Wnt signaling regulates chemokine production and cell migration of circulating human monocytes
The ß-catenin dependent canonical Wnt signaling pathway plays a crucial role in maintaining normal homeostasis. However, when dysregulated, Wnt signaling is closely associated with various pathological conditions, including inflammation and different types of cancer. Here, we show a new connection between the leukocyte inflammatory response and the Wnt signaling pathway. Specifically, we demonstrate that circulating human primary monocytes express distinct Wnt signaling components and are susceptible to stimulation by the classical Wnt ligand - Wnt-3a. Although this stimulation increased the levels of ß-catenin protein, the expression of the classical Wnt-target genes was not affected. Intriguingly, treating circulating human monocytes with Wnt-3a induces the secretion of cytokines and chemokines, enhancing monocyte migration. Mechanistically, the enhanced monocyte migration in response to Wnt stimuli is mediated through CCL2, a strong monocyte-chemoattractant. To further explore the physiological relevance of these findings, we conducted ex-vivo experiments using blood samples of patients with rheumatic joint diseases (RJD) – conditions where monocytes are known to be dysfunctional. Wnt-3a generated a unique cytokine expression profile, which was significantly distinct from that observed in monocytes obtained from healthy donors. Thus, our results provide the first evidence that Wnt-3a may serve as a potent stimulator of monocyte-driven immune processes. These findings contribute to our understanding of inflammatory diseases and, more importantly, shed light on the role of a core signaling pathway in the circulation. Overall design: Freshly isolated primary human classical monocytes (CD14+CD16-) from two donors were cultured for 8 hours in triplicates in cell repellent plates in the presence of control or Wnt-3a conditioned media.   Media were comprised of 80% L- or L-Wnt-3a- CM and 20% RPMI-1640 (both containing 10% FBS and 1% Penicillin/Streptomycin) at 37°C in 5% CO2. L cells and L-Wnt-3a cells were propagated according to the ATCC guidelines and CM were produced according to the ATCC protocols.  Total RNA was extracted using the Direct-zol RNA MiniPrep kit. Replicates of high RNA integrity (RIN = 7.8) were processed. Libraries were prepared using the NEBNext Ultra II RNA Library Prep kit with the NEBNext Poly(A) mRNA Magnetic Isolation Module, starting with ~ 500 ng of total RNA. Ten PCR cycles were performed during library amplification. Libraries were quantified by Qubit and TapeStation and sequenced on a NextSeq 500 instrument using a NextSeq 500/550 High Output Kit v2.5 (75 Cycles) kit.  Twelve FastQ files were uploaded to Partek Flow (Build version 10.0.21.1116; https://www.partek.com) for processing. Poly-A/T stretches and Illumina adapters were trimmed from the reads. Resulting reads with Phred score < 20 were filtered. Reads were mapped to the human GRCh38.p13 reference genome using STAR 2.7.8a with default parameters to reveal ~ 20 million reads per sample. Quantification to annotation model was performed using Partek Expectation/Maximization (E/M) algorithm  obtaining 33,331 genes.