Introduction: Dying cells release damage associated molecular patterns (DAMPs) like nucleotides into the extracellular fluid, orchestrating a profound immune response. Purinergic receptors decrypt the composition of extracellular nucleotides and translate it to distinct cellular reactions. M1 and M2 macrophages are immune cells involved in many diseases which react in a completely different way. Nevertheless, how the microenvironment exactly triggers their behavior is not fully understood.
Hypothesis: We hypothesize a distinct expression pattern of purinergic receptors on M1 and M2 macrophages which leads to an unique microenvironment recognition and behavior.
Methods: Macrophages were generated by bone marrow isolation and cultivation with macrophage colony stimulating factor (M-CSF). Bone marrow derived macrophages (BMDMs) were differentiated to M1 via addition of IFNγ and LPS. M2 differentiation was initiated by the addition of IL-4. Gene transcription quantification was assessed by real-time PCR. Intracellular Ca2+ signaling was quantified by Fluo-4 AM.
Results: Differentiation of BMDMs with either IFNγ/LPS or IL-4 leads to the upregulation of M1 or M2 specific gene transcription. Subsequent real-time PCR analysis of purinergic receptors revealed a strong relationship between the expression pattern and the differentiation to M1 or M2 macrophages. Whereas M1 macrophages upregulate predominantly Gαi coupled metabotropic P2Y receptors, M2 macrophages preferentially upregulate Gαq coupled P2Y receptors. Comparison of the two ADP-dependent P2Y receptors (P2Y1 and P2Y13) showed a M1 and M2 specific expression pattern with M1 macrophages solely expressing the Gαi coupled P2Y13 and M2 macrophages exclusively expressing the Gαq coupled P2Y1 receptor. In agreement with the specific expression pattern, ADP stimulation evokes a significant Ca2+ flux in M2 macrophages but failed to induce it in M1 macrophages.
Conclusion: Our experiments revealed for the first time that M1 and M2 macrophages express a unique purinergic receptor repertoire and sense the nucleotide based microenvironment differently. With this knowledge we could interfere with one macorphage subtype without disturbing the others.