Neutrophil GM-CSF receptor dynamics in acute lung injury

Abstract

GM‐CSF is important in regulating acute, persistent neutrophilic inflammation in certain settings, including lung injury. Ligand binding induces rapid internalization of the GM‐CSF receptor (GM‐CSFRα) complex, a process essential for signaling. Whereas GM‐CSF controls many aspects of neutrophil biology, regulation of GM‐CSFRα expression is poorly understood, particularly the role of GM‐CSFRα in ligand clearance and whether signaling is sustained despite major down‐regulation of GM‐CSFRα surface expression. We established a quantitative assay of GM‐CSFRα surface expression and used this, together with selective anti‐GM‐CSFR antibodies, to define GM‐CSFRα kinetics in human neutrophils, and in murine blood and alveolar neutrophils in a lung injury model. Despite rapid sustained ligand‐induced GM‐CSFRα loss from the neutrophil surface, which persisted even following ligand removal, pro‐survival effects of GM‐CSF required ongoing ligand‐receptor interaction. Neutrophils recruited to the lungs following LPS challenge showed initially high mGM‐CSFRα expression, which along with mGM‐CSFRβ declined over 24 hr; this was associated with a transient increase in bronchoalveolar lavage fluid (BALF) mGM‐CSF concentration. Treating mice in an LPS challenge model with CAM‐3003, an anti‐mGM‐CSFRα mAb, inhibited inflammatory cell influx into the lung and maintained the level of BALF mGM‐CSF. Consistent with neutrophil consumption of GM‐CSF, human neutrophils depleted exogenous GM‐CSF, independent of protease activity. These data show that loss of membrane GM‐CSFRα following GM‐CSF exposure does not preclude sustained GM‐CSF/GM‐CSFRα signaling and that this receptor plays a key role in ligand clearance. Hence neutrophilic activation via GM‐CSFR may play an important role in neutrophilic lung inflammation even in the absence of high GM‐CSF levels or GM‐CSFRα expression.

GM-CSF-based treatments in COVID-19: reconciling opposing therapeutic approaches

“…We, along with others 1,72 , suggest that in patients with COVID-19, dysregulated GM-CSF expression could induce overactivation of myeloid cells that secrete pro-inflammatory mediators and destructively infiltrate tissue, such as the lungs and potentially even the heart and the nervous system. This suggestion is consistent with the disease-driving mechanism of action of GM-CSF proposed in many preclinical models with pathologies similar to that of late stages of COVID-19, including models of chimeric antigen receptor (CAR) T cell-related CRS and neurotoxicity 76 , GvHD-associated CRS 31 , septic shock 77,78 , neuroinflammatory disease 21 , inflammatory lung conditions 71,[79][80][81][82][83][84][85] and acute cardiovascular diseases (myocarditis 86 , myocardial infarction 33 and vasculitis 87 ). Therapeutic inhibition of GM-CSF has shown benefit (including survival advantages) in all of these preclinical models by decreasing the production of multiple pro-inflammatory cytokines/chemokines and reducing tissue infiltration by inflammatory immune cells 2,3 .…”

“…Considering that neutrophil accumulation in the lung is a hallmark of ARDS 69 , it is noteworthy that acute lung injury has been reported as a potential complication of sargramostim use in rare cases 70 . GM-CSF has been shown to boost neutrophil survival in ARDS, and thus inhibition of the GM-CSF pathway has been proposed as a potential ARDS therapeutic approach 17,28,71 , contrary to recommendations in many of the aforementioned reports.…”

Therapeutic blockade of granulocyte macrophage colony-stimulating factor in COVID-19-associated hyperinflammation: challenges and opportunities

“… 25 , 43 , 44 , 45 , 46 Recent study findings suggest that GM-CSF receptor alpha blockade can inhibit inflammation in response to inhaled lipopolysaccharide in a mouse model of acute lung injury. 47 …”

Studies of molecular pathways associated with blood neutrophil corticosteroid insensitivity in equine asthma

“…GM-CSF is a key myeloid growth factor protein, which has important functional effects on mature cells, including neutrophils, monocytes, and eosinophils. It has been reported that GM-CSFRβ expression was also lower in BALF neutrophils compared to blood neutrophils in the equine model study (244). However, isolation of blood neutrophils is easier to conduct than for BALF neutrophils.…”