A influência de macrófagos M1, M2 e TAM, e do receptor P2X7 na invasividade e resistência de neuroblastoma / The influence of different macrophages' phenotypes, and of the P2X7 receptor, on the invasiveness and chemoresistance of neuroblastoma

O neuroblastoma é um tumor sólido muito comum em crianças. O estágio mais avançado da doença é altamente agressivo e invasivo, além de pouco responsivo à terapia, que é limitada por mecanismos de resistência e reincidência relacionados à metástase. Muitos estudos tem sido feitos para identificar mecanismos de invasão e quimioresistência de células tumorais, afim de aumentar a sobrevida dos pacientes com câncer. Nesse trabalho, nós estudamos o efeito dos macrófagos, as células imunes mais abundantes no microambiente tumoral, os TAMs (do inglês tumor-associated macrophage) e do receptor P2X7, um purinoreceptor acionado por ATP, nesses processos. Os TAMs respondem e atuam de acordo com a miríade de fatores que encontram, podendo gerar populações heterogêneas e com funções distintas, tanto antitumorais, como pró-tumorais. Altos níveis de ATP extracelular são encontrados no microambiente tumoral, podendo então ativar o receptor P2X7. Este receptor tem sido relacionado tanto a funções inflamatórias como funções na resolução da inflamação de macrófagos. Além disso, o receptor P2X7 está envolvido em uma variedade de eventos celulares, incluindo a secreção de mediadores pró-inflamatórios, a proliferação celular e a apoptose de células tumorais. Primeiramente, foi avaliado o papel do receptor P2X7 na polarização de macrófagos da derivados medula óssea de camundongos wild-type e nocaute para o P2X7 na presença e ausência de fatores secretados por células de neuroblastoma, e então foi estudada a influência desses diferentes macrófagos polarizados em eventos celulares de grande relevância clínica para o neuroblastoma: a invasividade e quimiorresistência. Os resultados demonstraram que, apesar do reconhecido envolvimento do receptor P2X7 na inflamação, a ausência deste receptor não atenua a expressão de marcadores característicos do fenótipo inflamatório, M1. O aumento da expressão do receptor P2Y2, também envolvido na inflamação, nessas células, sugere um mecanismo genético de compensação para não atenuação da inflamação em macrófagos que não expressam o receptor P2X7. Contudo, a ausência do receptor P2X7 levou a alterações no fenótipo alternativo, M2, de modo que a expressão de Tnf, marcador de M2, não foi reprimido. TAMs noucates para P2X7 tiveram a expressão de arg1, marcador de M2, suprimida, reforçando a importância do receptor P2X7 no estabelecimento de fenótipos ativados alternativamente. Nossos dados também sugerem que ausência do receptor P2X7 em TAMs permite a aquisição de um fenótipo capaz de tornar as células de neuroblastoma que expressam P2X7 mais invasivas e mais quimioresistentes à vincristina. Por outro lado, TAMs, independentemente da presença ou ausência do receptor P2X7, induziram a proliferação e quimioresistência das células de neuroblastoma silenciadas para o receptor P2X7, o que nos leva a concluir que o receptor P2X7 em TAMs é desfavorável à progressão de tumores expressando P2X7

Neuroblastoma is a highly common childhood solid tumor. The most advanced stage of the disease is highly aggressive and invasive, besides from being poorly responsive to therapies, which are limited by resistance and recurrence mechanisms related to metastasis. Several studies attempt to identify invasion and resistance mechanisms of the tumor cells in order to increase overall survival of the patients. On the present work, we investigated the effect of macrophages, the most abundant immune cells on the tumor microenvironment, called TAMs (tumor-associated macrophages), and of the P2X7 receptor, an ATP-gated purinoceptor, on these processes. TAMs and cancer cells crosstalk, and behave accordingly to a miriad of factors present at the TME, generating heterogeneous populations with distinct functionalities, either pro- or antitumor. High extracellular levels of ATP are found in the TME, being able to activate the P2X7 receptor. This receptor mediates both pro- and anti-inflammatory functions in macrophages. In addition, it is involved in several cellular events, including the secretion of pro-inflammatory mediators, cell proliferation and tumor cell apoptosis. At first, we evaluated the role of the P2X7 receptor on the polarization of bone marrow-derived macrophages (BMDM), either wild-type or knockout for the P2X7 receptor, in presence or absence or factors secreted by neuroblastoma cells. Next, we investigated the influence of the polarized macrophages in highly relevant cellular events for neuroblastoma, such as invasiveness and chemoresistance. Our results showed that, despite the known involvement of P2X7 receptor on inflammation, its absence did not decrease the expression if inflammatory markers of M1 macrophage populations. An increase in the expression of the P2Y2 receptor, also involved in inflammation, on these cells suggest a genetic compensation mechanism for preventing attenuation of inflammation when P2X7 is lacking. However, P2X7 receptor absence did compromise the M2 phenotype, driving the expression of Tnf. TAMs knockout for the P2X7 receptor were not able to express arg1, also an M2 marker, reinforcing a role of the P2X7 receptor on establishing alternative macrophage phenotypes. Our data also suggest that TAMs lacking the P2X7 receptor acquire a phenotype capable of turning P2X7R-expressing neuroblastoma cells more invasive and chemoresistant to vincristine. On the other hand, TAMs, independently on the presence of the P2X7 receptor, induced proliferation and resistance of neuroblastoma cells silenced for P2X7 receptor expression, leading us to the conclusion that the P2X7 receptor in TAMs is unfavorable for the progression of P2X7R-expressing tumors

Chronic hypoxia increases arterial blood pressure and reduces adenosine and ATP induced vasodilatation in skeletal muscle in healthy humans.

AIMS: To determine the role played by adenosine, ATP and chemoreflex activation on the regulation of vascular conductance in chronic hypoxia. METHODS: The vascular conductance response to low and high doses of adenosine and ATP was assessed in ten healthy men. Vasodilators were infused into the femoral artery at sea level and then after 8-12 days of residence at 4559 m above sea level. At sea level, the infusions were carried out while the subjects breathed room air, acute hypoxia (FI O2 = 0.11) and hyperoxia (FI O2 = 1); and at altitude (FI O2 = 0.21 and 1). Skeletal muscle P2Y2 receptor protein expression was determined in muscle biopsies after 4 weeks at 3454 m by Western blot. RESULTS: At altitude, mean arterial blood pressure was 13% higher (91 ± 2 vs. 102 ± 3 mmHg, P < 0.05) than at sea level and was unaltered by hyperoxic breathing. Baseline leg vascular conductance was 25% lower at altitude than at sea level (P < 0.05). At altitude, the high doses of adenosine and ATP reduced mean arterial blood pressure by 9-12%, independently of FI O2 . The change in vascular conductance in response to ATP was lower at altitude than at sea level by 24 and 38%, during the low and high ATP doses respectively (P < 0.05), and by 22% during the infusion with high adenosine doses. Hyperoxic breathing did not modify the response to vasodilators at sea level or at altitude. P2Y2 receptor expression remained unchanged with altitude residence. CONCLUSIONS: Short-term residence at altitude increases arterial blood pressure and reduces the vasodilatory responses to adenosine and ATP.