Human Monocytes (hMo-PB)

mCRP-Induced Monocyte Aggregation, Which was Concomitant with Increased Expression of FAK and M1 Phenotype Transition

Inflammation is a critical trigger for atherosclerosis, and C-reactive protein (CRP), particularly its dissociated monomeric form (mCRP), is significantly linked to disease progression. While the direct effects of mCRP on endothelial cells have been demonstrated, the mechanisms of interaction with blood monocytes remain unclear. Pastorello et al. aimed to elucidate the effects of mCRP on blood monocytes, specifically focusing on its role in promoting monocyte aggregation and differentiation into M1 macrophages via focal adhesion kinase (FAK) pathways, and assesses the potential inhibitory effects of C10M (CRP dissociation/mCRP inhibitor) on these processes.

Using freshly isolated human peripheral macrophages, Pastorello et al. observed a mCRP-induced aggregation pattern after 24 h (Fig. 1). In the absence of mCRP, control cultured peripheral monocytes did not cluster (Fig. 1A). Adding the CRP dissociation inhibitor C10M had no effect on clustering or cell appearance (Fig. 1B). However, 24 h exposure to mCRP induced noticeable clustering (Fig. 1). Pre-incubation with C10M eliminated floating clusters, though small adherent clumps remained (Fig. 1). Using a FAK inhibitor (Y397) inhibited mCRP-induced clustering and adherence (Fig. 1E-F).

Then, they performed the molecular mechanisms of mCRP-induced aggregation and motility changes. Human peripheral monocytes treated with mCRP showed significantly higher p-FAK expression compared to control cells or those treated with the inhibitor C10M (Fig. 2A-D). Pre-incubation with C10M partially blocked mCRP-induced p-FAK expression and nuclear translocation, while the FAK inhibitor completely blocked this effect (Fig. 2E-G). The increase in FAK expression induced by mCRP was significant, and both C10M and the FAK inhibitor significantly reduced it (Fig. 2H). Subsequent analysis of cell surface markers for the monocyte-macrophage phenotype indicated that mpCR treatment resulted in significant changes in the M1 phenotype.

Fig. 1. mCRP-induced aggregation of peripheral blood monocytes (Pastorello Y, Manu D, et al., 2024).

Fig. 2. Confocal analysis of FAK expression following mCRP treatment (Pastorello Y, Manu D, et al., 2024).

CX3CL1 Regulates the Differentiation of Human Peripheral Blood Monocytes into Osteoclasts.

It has been thought that peripheral blood monocytes migrate into synovial tissue of rheumatoid arthritis (RA) and differentiate into osteoclasts. Since osteoclasts are mainly involved in bone destruction, further studies are needed on the differentiation and activation of osteoclasts to clarify the pathogenesis of RA.

Chemokine (C-X3-C motif) ligand 1 (CX3CL1), also known as fractalkine, has dual functions as an adhesion molecule and chemoattractant. A correlation has been reported between the serum level of soluble CX3CL1 and disease activity in RA patients, suggesting that CX3CL1 plays important roles in the pathogenesis of RA. Muraoka' team initially examined the effects of CX3CL1 on osteoclast differentiation from peripheral blood monocytes. Peripheral blood monocytes from healthy donors were divided into CD16⁺ and CD16^- monocytes and then incubated with macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) for 7 days. Osteoclasts were identified as TRAP-positive MNC. As previously reported, CD16^- monocytes differentiated into osteoclasts when stimulated with M-CSF and RANKL (Fig. 3). Moreover, osteoclast differentiation from CD16^- monocytes was significantly increased by the stimulation with CX3CL1 in a dose-dependent manner (Fig. 3). On the other hand, CD16⁺ monocytes treated with M-CSF and RANKL did not differentiate into osteoclasts, even with CX3CL1 (Fig. 3).

Fig. 3. Effects of CX3CL1 on the differentiation of peripheral blood monocytes into osteoclasts (Muraoka, S., Kaneko, K., et al., 2021).