PPP1R12C Promotes Atrial Hypocontractility in Atrial Fibrillation.

BACKGROUND: Atrial fibrillation (AF)-the most common sustained cardiac arrhythmia-increases thromboembolic stroke risk 5-fold. Although atrial hypocontractility contributes to stroke risk in AF, the molecular mechanisms reducing myofilament contractile function remain unknown. We tested the hypothesis that increased expression of PPP1R12C (protein phosphatase 1 regulatory subunit 12C)-the PP1 (protein phosphatase 1) regulatory subunit targeting MLC2a (atrial myosin light chain 2)-causes hypophosphorylation of MLC2a and results in atrial hypocontractility. METHODS: Right atrial appendage tissues were isolated from human patients with AF versus sinus rhythm controls. Western blots, coimmunoprecipitation, and phosphorylation studies were performed to examine how the PP1c (PP1 catalytic subunit)-PPP1R12C interaction causes MLC2a dephosphorylation. In vitro studies of pharmacological MRCK (myotonic dystrophy kinase-related Cdc42-binding kinase) inhibitor (BDP5290) in atrial HL-1 cells were performed to evaluate PP1 holoenzyme activity on MLC2a. Cardiac-specific lentiviral PPP1R12C overexpression was performed in mice to evaluate atrial remodeling with atrial cell shortening assays, echocardiography, and AF inducibility with electrophysiology studies. RESULTS: In human patients with AF, PPP1R12C expression was increased 2-fold versus sinus rhythm controls (P=2.0×10-2; n=12 and 12 in each group) with >40% reduction in MLC2a phosphorylation (P=1.4×10-6; n=12 and 12 in each group). PPP1R12C-PP1c binding and PPP1R12C-MLC2a binding were significantly increased in AF (P=2.9×10-2 and 6.7×10-3, respectively; n=8 and 8 in each group). In vitro studies utilizing drug BDP5290, which inhibits T560-PPP1R12C phosphorylation, demonstrated increased PPP1R12C binding with both PP1c and MLC2a and dephosphorylation of MLC2a. Mice treated with lentiviral PPP1R12C vector demonstrated a 150% increase in left atrial size versus controls (P=5.0×10-6; n=12, 8, and 12), with reduced atrial strain and atrial ejection fraction. Pacing-induced AF in mice treated with lentiviral PPP1R12C vector was significantly higher than in controls (P=1.8×10-2 and 4.1×10-2, respectively; n=6, 6, and 5). CONCLUSIONS: Patients with AF exhibit increased levels of PPP1R12C protein compared with controls. PPP1R12C overexpression in mice increases PP1c targeting to MLC2a and causes MLC2a dephosphorylation, which reduces atrial contractility and increases AF inducibility. These findings suggest that PP1 regulation of sarcomere function at MLC2a is a key determinant of atrial contractility in AF.

Myosin Light Chain Dephosphorylation by PPP1R12C Promotes Atrial Hypocontractility in Atrial Fibrillation.

Background: Atrial fibrillation (AF), the most common sustained cardiac arrhythmia, increases thromboembolic stroke risk five-fold. Although atrial hypocontractility contributes to stroke risk in AF, the molecular mechanisms reducing myofilament contractile function remain unknown. We tested the hypothesis that increased expression of PPP1R12C, the PP1 regulatory subunit targeting atrial myosin light chain 2 (MLC2a), causes hypophosphorylation of MLC2a and results in atrial hypocontractility. Methods: Right atrial appendage tissues were isolated from human AF patients versus sinus rhythm (SR) controls. Western blots, co-immunoprecipitation, and phosphorylation studies were performed to examine how the PP1c-PPP1R12C interaction causes MLC2a de-phosphorylation. In vitro studies of pharmacologic MRCK inhibitor (BDP5290) in atrial HL-1 cells were performed to evaluate PP1 holoenzyme activity on MLC2a. Cardiac-specific lentiviral PPP1R12C overexpression was performed in mice to evaluate atrial remodeling with atrial cell shortening assays, echocardiography, and AF inducibility with EP studies. Results: In human patients with AF, PPP1R12C expression was increased two-fold versus SR controls ( P =2.0×10 -2 , n=12,12 in each group) with > 40% reduction in MLC2a phosphorylation ( P =1.4×10 -6 , n=12,12 in each group). PPP1R12C-PP1c binding and PPP1R12C-MLC2a binding were significantly increased in AF ( P =2.9×10 -2 and 6.7×10 -3 respectively, n=8,8 in each group). In vitro studies utilizing drug BDP5290, which inhibits T560-PPP1R12C phosphorylation, demonstrated increased PPP1R12C binding with both PP1c and MLC2a, and dephosphorylation of MLC2a. Lenti-12C mice demonstrated a 150% increase in LA size versus controls ( P =5.0×10 -6 , n=12,8,12), with reduced atrial strain and atrial ejection fraction. Pacing-induced AF in Lenti-12C mice was significantly higher than controls ( P =1.8×10 -2 and 4.1×10 -2 respectively, n= 6,6,5). Conclusions: AF patients exhibit increased levels of PPP1R12C protein compared to controls. PPP1R12C overexpression in mice increases PP1c targeting to MLC2a and causes MLC2a dephosphorylation, which reduces atrial contractility and increases AF inducibility. These findings suggest that PP1 regulation of sarcomere function at MLC2a is a key determinant of atrial contractility in AF.

B-arrestin-2 Signaling Is Important to Preserve Cardiac Function During Aging.

Experiments reported here tested the hypothesis that ß-arrestin-2 is an important element in the preservation of cardiac function during aging. We tested this hypothesis by aging ß-arrestin-2 knock-out (KO) mice, and wild-type equivalent (WT) to 12-16months. We developed the rationale for these experiments on the basis that angiotensin II (ang II) signaling at ang II receptor type 1 (AT1R), which is a G-protein coupled receptor (GPCR) promotes both G-protein signaling as well as ß-arrestin-2 signaling. ß-arrestin-2 participates in GPCR desensitization, internalization, but also acts as a scaffold for adaptive signal transduction that may occur independently or in parallel to G-protein signaling. We have previously reported that biased ligands acting at the AT1R promote ß-arrestin-2 signaling increasing cardiac contractility and reducing maladaptations in a mouse model of dilated cardiomyopathy. Although there is evidence that ang II induces maladaptive senescence in the cardiovascular system, a role for ß-arrestin-2 signaling has not been studied in aging. By echocardiography, we found that compared to controls aged KO mice exhibited enlarged left atria and left ventricular diameters as well as depressed contractility parameters with preserved ejection fraction. Aged KO also exhibited depressed relaxation parameters when compared to WT controls at the same age. Moreover, cardiac dysfunction in aged KO mice was correlated with alterations in the phosphorylation of myofilament proteins, such as cardiac myosin binding protein-C, and myosin regulatory light chain. Our evidence provides novel insights into a role for ß-arrestin-2 as an important signaling mechanism that preserves cardiac function during aging.

Deletion of P21-activated kinase-1 induces age-dependent increased visceral adiposity and cardiac dysfunction in female mice.

It is known that there is an age-related progression in diastolic dysfunction, especially prevalent in postmenopausal women, who develop heart failure with preserved ejection fraction (HFpEF, EF > 50%). Mechanisms and therapies are poorly understood, but there are strong correlations between obesity and HFpEF. We have tested the hypothesis that P21-activated kinase-1 (PAK1) preserves cardiac function and adipose tissue homeostasis during aging in female mice. Previous demonstrations in male mice by our lab that PAK1 activity confers cardio-protection against different stresses formed the rationale for this hypothesis. Our studies compared young (3-6 months) and middle-aged (12-15 months) female and male PAK1 knock-out mice (PAK1-/-) and wild-type (WT) equivalent. Female WT mice exhibited increased cardiac PAK1 abundance during aging. By echocardiography, compared to young WT female mice, middle-aged WT female mice showed enlargement of the left atrium as well as thickening of posterior wall and increased left ventricular mass; however, all contraction and relaxation parameters were preserved during aging. Compared to WT controls, middle-aged PAK1-/- female mice demonstrated worsening of cardiac function involving a greater enlargement of the left atrium, ventricular hypertrophy, and diastolic dysfunction. Moreover, with aging PAK1-/- female mice, unlike male PAK1-/- mice, exhibited increased adiposity with increased accumulation of visceral adipose tissue. Our data provide evidence for the significance of PAK1 signaling as an element in the preservation of cardiac function and adipose tissue homeostasis in females during aging.

Thirty-day experimental diabetes impairs contractility and increases fatigue resistance in rat diaphragm muscle associated with increased anti-oxidative activity.

Diabetes mellitus is a metabolic disorder that can generate tissue damage through several pathways. Alteration and dysfunction of skeletal muscle are reported including respiratory muscles, which may compromise respiratory parameters in diabetic patients. We have aimed to evaluate the diaphragm muscle contractility, tissue remodeling, oxidative stress, and inflammatory parameters from 30 day streptozotocin-treated rats. The diaphragm contractility was assessed using isolated muscle, tissue remodeling using histology and zymography techniques, and tissue oxidative stress and inflammatory parameters by enzyme activity assay. Our data revealed in the diabetes mellitus group an increase in maximum tetanic force (4.82 ± 0.13 versus 4.24 ± 0.18 N/cm2 (p = 0.015)) and fatigue resistance (139.16 ± 10.78 versus 62.25 ± 4.45 s (p < 0.001)), reduction of 35.4% in muscle trophism (p < 0.001), increase of 32.6% of collagen deposition (p = 0.007), reduction of 21.3% in N-acetylglucosaminidase activity (p < 0.001), and increase of 246.7% of catalase activity (p = 0.002) without changes in reactive oxygen species (p = 0.518) and tissue lipid peroxidation (p = 0.664). All observed changes are attributed to the poor glycemic control (471.20 ± 16.91 versus 80.00 ± 3.42 mg/dL (p < 0.001)), which caused defective tissue regeneration and increased catalase activity as a compensatory mechanism.

Effects of cryotherapy and microwave diathermy on the strength production capacity of elbow flexors in healthy men / Efeitos da crioterapia e da diatermia por micro-ondas sobre a capacidade de produção de força de flexores de cotovelo de homens saudáveis

Abstract Physiological effects of thermal changes in tissues might influence some physical properties of muscle fibers, such as strength. The aim of this study was to compare the effects of cryotherapy and microwave diathermy application on the strength production capacity of the elbow flexor muscles. Thirty male, healthy and sedentary subjects, with average age of 22.40 (±3.42) years, participated in this prospective study. Participants were submitted to assessment of isometric strength production capability by an adapted load cell. Half of volunteers received cryotherapy on the first day of application and microwave diathermy (MD) 48 hours later, whereas the other half was treated the other way around. Cryotherapy was applied up to the temperature of the biceps region reached 25ºC, and MD was applied up to 42ºC. Six peak strength reevaluations were made over 2 hours. There was significant increase in peak strength (PS) up to 15 minutes after cryotherapy, then there was a decrease in maximum isometric strength, however, statistically significant difference remained up to 1 hour and 30 minutes after cryotherapy. In MD, PS decreased significantly after application until 15 min. From this moment, PS returned close to the initial value, and in the last assessment, PS reduced again. Cryotherapy and MD differently interfered in isometric muscle strength production capacity of elbow flexors, while cooling generated increment, heating caused decline.

Resumo Os efeitos fisiológicos das mudanças térmicas nos tecidos podem influenciar propriedades físicas das fibras musculares, como a força. O objetivo deste estudo foi comparar os efeitos da aplicação da crioterapia e da diatermia por micro-ondas (DMO) sobre a capacidade de produção de força dos músculos flexores de cotovelo. Participaram deste estudo prospectivo 30 voluntários do sexo masculino, saudáveis, não praticantes de atividade física, com valor médio de 22,40 (±3,42) anos de idade. Foram submetidos à avaliação da capacidade de produção de força isométrica, por meio de uma célula de carga adaptada. Metade dos voluntários recebeu no primeiro dia aplicação da crioterapia e no outro dia (48 horas depois) a DMO, e a outra metade dos sujeitos o inverso. A crioterapia foi aplicada até que a temperatura na região bicipital atingisse 25ºC e a DMO foi aplicada até que atingisse 42ºC. Seis reavaliações do PF foram feitas ao longo de 2 horas. Houve incremento significativo no pico de força (PF) até 15 minutos após a aplicação da crioterapia, a partir desse momento houve decréscimo da força isométrica máxima, no entanto, a diferença estatisticamente significativa esteve presente até 90 minutos depois. Na DMO, o PF reduziu significativamente até 15 min após a aplicação do recurso. A partir deste momento, o PF foi retornando próximo ao valor inicial. Na última avaliação, o PF reduziu novamente. A crioterapia e a DMO interferiram de maneira diferente na capacidade de produção de força muscular isométrica de flexores de cotovelo, enquanto o resfriamento gerou incremento, o aquecimento causou declínio.

Duração dos efeitos de uma manipulação vertebral sobre a intensidade da dor e atividade eletromiográfica dos paravertebrais de indivíduos com lombalgia crônica mecânica / Duración de los efectos de manipulación vertebral sobre la intensidad de dolor y actividad electromiográfica de la columna en sujetos con dolor lumbar crónico mecánico / Duration of the effects of spinal manipulation on pain intensity and electromyographic activity of paravertebral parts of individuals with chronic mechanical low back pain

RESUMO O objetivo desta pesquisa foi avaliar os efeitos de uma intervenção manipulativa sobre a atividade eletromiográfica dos músculos paraverterbais e a intensidade da dor na coluna lombar imediatamente e 30 minutos após sua realização em indivíduos com dor lombar crônica mecânica. Foram avaliados 38 indivíduos, distribuídos aleatoriamente em dois grupos: o que recebeu a técnica de manipulação vertebral global (n=20) e o controle (n=18), que permanecia em decúbito lateral por dez segundos sobre cada lado do corpo. O sinal eletromiográfico dos paravertebrais ao nível L4-L5 direito e esquerdo foi coletado durante três ciclos do movimento de flexão-relaxamento-extensão do tronco. Nos intervalos entre os ciclos, os participantes relataram a intensidade de dor através da Escala Visual Analógica (EVA 100 mm). Foi observada redução significativa na intensidade da dor no grupo que recebeu a manipulação, ao contrário do grupo controle, em que a pontuação na EVA aumentou. O tamanho do efeito na intensidade da dor foi de 1,0 e 0,9 logo após a manipulação e 30 minutos depois. A razão de flexão/relaxamento (RFR) aumentou no grupo que foi submetido à manipulação, mas permaneceu inalterada no grupo controle. A RFR exibiu tamanhos de 0,6 e 0,5 entre os grupos nas duas avaliações. Foi possível constatar efeitos da manipulação nessas duas variáveis e sua continuidade no intervalo observado, concluindo-se que eles perduram pelo menos durante esse tempo.

RESUMEN En este estudio se evalúan los efectos de intervención manipulativa sobre la actividad electromiográfica de los músculos paravertebrales y la intensidad del dolor lumbar inmediatamente y treinta minutos después de realizada la actividad por sujetos con dolor lumbar crónica mecánica. Participaron 38 sujetos, los cuales fueron divididos al azar en dos grupos: el que había recibido la técnica de manejo vertebral global (n=20) y el grupo control (n=18), lo cual había permanecido en posición lateral por diez segundos sobre cada lado del cuerpo. Se recolectó el signo electromiográfico de los paravertebrales al nivel L4-L5 derecho e izquierdo durante tres ciclos de movimiento de flexión-relajamiento-extensión del tronco. Entre los intervalos de los ciclos, los participantes relataron la intensidad de dolor mediante la Escala Visual Analógica (EVA 100 mm). Los resultados mostraron una significativa disminución en la intensidad de dolor en el grupo que había recibido el manejo, mientras que el grupo control aumentó el puntaje de EVA. El efecto de la intensidad de dolor fue de 1,0 y 0,9 tras el manejo y treinta minutos después. La razón flexión/relajamiento (RFR) aumentó en el grupo al que se sometió al manejo, mientras que había permanecido inalterable en el grupo control. Los valores de los efectos de la RFR entre los grupos fueron de 0,6 y 0,5 en las dos evaluaciones. En estas dos variables se constataron efectos de manejo, que había seguido en el intervalo observado, lo que muestra su permanencia por lo menos durante el periodo.

ABSTRACT The objective of this research was to evaluate the effects of a manipulative intervention on the electromyographic activity of paraverterbral muscles and low back pain intensity, both immediately and 30 minutes after their application in individuals with chronic low back pain. Thirty-eight individuals were evaluated, being randomly divided into two groups: the one who received global vertebral manipulation technique (n=20), and control (n=18), which remained in lateral decubitus for 10 seconds on each side of the body. The electromyographic signal of paravertebral parts at L4-L5 level both right and left was collected during three cycles of flexion-relaxation-extension of the torso. In the intervals between cycles, participants reported the intensity of pain through the Visual Analog Scale (VAS, 100 mm). A significant reduction in pain intensity in the group that received the manipulation was observed, opposed to the control group, in which the score increased in VAS. The dimension of the effect on pain intensity was 1.0 and 0.9 right after the manipulation and 30 minutes later. The flexion/relaxation ratio (FRR) increased in the group that was subjected to manipulation, but remained unchanged in the control group. The FRR displayed effects between the groups that were 0.6 and 0.5 in both assessments. We were able to see effects of the manipulation in these two variables, and its continuation in the range observed, concluding that they linger at least during that time.

Análise da ativação neuromuscular do vasto medial oblíquo e vasto lateral com o uso da bandagem funcional / Analysis of neuromuscular activation of the vastus medialis obliquus and vastus lateralis with the use of functional taping

Alterações musculares e anatômicas são em sua maioria responsáveis pela síndrome patelofemoral (SDPF). Sabendo que a musculatura do quadríceps é de grande importância na estabilização da patela, questiona-se como o músculo Vasto Medial Oblíquo (VMO) influencia na estabilizaçãopatelar evitando a SDPF. Muitos pesquisadores tem investigado o uso da bandagem funcional como meio de ativação muscular. Objetivo: O presente estudo teve como objetivo analisar o uso da bandagem como meio de ativação do VMO no exercício de agachamento. Método: A atividade dos músculos VMO e Vasto lateral (VL) foi avaliada através de eletromiografia durante o agachamento com adução e o agachamento com o uso de bandagem. A amostra composta por 39 indivíduos foi dividida em quatro grupos: indivíduos do sexo masculino sedentários e atletas, eindivíduos do sexo feminino sedentárias e atletas. Resultados: Embora tenha sido encontrada uma maior ativação do VMO em relação ao VL, com a presente metodologia e variáveis estudadas, não foi possível demonstrar diferença estatística entre os grupos nos agachamentos com e sem o uso da bandagem. No entanto, é importante ressaltar que a ausência de diferença na ativação do VMO durante o agachamento com adução e com bandagem sugerem um efeito positivo e facilitador da bandagem na ativação muscular. Este resultado é muito importante no tratamento de lesões agudas onde o movimento ativo está limitado. Conclusão: Sugere-se a execução de novos estudos aonde outros parâmetros da eletromiografia e estimulação reflexa sejam abordados, a fim de investigar o real papel da bandagem funcional na ativação muscular.

Muscular and anatomical changes are mostly responsible for patella femoral syndrome (PFPS). Knowing that the quadriceps muscles are very important in stabilizing the patella, studies have questioned the influence of the Vastus Medialis Obliquus (VMO) in the patellar stabilization avoiding the PFPS. Many researchers have investigated the use of taping as a means of muscleactivation. Objective: The present study aimed to analyze the use of functional taping to activate the VMO during the squat exercise. Method: The activity of the VMO and Vastus Lateralis (VL) was assessed by electromyography during squats and squats with adduction using functional taping. The sample, composed of 39 individuals, was divided into four groups: males and females, both separated into sedentary and athletic types. Results: Although greater activation of the VMO has been found in comparison with the VL, with the applied methodology and variables, we could not demonstrate a statistical difference between groups in squats with and without the use of functional taping. However, it is important to emphasize that the lack of difference in the activation of VMO during squats with adduction and taping suggests a positive effect of the taping in muscleactivation. This result is very important in the treatment of acute injuries where active movement is limited. Conclusion: Future studies should be done with other electromyography parameters and reflex activation in order to investigate the actual role of functional taping in muscle activation.