Jean-Marie Boeynaems

This review article provides a historical perspective on the role of purinergic signalling in the regulation of various subsets of immune cells from early discoveries to current understanding. It is now recognised that adenosine 5′-triphosphate (ATP) and other nucleotides are released from cells following stress or injury. They can act on virtually all subsets of immune cells through a spectrum of P2X ligand-gated ion channels and G protein-coupled P2Y receptors. Furthermore, ATP is rapidly degraded into adenosine by ectonucleotidases such as CD39 and CD73, and adenosine exerts additional regulatory effects through its own receptors. The resulting effect ranges from stimulation to tolerance depending on the amount and time courses of nucleotides released, and the balance between ATP and adenosine. This review identifies the various receptors involved in the different subsets of immune cells and their effects on the function of these cells.

Background: The protective effect of HDL is mostly attributed to their metabolic function in reverse cholesterol transport (RCT), a process whereby excess cellular cholesterol is taken up from peripheral cells, processed in HDL particles, and later delivered to the liver for further metabolism and biliary secretion. Mechanistically, the purinergic P2Y₁₃ ADP-receptor is involved in hepatic HDL endocytosis (i.e., uptake of both HDL protein + lipid moieties), which is considered an important step of RCT. Accordingly, chow-fed P2Y₁₃ knockout (P2Y₁₃ ^-/-) mice exhibit lower hepatic HDL uptake, which translates into a decrease of hepatic free cholesterol content and biliary cholesterol and phospholipid secretion. Findings: The aim of this study was to determine the effect of high cholesterol diet (HCD) in P2Y₁₃ ^-/- mice, in order to mimic high dietary cholesterol intake, which is a major cause of dyslipidemia in humans. As previously reported with chow-diet, HCD did not affect plasma lipid levels in P2Y₁₃ ^-/- compared with control mice but decreased hepatic free and esterified cholesterol content (p < 0.05, P2Y₁₃ ^-/- versus control). Interestingly, biliary lipid secretion and macrophages-to-feces RCT were more dramatically impaired in P2Y₁₃ ^-/- mice fed a HCD than chow-diet. HCD did not enhance atherosclerosis in P2Y₁₃ ^-/- compared with control mice. Conclusion: This study demonstrates that high dietary cholesterol intake accentuated the metabolic phenotype of P2Y₁₃ ^-/- mice, with impaired hepatobiliary RCT. Although other animal models might be required to further evaluate the role of P2Y₁₃ receptor in atherosclerosis, P2Y₁₃ appears a promising target for therapeutic intervention aiming to stimulate RCT, particularly in individuals with lipid-rich diet.

A better education and training of clinical investigators and their teams is one of the factors that could foster the development of clinical research in Europe, a key objective of the Innovative Medicines Initiative (IMI). PharmaTrain (an IMI programme on training in medicines development) and ECRIN (European Clinical Research Infrastructures Network) have joined forces to address this issue. An advisory group composed of representatives of universities, pharmaceutical companies and other organisations met four times between June 2011 and July 2012. This resulted in a position paper proposing a strategy to improve and harmonize clinical investigator training in Europe, and including a detailed syllabus and list of learning outcomes. Major recommendations are the establishment of minimal and mutually recognized certification requirement for investigators throughout the EU and the creation of a European platform to provide a suitable course and examination infrastructure.

We have previously reported that ATPγS, a slowly hydrolyzed analog of ATP, inhibits the activation of human CD4⁺ T lymphocytes by anti-CD3 and anti-CD28 mAb. In this report we have partially characterized the signaling mechanisms involved in this immunosuppressive effect. ATPγS had no inhibitory effect on CD4⁺ T-cell activation induced by PMA and anti-CD28, indicating that it acts proximally to the TCR. It had no effect on the calcium rise induced by CD3/CD28 stimulation, but inhibited the phosphorylation of three kinases, ERK2, p38 MAPK and PKB, that play a key role in the activation of T cells. The receptor involved in these actions remains unidentified.

UTP‐induced chloride secretion by the intestinal mucosa mounted in Ussing chambers was assessed by measurement of the short‐circuit current (I_sc) in the presence of phloridzin in the case of jejunum or amiloride in the case of colon to eliminate any contribution of electrogenic Na⁺ movement to the net ionic transport. Since we have previously demonstrated the absence of chloride‐secretory response to apical UTP in the jejunum from P2Y₄‐null mice, in the present study we studied the response to basolateral UTP in the jejunum and to either apical or basolateral UTP in the colon, in both P2Y₂‐ and P2Y₄‐deficient mice. In the jejunum, the chloride‐secretory response to basolateral UTP was partially reduced in both P2Y₂‐ (40%) and P2Y₄‐ (60%) null mice. In the colon, both apical or basolateral UTP increased the I_sc. That response was abolished in a chloride‐free medium. The colonic chloride‐secretory response to either basolateral or apical UTP was abolished in P2Y₄‐deficient mice, but not significantly affected in P2Y₂‐deficient mice. The chloride‐secretory response to forskolin was potentiated by prior basolateral addition of UTP and this potentiation was abolished in P2Y₄‐null mice. The jejunum of mice homozygous for the ΔF508 mutation of cystic fibrosis transmembrane conductance regulator was responsive to UTP, but the magnitude of that response was smaller than in the wild‐type littermates. In conclusion, the P2Y₄ receptor fully mediates the chloride‐secretory response to UTP in both small and large intestines, except at the basolateral side of the jejunum, where both P2Y₂ and P2Y₄ receptors are involved. British Journal of Pharmacology (2005) 146, 364–369. doi:10.1038/sj.bjp.0706353