116 phosphorylation, endothelial dysfunction, and hypertension. These data demonstrate that Pin1 binds endothelial NO synthase and enables dephosphorylation of serine 116, which increases NO production and endothelium-dependent dilation, leading to blood pressure maintenance.

Protein kinase CbetaII-mediated phosphorylation of endothelial nitric oxide synthase threonine 495 mediates the endothelial dysfunction induced by FK506 (tacrolimus)

FK506 [tacrolimus; hexadecahydro-5,19-dihydroxy-3-[2-(4-hydroxy-3-methoxycyclohexyl)-1-methylethenyl]-14,16-dimethoxy-4,10,12,18-tetramethyl-8-(2-propenyl)-15,19-epoxy-3H-pyrido[2,1-c][1,4]oxa-azacyclotricosine-1,7,20,21(4H,23H)-tetrone] is used clinically to reduce the incidence of allograft rejection; however, chronic administration leads to endothelial dysfunction and hypertension. We have previously shown that FK506 activates Ca(2+)/diacylglycerol-dependent conventional protein kinase C (cPKC), which phosphorylates endothelial nitric oxide synthase (eNOS) at one of its inhibitory sites, Thr495. However, which cPKC isoform is responsible for phosphorylating eNOS Thr495 is unknown. The aim of the current study was to determine the cPKC isoform that is activated by FK506, leading to decreased endothelial function. FK506 reduced endothelium-dependent relaxation responses, yet had no effect on endothelium-independent relaxation responses in aortas from control mice. Of the various cPKC isoforms, only the administration of a PKCβ(II) isoform-specific peptide inhibitor restored aortic relaxation responses to that of controls. In aortic endothelial cells, FK506 significantly increased PKCβ(II) activation compared with vehicle-treated controls, and this was prevented by a PKCβ(II) isoform-specific peptide inhibitor. In addition, a PKCβ(II) isoform-specific peptide inhibitor prevented the increase in eNOS Thr495 phosphorylation induced by FK506. Taken together, our results indicate that β(II) is the cPKC isoform responsible for phosphorylating eNOS at the inhibitory site Thr495 in response to FK506. PKCβ(II) inhibition could prove beneficial in ameliorating the endothelial dysfunction and hypertension in patients treated with FK506.

FK506 binding protein 12 deficiency in endothelial and hematopoietic cells decreases regulatory T cells and causes hypertension

Patients treated with the immunosuppressive drug tacrolimus (FK506), which binds FK506 binding protein 12 (FKBP12) and then inhibits the calcium-dependent phosphatase calcineurin, exhibit decreased regulatory T cells, endothelial dysfunction, and hypertension; however, the mechanisms and whether altered T-cell polarization play a role are unknown. Tacrolimus treatment of mice for 1 week dose-dependently decreased splenic CD4(+)/FoxP3(+) (regulatory T cells), increased splenic CD4(+)/IL-17(+) (T-helper 17) cells, and caused endothelial dysfunction and hypertension. To determine the mechanisms, we crossed floxed FKBP12 mice with Tie2-Cre mice to generate offspring lacking FKBP12 in endothelial and hematopoietic cells only (FKBP12EC knockout [KO]). Given the role of FKBP12 in inhibiting transforming growth factor-β receptor activation, Tie2-Cre-mediated deletion of FKBP12 increased transforming growth factor-β receptor activation and SMAD2/3 signaling. FKBP12EC KO mice exhibited increased vascular expression of genes and proteins related to endothelial cell activation and inflammation. Serum levels of the proinflammatory cytokines IL-2, IL-6, interferon-γ, IL-17a, IL-21, and IL-23 were increased significantly, suggesting a T-helper 17 cell-mediated inflammatory state. Flow cytometry studies confirmed this, because splenic levels of CD4(+)/IL-17(+) cells were increased significantly, whereas CD4(+)/FoxP3(+) cells were decreased in FKBP12EC KO mice. Furthermore, spleens from FKBP12EC KO mice showed increased signal transducer and activator of transcription 3 activation, involved in T-helper 17 cell induction, and decreased signal transducer and activator of transcription 5 activation, involved in regulatory T-cell induction. FKBP12EC KO mice also exhibited endothelial dysfunction and hypertension. These data suggest that tacrolimus, through its activation of transforming growth factor-β receptors in endothelial and hematopoietic cells, may cause endothelial dysfunction and hypertension by activating endothelial cells, reducing regulatory T cells, and increasing T-helper 17 cell polarization and inflammation.

Disrupting function of FK506-binding protein 1b/12.6 induces the Ca²+-dysregulation aging phenotype in hippocampal neurons

With aging, multiple Ca(2+)-associated electrophysiological processes exhibit increased magnitude in hippocampal pyramidal neurons, including the Ca(2+)-dependent slow afterhyperpolarization (sAHP), L-type voltage-gated Ca(2+) channel (L-VGCC) activity, Ca(2+)-induced Ca(2+) release (CICR) from ryanodine receptors (RyRs), and Ca(2+) transients. This pattern of Ca(2+) dysregulation correlates with reduced neuronal excitability/plasticity and impaired learning/memory and has been proposed to contribute to unhealthy brain aging and Alzheimer's disease. However, little is known about the underlying molecular mechanisms. In cardiomyocytes, FK506-binding protein 1b/12.6 (FKBP1b) binds and stabilizes RyR2 in the closed state, inhibiting RyR-mediated Ca(2+) release. Moreover, we recently found that hippocampal Fkbp1b expression is downregulated, whereas Ryr2 and Frap1/Mtor (mammalian target of rapamycin) expression is upregulated with aging in rats. Here, we tested the hypothesis that disrupting FKBP1b function also destabilizes Ca(2+) homeostasis in hippocampal neurons and is sufficient to induce the aging phenotype of Ca(2+) dysregulation in young animals. Selective knockdown of Fkbp1b with interfering RNA in vitro (96 h) enhanced voltage-gated Ca(2+) current in cultured neurons, whereas in vivo Fkbp1b knockdown by microinjection of viral vector (3-4 weeks) dramatically increased the sAHP in hippocampal slice neurons from young-adult rats. Rapamycin, which displaces FKBP1b from RyRs in myocytes, similarly enhanced VGCC current and the sAHP and also increased CICR. Moreover, FKBP1b knockdown in vivo was associated with upregulation of RyR2 and mTOR protein expression. Thus, disruption of FKBP1b recapitulated much of the Ca(2+)-dysregulation aging phenotype in young rat hippocampus, supporting a novel hypothesis that declining FKBP function plays a major role in unhealthy brain aging.

Role of ryanodine receptor subtypes in initiation and formation of calcium sparks in arterial smooth muscle: comparison with striated muscle

Calcium sparks represent local, rapid, and transient calcium release events from a cluster of ryanodine receptors (RyRs) in the sarcoplasmic reticulum. In arterial smooth muscle cells (SMCs), calcium sparks activate calcium-dependent potassium channels causing decrease in the global intracellular [Ca2+] and oppose vasoconstriction. This is in contrast to cardiac and skeletal muscle, where spatial and temporal summation of calcium sparks leads to global increases in intracellular [Ca2+] and myocyte contraction. We summarize the present data on local RyR calcium signaling in arterial SMCs in comparison to striated muscle and muscle-specific differences in coupling between L-type calcium channels and RyRs. Accordingly, arterial SMC Ca(v)1.2 L-type channels regulate intracellular calcium stores content, which in turn modulates calcium efflux though RyRs. Downregulation of RyR2 up to a certain degree is compensated by increased SR calcium content to normalize calcium sparks. This indirect coupling between Ca(v)1.2 and RyR in arterial SMCs is opposite to striated muscle, where triggering of calcium sparks is controlled by rapid and direct cross-talk between Ca(v)1.1/Ca(v)1.2 L-type channels and RyRs. We discuss the role of RyR isoforms in initiation and formation of calcium sparks in SMCs and their possible molecular binding partners and regulators, which differ compared to striated muscle.

Cardiac and haemodynamic effects of tacrolimus in the halothane-anaesthetized dog

Tacrolimus (FK506) is a potent immunosuppressant widely used for the treatment of patients with solid organ transplantation and autoimmune diseases. The present study investigated the cardiac, haemodynamic and electrophysiological effects of tacrolimus. Tacrolimus in doses of 0.01 and 0.1 mg/kg was infused over 10 min. with a pause of 20 min. in halothane-anaesthetized dogs under monitoring of plasma drug concentrations (n = 5). Sub-therapeutic dose of 0.01 mg/kg hardly affected any of the cardiovascular variables except that it slightly delayed the repolarization. The clinically relevant dose of 0.1 mg/kg had negative chronotropic, inotropic and dromotropic effects, and lowered blood pressure by 70 +/- 12 mmHg, effects previously ascribed to Ca(2+) channel blocking action. Tacrolimus also delayed the repolarization process in a dose-dependent and reverse use-dependent manner with an increase in electrical vulnerability. The cardiovascular effects of tacrolimus were enhanced after the cessation of drug infusion, despite a decline in the plasma concentrations. In human embryonic kidney 293 cells, however, only supratherapeutic tacrolimus concentrations (>0.1 mumol/l) inhibited hERG K(+) current with a maximum inhibition of 28% at 10 mumol/l, indicating that other mechanisms might have also operated besides direct block of ionic channel function. The present study suggests that tacrolimus has negative chronotropic, inotropic and dromotropic effects in the heart, delays repolarization and lowers blood pressure. Moreover, the monitoring of the actual drug concentration may not necessarily reflect its effects on the cardiovascular system; thus, frequent monitoring of cardiovascular variables may be essential for tacrolimus-treated patients.

Effect of uncoupling endothelial nitric oxide synthase on calcium homeostasis in aged porcine endothelial cells

AIMS

The requirement of endothelial NO synthase (NOS3) calcium to produce NO is well described, although the effect of NO on intracellular calcium levels [Ca(2+)](i) is still confusing. Therefore, NO and [Ca(2+)](i) cross-talk were studied in parallel in endothelial cells possessing a functional or a dysfunctional NO pathway.

METHODS AND RESULTS

Dysfunctional porcine endothelial cells were obtained either in vitro by successive passages or in vivo from regenerated endothelium 1 month after coronary angioplasty. Activity of NOS3 was characterized by conversion of arginine to citrulline, BH(4) intracellular availability, cGMP, and superoxide anion production. Imaging of the Ca(2+) indicator FURA 2-AM was recorded and sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) pump activity was analysed by (45)Ca(2+) uptake into cells. In endothelial cells with a functional NO pathway, NOS3 inhibition increased [Ca(2+)](i) and, conversely, an NO donor decreased it. In aged cells with an uncoupled NOS3 as shown by the reduced BH(4) level, the increase in superoxide anion and the lower production of cGMP and the decrease in NO bioavailability were linearly correlated with the increase in basal [Ca(2+)](i). Moreover, when stimulated by bradykinin, the calcium response was reduced while its decay was slowed down. These effects on the calcium signalling were abolished in calcium-free buffer and were similarly induced by SERCA inhibitors. In aged cells, NO improved the reduced SERCA activity and tended to normalize the agonist calcium response.

CONCLUSION

In control endothelial cells, NO exerts a negative feedback on cytosolic Ca(2+) homeostasis. In aged cells, uncoupled NOS3 produced NO that was insufficient to control the [Ca(2+)](i). Consequently, under resting conditions, SERCA activity decreased and [Ca(2+)](i) increased. These alterations were reversible as exogenous NO, in a cGMP-independent way, refilled intracellular calcium stores, reduced calcium influx, and improved the agonist-evoked calcium response. Therefore, prevention of the decrease in NO in dysfunctional endothelium would normalize the calcium-dependent functions.

Tacrolimus reduces nitric oxide synthase function by binding to FKBP rather than by its calcineurin effect

Hypertension develops in many patients receiving the immunosuppressive drug tacrolimus (FK506). One possible mechanism for hypertension is a reduction in vasodilatory nitric oxide. We found that tacrolimus and a calcineurin autoinhibitory peptide significantly decreased vascular calcineurin activity; however, only tacrolimus altered intracellular calcium release in mouse aortic endothelial cells. In mouse aortas, incubation with tacrolimus increased protein kinase C activity and basal endothelial nitric oxide synthase phosphorylation at threonine 495 but reduced basal and agonist-induced endothelial nitric oxide synthase phosphorylation at serine 1177, a mechanism known to inhibit synthase activity. While this decreased nitric oxide production and endothelial function, the calcineurin autoinhibitory peptide had no such effects. Inhibition of ryanodine receptor opening or protein kinase C blocked the effects of tacrolimus. Since it is known that the FK506 binding protein (FKBP12/12.6) interacts with the ryanodine receptor to regulate calcium release, we propose this as the mechanism by which tacrolimus alters intracellular calcium and endothelial nitric oxide synthase rather than by its effect on calcineurin. Our study shows that prevention of the tacrolimus-induced intracellular calcium leak may attenuate endothelial dysfunction and the consequent hypertension.