A Novel Function for P2Y2 in Myeloid Recipient–Derived Cells during Graft-versus-Host Disease

Abstract

Acute graft-versus-host disease (GvHD) is a life-threatening complication of allogeneic hematopoietic cell transplantation. During the initiation phase of acute GvHD, endogenous danger signals such as ATP are released and inform the innate immune system via activation of the purinergic receptor P2X7 that a noninfectious damage has occurred. A second ATP-activated purinergic receptor involved in inflammatory diseases is P2Y2. In this study, we used P2y2 2/2 mice to test the role of this receptor in GvHD. P2y2recipients experienced reduced GvHD-related mortality, IL-6 levels, enterocyte apoptosis, and histopathology scores. Chimeric mice with P2y2 deficiency restricted to hematopoietic tissues survived longer after GvHD induction than did wild-type mice. P2y2 deficiency of the recipient was connected to lower levels of myeloperoxidase in the intestinal tract of mice developing GvHD and a reduced myeloid cell signature. Selective deficiency of P2Y2 in inflammatory monocytes decreased GvHD severity. Mechanistically, P2y2 2/2 inflammatory monocytes displayed defective ERK activation and reactive oxygen species production. Compatible with a role of P2Y2 in human GvHD, the frequency of P2Y2 + cells in inflamed GvHD lesions correlated with histopathological GvHD severity. Our findings indicate a novel function for P2Y2 in ATP-activated recipient myeloid cells during GvHD, which could be exploited when targeting danger signals to prevent GvHD.

Acute Graft-versus-Host Disease — Biologic Process, Prevention, and Therapy

“…Nonetheless, GVHD mouse models have been the basis for much of our understanding of GVHD biology. The earliest acute GVHD pathophysiological events are neoangiogenesis 14,15 and intestinal tract infiltration by innate myeloid cells such as neutrophil granulocytes (neutrophils) 16–19 and monocytes 20,21 , first-wave immune responders to tissue injury and foreign pathogens. Recipient neutrophils impact GVHD through their activation and reactive oxygen species (ROS) production in the GI tract 17 .…”

“…The DAMPS comprise molecules released into the extracellular space only when tissue damage occurs that cause immune activation 23 . GVHD can be enhanced by extracellular adenosine triphosphate (ATP) activating the purinergic P2X7 receptor 24 and P2Y2 receptor 20 . ATP is metabolized by the ectonucleotidase CD39, expressed by endothelial and immune cells, into adenosine monophosphate and then into anti-inflammatory adenosine (by CD73, expressed in acute GVHD organs such as colon, liver, and lung; endothelial cells; leukocytes) 25 .…”

The Dynamics of Apoptotic Cell Clearance

“…P2Y2 is expressed at relatively high levels on numerous myeloid cell populations in mice and humans, including tissue-resident macrophages in the lung and peritoneum of mice (Chen et al, 2006; Gautier et al, 2012; Kaufmann et al, 2005; Kronlage et al, 2010). With high sensitivity to both ATP and UTP (maximal responses in ~0.1μM range) (Junger, 2011), P2Y2 has been shown to promote vascular adhesion, motility, and apoptotic cell clearance in a number of different studies of acute and long term inflammation and adaptive immune responses (Elliott et al, 2009; Idzko et al, 2007; Jin et al, 2014; Klämbt et al, 2015; Ma et al, 2013b; McDonald et al, 2010; Shah et al, 2014; Wang and Kubes, 2016). In the context of cell clearance, depletion of extracellular nucleotides or deletion of P2Y2 in mice was shown to cause a delay in the clearance of apoptotic cells by macrophages in the thymus (Elliott et al, 2009).…”

Altered homeostatic regulation of innate and adaptive immunity in lower gastrointestinal tract GVHD pathogenesis

“…ATP is released from damaged cells and binds to the P2X family of purinergic receptors, including P2X7 and P2Y2 (49)(50)(51). ATP engagement of P2X7 on host hematopoietic APCs enhanced their activation, amplified stimulation of the alloreactive donor CD4 + T cells, and enhanced Th1 responses (50), whereas interruption of this pathway decreased GI tract GVHD (50).…”

“…Systemic administration of broad-spectrum P2X7 antagonists attenuated GVHD (50,52). Likewise, GVHD was mitigated by the absence of another ATP purinergic receptor, P2Y2, on the host hematopoieticderived APCs (51). Increased extracellular ATP is regulated by ectonucleotidases such as CD73 (ecto-5-nucleotidase), which converts AMP to adenosine (53).…”