Guillain-Barre syndrome following COVID-19 vaccination: a study of 70 case reports.

Background and objective: Guillain-Barre syndrome (GBS) has been found to have some interesting association with vaccinations. This paper mainly focuses on exploring different associations between COVID-19 vaccination and GBS. Methods: Electronic databases such as PubMed, Google Scholar, Cochrane, and Embase were searched using MESH terms for case reports published till 1 August 2023 from which 70 case reports were documented involving 103 individuals from 23 different countries. Result and discussion: The case reports were from a wide range of individuals aged from 13 to 87 years with an average age of 53±20 interquartile range years along with male predominance. The average time between receiving the vaccine and the onset of symptoms was 13.08±2.14 days. Prominent clinical features included back pain, facial diplegia, weakness, and paraesthesia whereas the main diagnostic studies were cerebrospinal fluid (CSF) analysis and electromagnetic studies. The principal diagnostic clue was albumin-cytological dissociation in CSF while being negative for anti-ganglioside antibodies or SARS-CoV-2. Available treatment options consisted of intravenous immunoglobulin and Plasmapheresis. Patients with comorbidities such as diabetes mellitus, hypertension, dyslipidemia, permanent atrial fibrillation, hypothyroidism, Hashimoto's thyroiditis, Chronic Obstructive Pulmonary Disease, asthma, osteoporosis, migraine, rheumatoid arthritis, osteoarthritis, ulcerative colitis, coeliac disease, seizures, bipolar disorder, endometriosis, multiple sclerosis, bell's palsy, squamous cell carcinoma, prostate cancer were included in our study. Conclusion: Overall, this review evaluated innovative and clinically relevant associations between COVID-19 vaccination and GBS. Understanding of this uncommon potential side effect of COVID-19 vaccination is crucial for prompt diagnosis and appropriate treatment. Importantly, GBS should not be considered a contraindication to vaccination. This underscores the importance of ongoing research to enhance the safety and efficacy of COVID-19 vaccination efforts.

LRRC8A anion channels modulate vascular reactivity via association with myosin phosphatase rho interacting protein.

Leucine-rich repeat containing 8A (LRRC8A) volume regulated anion channels (VRACs) are activated by inflammatory and pro-contractile stimuli including tumor necrosis factor alpha (TNFα), angiotensin II and stretch. LRRC8A associates with NADPH oxidase 1 (Nox1) and supports extracellular superoxide production. We tested the hypothesis that VRACs modulate TNFα signaling and vasomotor function in mice lacking LRRC8A exclusively in vascular smooth muscle cells (VSMCs, Sm22α-Cre, Knockout). Knockout (KO) mesenteric vessels contracted normally but relaxation to acetylcholine (ACh) and sodium nitroprusside (SNP) was enhanced compared to wild type (WT). Forty-eight hours of ex vivo exposure to TNFα (10 ng/mL) enhanced contraction to norepinephrine (NE) and markedly impaired dilation to ACh and SNP in WT but not KO vessels. VRAC blockade (carbenoxolone, CBX, 100 µM, 20 min) enhanced dilation of control rings and restored impaired dilation following TNFα exposure. Myogenic tone was absent in KO rings. LRRC8A immunoprecipitation followed by mass spectroscopy identified 33 proteins that interacted with LRRC8A. Among them, the myosin phosphatase rho-interacting protein (MPRIP) links RhoA, MYPT1 and actin. LRRC8A-MPRIP co-localization was confirmed by confocal imaging of tagged proteins, Proximity Ligation Assays, and IP/western blots. siLRRC8A or CBX treatment decreased RhoA activity in VSMCs, and MYPT1 phosphorylation was reduced in KO mesenteries suggesting that reduced ROCK activity contributes to enhanced relaxation. MPRIP was a target of redox modification, becoming oxidized (sulfenylated) after TNFα exposure. Interaction of LRRC8A with MPRIP may allow redox regulation of the cytoskeleton by linking Nox1 activation to impaired vasodilation. This identifies VRACs as potential targets for treatment or prevention of vascular disease.

LRRC8A anion channels modulate vasodilation via association with Myosin Phosphatase Rho Interacting Protein (MPRIP).

Background: In vascular smooth muscle cells (VSMCs), LRRC8A volume regulated anion channels (VRACs) are activated by inflammatory and pro-contractile stimuli including tumor necrosis factor alpha (TNFα), angiotensin II and stretch. LRRC8A physically associates with NADPH oxidase 1 (Nox1) and supports its production of extracellular superoxide (O 2 -• ). Methods and Results: Mice lacking LRRC8A exclusively in VSMCs (Sm22α-Cre, KO) were used to assess the role of VRACs in TNFα signaling and vasomotor function. KO mesenteric vessels contracted normally to KCl and phenylephrine, but relaxation to acetylcholine (ACh) and sodium nitroprusside (SNP) was enhanced compared to wild type (WT). 48 hours of ex vivo exposure to TNFα (10ng/ml) markedly impaired dilation to ACh and SNP in WT but not KO vessels. VRAC blockade (carbenoxolone, CBX, 100 µM, 20 min) enhanced dilation of control rings and restored impaired dilation following TNFα exposure. Myogenic tone was absent in KO rings. LRRC8A immunoprecipitation followed by mass spectroscopy identified 35 proteins that interacted with LRRC8A. Pathway analysis revealed actin cytoskeletal regulation as the most closely associated function of these proteins. Among these proteins, the Myosin Phosphatase Rho-Interacting protein (MPRIP) links RhoA, MYPT1 and actin. LRRC8A-MPRIP co-localization was confirmed by confocal imaging of tagged proteins, Proximity Ligation Assays, and IP/western blots which revealed LRRC8A binding at the second Pleckstrin Homology domain of MPRIP. siLRRC8A or CBX treatment decreased RhoA activity in cultured VSMCs, and MYPT1 phosphorylation at T853 was reduced in KO mesenteries suggesting that reduced ROCK activity contributes to enhanced relaxation. MPRIP was a target of redox modification, becoming oxidized (sulfenylated) after TNFα exposure. Conclusions: Interaction of Nox1/LRRC8A with MPRIP/RhoA/MYPT1/actin may allow redox regulation of the cytoskeleton and link Nox1 activation to both inflammation and vascular contractility.

Diagnostic implications of neuroimaging in epilepsy and other seizure disorders.

Epilepsy is the most common neurological disorder that affects ~1-2% of the global population, leading to presentation in the emergency room. The neuroimaging modalities have an important application in diagnosing new onset unprovoked seizures and epilepsy. This article discusses the various neuroimaging modalities for diagnosing seizures and epilepsy and addresses that the MRI is the investigation of choice, and urgent imaging is more commonly done by computed tomography in patients with new-onset seizures. The goal of the article was to diagnose seizures and epilepsy for early intervention to prevent complications or damage to the brain. MRI detects even small cortical epileptogenic lesions, whereas computed tomography is used in screening, diagnosis, evaluation, and monitoring of the prognosis of seizures in children. Magnetic resonance spectroscopy provides biochemical measurements of reduced N-acetyl aspartate and increased creatinine and choline in dysfunctioning epileptic zones. Volumetric MRI is very sensitive and specific in determining seizures originating in extratemporal and extrahippocampal sites. Even though diffusion tensor magnetic resonance imaging has a limited role, it is used in specific pediatric patient groups with temporal lobe epilepsy. Functional radionuclide imaging modalities (positron emission tomography and single-photon emission computerized tomography) are increasingly significant for the identification of the epileptic region. Furthermore, the authors recommend the use of artificial intelligence and further research on imaging modalities for early diagnosis of seizures and epilepsy.

Adipose-targeted SWELL1 deletion exacerbates obesity- and age-related nonalcoholic fatty liver disease.

Healthy expansion of adipose tissue is critical for the maintenance of metabolic health, providing an optimized reservoir for energy storage in the form of triacylglycerol-rich lipoproteins. Dysfunctional adipocytes that are unable to efficiently store lipid can result in lipodystrophy and contribute to nonalcoholic fatty liver disease (NAFLD) and metabolic syndrome. Leucine-rich repeat containing protein 8a/SWELL1 functionally encodes the volume-regulated anion channel complex in adipocytes, is induced in early obesity, and is required for normal adipocyte expansion during high-fat feeding. Adipose-specific SWELL1 ablation (Adipo KO) leads to insulin resistance and hyperglycemia during caloric excess, both of which are associated with NAFLD. Here, we show that Adipo-KO mice exhibited impaired adipose depot expansion and excess lipolysis when raised on a variety of high-fat diets, resulting in increased diacylglycerides and hepatic steatosis, thereby driving liver injury. Liver lipidomic analysis revealed increases in oleic acid-containing hepatic triacylglycerides and injurious hepatic diacylglyceride species, with reductions in hepatocyte-protective phospholipids and antiinflammatory free fatty acids. Aged Adipo-KO mice developed hepatic steatosis on a regular chow diet, and Adipo-KO male mice developed spontaneous, aggressive hepatocellular carcinomas (HCCs). These data highlight the importance of adipocyte SWELL1 for healthy adipocyte expansion to protect against NAFLD and HCC in the setting of overnutrition and with aging.

A giant isolated primary splenic hydatidosis: A case report.

Introduction: and importance: Hydatid cyst disease is caused by Echinococcus tapeworm and is one of the major health problems in endemic regions like Nepal. The cases of splenic hydatidosis are quite rare and giant isolated primary splenic hydatidosis is even rarer. The patients present with vague symptoms or no symptoms at all. Here we report a case of isolated splenic hydatid cyst. So, we should think the differential diagnosis of splenic hydatidosis in any abdominal case of endemic regions. Case presentation: A 27-year-old female presented with left-side abdominal pain for the past 7 months without any particular attraction. Abdominal ultrasound showed a well-defined cystic mass on the upper pole with low-level internal floating debris. Contrast Enhanced CT scan showed well defined cystic lesion measuring about 10.8 × 9.6 × 8.5 cm in the upper pole of the spleen with an exophytic component and minimal homogenous wall enhancement. Laparoscopic Splenectomy was done and albendazole for 3 weeks was prescribed after all the patient was completely normal. Clinical discussion: In this case, the optimal treatment of giant isolated splenic hydatidosis was splenectomy and prescription of albendazole. Conclusion: We believe in any abdominal case of the endemic region, the hydatid cyst of the spleen should be taken as one of the differential diagnoses and should be managed appropriately before the complication arises.

Dysentery and leg ulcer as an atypical presentation of systemic lupus erythematosus: A case report.

INTRODUCTION: Due to heterogeneity in the organs involved and a variety of influencing factors, a wide range of clinical manifestations are possible in systemic lupus erythematosus (SLE). In our knowledge, a combination of leg ulcer and dysentery as presenting symptoms of SLE has never been reported previously. PATIENT CONCERNS: A 13-year-old female child presented with a chronic wound over right medial malleolus for 6 months, and passing of watery stool, later mixed with blood, for 4 days. On examination, she had a fever of 38.5°C. Lab reports revealed anemia, thrombocytopenia, proteinuria, and features of urinary tract infection. Renal biopsy showed membranous glomerulonephropathy. She was positive for antinuclear antibodies (ANA) and antidouble stranded DNA (anti-dsDNA). Immunofluorescence revealed reduced C4 and C3 levels. Abdominal ultrasound showed symmetrical circumscribed thickening, and edematous cecum and ascending colon. DIAGNOSIS: The patient was diagnosed with SLE based on the Systemic Lupus International Collaborating Clinics classification criteria. INTERVENTIONS: The patient was treated with prednisolone, hydroxychloroquine, metronidazole, ciprofloxacin, trypsin-chymotrypsin, zinc, calcium, and calcitriol tablets. OUTCOMES: Fever subsided within 3 days of treatment. Gastrointestinal symptoms subsided within 1 week of treatment. On 31 day of treatment, the wound had been reduced and showed features of healing. CONCLUSION: Dysentery and leg ulcers can be the manifestations of SLE. Therefore, SLE should also be considered when a patient presents with such symptoms. Any suspicion of infection in SLE should be treated aggressively with antibiotics.

Mechanosensitive TRPV4 is required for crystal-induced inflammation.

Crystal structures activate innate immune cells, especially macrophages and initiate inflammatory responses. We aimed to understand the role of the mechanosensitive TRPV4 channel in crystal-induced inflammation. Real-time RT-PCR, RNAscope in situ hybridisation, and Trpv4eGFP mice were used to examine TRPV4 expression and whole-cell patch-clamp recording and live-cell Ca2+ imaging were used to study TRPV4 function in mouse synovial macrophages and human peripheral blood mononuclear cells (PBMCs). Both genetic deletion and pharmacological inhibition approaches were used to investigate the role of TRPV4 in NLRP3 inflammasome activation induced by diverse crystals in vitro and in mouse models of crystal-induced pain and inflammation in vivo. TRPV4 was functionally expressed by synovial macrophages and human PBMCs and TRPV4 expression was upregulated by stimulation with monosodium urate (MSU) crystals and in human PBMCs from patients with acute gout flares. MSU crystal-induced gouty arthritis were significantly reduced by either genetic ablation or pharmacological inhibition of TRPV4 function. Mechanistically, TRPV4 mediated the activation of NLRP3 inflammasome by diverse crystalline materials but not non-crystalline NLRP3 inflammasome activators, driving the production of inflammatory cytokine interleukin-1ß which elicited TRPV4-dependent inflammatory responses in vivo. Moreover, chemical ablation of the TRPV1-expressing nociceptors significantly attenuated the MSU crystal-induced gouty arthritis. In conclusion, TRPV4 is a common mediator of inflammatory responses induced by diverse crystals through NLRP3 inflammasome activation in macrophages. TRPV4-expressing resident macrophages are critically involved in MSU crystal-induced gouty arthritis. A neuroimmune interaction between the TRPV1-expressing nociceptors and the TRPV4-expressing synovial macrophages contributes to the generation of acute gout flares.

Resident cardiac macrophages mediate adaptive myocardial remodeling.

Cardiac macrophages represent a heterogeneous cell population with distinct origins, dynamics, and functions. Recent studies have revealed that C-C Chemokine Receptor 2 positive (CCR2+) macrophages derived from infiltrating monocytes regulate myocardial inflammation and heart failure pathogenesis. Comparatively little is known about the functions of tissue resident (CCR2-) macrophages. Herein, we identified an essential role for CCR2- macrophages in the chronically failing heart. Depletion of CCR2- macrophages in mice with dilated cardiomyopathy accelerated mortality and impaired ventricular remodeling and coronary angiogenesis, adaptive changes necessary to maintain cardiac output in the setting of reduced cardiac contractility. Mechanistically, CCR2- macrophages interacted with neighboring cardiomyocytes via focal adhesion complexes and were activated in response to mechanical stretch through a transient receptor potential vanilloid 4 (TRPV4)-dependent pathway that controlled growth factor expression. These findings establish a role for tissue-resident macrophages in adaptive cardiac remodeling and implicate mechanical sensing in cardiac macrophage activation.

The SWELL1-LRRC8 complex regulates endothelial AKT-eNOS signaling and vascular function.

The endothelium responds to numerous chemical and mechanical factors in regulating vascular tone, blood pressure, and blood flow. The endothelial volume-regulated anion channel (VRAC) has been proposed to be mechanosensitive and thereby sense fluid flow and hydrostatic pressure to regulate vascular function. Here, we show that the leucine-rich repeat-containing protein 8a, LRRC8A (SWELL1), is required for VRAC in human umbilical vein endothelial cells (HUVECs). Endothelial LRRC8A regulates AKT-endothelial nitric oxide synthase (eNOS) signaling under basal, stretch, and shear-flow stimulation, forms a GRB2-Cav1-eNOS signaling complex, and is required for endothelial cell alignment to laminar shear flow. Endothelium-restricted Lrrc8a KO mice develop hypertension in response to chronic angiotensin-II infusion and exhibit impaired retinal blood flow with both diffuse and focal blood vessel narrowing in the setting of type 2 diabetes (T2D). These data demonstrate that LRRC8A regulates AKT-eNOS in endothelium and is required for maintaining vascular function, particularly in the setting of T2D.

ORAI1 and ORAI2 modulate murine neutrophil calcium signaling, cellular activation, and host defense.

Calcium signals are initiated in immune cells by the process of store-operated calcium entry (SOCE), where receptor activation triggers transient calcium release from the endoplasmic reticulum, followed by opening of plasma-membrane calcium-release activated calcium (CRAC) channels. ORAI1, ORAI2, and ORAI3 are known to comprise the CRAC channel; however, the contributions of individual isoforms to neutrophil function are not well understood. Here, we show that loss of ORAI1 partially decreases calcium influx, while loss of both ORAI1 and ORAI2 completely abolishes SOCE. In other immune-cell types, loss of ORAI2 enhances SOCE. In contrast, we find that ORAI2-deficient neutrophils display decreased calcium influx, which is correlated with measurable differences in the regulation of neutrophil membrane potential via KCa3.1. Decreased SOCE in ORAI1-, ORAI2-, and ORAI1/2-deficient neutrophils impairs multiple neutrophil functions, including phagocytosis, degranulation, leukotriene, and reactive oxygen species (ROS) production, rendering ORAI1/2-deficient mice highly susceptible to staphylococcal infection. This study demonstrates that ORAI1 and ORAI2 are the primary components of the neutrophil CRAC channel and identifies subpopulations of neutrophils where cell-membrane potential functions as a rheostat to modulate the SOCE response. These findings have implications for mechanisms that modulate neutrophil function during infection, acute and chronic inflammatory conditions, and cancer.

SWELL signalling in adipocytes: can fat 'feel' fat?

Obesity is becoming a global epidemic, predisposing to Type 2 diabetes, cardiovascular disease, fatty liver disease, pulmonary disease, osteoarthritis and cancer. Therefore, understanding the biology of adipocyte expansion in response to overnutrition is critical to devising strategies to treat obesity, and the associated burden of morbidity and mortality. Through exploratory patch-clamp experiments in freshly isolated primary murine and human adipocytes, we recently determined that SWELL1/LRRC8a, a leucine-rich repeat containing transmembrane protein, functionally encoded an ion channel signalling complex (the volume-regulated anion channel, or VRAC) on the adipocyte plasma membrane. The SWELL1-/LRRC8 channel complex activates in response to increases in adipocyte volume and in the context of obesity. SWELL1 is also required for insulin-PI3K-AKT2 signalling to regulate adipocyte growth and systemic glycaemia. This commentary delves further into our working models for the molecular mechanisms of adipocyte SWELL1-mediated VRAC activation, proposed signal transduction mechanisms, and putative impact on adipocyte hypertrophy during caloric excess.

SWELL1 is a glucose sensor regulating ß-cell excitability and systemic glycaemia.

Insulin secretion is initiated by activation of voltage-gated Ca2+ channels (VGCC) to trigger Ca2+-mediated insulin vesicle fusion with the ß-cell plasma membrane. The firing of VGCC requires ß-cell membrane depolarization, which is regulated by a balance of depolarizing and hyperpolarizing ionic currents. Here, we show that SWELL1 mediates a swell-activated, depolarizing chloride current (ICl,SWELL) in both murine and human ß-cells. Hypotonic and glucose-stimulated ß-cell swelling activates SWELL1-mediated ICl,SWELL and this contributes to membrane depolarization and activation of VGCC-dependent intracellular calcium signaling. SWELL1 depletion in MIN6 cells and islets significantly impairs glucose-stimulated insulin secretion. Tamoxifen-inducible ß-cell-targeted Swell1 KO mice have normal fasting serum glucose and insulin levels but impaired glucose-stimulated insulin secretion and glucose tolerance; and this is further exacerbated in mild obesity. Our results reveal that ß-cell SWELL1 modulates insulin secretion and systemic glycaemia by linking glucose-mediated ß-cell swelling to membrane depolarization and activation of VGCC-triggered calcium signaling.

Induction of adipose and hepatic SWELL1 expression is required for maintaining systemic insulin-sensitivity in obesity.

Obesity is associated with a loss of insulin-sensitivity and systemic dysglycemia, resulting in Type 2 diabetes, however the molecular mechanisms underlying this association are unclear. Through adipocyte patch-clamp studies, we recently showed that SWELL1 is required for the Volume-Regulated Anion Current (VRAC) in adipocytes and that SWELL1-mediated VRAC is activated by both mechanical and pathophysiological adipocyte expansion. We also demonstrated that adipocyte SWELL1 is required for maintaining insulin signaling and glucose homeostasis, particularly in the setting of obesity. Here we show that SWELL1 protein expression is induced in subcutaneous fat, visceral fat and liver in the setting of obesity. Long- term AAV/rec2-shRNA mediated SWELL1 knock-down in both fat and liver are associated with increased weight gain, increased adiposity and exacerbated insulin resistance in mice raised on a high-fat diet. These data further support the notion that SWELL1 induction occurs in insulin- sensitive tissues (liver and adipose) in the setting of over-nutrition and contributes to improved systemic glycemia by supporting enhanced insulin-sensitivity.

TRPM7 senses oxidative stress to release Zn2+ from unique intracellular vesicles.

TRPM7 (transient receptor potential cation channel subfamily M member 7) regulates gene expression and stress-induced cytotoxicity and is required in early embryogenesis through organ development. Here, we show that the majority of TRPM7 is localized in abundant intracellular vesicles. These vesicles (M7Vs) are distinct from endosomes, lysosomes, and other familiar vesicles or organelles. M7Vs accumulate Zn2+ in a glutathione-enriched, reduced lumen when cytosolic Zn2+ concentrations are elevated. Treatments that increase reactive oxygen species (ROS) trigger TRPM7-dependent Zn2+ release from the vesicles, whereas reduced glutathione prevents TRPM7-dependent cytosolic Zn2+ influx. These observations strongly support the notion that ROS-mediated TRPM7 activation releases Zn2+ from intracellular vesicles after Zn2+ overload. Like the endoplasmic reticulum, these vesicles are a distributed system for divalent cation uptake and release, but in this case the primary divalent ion is Zn2+ rather than Ca2.

SWELL1 is a regulator of adipocyte size, insulin signalling and glucose homeostasis.

Adipocytes undergo considerable volumetric expansion in the setting of obesity. It has been proposed that such marked increases in adipocyte size may be sensed via adipocyte-autonomous mechanisms to mediate size-dependent intracellular signalling. Here, we show that SWELL1 (LRRC8a), a member of the Leucine-Rich Repeat Containing protein family, is an essential component of a volume-sensitive ion channel (VRAC) in adipocytes. We find that SWELL1-mediated VRAC is augmented in hypertrophic murine and human adipocytes in the setting of obesity. SWELL1 regulates adipocyte insulin-PI3K-AKT2-GLUT4 signalling, glucose uptake and lipid content via SWELL1 C-terminal leucine-rich repeat domain interactions with GRB2/Cav1. Silencing GRB2 in SWELL1 KO adipocytes rescues insulin-pAKT2 signalling. In vivo, shRNA-mediated SWELL1 knockdown and adipose-targeted SWELL1 knockout reduce adiposity and adipocyte size in obese mice while impairing systemic glycaemia and insulin sensitivity. These studies identify SWELL1 as a cell-autonomous sensor of adipocyte size that regulates adipocyte growth, insulin sensitivity and glucose tolerance.

TRPM7, the Mg(2+) inhibited channel and kinase.

TRPM7 is a ubiquitously expressed nonselective cation channel fused to a C-terminal alpha kinase. TRPM7 current is typically small at physiological magnesium concentrations, but large outwardly rectifying currents develop in low-magnesium extracellular solution when cells are dialyzed with magnesium free solutions during whole-cell patch clamp recordings. In addition to regulation by magnesium, TRPM7 current is potentiated by low extracellular pH and inhibited by depletion of phosphatidylinositol 4,5-bisphosphate (PIP(2)) during phospholipase C mediated signaling events. A diverse body of literature has implicated TRPM7 in fundamental cellular processes including death, survival, proliferation, cell cycle progression, magnesium homeostasis and responses to shear stress and oxidative stress. Global deletion of TRPM7 in mouse results in embryonic lethality and a thymocyte-restricted conditional knockout exhibits defective thymopoeisis, suggesting a role for TRPM7 in development and organogenesis. In disease states, TRPM7 has been linked to Guamanian amyotrophic lateral sclerosis and parkinsonian dementia (ALS/PD), various forms of neoplasia, hypertension and delayed neuronal death following cerebral ischemia.

Cardiac-specific elevations in thyroid hormone enhance contractility and prevent pressure overload-induced cardiac dysfunction.

Thyroid hormone (TH) is critical for cardiac development and heart function. In heart disease, TH metabolism is abnormal, and many biochemical and functional alterations mirror hypothyroidism. Although TH therapy has been advocated for treating heart disease, a clear benefit of TH has yet to be established, possibly because of peripheral actions of TH. To assess the potential efficacy of TH in treating heart disease, type 2 deiodinase (D2), which converts the prohormone thyroxine to active triiodothyronine (T3), was expressed transiently in mouse hearts by using the tetracycline transactivator system. Increased cardiac D2 activity led to elevated cardiac T3 levels and to enhanced myocardial contractility, accompanied by increased Ca(2+) transients and sarcoplasmic reticulum (SR) Ca(2+) uptake. These phenotypic changes were associated with up-regulation of sarco(endo)plasmic reticulum calcium ATPase (SERCA) 2a expression as well as decreased Na(+)/Ca(2+) exchanger, beta-myosin heavy chain, and sarcolipin (SLN) expression. In pressure overload, targeted increases in D2 activity could not block hypertrophy but could completely prevent impaired contractility and SR Ca(2+) cycling as well as altered expression patterns of SERCA2a, SLN, and other markers of pathological hypertrophy. Our results establish that elevated D2 activity in the heart increases T3 levels and enhances cardiac contractile function while preventing deterioration of cardiac function and altered gene expression after pressure overload.

Regulation of myocardial contractility and cell size by distinct PI3K-PTEN signaling pathways.

The PTEN/PI3K signaling pathway regulates a vast array of fundamental cellular responses. We show that cardiomyocyte-specific inactivation of tumor suppressor PTEN results in hypertrophy, and unexpectedly, a dramatic decrease in cardiac contractility. Analysis of double-mutant mice revealed that the cardiac hypertrophy and the contractility defects could be genetically uncoupled. PI3Kalpha mediates the alteration in cell size while PI3Kgamma acts as a negative regulator of cardiac contractility. Mechanistically, PI3Kgamma inhibits cAMP production and hypercontractility can be reverted by blocking cAMP function. These data show that PTEN has an important in vivo role in cardiomyocyte hypertrophy and GPCR signaling and identify a function for the PTEN-PI3Kgamma pathway in the modulation of heart muscle contractility.