Peter Schott

Mechanical Load-Dependent Regulation of Gene Expression in Monocrotaline-Induced Right Ventricular Hypertrophy in the Rat

Abstract— Rats treated with monocrotaline (MCT) develop pulmonary hypertension. Their right ventricles (RVs) exhibit severe pressure overload-induced hypertrophy, whereas the left ventricles (LVs) are normally loaded. In contrast, enhanced neuroendocrine stimulation during the transition to heart failure affects both ventricles. We assessed gene expression levels of Ca2+-regulating proteins in RVs and LVs of control and MCT rats in transition to heart failure to identify biomechanical load-regulated genes. In MCT RVs, both mRNA and protein levels of the Ca2+-ATPase of the sarcoplasmic/endoplasmic reticulum (SERCA2a) were reduced by 36% (P =0.001) and 17% (P =0.016), respectively, compared with control RVs. Phospholamban and ryanodine receptor mRNA levels likewise were reduced (by 27% [P =0.05] and 21% [P =0.011], respectively) in MCT RVs, whereas sarcolemmal Na+-Ca2+ exchanger expression was not altered. MCT LVs exhibited no significant expression changes compared with control LVs. Isometrically contracting MCT intact RV trabeculae showed enhanced baseline force development. Although control RV preparations exhibited a positive force-frequency relationship, MCT RVs showed a negative force-frequency relationship and blunted postrest potentiation. Contractile function of MCT LV trabeculae was normal. Maximum Ca2+-activated tension was enhanced by 64% in permeabilized RV MCT preparations (P =0.013). &bgr;-Myosin heavy chain protein was upregulated in MCT RVs (P <0.001) but unaltered in MCT LVs. Degradation of troponin T was prominent in MCT RVs, a phenomenon not observed in the LV. Enhanced biomechanical load is necessary to induce the gene expression changes associated with the hypertrophic phenotype of the pressure-overloaded RV. Neuroendocrine factors, which equally affect both chambers, are not sufficient to alter the expression of Ca2+-cycling proteins.

Excessive Sarcoplasmic/Endoplasmic Reticulum Ca2+-ATPase Expression Causes Increased Sarcoplasmic Reticulum Ca2+ Uptake but Decreases Myocyte Shortening

Background—Increasing sarcoplasmic/endoplasmic reticulum (SR) Ca2+-ATPase (SERCA) uptake activity is a promising therapeutic approach for heart failure. We investigated the effects of different levels of SERCA1a expression on contractility and Ca2+ cycling. We tested whether increased SERCA1a expression levels enhance myocyte contractility in a gene-dose–dependent manner. Methods and Results—Rabbit isolated cardiomyocytes were transfected at different multiplicities of infection (MOIs) with adenoviruses encoding SERCA1a (or &bgr;-galactosidase as control). Myocyte relaxation half-time was decreased by 10% (P=0.052) at SERCA1a MOI 10 and by 28% at MOI 50 (P<0.05). Myocyte fractional shortening was increased by 12% at MOI 10 (P<0.05) but surprisingly decreased at MOI 50 (−22%, P<0.05) versus control. SR Ca2+ uptake (in permeabilized myocytes) demonstrated a gene-dose–dependent decrease in Km by 29% and 46% and an increase in Vmax by 37% and 72% at MOI 10 and MOI 50, respectively (all P<0.05 versus control). Ca2+ transient amplitude was increased in Ad-SERCA1a–infected myocytes at MOI 10 (by 121%, P<0.05), but at MOI 50, the Ca2+ transient amplitude was not significantly changed. Caffeine-induced Ca2+ transients indicated significantly increased SR Ca2+ content in Ad-SERCA1a–infected cells, by 72% at MOI 10 and by 87% at MOI 50. Mathematical simulations demonstrate that the functional increase in SR Ca2+-ATPase uptake activity at MOI 50 (and increased cytosolic Ca2+ buffering) is sufficient to curtail the Ca2+ transient amplitude and explain the reduced contraction. Conclusions—Moderate SERCA1a gene transfer and expression improve contractility and Ca2+ cycling. However, higher SERCA1a expression levels can impair myocyte shortening because of higher SERCA activity and Ca2+ buffering.

Biventricular Pacing Improves the Blunted Force–Frequency Relation Present During Univentricular Pacing in Patients With Heart Failure and Conduction Delay

Background— In patients with chronic heart failure (CHF) and conduction delay, biventricular (BiV) and left ventricular (LV) pacing similarly improve systolic function at resting heart rates. We hypothesized that BiV and univentricular pacing differentially affect contractile function at increasing heart rates. Methods and Results— Twenty-two patients (aged 66±2 years, QRS 179±8 ms, LV ejection fraction 23±1%) underwent cardiac catheterization before device implantation to measure LV hemodynamics at baseline (rate 68±2 bpm; sinus rhythm n=18; atrial fibrillation n=4) and during BiV, LV, and right ventricular (RV) stimulation at 80, 100, 120, and 140 bpm. BiV and LV pacing at 80 bpm equally augmented dP/dtmax as compared with baseline and RV pacing (P<0.001). Stimulation rate significantly interacted with the effect of BiV, LV, and RV pacing on LV end-diastolic pressure (LVEDP), systolic pressure (LVSP), and dP/dtmax. Increasing the rate from 80 to 140 bpm enhanced dP/dtmax from 913±28 to 1119±50 mm Hg/s during BiV stimulation (P<0.001) but had no significant effect on contractility during single-site LV (951±47 versus 1002±54 mm Hg/s) or RV (800±46 versus 881±49 mm Hg/s) pacing. At 140 bpm, LVEDP was lower and LVSP higher during BiV pacing than during RV and LV pacing (LVEDP 12±1 versus 17±1 and 16±1 mm Hg, P<0.001; LVSP 112±5 versus 106±5 and 108±6 mm Hg, P<0.01 and P=0.09; BiV versus RV and LV pacing, respectively). Conclusions— Different modes of ventricular stimulation alter the in vivo force–frequency relation of CHF patients. In contrast to single-site LV and RV pacing, contractile function improves with increasing heart rates during BiV stimulation. This effect may contribute to the enhanced exercise capacity during BiV pacing and could provide a functional benefit over LV-only pacing in patients for whom resynchronization therapy is indicated.

Relevance of brain natriuretic peptide in preload-dependent regulation of cardiac sarcoplasmic reticulum Ca2+ ATPase expression.

Background— In heart failure (HF), ventricular myocardium expresses brain natriuretic peptide (BNP). Despite the association of elevated serum levels with poor prognosis, BNP release is considered beneficial because of its antihypertrophic, vasodilating, and diuretic properties. However, there is evidence that BNP-mediated signaling may adversely influence cardiac remodeling, with further impairment of calcium homeostasis. Methods and Results— We studied the effects of BNP on preload-dependent myocardial sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) expression. In rabbit isolated muscle strips stretched to high preload and shortening isotonically over 6 hours, the SERCA/glyceraldehyde phosphate dehydrogenase mRNA ratio was enhanced by 168% (n=8) compared with unloaded preparations (n=8; P<0.001). Recombinant human BNP at a concentration typically found in end-stage HF patients (350 pg/mL) abolished SERCA upregulation by stretch (n=9; P<0.0001 versus BNP free). Inhibition of cyclic guanosine 3′,5′ monophosphate (cGMP)–phosphodiesterase-5 mimicked this effect, whereas inhibition of cGMP-dependent protein kinase restored preload-dependent SERCA upregulation in the presence of recombinant human BNP. Furthermore, in myocardium from human end-stage HF patients undergoing cardiac transplantation (n=15), BNP expression was inversely correlated with SERCA levels. Moreover, among 23 patients treated with left ventricular assist devices, significant SERCA2a recovery occurred in those downregulating BNP. Conclusions— Our data indicate that preload stimulates SERCA expression. BNP antagonizes this mechanism via guanylyl cyclase-A, cGMP, and cGMP-dependent protein kinase. This novel action of BNP to uncouple preload-dependent SERCA expression may adversely affect contractility in patients with HF.

Intrathoracic impedance monitoring to detect chronic heart failure deterioration: Relationship to changes in NT-proBNP

An alert algorithm, based on intrathoracic impedance monitoring, has been incorporated into a cardiac resynchronisation device (CRT) to detect pulmonary fluid accumulation, and to audibly alert patients to decompensating chronic heart failure (CHF).

Cardiac resynchronization therapy and atrial overdrive pacing for the treatment of central sleep apnoea

The combined therapeutic impact of atrial overdrive pacing (AOP) and cardiac resynchronization therapy (CRT) on central sleep apnoea (CSA) in chronic heart failure (CHF) so far has not been investigated. We aimed to evaluate the effect of CRT alone and CRT + AOP on CSA in CHF patients and to compare the influence of CRT on CHF between CSA positive and CSA negative patients.

Interferon-α treatment of hepatitis C virus-associated mixed cryoglobulinemia

BACKGROUND/AIMS Chronic hepatitis C virus infection is frequently associated with mixed cryoglobulinemia. The efficacy of interferon-alpha treatment in the presence of cryoglobulinemia, particularly the rate of sustained responders, has not yet been well defined. METHODS Fifty-nine consecutive patients with chronic HCV infection were studied prospectively with regard to the presence of cryoglobulinemia and their biochemical and virological response to interferon-alpha2a therapy. RESULTS Cryoglobulins were detected in sera of 23 patients. For this latter group of patients, significant differences were found compared to the 36 patients without cryoglobulinemia, i.e. the prevalence of female sex was higher, the duration of liver disease was longer and distinctive laboratory abnormalities, e.g. higher rheumatoid factor activity, were noted as well as a higher prevalence of cirrhosis. The distribution of HCV genotypes and serum HCV RNA titers was similar in the two groups. Interferon-alpha treatment regimens were not different regarding mean cumulative dose and mean duration of therapy. The response to therapy was almost identical, i.e. 35% of patients with cryoglobulinemia showed a sustained response compared to 22% of patients without cryoglobulinemia. The percentages of patients showing a relapse or breakthrough were similar in both groups. Pre-treatment viremia levels were higher in non-responders compared to sustained responders. Non-responders appeared to be more frequent among patients infected with genotypes 1a and 1b, especially among male patients without cryoglobulinemia. CONCLUSIONS The presence of cryoglobulinemia per se in chronic HCV-infected patients does not adversely affect the outcome of interferon-alpha therapy, including the rate of sustained response.

Hepatitis C virus infection-associated non-cryoglobulinaemic monoclonal IgMκ gammopathy responsive to interferon-α treatment

Abstract Background/Aims: An association of HCV infection with lymphoproliferative disorders, particularly B-cell non-Hodgkins lymphoma has been described. In the majority of reported patients, mixed cryoglobulinaemia was present as well. Rarely, HCV-associated lymphoproliferative disorders have been observed in the absence of cryoglobulinaemia. In these latter patients, the response to interferon-α is largely unknown. Case Report: We report a case of an asymptomatic 31-year-old male with chronic HCV infection and non-cryoglobulinaemic monoclonal IgMκ gammopathy responsive to interferon-α therapy. Prior to therapy, elevated plasma transaminase activities known for longer than a year, serum anti-HCV antibodies and HCV RNA detected by reverse transcriptase-polymerase chain reaction were presnet. Serum IgM concentration was markedly elevated, immunofixation demonstrated monoclonal serum IgM, and urine κ-light chains were detected. Cryoglobulins were undetectable in several consecutive serum samples. Bone marrow aspirate and biopsy specimens were unremarkable. Further evaluation, e.g. by ultrasonography and radiography, did not reveal evidence for lymphoma. Treatment with interferon-α 2a for 12 months resulted in a long-term sustained response to HCV infection and in a normalisation of serum IgM concentration. Conclusion: Therefore, the corresponding effects of interferon-α on HCV infection and on a monoclonal B-cell population observed in the present case might suggest a pathogenetic connection, similarly, to what has been described for HCV and mixed cryoglobulinaemia. The molecular events, however, leading to HCV-induced monoclonal B-cell expansion remain unknown.

Proteome changes in CaMKIIδC-overexpressing cardiac myocytes

Recent studies have demonstrated that the expression as well as the activity of Ca/calmodulin-dependent protein kinase IIδ(C) (CaMKIIδ(C)) is increased in heart failure. Transgenic overexpression of CaMKIIδ(C) in mouse hearts results in severe dilated cardiomyopathy. So far, little is known about CaMKIIδ(C)-induced changes in gene expression and proteome alteration. We hypothesize that proteome changes similar to those found in advanced heart failure can be assessed even after short term overexpression of CaMKIIδ(C) in an in vitro culture model. Thus, we designed a study using a proteomic approach combined with adenovirus-mediated gene transfer of CaMKIIδ(C) to identify early CaMKIIδ(C)-induced changes in cardiac myocyte phenotype on proteome level. CaMKIIδ(C) was overexpressed by adenovirus-mediated gene transfer in isolated cardiac myocytes of adult rabbits for 48 h. Proteome changes were analyzed by two-dimensional gel electrophoresis and mass spectrometry (MS). Overexpression of CaMKIIδ(C) resulted in a decreased expression of 21 proteins (at least twofold change of expression, P<.05, n=10). Using in-gel digest and MS, we identified 13 out of these 21 proteins. CaMKIIδ(C) overexpression leads to a reduced abundance of NADH dehydrogenase, lactate dehydrogenase, pyruvate kinase, dihydrolipoamide succinyltransferase, creatine kinase M, heat shock protein 70, elongation factor Tu, and superoxide dismutase. The profile of the proteome changes induced by CaMKIIδ(C) overexpression after 48 h displayed striking alterations of metabolic proteins, cell-protecting proteins including antioxidants, and proteins involved in protein synthesis. Interestingly, the observed proteome changes are in common with the phenotype of failing cardiac myocytes on the protein level. These altered proteins may act individually as contributors to heart failure, which is observed after overexpression of CaMKIIδ(C) in genetically altered mice.

The contractile adaption to preload depends on the amount of afterload

The Frank–Starling mechanism (rapid response (RR)) and the secondary slow response (SR) are known to contribute to increases contractile performance. The contractility of the heart muscle is influenced by pre‐load and after‐load. Because of the effect of pre‐load vs. after‐load on these mechanisms in not completely understood, we studied the effect in isolated muscle strips.