EXTRACELLULAR ACIDOSIS DRIVES THE DIFFERENTIATION OF HUMAN MONOCYTES INTO DENDRITIC CELLS : A POSSIBLE INTERPLAY BETWEENTHE ARYL HYDROCARBON RECEPTOR AND mTOR

FERNANDO ERRA DÍAZ; EZEQUIEL DANTAS; GABRIEL DUETTE; AUGUSTO VARESE; IGNACIO MAZZITELLI; VALERIA OCHOA; NOELIA MIRET; ANDREA RANDI; JUAN SABATTÉ; JORGE GEFFNER

Mar del Plata

Congreso; LXIII Reunión Científica Anual de la Sociedad Argentina de Investigación Clínica; 2018

Sociedad Argentina de Investigación Clínica

Differentiation of monocytes into macrophages and dendritic cells (DCs) is likely determined by the properties of the inflammatory milieu, however, little is known about the identity of the factors that control the polarization of monocytes toward each of these fates. Local acidic pH is a common feature of inflammation and the tumor microenvironment. We have previously shown that acidosis was able to skew monocyte differentiation towards a DC phenotype when culturing PBMCs or isolated monocytes (>85% purity) in the presence of PHA (2ug/ml) or allogeneic lymphocytesat pH 6.5 adjusted media.Similar resultswere obtained for isolated monocytes cultured for 7 days at pH 6.5 in medium supplemented with 0.1% BSA, in the absence of any other stimulus. Here we report that culturing isolated monocytes for 7 days at pH 7.3 or pH 6.5 in serum-free media, in the sole presence of M-CSF (50ng/ml) , resulted in 5.7±5vs 60.8±10% of CD1a+ CD14- cells (mean±SE,n=7,p<0.001). ThisCD1a+ cells significantly (p<0.01) up-regulated the expression of HLA-DR and CD86 upon LPS stimulation and promoted the expansion of allogeneic T cellsin mixed lymphocyte reactions in a much more efficient way than monocyte derived macrophages (p<0.01). Interestingly, acidosis induced DC differentiation in this context was not observed when cultures were performed with 10% FCS supplementation, suggesting that this nutrient starved environment favored this phenomenon.In spite of this, we found thatculturing monocytes in RPMI + 10% FCS in the presence of M-CSF(100ng/ml) plus the addition of IL-4 (30ng/ml)or IL-4 + TNFα(5ng/ml)at pH 7.3 or pH 6.5 resulted in (6,1±3 vs 27,8±7 and 26,4±4 vs 72,6±2 CD1a+/CD14-/CD16-cells respectively) (n=4 p=0.02 and n=15,p<0.001).Interestingly, temsirolimus (100-1 nM) , an mTor inhibitor, was able to mimic the effect of acidosis over DC differentiation ( 24,5±4 vs 76,8±3 n=12 p<0.001), suggesting a mechanistic link between low pH and mTORC1 inhibition. Finally, we found that acidosis induced DC differentiationwas abrogated by the pharmacological inhibition of the aryl hydrocarbon receptor(AHR)( 76,62±3 vs 27±9,n=5 , p<0.01).Our results suggest that local acidosis,by modulating the AHR and mTORC1 activities, might be skewing the differentiation of monocytes towards DCs during the course of inflammatory processes.