RhoA- and Actin-Dependent Functions of Macrophages from the Rodent Cardiac Transplantation Model Perspective -Timing Is the Essence

Abstract

The small GTPase RhoA, and its down-stream effector ROCK kinase, and the interacting Rac1 and mTORC2 pathways, are the principal regulators of the actin cytoskeleton and actin-related functions in all eukaryotic cells, including the immune cells. As such, they also regulate the phenotypes and functions of macrophages in the immune response and beyond. Here, we review the results of our and other’s studies on the role of the actin and RhoA pathway in shaping the macrophage functions in general and macrophage immune response during the development of chronic (long term) rejection of allografts in the rodent cardiac transplantation model. We focus on the importance of timing of the macrophage functions in chronic rejection and how the circadian rhythm may affect the anti-chronic rejection therapies.

The Effect of Magnetic Field Gradient and Gadolinium-Based MRI Contrast Agent Dotarem on Mouse Macrophages

“…We showed previously that the inhibition of RhoA-GEFs with Rhosin or Y16 [ 46 ], macrophage-specific RhoA deletion [ 55 ], or inhibition of ROCK [ 5 ] by Y27632 [ 36 ] caused extreme elongation of macrophages (they acquired the so-called hummingbird phenotype), redistribution of macrophage organelles and receptors, and affected gene transcription. We also showed that similar changes were induced in the macrophages exposed to the magnetic field gradient [ 35 , 41 ]. We also showed that magnetic field exposure caused aggregation of the TRPM2 (the cation channel transient receptor potential melastatin 2/Transient Receptor Potential Cation Channel Subfamily M Member 2) that is a Ca 2+ channel regulating calcium homeostasis [ 62 ].…”

“…Knowing that the cell length and shape reflect actin distribution/dynamics and polymerization status, these findings indicate that Dotarem affects (directly or indirectly) the actin cytoskeleton of macrophages. Because the actin cytoskeleton also plays a role in anchoring cell organelles in their proper position within the cell, which is crucial for cell identity and functioning [ 40 , 41 ], we also studied the effect of Dotarem on the distribution of mitochondria, Golgi complex, and endoplasmic reticulum (ER) in RAW 264.4 macrophages. To study mitochondria distribution, we immunostained macrophages with the mitochondrial marker TOMM20 antibody against mitochondrial import receptor subunit TOM20 [ 42 ].…”

“…We hypothesized that the clustering may render the channels nonfunctional, which may disrupt calcium homeostasis and calcium-dependent processes such as actin polymerization [27,35]. It is well established that the actin dynamics and polymerization status are regulated by the small GTPase RhoA pathway [41]; thus, our findings on cell elongation and organelle redistribution suggest that the gadolinium (Dotarem) and magnetic field gradient may affect various components of the RhoA pathway (Figure 12, see Section 4). A diagram summarizing the effect of Dotarem on cell length and organelle distribution is shown in Figure 11.…”

“…Our previous in vivo and in vitro studies on the role of macrophages in the development of chronic (long-term) rejection of transplanted organs showed that macrophage length, distribution of organelles, and gene expression are regulated by the RhoA pathway [ 36 , 41 , 46 , 47 , 55 ]. RhoA is a small GTPase that controls actin dynamics and polymerization [ 56 ].…”

Native Low-Density Lipoproteins Act in Synergy with Lipopolysaccharide to Alter the Balance of Human Monocyte Subsets and Their Ability to Produce IL-1 Beta, CCR2, and CX3CR1 In Vitro and In Vivo: Implications in Atherogenesis

“…Atherosclerotic plaque formation is a highly dynamic process involving the adhesion of circulating monocytes to the tunica intima, wherein these cells differentiate into macrophages [3]. Then, monocyte-derived macrophages can migrate to the subendothelial space and turn into foam cells after ingesting oxidized low-density lipoproteins (oxLDL), triggering an inflammatory response that injures endothelial cells and promotes arterial remodeling [4].…”