Pregnancy is associated with decreased cardiac proteasome activity and oxidative stress in mice

Gestational arsenite exposure alters maternal postpartum heart size and induces Ca 2+ handling dysregulation in cardiomyocytes

Cardiovascular disease is the leading cause of mortality in the US. Studies suggest a role for environmental exposures in the etiology of cardiovascular disease, including exposure to arsenic through drinking water. Arsenic exposure during pregnancy has been shown to have effects on offspring, but few studies have examined impacts on maternal cardiovascular health. While our prior work documented the detrimental effect of arsenic on the maternal heart during pregnancy, our current study examines the effect of gestational arsenic exposure on the maternal heart postpartum. Timed-pregnant wild-type (C57BL/6J) mice were exposed to 0, 100 or 1000 µg/L sodium arsenite (NaAsO2) via drinking water from embryonic day 2.5 (E2.5) until parturition. Postpartum heart structure and function was assessed via transthoracic echocardiography and gravimetric measurement. Hypertrophic markers were probed via qRT-PCR and western blot. Isolated cardiomyocyte Ca 2+ -handling and contraction were also assessed, and expression of proteins associated with Ca 2+ handling and contraction. Interestingly, we found that exposure to either 100 or 1000 µg/L sodium arsenite increased postpartum heart size at P12 vs. non-exposed postpartum controls. At the cellular level, we found altered cardiomyocyte Ca 2+ -handling and contraction. We also found altered expression of key contractile proteins, including α-Actin and cardiac myosin binding protein C (cMyBP-c). Together, these findings suggest that gestational arsenic exposure impacts the postpartum maternal heart, possibly inducing long-term cardiovascular changes. Furthermore, these findings highlight the importance of reducing arsenic exposure during pregnancy, and the need for more research on the impact of arsenic and other environmental exposures on maternal heart health and adverse pregnancy events.

New & Noteworthy

Gestational exposure to sodium arsenite at environmentally relevant doses (100 and 1000 µg/L) increases postpartum heart size, and induces dysregulated Ca 2+ homeostasis and impaired shortening in isolated cardiomyocytes. This is the first study to demonstrate that gestational arsenic exposure impacts postpartum heart structure and function beyond the exposure period.

The role of the immunoproteasome in cardiovascular disease

The ubiquitinproteasome system (UPS) is the main mechanism responsible for the intracellular degradation of misfolded or damaged proteins. Under inflammatory conditions, the immunoproteasome, an isoform of the proteasome, can be induced, enhancing the antigen-presenting function of the UPS. Furthermore, the immunoproteasome also serves nonimmune functions, such as maintaining protein homeostasis and regulating signalling pathways, and is involved in the pathophysiological processes of various cardiovascular diseases (CVDs). This review aims to provide a comprehensive summary of the current research on the involvement of the immunoproteasome in cardiovascular diseases, with the ultimate goal of identifying novel strategies for the treatment of these conditions.

Regression of cardiac hypertrophy in health and disease: mechanisms and therapeutic potential

Left ventricular hypertrophy is a leading risk factor for cardiovascular morbidity and mortality. Although reverse ventricular remodelling was long thought to be irreversible, evidence from the past three decades indicates that this process is possible with many existing heart disease therapies. The regression of pathological hypertrophy is associated with improved cardiac function, quality of life and long-term health outcomes. However, less than 50% of patients respond favourably to most therapies, and the reversibility of remodelling is influenced by many factors, including age, sex, BMI and disease aetiology. Cardiac hypertrophy also occurs in physiological settings, including pregnancy and exercise, although in these cases, hypertrophy is associated with normal or improved ventricular function and is completely reversible postpartum or with cessation of training. Studies over the past decade have identified the molecular features of hypertrophy regression in health and disease settings, which include modulation of protein synthesis, microRNAs, metabolism and protein degradation pathways. In this Review, we summarize the evidence for hypertrophy regression in patients with current first-line pharmacological and surgical interventions. We further discuss the molecular features of reverse remodelling identified in cell and animal models, highlighting remaining knowledge gaps and the essential questions for future investigation towards the goal of designing specific therapies to promote regression of pathological hypertrophy.

GRSF1 deficiency in skeletal muscle reduces endurance in aged mice

GRSF1 is a mitochondrial RNA-binding protein important for maintaining mitochondrial function. We found that GRSF1 is highly expressed in cultured skeletal myoblasts differentiating into myotubes. To understand the physiological function of GRSF1 in vivo, we generated mice in which GRSF1 was specifically ablated in skeletal muscle. The conditional knockout mice (Grsf1cKO) appeared normal until 7-9 months of age. Importantly, however, a reduction of muscle endurance compared to wild-type controls was observed in 16- to 18-month old Grsf1cKO mice. Transcriptomic analysis revealed more than 200 mRNAs differentially expressed in Grsf1cKO muscle at this age. Notably, mRNAs encoding proteins involved in mitochondrial function, inflammation, and ion transport, including Mgarp, Cxcl10, Nfkb2, and Sln mRNAs, were significantly elevated in aged Grsf1cKO muscle. Our findings suggest that GRSF1 deficiency exacerbates the functional decline of aged skeletal muscle, likely through multiple downstream effector proteins.

Pulmonary Hypertension in Pregnancy: A Review

Pulmonary hypertension (PH) is a disease, which targets the pulmonary vasculature affecting the heart and the lungs, and is characterized by a vast array of signs and symptoms. These manifestations of PH in pregnancy are highly variable and non-specific hence, it is prudent to have a very keen and high index of suspicion while evaluating these patients. This rare disease can be extremely debilitating and can be associated with a poor overall prognosis. Pregnancy in women with PH puts them at an elevated risk because the physiological changes associated with pregnancy are not well endured leading to even higher morbidity and mortality in these patients. Although there are various modalities for evaluation and workup of PH, right heart catheterization (RHC) remains the gold standard. A mean pulmonary artery pressure (PAP) of more than 20 mm of Hg is considered diagnostic. It is indeed heartening to see that in the past decade many novel therapeutic modalities have emerged and along with a better understanding of the disease process have proved to be promising in terms of reducing the adverse outcomes and preventing death in this population of patients.

Proteasome Levels and Activity in Pregnancies Complicated by Severe Preeclampsia and Hemolysis, Elevated Liver Enzymes, and Thrombocytopenia (HELLP) Syndrome

Excessive accumulation of misfolded proteins was recently demonstrated in preeclampsia. We examined levels and activity of circulatory proteasome and immunoproteasome (inflammatory subtype) in preeclampsia and hemolysis, elevated liver enzymes, and thrombocytopenia (HELLP) syndrome. We analyzed samples from women with hypertensive pregnancy disorders (n=115), including preeclampsia with severe features (sPE) and HELLP syndrome, and normotensive controls (n=45). Plasma proteasome and immunoproteasome immunoreactivity were determined by quantifying the α-subunit of the 20S core and β5i (proteasome subunit beta 8 [PSMB8]), respectively. Plasma proteasome activity was analyzed with fluorogenic substrates. MG132, lactacystin, and ONX0914 were used to inhibit the circulating proteasome and immunoproteasome, respectively. Plasma cytokine profiles were evaluated by multiplex immunoassay. Placental expression of β5 (constitutive proteasome) and β5i (immunoproteasome) was interrogated by immunohistochemistry. Women with sPE had increased plasma 20S levels ( P<0.001) and elevated lytic activities (chymotrypsin-like 7-fold, caspase-like 4.2-fold, trypsin-like 2.2-fold; P <0.001 for all) compared with pregnant controls. Women with features of HELLP displayed the highest plasma proteasome levels and activity, which correlated with decreased IFN-γ (interferon-γ), and increased IL (interleukin)-8 and IL-10. In sPE and HELLP, chymotrypsin-like activity was suppressed by proteasome inhibitors including ONX0914. Compared with gestational age-matched controls, sPE placentas harbored increased β5 and β5i immunostaining in trophoblasts. β5i signal was elevated in HELLP with predominant staining in villous core, extravillous trophoblasts in placental islands, and extracellular vesicles in intervillous spaces. Pregnancy represents a state of increased proteostatic stress. sPE and HELLP were characterized by significant upregulation in circulating levels and lytic activity of the proteasome that was partially explained by placental immunoproteasome upregulation.

Metabolic Coordination of Physiological and Pathological Cardiac Remodeling

Metabolic pathways integrate to support tissue homeostasis and to prompt changes in cell phenotype. In particular, the heart consumes relatively large amounts of substrate not only to regenerate ATP for contraction but also to sustain biosynthetic reactions for replacement of cellular building blocks. Metabolic pathways also control intracellular redox state, and metabolic intermediates and end products provide signals that prompt changes in enzymatic activity and gene expression. Mounting evidence suggests that the changes in cardiac metabolism that occur during development, exercise, and pregnancy as well as with pathological stress (eg, myocardial infarction, pressure overload) are causative in cardiac remodeling. Metabolism-mediated changes in gene expression, metabolite signaling, and the channeling of glucose-derived carbon toward anabolic pathways seem critical for physiological growth of the heart, and metabolic inefficiency and loss of coordinated anabolic activity are emerging as proximal causes of pathological remodeling. This review integrates knowledge of different forms of cardiac remodeling to develop general models of how relationships between catabolic and anabolic glucose metabolism may fortify cardiac health or promote (mal)adaptive myocardial remodeling. Adoption of conceptual frameworks based in relational biology may enable further understanding of how metabolism regulates cardiac structure and function.

Ubiquitin proteasome system (UPS) activation in the cardiac hypertrophy of hyperthyroidism

Ubiquitin proteasome system (UPS) is the main proteolytic pathway in eukaryotic cells. Changes in proteasome expression and activity have been associated to cardiovascular diseases as cardiac hypertrophy. Considering that cardiac hypertrophy is commonly associated to hyperthyroidism condition, the present study aimed to investigate the contribution of UPS in cardiac hypertrophy induced by thyroid hormones. Hyperthyroidism was induced in male Wistar rats by intraperitoneal injections of triiodothyronine (T3; 7  μg/100 g of body weight) for 7 days and confirmed by raised levels of total T3 and decreased levels of total T4. In addition, systolic blood pressure and heart rate were significantly increased in hyperthyroid group. Cardiac hypertrophy was confirmed in hyperthyroid group by increased heart weight/tibia length ratio and by increased α-MHC/β-MHC relative expression. Both catalytic (20SPT) and regulatory subunits (19SPT) of the constitutive proteasome were upregulated in hyperthyroid hearts. In addition, the transcripts that encode immunoproteasome subunits were also elevated. Furthermore, ATP-dependent chymotrypsin-like activity (26SPT) was significantly increased in hyperthyroid group. Despite the upregulation and activation of UPS in hyperthyroid hearts, the content of polyubiquitinated proteins was unaltered in relation to control. Together, these results evidence the activation of cardiac proteasome by thyroid hormones, which possibly contribute to the maintenance of protein quality control and regulation of cardiac hypertrophy in response to thyroid hormones.

Perinatal changes in estradiol and Ang II concentrations in pregnant women with pulmonary arterial hypertension and their correlation

Objective: This study aimed to analyze the perinatal changes of plasma estradiol (E₂) and angiotensin II (Ang II) in pregnant women with pulmonary arterial hypertension before and after cesarean section. Methods: Depending on pulmonary arterial pressure, the subjects were divided into two groups, moderate group, and severe group. Plasma concentrations of E₂ and Ang II were determined at different time points using electrochemiluminescence immunoassay and ELISA, respectively. The correlation between E2 and Ang II concentrations was analyzed. Results: Intragroup comparison indicated that E2 levels at different time points after surgery decreased in the two groups than before, with a greater reduction in the severe group. Besides, both groups showed a reduction in Ang II concentrations after surgery. As indicated by intragroup comparison, there was a significant difference at each time point in the two groups. The reduction in Ang II concentrations was more conspicuous at 48 h and 72 h after surgery (cesarean section) than before for the two groups. Moreover, E₂ concentrations were correlated positively with AngII concentrations. Conclusion: Plasma concentrations of E₂ and Ang II decreased after delivery. The plasma concentrations of E₂ and Ang II were correlated with each other.

Matrix Metalloproteinases System and Types of Fibrosis in Rat Heart during Late Pregnancy and Postpartum

Background and objectives: Cardiac remodeling in pregnancy and postpartum is poorly understood. The aim of this study was to evaluate changes in cardiac fibrosis (pericardial, perivascular, and interstitial), as well as the expression of matrix metalloproteinases (MMP-1, MMP-2, and MMP-9) and their inhibitors (Tissue inhibitors of metalloproteinases, TIMP-1 and TIMP-4) during late pregnancy and postpartum in rat left ventricle. Materials and Methods: Female Sprague–Dawley rats were used for this study. Rats were divided three groups: non-pregnant, late pregnancy, and postpartum. The heart was weighed and cardiac fibrosis was studied by conventional histological procedures. The expression and transcript level of target proteins were evaluated using immunoblot techniques and quantitative PCR. Results: The experiments showed an increase of perivascular, pericardial, and interstitial fibrosis in heart during pregnancy and its reversion in postpartum. Moreover, in late pregnancy, MMP-1, MMP-2, and MMP-9 metalloproteinases were downregulated and TIMP-1 and TIMP-4 were upregulated in left ventricle. Conclusions: Our data suggest that the metalloproteinases system is involved in the cardiac extracellular matrix remodeling during pregnancy and its reversion in postpartum, this improves the knowledge of the adaptive cardiac remodeling in response to a blood volume overload present during pregnancy.

Maternal cardiac messenger RNA expression of extracellular matrix proteins in mice during pregnancy and the postpartum period

IMPACT STATEMENT

This study provides the first comprehensive analysis of extracellular matrix protein (ECM) gene expression combined with echocardiographic analyses of heart functional parameters in the murine heart during pregnancy and the early postpartum period. Our findings show regulation of all Timp, selected Mmps, and Col1a1, Col3a1, and Col8a1 mRNA levels with reproductive status, with the greatest number of significant changes occurring in the early postpartum period. Left ventricle cardiac diastolic parameters were the first to change during pregnancy and remained elevated postpartum, whereas systolic parameters were increased in late pregnancy and began to recover during the first week postpartum. These novel findings indicate that although some ECM genes are elevated during late pregnancy, that the postpartum period is a time of robust altered ECM gene expression. These studies provide a basis for examining ECM proteins and their activities in the normal pregnant and postpartum heart and in models of postpartum cardiomyopathy.

Subnormothermic Perfusion in the Isolated Rat Liver Preserves the Antioxidant Glutathione and Enhances the Function of the Ubiquitin Proteasome System

The reduction of oxidative stress is suggested to be one of the main mechanisms to explain the benefits of subnormothermic perfusion against ischemic liver damage. In this study we investigated the early cellular mechanisms induced in isolated rat livers after 15 min perfusion at temperatures ranging from normothermia (37°C) to subnormothermia (26°C and 22°C). Subnormothermic perfusion was found to maintain hepatic viability. Perfusion at 22°C raised reduced glutathione levels and the activity of glutathione reductase; however, lipid and protein oxidation still occurred as determined by malondialdehyde, 4-hydroxynonenal-protein adducts, and advanced oxidation protein products. In livers perfused at 22°C the lysosomal and ubiquitin proteasome system (UPS) were both activated. The 26S chymotrypsin-like (β5) proteasome activity was significantly increased in the 26°C (46%) and 22°C (42%) groups. The increased proteasome activity may be due to increased Rpt6 Ser120 phosphorylation, which is known to enhance 26S proteasome activity. Together, our results indicate that the early events produced by subnormothermic perfusion in the liver can induce oxidative stress concomitantly with antioxidant glutathione preservation and enhanced function of the lysosomal and UPS systems. Thus, a brief hypothermia could trigger antioxidant mechanisms and may be functioning as a preconditioning stimulus.

Decreased reactive oxygen species production and NOX1, NOX2, NOX4 expressions contribute to hyporeactivity to phenylephrine in aortas of pregnant SHR

AIMS

We determined whether decreased reactive oxygen species (ROS) production in the aorta of pregnant spontaneously hypertensive rats (SHR) resulted in increased nitric oxide (NO) bioavailability and hyporeactivity to phenylephrine (PE).

MAIN METHODS

Systemic and aortic oxidative stress were measured in pregnant and non-pregnant Wistar rats and SHR. Furthermore, the hypotensive effects of apocynin (30 mg/kg) and Tempol (30 mg/kg) were analyzed. Intact aortic rings of pregnant and non-pregnant rats were stimulated with PE in the absence of or after incubation (30 min) with apocynin (100 μmol/L). The effect of apocynin on the concentrations of NO and ROS were measured in aortic endothelial cells (AEC) using DAF-2DA (10 mmol/L) and DHE (2.5 mmol/L), respectively. Western blotting was performed to analyze eNOS, NOX1, NOX2, NOX4 and SOD expression. ROS production was analyzed by the lucigenin chemiluminescence method.

KEY FINDINGS

Aortic oxidative stress and ROS concentration in AEC were reduced in pregnant Wistar rats and SHR, when compared to non-pregnant rats. ROS production and NOX1, NOX2 and NOX4 expression in the aortas were decreased in pregnant SHR, but not in pregnant Wistar rats. Increased eNOS expression in aortas and NO concentration in AEC were observed in pregnant Wistar rats and SHR. Apocynin reduced PE-induced vasoconstriction in the aortas of non-pregnant Wistar rats and SHR, and pregnant Wistar rats, but not in the aortas of pregnant SHR.

SIGNIFICANCE

Taken together, these results suggest that ROS production was decreased in the aortas of pregnant SHR and could contribute to higher NO bioavailability and hyporeactivity to PE in the aortas of pregnant SHR.

Statement on pregnancy in pulmonary hypertension from the Pulmonary Vascular Research Institute

Pregnancy outcomes in patients with pulmonary hypertension remain poor despite advanced therapies. Although consensus guidelines recommend against pregnancy in pulmonary hypertension, it may nonetheless occasionally occur. This guideline document sought to discuss the state of knowledge of pregnancy effects on pulmonary vascular disease and to define usual practice in avoidance of pregnancy and pregnancy management. This guideline is based on systematic review of peer-reviewed, published literature identified with MEDLINE. The strength of the literature was graded, and when it was inadequate to support high-level recommendations, consensus-based recommendations were formed according to prespecified criteria. There was no literature that met standards for high-level recommendations for pregnancy management in pulmonary hypertension. We drafted 38 consensus-based recommendations on pregnancy avoidance and management. Further, we identified the current state of knowledge on the effects of sex hormones during pregnancy on the pulmonary vasculature and right heart and suggested areas for future study. There is currently limited evidence-based knowledge about both the basic molecular effects of sex hormones and pregnancy on the pulmonary vasculature and the best practices in contraception and pregnancy management in pulmonary hypertension. We have drafted 38 consensus-based recommendations to guide clinicians in these challenging topics, but further research is needed in this area to define best practices and improve patient outcomes.

The ubiquitin-proteasome system and autophagy are defective in the taurine-deficient heart

Taurine depletion leads to impaired mitochondrial function, as characterized by reduced ATP production and elevated superoxide generation. These defects can fundamentally alter cardiomyocyte function and if left unchanged can result in cell death. To protect against these stresses, cardiomyocytes possess quality control processes, such as the ubiquitin-proteasome system (UPS) and autophagy, which can rejuvenate cells through the degradation of damaged proteins and organelles. Hence, the present study tested the hypothesis that reactive oxygen species generated by damaged mitochondria initiates UPS and autophagy in the taurine-deficient heart. Using transgenic mice lacking the taurine transporter (TauTKO) as a model of taurine deficiency, it was shown that the levels of ubiquitinated protein were elevated, an effect associated with a decrease in ATP-dependent 26S β5 proteasome activity. Treating the TauTKO mouse with the mitochondria-specific antioxidant, mitoTEMPO, largely abolished the increase in ubiquitinated protein content. The TauTKO heart was also associated with impaired autophagy, characterized by an increase in the initiator, Beclin-1, and autophagosome content, but a defect in the generation of active autophagolysosomes. Although mitoTEMPO treatment only restores the oxidative balance within the mitochondria, it appeared to completely disrupt the crosstalk between the damaged mitochondria and the quality control processes. Thus, mitochondrial oxidative stress is the main trigger initiating the quality control systems in the taurine-deficient heart. We conclude that the activation of the UPS and autophagy is another fundamental function of mitochondria.

Regulation of ubiquitin-proteasome and autophagy pathways after acute LPS and epoxomicin administration in mice

Background

The ubiquitin-proteasome pathway (UPP) is a major protein degradation pathway that is activated during sepsis and has been proposed as a therapeutic target for preventing skeletal muscle loss due to cachexia. Although several studies have investigated the modulation of proteasome activity in response to LPS administration, none have characterized the overall UPP response to LPS administration in the fate of proteasome inhibition.

Methods

Here, we determined the modulation pattern of the main key components of the UPP in the gastrocnemius (GAS) of mice during the acute phase of lipopolysaccharide (LPS)-mediated endotoxemia (7.5 mg/kg – 8 h) by measuring all three β1, β2 and β5 activites of the 20S and 26S proteasomes, the levels of steady state polyubiquitinated proteins, mRNA levels of muscle ligases, as well as signaling pathways regulating the UPP. Another goal was to assess the effects of administration of a specific proteasome inhibitor (epoxomicin, 0.5 mg/kg) on UPP response to sepsis.

Results

The acute phase of LPS-induced endotoxemia lowered GAS/body weight ratio and increased MuRF1 and MAFbx mRNA concomitantly to an activation of the pathways known to regulate their expression. Unexpectedly, we observed a decrease in all 20S and 26S proteasome activities measured in GAS, which might be related to oxidative stress, as oxidized proteins (carbonyl levels) increase with LPS. While significantly inhibiting 20S and 26S proteasome β5 activities in heart and liver, epoxomicin did not lower proteasome activity in GAS. However, the increase in mRNA expression of the muscle ligases MuRF1 and MAFbx were partially rescued without affecting the other investigated signaling pathways. LPS also strongly activated autophagy, which could explain the observed GAS atrophy with LPS-induced reduction of proteasome activity.

Conclusions

Our results highlight an opposite regulation of UPP in the early hours of LPS-induced muscle atrophy by showing reduced proteasome activities and increased mRNA expression of muscle specific ligases. Furthermore, our data do not support any preventive effect of epoxomicin in muscle atrophy due to acute cachexia since proteasome activities are not further repressed.

Progress in solving the sex hormone paradox in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a devastating and progressive disease with marked morbidity and mortality. Even though being female represents one of the most powerful risk factors for PAH, multiple questions about the underlying mechanisms remain, and two "estrogen paradoxes" in PAH exist. First, it is puzzling why estrogens have been found to be protective in various animal models of PAH, whereas PAH registries uniformly demonstrate a female susceptibility to the disease. Second, despite the pronounced tendency for the disease to develop in women, female PAH patients exhibit better survival than men. Recent mechanistic studies in classical and in novel animal models of PAH, as well as recent studies in PAH patients, have significantly advanced the field. In particular, it is now accepted that estrogen metabolism and receptor signaling, as well as estrogen interactions with key pathways in PAH development, appear to be potent disease modifiers. A better understanding of these interactions may lead to novel PAH therapies. It is the purpose of this review to 1) review sex hormone synthesis, metabolism, and receptor physiology; 2) assess the context in which sex hormones affect PAH pathogenesis; 3) provide a potential explanation for the observed estrogen paradoxes and gender differences in PAH; and 4) identify knowledge gaps and future research opportunities. Because the majority of published studies investigated 17β-estradiol and/or its metabolites, this review will primarily focus on pulmonary vascular and right ventricular effects of estrogens. Data for other sex hormones will be discussed very briefly.

Pregnancy as a cardiac stress model

Cardiac hypertrophy occurs during pregnancy as a consequence of both volume overload and hormonal changes. Both pregnancy- and exercise-induced cardiac hypertrophy are generally thought to be similar and physiological. Despite the fact that there are shared transcriptional responses in both forms of cardiac adaptation, pregnancy results in a distinct signature of gene expression in the heart. In some cases, however, pregnancy can induce adverse cardiac events in previously healthy women without any known cardiovascular disease. Peripartum cardiomyopathy is the leading cause of non-obstetric mortality during pregnancy. To understand how pregnancy can cause heart disease, it is first important to understand cardiac adaptation during normal pregnancy. This review provides an overview of the cardiac consequences of pregnancy, including haemodynamic, functional, structural, and morphological adaptations, as well as molecular phenotypes. In addition, this review describes the signalling pathways responsible for pregnancy-induced cardiac hypertrophy and angiogenesis. We also compare and contrast cardiac adaptation in response to disease, exercise, and pregnancy. The comparisons of these settings of cardiac hypertrophy provide insight into pregnancy-associated cardiac adaptation.

Genetics of proteasome diseases

The proteasome is a large, multiple subunit complex that is capable of degrading most intracellular proteins. Polymorphisms in proteasome subunits are associated with cardiovascular diseases, diabetes, neurological diseases, and cancer. One polymorphism in the proteasome gene PSMA6 (-8C/G) is associated with three different diseases: type 2 diabetes, myocardial infarction, and coronary artery disease. One type of proteasome, the immunoproteasome, which contains inducible catalytic subunits, is adapted to generate peptides for antigen presentation. It has recently been shown that mutations and polymorphisms in the immunoproteasome catalytic subunit PSMB8 are associated with several inflammatory and autoinflammatory diseases including Nakajo-Nishimura syndrome, CANDLE syndrome, and intestinal M. tuberculosis infection. This comprehensive review describes the disease-related polymorphisms in proteasome genes associated with human diseases and the physiological modulation of proteasome function by these polymorphisms. Given the large number of subunits and the central importance of the proteasome in human physiology as well as the fast pace of detection of proteasome polymorphisms associated with human diseases, it is likely that other polymorphisms in proteasome genes associated with diseases will be detected in the near future. While disease-associated polymorphisms are now readily discovered, the challenge will be to use this genetic information for clinical benefit.

Calcineurin activity is required for cardiac remodelling in pregnancy

AIMS

Calcium fluctuations and cardiac hypertrophy occur during pregnancy, but the role of the well-studied calcium-activated phosphatase, calcineurin, has not been studied in this setting. The purpose of this study was to determine whether calcineurin signalling is required for cardiac remodelling during pregnancy in mice.

METHODS AND RESULTS

We first examined calcineurin expression in the heart of mice during pregnancy. We found both calcineurin levels and activity were significantly increased in early-pregnancy and decreased in late-pregnancy. Since progesterone levels start to rise in early-pregnancy, we investigated whether progesterone alone was sufficient to modulate calcineurin levels in vivo. After implantation of progesterone pellets in non-pregnant female mice, cardiac mass increased, whereas cardiac function was maintained. In addition, calcineurin levels increased, which is also consistent with early-pregnancy. To determine whether these effects were occurring in the cardiac myocytes, we treated neonatal rat ventricular myocytes (NRVMs) with pregnancy-associated sex hormones. We found that progesterone treatment, but not oestradiol, increased calcineurin levels. To obtain a functional read-out of increased calcineurin activity, we measured the activity of the transcription factor NFAT, a downstream target of calcineurin. Progesterone treatment significantly increased NFAT activity in NRVMs, and this was blocked by the calcineurin inhibitor cyclosporine A (CsA), showing that the progesterone-mediated increase in NFAT activity requires calcineurin activity. Importantly, CsA treatment of mice completely blocked pregnancy-induced cardiac hypertrophy.

CONCLUSION

Our results show that calcineurin is required for pregnancy-induced cardiac hypertrophy, and that calcineurin activity in early-pregnancy is due at least in part to increased progesterone.

Crude and purified proteasome activity assays are affected by type of microplate

Measurement of proteasome activity is fast becoming a commonly used assay in many laboratories. The most common method to measure proteasome activity involves measuring the release of fluorescent tags from peptide substrates in black microplates. Comparisons of black plates used for measuring fluorescence with different properties show that the microplate properties significantly affect the measured activities of the proteasome. The microplate that gave the highest reading of trypsin-like activity of the purified 20S proteasome gave the lowest reading of chymotrypsin-like activity of the 20S proteasome. Plates with medium binding surfaces from two different companies showed an approximately 2-fold difference in caspase-like activity for purified 20S proteasomes. Even standard curves generated using free 7-amino-4-methylcoumarin (AMC) were affected by the microplate used. As such, significantly different proteasome activities, as measured in nmol AMC released/mg/min, were obtained for purified 20S proteasomes as well as crude heart and liver samples when using different microplates. The naturally occurring molecule betulinic acid activated the chymotrypsin-like proteasome activity in three different plates but did not affect the proteasome activity in the nonbinding surface microplate. These findings suggest that the type of proteasome activity being measured and sample type are important when selecting a microplate.