MCU gain- and loss-of-function models define the duality of mitochondrial calcium uptake in heart failure

Background

Mitochondrial calcium (mCa2+) uptake through the mitochondrial calcium uniporter channel (mtCU) stimulates metabolism to meet acute increases in cardiac energy demand. However, excessive mCa2+ uptake during stress, as in ischemia-reperfusion, initiates permeability transition and cell death. Despite these often-reported acute physiological and pathological effects, a major unresolved controversy is whether mtCU-dependent mCa2+ uptake and long-term elevation of cardiomyocyte mCa2+ contributes to the heart's adaptation during sustained increases in workload.

Objective

We tested the hypothesis that mtCU-dependent mCa2+ uptake contributes to cardiac adaptation and ventricular remodeling during sustained catecholaminergic stress.

Methods

Mice with tamoxifen-inducible, cardiomyocyte-specific gain (αMHC-MCM × flox-stop-MCU; MCU-Tg) or loss (αMHC-MCM × Mcufl/fl; Mcu-cKO) of mtCU function received 2-wk catecholamine infusion.

Results

Cardiac contractility increased after 2d of isoproterenol in control, but not Mcu-cKO mice. Contractility declined and cardiac hypertrophy increased after 1-2-wk of isoproterenol in MCU-Tg mice. MCU-Tg cardiomyocytes displayed increased sensitivity to Ca2+- and isoproterenol-induced necrosis. However, loss of the mitochondrial permeability transition pore (mPTP) regulator cyclophilin D failed to attenuate contractile dysfunction and hypertrophic remodeling, and increased isoproterenol-induced cardiomyocyte death in MCU-Tg mice.

Conclusions

mtCU mCa2+ uptake is required for early contractile responses to adrenergic signaling, even those occurring over several days. Under sustained adrenergic load excessive MCU-dependent mCa2+ uptake drives cardiomyocyte dropout, perhaps independent of classical mitochondrial permeability transition pore opening, and compromises contractile function. These findings suggest divergent consequences for acute versus sustained mCa2+ loading, and support distinct functional roles for the mPTP in settings of acute mCa2+ overload versus persistent mCa2+ stress.

Extra-cardiac BCAA catabolism lowers blood pressure and protects from heart failure

Pharmacologic activation of branched-chain amino acid (BCAA) catabolism is protective in models of heart failure (HF). How protection occurs remains unclear, although a causative block in cardiac BCAA oxidation is widely assumed. Here, we use in vivo isotope infusions to show that cardiac BCAA oxidation in fact increases, rather than decreases, in HF. Moreover, cardiac-specific activation of BCAA oxidation does not protect from HF even though systemic activation does. Lowering plasma and cardiac BCAAs also fails to confer significant protection, suggesting alternative mechanisms of protection. Surprisingly, activation of BCAA catabolism lowers blood pressure (BP), a known cardioprotective mechanism. BP lowering occurred independently of nitric oxide and reflected vascular resistance to adrenergic constriction. Mendelian randomization studies revealed that elevated plasma BCAAs portend higher BP in humans. Together, these data indicate that BCAA oxidation lowers vascular resistance, perhaps in part explaining cardioprotection in HF that is not mediated directly in cardiomyocytes.

Abstract P3053: Mitochondrial Calcium Accumulation Drives The Progression Of Non-ischemic Heart Failure: Integrated Lessons From Genetic Mouse Models

Acute mitochondrial calcium ( m Ca 2+ ) uptake stimulates bioenergetics to meet increased ATP demand, but when excessive predisposes to necrotic cell death. A major unresolved controversy is whether chronic alterations in cardiomyocyte m Ca 2+ homeostasis contribute to maladaptive remodeling and contractile dysfunction in non-ischemic heart disease. We hypothesized that cardiomyocyte m Ca 2+ accumulation drives cardiac maladaptation in response to stressors that chronically increase workload and cytosolic Ca 2+ cycling. We subjected mice with adult, cardiomyocyte-specific manipulation of m Ca 2+ uptake through the mitochondrial calcium uniporter ( Mcu deletion, Mcu -cKO; MCU overexpression, MCU-Tg) or m Ca 2+ efflux through the mitochondrial sodium-calcium exchanger, NCLX (NCLX overexpression, NCLX-OE), to chronic pressure or neurohormonal overload. Fractional shortening failed to increase in Mcu -cKO mice over the first days of isoproterenol (Iso) infusion. Mortality was increased in Mcu -cKO mice over this period, and this effect was recapitulated in NCLX-OE mice infused with angiotensin II + phenylephrine (PE), although contractility did not decline in either case. Hypertrophic responses to chronic stress were attenuated in NCLX-OE but not Mcu -cKO hearts, and adenoviral NCLX expression limited mitochondrial metabolism, protein synthesis, and cell growth in neonatal rat cardiomyocytes treated with PE. These data indicate that m Ca 2+ accumulation is required for cardiac hypertrophy, but MCU is not. MCU-Tg hearts decompensated towards failure with 1-2 weeks of Iso. Although these hearts exhibited increased cardiomyocyte necrosis, deletion of the mPTP regulator cyclophilin D failed to rescue contractility, suggesting that m Ca 2+ overload causes cardiac failure, even independent of permeability transition. Fitting with this view, NCLX-OE attenuated the decline in contractile function that occurred with 12-week pressure overload. We conclude that despite initial adaptive effects, sustained m Ca 2+ elevation drives the progression of non-ischemic heart disease triggered by a chronic increase in cardiac workload. Our findings raise concern over proposed therapeutic strategies aiming to augment m Ca 2+ accumulation in heart failure.

Altered composition of the mitochondrial Ca2+uniporter in the failing human heart

Heart failure (HF) is a leading cause of hospitalization and mortality worldwide. Yet, there is still limited knowledge on the underlying molecular mechanisms, because human tissue for research is scarce, and data obtained in animal models is not directly applicable to humans. Thus, studies of human heart specimen are of particular relevance. Mitochondrial Ca2+ handling is an emerging topic in HF progression because its regulation is central to the energy supply of the heart contractions as well as to avoiding mitochondrial Ca2+ overload and the ensuing cell death induction. Notably, animal studies have already linked impaired mitochondrial Ca2+ transport to the initiation/progression of HF. Mitochondrial Ca2+ uptake is mediated by the Ca2+uniporter (mtCU) that consists of the MCU pore under tight control by the Ca2+-sensing MICU1 and MICU2. The MICU1/MCU protein ratio has been validated as a predictor of the mitochondrial Ca2+ uptake phenotype. We here determined for the first time the protein composition of the mtCU in the human heart. The two regulators MICU1 and MICU2, were elevated in the failing human heart versus non-failing controls, while the MCU density was unchanged. Furthermore, the MICU1/MCU ratio was significantly elevated in the failing human hearts, suggesting altered gating of the MCU by MICU1 and MICU2. Based on a small cohort of patients, the decrease in the cardiac contractile function (ejection fraction) seems to correlate with the increase in MICU1/MCU ratio. Our findings therefore indicate a possible role for adaptive/maladaptive changes in the mtCU composition in the initiation/progression of human HF in humans and point to a potential therapeutic target at the level of the MICU1-dependent regulation of the mtCU.

Abstract P388: Extra-cardiac BCAA Catabolism Lowers Blood Pressure And Protects From Heart Failure

Pharmacologic activation of branched chain amino acid (BCAA) catabolism is protective in numerous models of heart failure (HF). How this protection occurs has remained unclear, although a causative block in cardiac BCAA oxidation has been proposed. We use here in vivo heavy isotope infusion studies to show that cardiac preference for BCAA oxidation increases, rather than decreases, in multiple models of HF. We use various genetic models to show that cardiac-specific activation of BCAA oxidation does not protect from HF, even though systemic activation of BCAA oxidation does. Lowering plasma and cardiac BCAAs by genetic means is also not sufficient to confer protection comparable to that conferred by pharmacologic activation of BCAA oxidation, suggesting alternative mechanisms of protection. Surprisingly, telemetry and invasive hemodynamic studies showed that pharmacological activation of BCAA catabolism lowers blood pressure, a well-established cardioprotective mechanism. The effects on blood pressure occurred independently of nitric oxide (NO), and reflected a vascular resistance to adrenergic constriction. Finally, mendelian randomization studies revealed that elevations in plasma BCAAs portend higher blood pressure in large human cohorts. Together, these data indicate that activation of BCAA oxidation lowers blood pressure and protects from heart failure independently of any direct effects on the heart itself.

Abstract 506: Enhanced Mitochondrial Calcium Uptake During Chronic β-adrenergic Stimulation Causes Maladaptive Remodeling and Impaired Left Ventricular Function Independent of Cyclophilin D-mediated Mitochondrial Permeability Transition

The mitochondrial calcium uniporter (MCU) forms the pore of the mitochondrial calcium uniporter channel (mtCU) and is required for rapid mitochondrial Ca 2+ ( m Ca 2+ ) uptake. MCU is necessary to increase cardiac energetics to fuel an increase in cardiac contractility during acute sympathetic stimulation. However, little is known about how MCU-dependent Ca 2+ flux may contribute to the heart’s adaptations to chronic stress. We therefore compared mice with adult cardiomyocyte (ACM)-specific loss ( Mcu fl/fl ; Mcu-cKO) or gain (CAG-CAT-MCU; MCU-Tg) of MCU function to examine the role of MCU-dependent m Ca 2+ uptake in a model of chronic catecholamine overload. In vitro characterization of ACMs confirmed that MCU overexpression enhanced and Mcu deletion inhibited acute m Ca 2+ uptake. Neither loss nor gain of MCU function altered baseline contractile function in vivo . In αMHC-MCM control mice, fractional shortening was transiently increased after 2 days of isoproterenol infusion. This initial increase in contractility was attenuated in MCU-cKO mice. In contrast, MCU-Tg mice exhibited decreased fractional shortening at 7 and 14 days of isoproterenol infusion. This detrimental effect on contractile function was associated with increased LV dilation, HW/BW ratio, and lung edema. MCU-Tg cardiomyocytes in vitro exhibited increased ROS production and a trend towards increased cell death upon elevation of cytosolic Ca 2+ with ionomycin. These data prompted us to test the hypothesis that isoproterenol-induced contractile dysfunction in MCU-Tg hearts is caused by cardiomyocyte dropout due to m Ca 2+ overload and mitochondrial permeability transition. However, genetic deletion of the mPTP component cyclophilin D did not prevent the decline in contractile function, diminish cardiomyocyte death, or attenuate LV remodeling in MCU-Tg animals during chronic isoproterenol infusion. We conclude that although mtCU-dependent m Ca 2+ uptake is essential for early energetic adaptations to high adrenergic load, under conditions of chronic adrenergic stress it is maladaptive and predisposes to heart failure. Our data suggest that this maladaptive response occurs via mechanisms independent of cyclophilin D-mediated permeability transition.

Abcg2-expressing side population cells contribute to cardiomyocyte renewal through fusion

The adult mammalian heart has a limited regenerative capacity. Therefore, identification of endogenous cells and mechanisms that contribute to cardiac regeneration is essential for the development of targeted therapies. The side population (SP) phenotype has been used to enrich for stem cells throughout the body; however, SP cells isolated from the heart have been studied exclusively in cell culture or after transplantation, limiting our understanding of their function in vivo. We generated a new Abcg2-driven lineage-tracing mouse model with efficient labeling of SP cells. Labeled SP cells give rise to terminally differentiated cells in bone marrow and intestines. In the heart, labeled SP cells give rise to lineage-traced cardiomyocytes under homeostatic conditions with an increase in this contribution following cardiac injury. Instead of differentiating into cardiomyocytes like proposed cardiac progenitor cells, cardiac SP cells fuse with preexisting cardiomyocytes to stimulate cardiomyocyte cell cycle reentry. Our study is the first to show that fusion between cardiomyocytes and non-cardiomyocytes, identified by the SP phenotype, contribute to endogenous cardiac regeneration by triggering cardiomyocyte cell cycle reentry in the adult mammalian heart.

Spatial Separation of Mitochondrial Calcium Uptake and Extrusion for Energy-Efficient Mitochondrial Calcium Signaling in the Heart

Mitochondrial Ca²⁺ elevations enhance ATP production, but uptake must be balanced by efflux to avoid overload. Uptake is mediated by the mitochondrial Ca²⁺ uniporter channel complex (MCUC), and extrusion is controlled largely by the Na⁺/Ca²⁺ exchanger (NCLX), both driven electrogenically by the inner membrane potential (ΔΨ_m). MCUC forms hotspots at the cardiac mitochondria-junctional SR (jSR) association to locally receive Ca²⁺ signals; however, the distribution of NCLX is unknown. Our fractionation-based assays reveal that extensively jSR-associated mitochondrial segments contain a minor portion of NCLX and lack Na⁺-dependent Ca²⁺ extrusion. This pattern is retained upon in vivo NCLX overexpression, suggesting extensive targeting to non-jSR-associated submitochondrial domains and functional relevance. In cells with non-polarized MCUC distribution, upon NCLX overexpression the same given increase in matrix Ca²⁺ expends more ΔΨ_m. Thus, cardiac mitochondrial Ca²⁺ uptake and extrusion are reciprocally polarized, likely to optimize the energy efficiency of local calcium signaling in the beating heart.

MCUB Regulates the Molecular Composition of the Mitochondrial Calcium Uniporter Channel to Limit Mitochondrial Calcium Overload During Stress

BACKGROUND

The mitochondrial calcium uniporter (mtCU) is an ≈700-kD multisubunit channel residing in the inner mitochondrial membrane required for mitochondrial Ca²⁺ (_mCa²⁺) uptake. Here, we detail the contribution of MCUB, a paralog of the pore-forming subunit MCU, in mtCU regulation and function and for the first time investigate the relevance of MCUB to cardiac physiology.

METHODS

We created a stable MCUB knockout cell line (MCUB^-/-) using CRISPR-Cas9n technology and generated a cardiac-specific, tamoxifen-inducible MCUB mutant mouse (CAG-CAT-MCUB x MCM; MCUB-Tg) for in vivo assessment of cardiac physiology and response to ischemia/reperfusion injury. Live-cell imaging and high-resolution spectrofluorometery were used to determine intracellular Ca²⁺ exchange and size-exclusion chromatography; blue native page and immunoprecipitation studies were used to determine the molecular function and impact of MCUB on the high-molecular-weight mtCU complex.

RESULTS

Using genetic gain- and loss-of-function approaches, we show that MCUB expression displaces MCU from the functional mtCU complex and thereby decreases the association of mitochondrial calcium uptake 1 and 2 (MICU1/2) to alter channel gating. These molecular changes decrease MICU1/2-dependent cooperative activation of the mtCU, thereby decreasing _mCa²⁺ uptake. Furthermore, we show that MCUB incorporation into the mtCU is a stress-responsive mechanism to limit _mCa²⁺ overload during cardiac injury. Indeed, overexpression of MCUB is sufficient to decrease infarct size after ischemia/reperfusion injury. However, MCUB incorporation into the mtCU does come at a cost; acute decreases in _mCa²⁺ uptake impair mitochondrial energetics and contractile function.

CONCLUSIONS

We detail a new regulatory mechanism to modulate mtCU function and _mCa²⁺ uptake. Our results suggest that MCUB-dependent changes in mtCU stoichiometry are a prominent regulatory mechanism to modulate _mCa²⁺ uptake and cellular physiology.

Impaired mitochondrial calcium efflux contributes to disease progression in models of Alzheimer's disease

Impairments in neuronal intracellular calcium (_iCa²⁺) handling may contribute to Alzheimer’s disease (AD) development. Metabolic dysfunction and progressive neuronal loss are associated with AD progression, and mitochondrial calcium (_mCa²⁺) signaling is a key regulator of both of these processes. Here, we report remodeling of the _mCa²⁺ exchange machinery in the prefrontal cortex of individuals with AD. In the 3xTg-AD mouse model impaired _mCa²⁺ efflux capacity precedes neuropathology. Neuronal deletion of the mitochondrial Na⁺/Ca²⁺ exchanger (NCLX, Slc8b1 gene) accelerated memory decline and increased amyloidosis and tau pathology. Further, genetic rescue of neuronal NCLX in 3xTg-AD mice is sufficient to impede AD-associated pathology and memory loss. We show that _mCa²⁺ overload contributes to AD progression by promoting superoxide generation, metabolic dysfunction and neuronal cell death. These results provide a link between the calcium dysregulation and metabolic dysfunction hypotheses of AD and suggest _mCa²⁺ exchange as potential therapeutic target in AD.

Dysregulation of intracellular calcium is reported in Alzheimer’s disease. Here the authors show that loss of the mitochondrial Na⁺ /Ca²⁺ exchanger, NCLX – primary route of mitochondrial calcium efflux, precedes neuronal pathology in experimental models and contributes to Alzheimer’s disease progression.

Abstract 857: MCUB Regulates the Molecular Composition of the Mitochondrial Calcium Uniporter Channel During Cardiac Stress to Limit Mitochondrial Calcium Overload

The mitochondrial calcium uniporter (mtCU) is a ~700 kD multi-subunit channel residing in the inner mitochondrial membrane required for mitochondrial Ca 2+ ( m Ca 2+ ) uptake. Mitochondrial Calcium Uniporter B ( MCUB ) is reported to negatively regulate m Ca 2+ uptake, but its precise functional role and contribution to cardiac physiology remain unresolved. Size exclusion chromatography of ventricular mitochondria revealed MCUB was absent from high-molecular weight (MW) mtCU complexes in sham animals, but present 24 hours following myocardial ischemia-reperfusion injury (IR). To investigate MCUB ’s contribution to mtCU regulation we created a MCUB -/- cell line by CRISPR-Cas9n. MCUB deletion increased histamine-mediated [ m Ca 2+ ] transient amplitude by ~50% vs. WT controls (mito-R-GECO1). MCUB deletion increased mtCU capacitance (mitoplast patch-clamp) and rate of [ m Ca 2+ ] uptake. Size-exclusion chromatography revealed loss of MCUB increased MCU incorporation into high-MW mtCU, suggesting stoichiometric replacement and overall more functional mtCU’s. To examine MCUB’s role in cardiac physiology we generated a cardiac-specific, tamoxifen-inducible MCUB mouse model (CAG-CAT-MCUB x MCM; MCUB-Tg). FPLC revealed MCUB was undetected in high-MW mtCU complexes of Cre controls, but enriched in MCUB-Tg hearts. MCUB incorporation decreased the presence of channel gatekeepers, MICU1/2, and decreased the MW of the mtCU complex. Immunoprecipitations suggest MCUB interacts with MCU but not MICU1/2. MCUB-Tg adult cardiomyocytes (ACMs) expressing AAV9-mitycam ( m Ca 2+ reporter) were paced and displayed a ~30% decrease in m Ca 2+ transient peak amplitude with significantly reduced m Ca 2+ uptake rates vs controls. A reduction in OxPhos reserve capacity correlated with a severe impairment in cardiac contractile reserve (LV invasive hemodynamics during isoproterenol infusion). MCUB-Tg cardiac mitochondria were resistant to Ca 2+ -induced permeability transition and MCUB-Tg mice displayed ~50% decrease in infarct size per area-at-risk after in vivo IR-injury. These data suggest MCUB regulation of the mtCU is an endogenous compensatory mechanism to decrease m Ca 2+ overload during ischemic injury, but maladaptive to cardiac energetic responsiveness.

Abstract 737: N -ethylmaleimide sensitive factor (NSF) is Essential in Necrotic Cell Death

Necrotic cell death is the main way in which cells die during myocardial infarction (MI) and heart failure (HF), yet the molecular mechanisms regulating necrotic cell death are poorly defined. To elucidate the key regulators of plasma membrane rupture during necrotic cell death a genome-wide shRNA loss-of-function screen was performed which identified components of SNARE-mediated membrane fusion as potential facilitators of Ca 2+ and ROS-induced necrosis. To examine if the SNARE machinery is involved in cellular necrosis we targeted N-ethylmaleimide sensitive Factor (NSF) due to its requirement in SNARE recycling, lack of gene homologs, and redox sensitivity. Deletion of NSF from 3T3 fibroblasts by CRISPR-Cas9n (Nsf -/- ), inhibited membrane rupture and improved cell viability following Ca 2+ overload (ionomycin), ROS (H 2 O 2 ), and necroptotic (TNFa, CHX, zVAD)-induced cell death but did not alter apoptotic (staurosporine) cellular demise. We next created a cardiac-specific conditional Nsf knockout mouse model to determine if NSF contributes to myocyte death during IR injury. Loss of NSF in cardiomyocytes did not alter baseline cardiac function or structure. Currently, studies are underway to determine if NSF contributes to necrotic cell as occurs in IR injury and heart failure. In summary, our results suggest that NSF is an important molecular component of membrane rupture and pathogenic cell death.

Abstract 277: Enhanced Mitochondrial Calcium Uptake Promotes Deleterious Remodeling and Impaired Left Ventricular Function During Chronic Adrenergic Stimulation

The mitochondrial calcium uniporter (MCU) constitutes the pore-forming unit of the mitochondrial calcium uniporter channel (mtCU) and is necessary for mitochondrial Ca 2+ ( m Ca 2+ ) uptake. We previously reported that MCU is required to increase cardiac energetics and contractility in response to acute β-adrenergic stimulation. However, deletion of MCU has no detrimental effect on basal cardiac function or metabolism. While these findings support a role for MCU-dependent Ca 2+ flux in functional adaptations to acute stress, little is known about the involvement of MCU in cardiac responses to sustained stress. We compared mice with adult, cardiomyocyte (ACM)-specific loss ( Mcu fl/fl ; Mcu -cKO) or gain (CAG-CAG-MCU; MCU-Tg) of MCU function to explore the role of m Ca 2+ uptake in a model of chronic catecholamine overload. Biophysical characterization confirmed that MCU overexpression enhanced and MCU deletion inhibited ACM m Ca 2+ uptake. Neither loss nor gain of MCU had a significant impact on baseline contractile function. In αMHC-MCM control mice, fractional shortening was transiently increased after 2 days of isoproterenol infusion (Fig 1). This early increase in contractility was attenuated in Mcu -cKO mice. MCU-Tg mice exhibited decreased fractional shortening at 7 and 14 days of isoproterenol infusion. This detrimental effect on LV function was associated with increased LV dilation, HW/BW ratio, and lung edema as compared to αMHC-MCM controls. These data suggest that although mtCU-dependent m Ca 2+ uptake is essential for early energetic adaptations to high adrenergic load, under conditions of chronic adrenergic stress it is maladaptive and predisposes to heart failure.

Abstract 539: MCUB Regulates the Macromolecular Composition of the Mitochondrial Calcium Uniporter Channel to Limit Mitochondrial Calcium Overload During Ischemic Cardiac Injury

The mitochondrial calcium uniporter channel (mtCU) resides in the inner mitochondrial membrane and is a multi-subunit complex required for mitochondrial Ca 2+ ( m Ca 2+ ) uptake. RNA-seq and PCR analysis of mtCU component expression revealed that MCUB expression increases after myocardial infarction. To investigate how MCUB , a paralog of the MCU gene, contributes to mtCU regulation we created a MCUB -/- cell line (HeLa) using CRISPR-Cas9n. MCUB deletion increased histamine-mediated m [Ca 2+ ] transient amplitude by ~50% vs. WT controls (mito-R-GECO). Biophysical characterization found MCUB deletion increased mtCU capacitance and rate of m [Ca 2+ ] uptake. FPLC fractionation of mtCU revealed loss of MCUB increased MCU incorporation into the supercomplex, suggesting MCUB replacement of MCU and overall increase in functional mtCU supercomplexes. Next, we generated a cardiac-specific, tamoxifen-inducible MCUB overexpression mouse model (CAG-CAT-MCUB x MCM; MCUB-Tg) to examine how the MCUB/MCU ratio regulates mtCU function and cardiac physiology. MCUB-Tg mice were infected with AAV9-mitycam (mito genetic calcium reporter) and adult cardiomyocytes were isolated to record [ m Ca 2+ ] transients during pacing. Increasing the MCUB/MCU ratio decreased [ m Ca 2+ ] peak amplitude by ~30% and significantly reduced the [ m Ca 2+ ] uptake rate. FPLC assessment of the mtCU revealed MCUB was undetectable in the supercomplex fraction (~700kD) of Cre controls, but enriched in MCUB -Tg hearts. Examining the oxygen consumption rate of cardiomyocytes isolated from MCUB- Tg hearts found decreased maximal respiration and spare reserve capacity, which correlated with severe impairment in isoproterenol-induced contractile reserve. Mitochondria from MCUB -Tg mouse hearts were resistant to Ca 2+ induced mitochondrial swelling suggesting MCUB protects against permeability transition. MCUB -Tg mice subjected to myocardial ischemia reperfusion injury had a ~50% decrease in infarct size suggesting increased MCUB expression prevents m Ca 2+ overload and limits cell death. These data suggest that MCUB regulation of the mtCU is an endogenous compensatory mechanism to decrease m Ca 2+ overload during ischemic injury, but maladaptive in mitochondrial energetic responsiveness.

Abstract 432: MCUB Regulates Mitochondrial Calcium Uniporter Channel Gating and Modulates Bioenergetics and Cell Death

The mitochondrial calcium uniporter (MCU) is a high-capacity, inward-rectifying channel in the inner mitochondrial membrane and is required for mitochondrial Ca 2+ ( m Ca 2+ ) uptake. m Ca 2+ signaling regulates bioenergetics and activates the mitochondrial permeability transition pore (MPTP) which are cellular processes implicated in cardiac pathophysiology warranting further research into the molecular regulation of the MCU. Recently, a MCU gene paralog, MCUB , was identified as a possible component of the channel. To investigate MCUB’s contribution to uniporter regulation we created a MCUB -/- HeLa cell line using CRISPR-Cas9n. Here, we report that loss of MCUB increased m Ca 2+ transient amplitude after IP3R stimulation (52% vs. con) suggesting MCUB negatively regulates m Ca 2+ uptake. Mitoplast patch-clamping confirmed that loss of MCUB increases MCU current density, suggesting MCUb modulates channel capacitance. Permeabilized MCUB -/- and WT cells exposed to various levels of Ca 2+ (0.5-20μM) revealed that MCUB -/- cells exhibited m Ca 2+ uptake at lower Ca 2+ concentrations than controls, suggesting MCUB contributes to channel gating. In m Ca 2+ retention capacity experiments MCUB -/- cells required ~30% less bath Ca 2+ to induce depolarization, suggesting a predisposition to m Ca 2+ overload. Next, we generated a cardiac-specific, tamoxifen-inducible MCUB overexpression mouse model ( MCUB -Tg). Cardiomyocytes isolated from MCUB -Tg hearts exhibited decreased m Ca 2+ uptake at low-Ca 2+ (59% vs. con) and isolated mitochondria exhibited a reduction in Ca 2+ -induced swelling (37% vs. con), suggesting a resistance to permeability transition. MCUB -Tg mice displayed a significant impairment in isoproterenol-induced contractile reserve and this correlated with a loss of isoproterenol-mediated activation of pyruvate dehydrogenase. In summary, our results suggest that MCUB limits m Ca 2+ uptake by altering channel-gating and thereby regulates bioenergetics and MPTP opening.

Abstract 44: NSF is Required for Plasma Membrane Blebbing Occurring in Necrotic Cell Death

The loss of cells that occurs during MI and HF is largely due to necrotic cell death, yet the molecular mechanisms underlying necrosis, specifically plasma membrane rupture, are not well defined. A genome-wide, shRNA loss-of-function screen identified components of SNARE-mediated membrane fusion as potential facilitators of Ca 2+ and ROS-induced membrane rupture. Here, we targeted Nsf (N-ethylmaleimide sensitive factor) due to its requirement in SNARE recycling, redox sensitivity, and lack of gene homologs. Deletion of Nsf from 3T3 fibroblasts, using CRISPR-Cas9n ( Nsf -/- ), inhibited membrane rupture and improved cell viability following Ca 2+ overload (ionomycin) and ROS (H 2 O 2 ) induced cell death. Further, stable overexpression of NSF augmented membrane rupture and decreased cell viability following necrotic insults. Next, using high-resolution live cell microscopy we examined membrane blebs - herniations of the plasma membrane that precede rupture and necrosis. Nsf -/- and WT cells were treated with ionomycin or H 2 O 2 and imaged for 4h with automated Z-stack images taken every 5m. Ionomycin and H 2 O 2 induced prominent blebs in nearly every WT cell followed by membrane rupture. Strikingly, loss of Nsf ablated bleb formation (Fig 1). Studies are ongoing in cardiac-specific Nsf -/- mice to define if this novel mechanism contributes to myocyte death during IR injury. Deletion of Nsf in adult cardiomyocytes does not result in a baseline phenotype, increasing the translational potential of NSF targeted therapy. In summary, our results identify a new molecular component required for membrane blebbing that occurs during pathogenic cell death.

The mitochondrial Na+/Ca2+ exchanger is essential for Ca2+ homeostasis and viability

Mitochondrial calcium (_mCa²⁺) has a central role in both metabolic regulation and cell death signalling, however its role in homeostatic function and disease is controversial. Slc8b1 encodes the mitochondrial Na⁺/Ca²⁺ exchanger (NCLX), which is proposed to be the primary mechanism for _mCa²⁺ extrusion in excitable cells. Here we show that tamoxifen-induced deletion of Slc8b1 in adult mouse hearts causes sudden death, with less than 13% of affected mice surviving after 14 days. Lethality correlated with severe myocardial dysfunction and fulminant heart failure. Mechanistically, cardiac pathology was attributed to _mCa²⁺ overload driving increased generation of superoxide and necrotic cell death, which was rescued by genetic inhibition of mitochondrial permeability transition pore activation. Corroborating these findings, overexpression of NCLX in the mouse heart by conditional transgenesis had the beneficial effect of augmenting _mCa²⁺ clearance, preventing permeability transition and protecting against ischaemia-induced cardiomyocyte necrosis and heart failure. These results demonstrate the essential nature of _mCa²⁺ efflux in cellular function and suggest that augmenting _mCa²⁺ efflux may be a viable therapeutic strategy in disease.

Exercise training provides cardioprotection by activating and coupling endothelial nitric oxide synthase via a β3-adrenergic receptor-AMP-activated protein kinase signaling pathway

Exercise training confers sustainable protection against ischemia/reperfusion injury. However, the mechanism by which this process occurs is not fully understood. Previously, it was shown that β₃-adrenergic receptors (β₃-ARs) play a critical role in regulating the activation of endothelial nitric oxide synthase (eNOS) in response to exercise and play a critical role in exercise-mediated cardioprotection. Intriguingly, a deficiency in β₃-ARs led to increased myocardial injury following exercise training. The purpose of the current study was to determine mechanisms by which β₃-ARs are linked to eNOS activation and to determine the mechanism responsible for the exacerbated ischemia/reperfusion injury displayed by β₃-AR deficient (β₃-AR KO) mice after exercise training. Wild-type (n = 37) and β₃-AR KO (n = 40) mice were subjected to voluntary wheel running for 4 weeks. Western blot analysis revealed that neither protein kinase B nor protein kinase A linked β₃-ARs to eNOS following exercise training. However, analysis revealed a role for AMP-activated protein kinase (AMPK). Specifically, exercise training increased the phosphorylation of AMPK in the hearts of wild-type mice, but failed to do so in the hearts of β₃-AR KO mice. Additional studies revealed that exercise training rendered eNOS less coupled and increased NOS-dependent superoxide levels in β₃-AR KO mice. Finally, supplementing β₃-AR KO mice with the eNOS coupler, tetrahydrobiopterin, during the final week of exercise training reduced myocardial infarction. These findings provide important information that exercise training protects the heart in the setting of myocardial ischemia/reperfusion injury by activating and coupling eNOS via the stimulation of a β₃-AR-AMPK signaling pathway.

Angiotensin type 2-receptor (AT2R) activation induces hypotension in apolipoprotein E-deficient mice by activating peroxisome proliferator-activated receptor-γ

Angiotensin II (Ang II) modulates blood pressure and atherosclerosis development through its vascular type-1 (AT1R) and type-2 (AT2R) receptors, which have opposing effects. AT2R activation produces hypotension, and is anti-atherogenic. Targeted overexpression of AT2Rs in vascular smooth muscle cells (VSMCs) indicates that these effects are due to increased nitric oxide (NO) generation. However, the role of endogenous VSMC AT2Rs in these events is unknown. Effect of 7-day low-dose Ang II-infusion (12 µg/kg/hr) on blood pressure was tested in 9-week-old apoE((-/-)) mice fed a low or high cholesterol diet (LCD or HCD, respectively). Cardiac output was measured by echocardiography. Immunohistochemistry was performed to localize and quantify AT2Rs and p-Ser(1177)-endothelial nitric oxide synthase (eNOS) levels in the aortic arch. PD123319 and GW-9662 were used to selectively block the AT2R and peroxisome proliferator-activated receptor-γ (PPAR-γ), respectively. Ang II infusion decreased blood pressure by 12 mmHg (P < 0.001) in LCD/apoE((-/-)) mice without altering cardiac output; a response blocked by PD123319. Although, AT2R stimulation neither activated eNOS (p-Ser(1177)-eNOS) nor changed plasma NO metabolites, it caused an ~6-fold increase in VSMC PPAR-γ levels (P < 0.001) and the AT2R-mediated hypotension was abolished by GW-9662. AT2R-mediated hypotension was also inhibited by HCD, which selectively decreased VSMC AT2R expression by ~6-fold (P < 0.01). These findings suggest a novel pathway for the Ang II/AT2R-mediated hypotensive response that involves PPAR-γ, and is down regulated by a HCD.

Sodium Sulfide Attenuates Ischemic-Induced Heart Failure by Enhancing Proteasomal Function in an Nrf2-Dependent Manner

BACKGROUND

Therapeutic strategies aimed at increasing hydrogen sulfide (H2S) levels exert cytoprotective effects in various models of cardiovascular injury. However, the underlying mechanism(s) responsible for this protection remain to be fully elucidated. Nuclear factor E2-related factor 2 (Nrf2) is a cellular target of H2S and facilitator of H2S-mediated cardioprotection after acute myocardial infarction. Here, we tested the hypothesis that Nrf2 mediates the cardioprotective effects of H2S therapy in the setting of heart failure.

METHODS AND RESULTS

Mice (12 weeks of age) deficient in Nrf2 (Nrf2 KO; C57BL/6J background) and wild-type littermates were subjected to ischemic-induced heart failure. Wild-type mice treated with H2S in the form of sodium sulfide (Na2S) displayed enhanced Nrf2 signaling, improved left ventricular function, and less cardiac hypertrophy after the induction of heart failure. In contrast, Na2S therapy failed to provide protection against heart failure in Nrf2 KO mice. Studies aimed at evaluating the underlying cardioprotective mechanisms found that Na2S increased the expression of proteasome subunits, resulting in an increased proteasome activity and a reduction in the accumulation of damaged proteins. In contrast, Na2S therapy failed to enhance the proteasome and failed to attenuate the accumulation of damaged proteins in Nrf2 KO mice. Additionally, Na2S failed to improve cardiac function when the proteasome was inhibited.

CONCLUSIONS

These findings indicate that Na2S therapy enhances proteasomal activity and function during the development of heart failure in an Nrf2-dependent manner and that this enhancement leads to attenuation in cardiac dysfunction.

Abstract 93: Genetic Deletion of Slc8b1, the Mitochondrial Sodium/Calcium Exchanger, Causes Sudden Cardiac Death and Overexpression Protects Against Myocardial Infarction and Pressure-Overload Heart Failure

Mitochondrial calcium ( m Ca 2+ ) signaling is critical for both energy production and the activation of cell death pathways in the heart. Further, m Ca 2+ overload is hypothesized to be a significant contributor to the development and progression of heart failure (HF). The mitochondrial sodium/calcium exchanger (mNCX) is hypothesized to be the primary mechanism of m Ca 2+ efflux, but to date no study has genetically confirmed its identity or function in an in vivo system. To investigate the role of mNCX in HF, we generated mutant mice with loxP sites flanking exons 5-7 of the candidate gene, Slc8b1 (also known as NCLX) , and crossed them with a tamoxifen (tamox)-inducible cardiac-specific Cre mouse to delete mNCX in the adult heart (mNCX-cKO). Cardiomyocytes isolated from mNCX-cKO mice displayed a significant reduction in m Ca 2+ efflux rate and Ca 2+ uptake capacity. Tamoxifen-induced ablation of mNCX resulted in sudden death with only 54% of mice surviving 8d post-tamoxifen treatment (Fig 1). Assessment of mNCX-cKO hearts 2d post-tamox revealed significant remodeling characterized by dilation and a decrease in %EF (Fig 2). Next, we generated a conditional, cardiac-specific mNCX overexpression mouse model (mNCX-Tg) to evaluate if increased m Ca 2+ efflux would alter the progression of HF. mNCX-Tg and controls were subjected to both myocardial infarction (LCA ligation) and pressure-overload induced HF (transverse aortic constriction). mNCX-Tg mice displayed preserved LV function, structure and a reduction in HF indices in both models. For the first time we show that mNCX is essential for m Ca 2+ efflux in cardiomyocytes and that mNCX represents a novel therapeutic target in HF.

Abstract 92: The Mitochondrial Calcium Uniporter is Necessary for Metabolic Matching of Contractile Demand During Acute Sympathetic Stress

Contractility is mediated by a variable flux in intracellular calcium (Ca 2+ ), which is proposed to be integrated into mitochondria to regulate cardiac energetics. Moreover, m Ca 2+ -overload is known to activate the mitochondrial permeability transition pore (MPTP) and induce cell death. Recent studies have reported that the Mcu gene encodes the channel-forming portion of the mitochondrial calcium uniporter (MCU) and is required for m Ca 2+ uptake. To examine the role of m Ca 2+ in the heart, we generated a conditional, cardiac-specific knockout model and deleted Mcu in adult mice ( Mcu-cKO ). Loss of Mcu protected against myocardial ischemia-reperfusion (IR) injury by preventing the activation of the MPTP. In addition while we found no baseline phenotype, Mcu -cKO mice lacked contractile responsiveness to beta-adrenergic receptor stimulation as assessed by invasive hemodynamics (Fig 1) and in parallel were unable to activate mitochondrial dehydrogenases and increase cardiac NADH levels. Further experimental analyses in isolated adult cardiomyocytes confirmed a lack of energetic responsiveness to acute sympathetic stress (isoproterenol failure to mediate an increase in NADH, Fig 2), supporting the hypothesis that the physiological function of the MCU in the heart is to modulate Ca 2+ -dependent metabolism during the ‘fight or flight’ response.

The Mitochondrial Calcium Uniporter Matches Energetic Supply with Cardiac Workload during Stress and Modulates Permeability Transition

Cardiac contractility is mediated by a variable flux in intracellular calcium (Ca(2+)), thought to be integrated into mitochondria via the mitochondrial calcium uniporter (MCU) channel to match energetic demand. Here, we examine a conditional, cardiomyocyte-specific, mutant mouse lacking Mcu, the pore-forming subunit of the MCU channel, in adulthood. Mcu(-/-) mice display no overt baseline phenotype and are protected against mCa(2+) overload in an in vivo myocardial ischemia-reperfusion injury model by preventing the activation of the mitochondrial permeability transition pore, decreasing infarct size, and preserving cardiac function. In addition, we find that Mcu(-/-) mice lack contractile responsiveness to acute β-adrenergic receptor stimulation and in parallel are unable to activate mitochondrial dehydrogenases and display reduced bioenergetic reserve capacity. These results support the hypothesis that MCU may be dispensable for homeostatic cardiac function but required to modulate Ca(2+)-dependent metabolism during acute stress.

Hydrogen sulfide attenuates high fat diet-induced cardiac dysfunction via the suppression of endoplasmic reticulum stress

Diabetic cardiomyopathy is a significant contributor to the morbidity and mortality associated with diabetes and metabolic syndrome. However, the underlying molecular mechanisms that lead to its development have not been fully elucidated. Hydrogen sulfide (H2S) is an endogenously produced signaling molecule that is critical for the regulation of cardiovascular homeostasis. Recently, therapeutic strategies aimed at increasing its levels have proven cardioprotective in models of acute myocardial ischemia-reperfusion injury and heart failure. The precise role of H2S in the pathogenesis of diabetic cardiomyopathy has not yet been established. Therefore, the goal of the present study was to evaluate circulating and cardiac H2S levels in a murine model of high fat diet (HFD)-induced cardiomyopathy. Diabetic cardiomyopathy was produced by feeding mice HFD (60% fat) chow for 24 weeks. HFD feeding reduced both circulating and cardiac H2S and induced hallmark features of type-2 diabetes. We also observed marked cardiac dysfunction, evidence of cardiac enlargement, cardiac hypertrophy, and fibrosis. H2S therapy (SG-1002, an orally active H2S donor) restored sulfide levels, improved some of the metabolic perturbations stemming from HFD feeding, and attenuated HFD-induced cardiac dysfunction. Additional analysis revealed that H2S therapy restored adiponectin levels and suppressed cardiac ER stress stemming from HFD feeding. These results suggest that diminished circulating and cardiac H2S levels play a role in the pathophysiology of HFD-induced cardiomyopathy. Additionally, these results suggest that H2S therapy may be of clinical importance in the treatment of cardiovascular complications stemming from diabetes.

Hydrogen sulfide provides cardioprotection against myocardial/ischemia reperfusion injury in the diabetic state through the activation of the RISK pathway

Background

Coronary artery disease remains the principal cause of death in patients with diabetes mellitus. Diabetic mice display exacerbated injury following myocardial ischemia-reperfusion (MI/R) and are resistant to most therapeutic interventions. We have reported that sodium sulfide (Na₂S) therapy confers cardioprotection during MI/R in non-diabetic mice. Here we tested the hypothesis that Na₂S therapy would limit the extent of myocardial injury following MI/R when administered at the time of reperfusion.

Methods and results

Diabetic mice (db/db, 12 weeks of age) were subjected to transient myocardial ischemia for a period of 30 minutes followed by reperfusion up to 24 hours. Na₂S (0.05 to 1 mg/kg) or saline (vehicle) was administered into the left ventricular lumen at the time of reperfusion. Na₂S therapy significantly decreased myocardial injury in the db/db diabetic mouse, as evidenced by a reduction in infarct size and circulating troponin-I levels. The reduction in myocardial injury was also associated with a reduction in oxidative stress and a decrease in cleaved caspase-3 expression. In an effort to evaluate the signaling mechanism responsible for the observed cardioprotection, additional groups of mice were sacrificed during early reperfusion. Hearts were excised and processed for Western blot analysis. These studies revealed that Na₂S therapy activated the Erk1/2 arm of the Reperfusion Injury Salvage Kinase (RISK) pathway.

Conclusion

These findings provide important information that myocardial Erk1/2 activation by Na₂S therapy following MI/R sets into motion events, which ultimately lead to cardioprotection in the setting of diabetes.

A proliferative burst during preadolescence establishes the final cardiomyocyte number

It is widely believed that perinatal cardiomyocyte terminal differentiation blocks cytokinesis, thereby causing binucleation and limiting regenerative repair after injury. This suggests that heart growth should occur entirely by cardiomyocyte hypertrophy during preadolescence when, in mice, cardiac mass increases many-fold over a few weeks. Here, we show that a thyroid hormone surge activates the IGF-1/IGF-1-R/Akt pathway on postnatal day 15 and initiates a brief but intense proliferative burst of predominantly binuclear cardiomyocytes. This proliferation increases cardiomyocyte numbers by ~40%, causing a major disparity between heart and cardiomyocyte growth. Also, the response to cardiac injury at postnatal day 15 is intermediate between that observed at postnatal days 2 and 21, further suggesting persistence of cardiomyocyte proliferative capacity beyond the perinatal period. If replicated in humans, this may allow novel regenerative therapies for heart diseases.

Chronic exercise downregulates myocardial myoglobin and attenuates nitrite reductase capacity during ischemia-reperfusion

The infarct sparing effects of exercise are evident following both long-term and short-term training regimens. Here we compared the infarct-lowering effects of nitrite therapy, voluntary exercise, and the combination of both following myocardial ischemia-reperfusion (MI/R) injury. We also compared the degree to which each strategy increased cardiac nitrite levels, as well as the effects of each strategy on the nitrite reductase activity of the heart. Mice subjected to voluntary wheel running (VE) for 4weeks displayed an 18% reduction in infarct size when compared to sedentary mice, whereas mice administered nitrite therapy (25mg/L in drinking water) showed a 53% decrease. However, the combination of VE and nitrite exhibited no further protection than VE alone. Although the VE and nitrite therapy mice showed similar nitrite levels in the heart, cardiac nitrite reductase activity was significantly reduced in the VE mice. Additionally, the cardiac protein expression of myoglobin, a known nitrite reductase, was also reduced after VE. Further studies revealed that cardiac NFAT activity was lower after VE due to a decrease in calcineurin activity and an increase in GSK3β activity. These data suggest that VE downregulates cardiac myoglobin levels by inhibiting calcineurin/NFAT signaling. Additionally, these results suggest that the modest infarct sparing effects of VE are the result of a decrease in the hearts ability to reduce nitrite to nitric oxide during MI/R.

Abstract 333: Deficiency of DJ-1 Leads to Increased Injury following Myocardial Ischemia by Enhancing Apoptosis and Oxidative Stress

Background: DJ-1 is a ubiquitously expressed protein that has typically been associated with the development of early onset Parkinson’s disease. Recent data suggests that it also plays a role in the cellular response to stress. Although much is known about DJ-1 in the brain, very little has been investigated in the heart. Here, we tested the hypothesis that a deficiency in DJ-1 would enhance myocardial ischemia-reperfusion (MI/R) injury.

Methods and Results: Wild-type (WT) control and DJ-1 knockout (DJ-1 KO) mice were subjected to 45 min of left coronary artery ischemia followed by 24 hrs of reperfusion. The deficiency of DJ-1 significantly increased myocardial infarct size relative to both the area-at-risk and entire left ventricle, as well as increased circulating troponin-I levels (Panels A-B). Echocardiography and hemodynamic analysis at 1 week of reperfusion revealed that DJ-1 KO mice experienced greater left ventricular dilatation and hypertrophy, displayed exacerbated left ventricular dysfunction, and displayed worse contractility and relaxation when compared to WT controls. In an effort to evaluate the signaling mechanism responsible for the increased injury in DJ-1 KO mice, additional WT and KO animals were subjected to 45 min of ischemia followed by 4 hrs of reperfusion. DJ-1 KO hearts were found to display higher levels of oxidative stress, greater caspase-3 activity (Panel C), enhanced phosphorylation of Jnk, and enhanced activation of the mitochondrial fission protein, dynamin-related protein 1 (Drp1).

Conclusions: These findings provide important information that DJ-1 plays a protective role in heart against acute MI/R injury.

Hydrogen sulfide preconditions the db/db diabetic mouse heart against ischemia-reperfusion injury by activating Nrf2 signaling in an Erk-dependent manner

Hydrogen sulfide (H2S) therapy protects nondiabetic animals in various models of myocardial injury, including acute myocardial infarction and heart failure. Here, we sought to examine whether H2S therapy provides cardioprotection in the setting of type 2 diabetes. H2S therapy in the form of sodium sulfide (Na2S) beginning 24 h or 7 days before myocardial ischemia significantly decreased myocardial injury in db/db diabetic mice (12 wk of age). In an effort to evaluate the signaling mechanism responsible for the observed cardioprotection, we focused on the role of nuclear factor E2-related factor (Nrf2) signaling. Our results indicate that diabetes does not alter the ability of H2S to increase the nuclear localization of Nrf2, but does impair aspects of Nrf2 signaling. Specifically, the expression of NADPH quinine oxidoreductase 1 was increased after the acute treatment, whereas the expression of heme-oxygenase-1 (HO-1) was only increased after 7 days of treatment. This discrepancy was found to be the result of an increased nuclear expression of Bach1, a known repressor of HO-1 transcription, which blocked the binding of Nrf2 to the HO-1 promoter. Further analysis revealed that 7 days of Na2S treatment overcame this impairment by removing Bach1 from the nucleus in an Erk1/2-dependent manner. Our findings demonstrate for the first time that exogenous administration of Na2S attenuates myocardial ischemia-reperfusion injury in db/db mice, suggesting the potential therapeutic effects of H2S in treating a heart attack in the setting of type 2 diabetes.

Thioredoxin 1 is essential for sodium sulfide-mediated cardioprotection in the setting of heart failure

OBJECTIVE

The aim of this study was to determine whether thioredoxin 1 (Trx1) mediates the cardioprotective effects of hydrogen sulfide (H2S) in a model of ischemic-induced heart failure (HF).

APPROACH AND RESULTS

Mice with a cardiac-specific overexpression of a dominant negative mutant of Trx1 and wild-type littermates were subjected to ischemic-induced HF. Treatment with H2S as sodium sulfide (Na2S) not only increased the gene and protein expression of Trx1 in the absence of ischemia but also augmented the HF-induced increase in both. Wild-type mice treated with Na2S experienced less left-ventricular dilatation, improved left-ventricular function, and less cardiac hypertrophy after the induction of HF. In contrast, Na2S therapy failed to improve any of these parameters in the dominant negative mutant of Trx1 mice. Studies aimed at evaluating the underlying cardioprotective mechanisms found that Na2S therapy inhibited HF-induced apoptosis signaling kinase-1 signaling and nuclear export of histone deacetylase 4 in a Trx1-dependent manner.

CONCLUSIONS

These findings provide novel information that the upregulation of Trx1 by Na2S therapy in the setting of HF sets into motion events, such as the inhibition of apoptosis signaling kinase-1 signaling and histone deacetylase 4 nuclear export, which ultimately leads to the attenuationof left-ventricular remodeling.

Ts65Dn -- localization of the translocation breakpoint and trisomic gene content in a mouse model for Down syndrome

Fluorescent in situ hybridization (FISH) -- using mouse chromosome paints, probes for the mouse major centromeric satellite DNA, and probes for genes on chromosomes (Chr) 16 and 17 -- was employed to locate the breakpoint in a translocation used to produce a mouse model for Down syndrome. The Ts65Dn trisomy is derived from the reciprocal translocation T(16;17)65Dn. The Ts65Dn mouse carries a marker chromosome containing the distal segment of Chr 16, a region that shows linkage conservation with human Chr 21, and the proximal end of Chr 17. This chromosome confers trisomy for most of the genes in the Chr 16 segment and Ts65Dn mice show many of the phenotypic features characteristic of Down syndrome. We used FISH on metaphase chromosomes from translocation T65Dn/+ heterozygotes and Ts65Dn mice to show that the Chr 17 breakpoint is distal to the heterochromatin of Chr 17, that the Ts65Dn marker chromosome contains a small portion of Chr 17 euchromatin, that the Chr 16 breakpoint lies between the Ncam2 and Gabpa/App genes, and that the Ts65Dn chromosome contains >80% of the human Chr 21 homologs. The significance of this finding is discussed in terms of the utility of this mouse model.

Potential interaction between warfarin and boldo-fenugreek

A patient was treated with warfarin for atrial fibrillation. During treatment, an increase in international normalized ratio (INR) and her admission that she was taking a variety of natural products, to include boldo and fenugreek, led us to suspect that some of these natural products could alter the effect of warfarin. When she stopped the culpable products, the INR returned to normal after 1 week. The herb-drug interaction was observed a second time after both products were reintroduced a few days later. The imputability of this interaction to both natural products, as determined by the Naranjo algorithm, suggests a probable association between boldo-fenugreek and increased bleeding time in patients treated with warfarin. No undesirable reaction was reported during telephone discussions with the patient. Nevertheless, we recommend that clinicians treating patients with anticoagulant therapy be vigilant when patients also take herbal agents.

Osteoporosis: a new challenge in cystic fibrosis

The increased life expectancy of patients with cystic fibrosis (CF) may lead to medical complications such as osteoporosis. Based on data collected through a MEDLINE search (1985-May 1999) and review of references for additional relevant articles, nutrition status, weight, and disease severity are factors most highly correlated with osteopenia. Links also were noted with calcium and vitamin D intake, hypogonadism, chronic inflammation, and age, but findings in these areas are not consistent from one report to the next. Increased fracture rates and kyphosis are consequences of osteoporosis. Simple measures such as compliance with recommended nutrition guidelines and restrictions in corticosteroid therapy could be considered first-line management options. Further studies must be conducted to clarify factors involved in the etiology of osteoporosis in patients with CF and to identify the best treatment and prevention methods.

Comparison of the acute cardiotoxicity of the antimalarial drug halofantrine in vitro and in vivo in anaesthetized guinea-pigs

1. Several unrelated drugs have pro-arrhythmic activity associated with an ability to prolong the QT interval of the ECG. The aim of this work was to examine the effects of the antimalarial drug halofantrine in vivo and in vitro. 2. In anaesthetized guinea-pigs consecutive bolus doses of halofantrine (0.3, 1, 3, 10 and 30 mg kg(-1), i.v.) at 25 min intervals caused dose-dependent prolongation of the rate corrected QTc interval and bradycardia. The change in heart rate became significant after administration of 10 mg kg(-1) halofantrine (-23+/-9 beats min[-1]) whereas the increase in QTc was significant with only 1 mg kg(-1) halofantrine (22+/-10 ms). It was only with the highest dose of halofantrine that the PR interval was increased (from 52+/-3 to 67+/-4 ms) and second degree atrioventricular (AV) block (type 1 Mobitz) occurred in all animals. No changes were observed in any parameters in a separate group of guinea-pigs which received vehicle (dimethylacetamide 60% propylene glycol 40%) at equivalent time points. 3. The blood concentrations of halofantrine ranged from 0.26+/-0.17 microM after administration of 0.3 mg kg(-1) to 2.79+/-0.87 microM after 30 mg kg(-1), i.v. There was a significant correlation between the blood concentrations of halofantrine and the changes in QTc interval. 4 In guinea-pig left papillary muscles the effective refractory period was increased significantly 60 min after addition of halofantrine; from 161+/-4 to 173+/-6 ms with 10 microM, 156+/-8 to 174+/-6 ms with 30 microM and 165+/-6 to 179+/-5 ms with 100 microM halofantrine. However, the vehicle (0.1% Tween 80 in DMSO; final concentration of vehicle in Krebs, 1%) also increased the effective refractory period from 164+/-5 to 173+/-6 ms. Similar results were obtained in right ventricular strips but left atrial effective refractory periods were not altered by either the vehicle or halofantrine. 5. The results of these experiments suggest that any direct effects that halofantrine may have had on the effective refractory period of cardiac muscle cannot be separated from those of the vehicle. The prolongation of QTc and consistent observation of AV block with halofantrine in anaesthetized guinea-pigs suggest that in vivo models may be more useful for further studies investigating the mechanisms underlying the cardiotoxicity of halofantrine.

Fine tuning of epitopic dominance induced by lung cancer on the IgG response to bovine betalactoglobulin: towards a paraneoplastic immune marker

BACKGROUND

Investigating the humoral immune response to mucosal antigens in patients with lung cancer, we have documented a preferential immunoglobulin G (IgG) binding to cryptic epitopes unmasked by the proteolysis of bovine beta-lactoglobulin (BLG). In contrast, IgG from healthy controls and patients with chronic bronchitis (COPD) bind preferentially to continuous epitopes presented on both native (n) and denaturated (d) forms of this antigen. The present study further characterized the differences in the epitope profiles recognized on BLG.

METHODS

The capacity of individual sera from 65 lung cancer patients, tested before and after cancer removal for the patients with early stage lung carcinoma, 65 healthy controls, and 52 patients with COPD, to prevent the binding of pooled IgG fractions from each population as well as murine monoclonal antibodies (MoAb), specific for BLG, to solid phase bound antigen was evaluated in enzyme-linked immunoadsorbent assay using streptavidin-biotin technology. Some of these experiments were also performed with sera from 42 patients diagnosed with other cancers.

RESULTS

Compared with control sera and sera from patients with other solid tumors, lung cancer patient sera showed distinct capacities to prevent the binding of murine MoAb as well as human pooled IgG fractions to n- and d-BLG. The inhibition capacities of lung cancer sera changed as soon as five weeks after cancer removal.

CONCLUSIONS

The results indicate that the difference in epitope specificity exhibited by lung cancer sera is not restricted to cryptic epitopes, but also affects continuous and discontinuous epitopes, accessible only on the native antigen. A high level of binding discrimination between antibodies from the study populations is also observed at the level of the epitope. This deviation in the epitope specificity of antibodies changes soon after cancer removal, suggesting a tumor-dependent disturbance. Also documented in the Dermatophagoides pteronyssinus model, it opens the way to a new class of paraneoplastic immune markers for this malignancy, with, at first glance, a high specificity level.

The value of prescribed 'high-fibre' diets for the treatment of the irritable bowel syndrome

The symptoms of 72 patients with irritable bowel syndrome were assessed by questionnaire before and 6 months after a high-fibre diet had been prescribed, to find whether those who achieved the highest fibre intake did any better than those with smaller intakes. Dietary fibre intakes were measured after 6 months by a 7-day weighed food inventory. There was a significant inverse association between the presence of symptoms and fibre intake for: incomplete defaecation, urgency and hard stools with total fibre intake; urgency and hard stools with cereal fibre intake; and borborygmi with fibre intake at breakfast. All patients with constipation, mucus, urgency or watery stools at the beginning of the study, and who were consuming more than 30 g fibre by the end, reported an improvement in these symptoms. Increasing intakes of fibre were not related in any way to abdominal distension, diarrhoea, flatulence or patient's feelings about the working of their bowels. Therefore, this study suggests that the symptoms which benefit most from the prescription of a high-fibre diet are hard stools, constipation and urgency.

The use of a microcomputer for non-linear optimisation of doses in external radiotherapy

The study presents software for a microcomputer designed to determine the optimum dose distribution in external radiotherapy, either by calculating the doses delivered and the field width (in linear programming) or, in addition, by calculating the beam geometry (non-linear optimisation). Various optimisation criteria can be selected, namely the homogeneity, the concentration on the target and the total dose in a sensitive area. The article outlines an example.

Effect of a benzoic acid-detergent germicide on denture-borne Candida albicans

Benzoic acid combined with a detergent was used to safely and effectively decontaminate dentures colonized with Candida albicans. Surface decontamination was accomplished by soaking the dentures in the germicide solution for a period of 6 hours to overnight. Decontamination may occur in as little as 10 minutes when soaking is combined with ultrasonic enhancement.

[Conception of a program for the treatment and statistical interrogation of data, LOGIST]

This paper presents a general program which cannot only be used for the treatment and the statistical interrogations, but also for basic operations, such as the validity check and the preparation of data which is often necessary for other programs. Its use of language is simple, suitable and accessible to non-specialists. The program is sufficiently complete so that it can treat some complex problems without requiring complementary programs. It can treat several problems simultaneously. This allows one to gain data-reading time and the program is therefore economical. Its domain of use is large: epidemiological studies, psychological and sociological investigations, biological studies, clinical research, chronological follow-up, examinations of faculties, . . . . The program is written in FORTRAN IV and thus transferable. It contains more than 25 000 instructions but needs limited place in the core memory (less than 64 000 words). Its structure allows further evolution and addition of new procedures or new methods. A transformation into a conversational form is considered.

[The microcomputer in bacteriology. Value in the automated performance of antibiograms in hospitals]

In microbiology, most computerization is carried out by means of important centralized computers. On the contrary, our work is based upon the use of inexpensive microcomputers. We have developed general programs for the acquisition of data, their correction, and retrieval of lists arranged according to desired parameters (hospital department, germ, or sample) and various statistics, especially with respect to germ sensitivity. This system has been used on a routine basis since April 1982 in the Bacteriology Laboratory of Nancy University Hospital. It could easily be adapted to other laboratories and could provide a wide range of essential epidemiological data on the resistance of bacterial strains to antibiotics and their evolution with time.

Monoclonal antibodies directed against different antigenic determinants of rotavirus

We have developed a series of monoclonal antibodies against the calf strain RIT 4237 (subgroup 1) and the human strain 82-561 (subgroup 3) of rotavirus, both grown in tissue culture, and also against the human rotavirus 81-2162 (subgroup 2), extracted from a fecal specimen. A variety of different specificities was observed among these antibodies, namely, antibodies against group and subgroup determinants, as well as neutralizing antibodies. By using monoclonal antibodies against the subgroup antigen in an enzyme-linked immunoassay system, the constant predominance of subgroup 2 viruses in humans was confirmed in 74 stools collected from children in Brussels who suffered a diarrheal illness between July 1981 and June 1983. The availability of these antibodies also made it possible to improve the sensitivity and the specificity of the test system.

Protection studies in colostrum-deprived piglets of a bovine rotavirus vaccine candidate using human rotavirus strains for challenge

Studies were performed to evaluate the potential use of the bovine RIT 4237 rotavirus strain as a vaccine candidate against infection with human rotaviruses. Initial experiments revealed that colostrum-deprived piglets were susceptible to infection with several human strains, except for those belonging to subgroup 1. Subsequently, different immunization procedures with RIT 4237 were studied in this animal model. It was found that a two-dose administration, either given intramuscularly (twice) or once intramuscularly and once intragastrically, was necessary to induce a significant serum antibody response. Finally, the protective effect of the latter vaccination schedules against subgroup 2 and 3 rotavirus strains of human origin was evaluated by artificial challenge. In both cases, prior administration of live RIT 4237 significantly decreased fecal shedding of the challenge virus when compared with control animals.

Prevalence of subgroup 1, 2, and 3 rotaviruses in Belgian children suffering from acute diarrhea (1978-1981)

The relative prevalence of human rotavirus subgroups was studied during a 3-year period (1978-1981) by means of a sensitive complement fixation technique. Among 93 rotavirus isolates from children with acute gastroenteritis in Brussels, the prevalence of subgroups 1, 2, and 3 was, respectively 24, 17, and 32%. The remaining 27% of strains could not be typed, but no evidence for the existence of any new subgroup was found. The proportion of strains belonging to the different subgroups remained roughly constant during the study period, showing the simultaneous occurrence of the various subgroups of viruses, even during the annual winter peak of rotavirus gastroenteritis.

Viricidal capability of resin-triiodide demand-type disinfectant

Polyoma, Newcastle disease virus, and adenovirus, as well as two coliphages, lambda and T4, were inactivated by strong base quaternary ammonium anion-exchange resin-triiodide. Organic matter interfered with viral inactivation capability of the resin-triiodide. The viruses, as they were being inactivated by the resin disinfectant beads, were not retained or filtered by the beads.

Software for linear and non-linear optimization in external radiotherapy

The study presents a set of programs designed to determine optimum dose distribution either by calculation of beam intensities and field width (in linear programming) or, in addition, by calculation of beam geometry (non-linear optimization). Various optimization criteria can be selected: homogeneity, concentration on target, entire dose in a sensitive area. The optimization method used is the gradient projection method, and doses are calculated by Cunningham formulae. The article describes the program operating modes, the main subroutines and their functions and specifications, and outlines an example.

Enzyme-linked immunosorbent assays adapted for serotyping of human rotavirus strains

Five enzyme-linked immunosorbent assay systems were adapted for serotyping human rotavirus strains and were compared with a sensitive complement fixation test in terms of specificity and sensitivity. The assays differed mainly with regard to the antibody systems involved in the double sandwich. Serotype differentiation of 34 rotavirus strains was achieved by determining a neutralization endpoint titer, either with a constant antiserum-varying antigen dilution method or vice versa. The procedure which proved to be highly specific and sensitive was one with two type-specific hyperimmune sera (enzyme-linked immunosorbent assay system 5) instead of only one, as in the four other systems.