Macrophage/monocyte-specific deletion of Ras homolog gene family member A (RhoA) downregulates fractalkine receptor and inhibits chronic rejection of mouse cardiac allografts

Abstract

Background The cellular and molecular mechanisms of chronic rejection of transplanted organs remain obscure. It is known however that macrophages play a critical role in the injury and repair of allografts. Among multiple factors influencing macrophage infiltration to allografts, the fractalkine CX3CL1/ CX3CR1 signaling pathway and actin cytoskeleton, which is regulated by a small GTPase RhoA, are of the utmost importance. To define the role of macrophage/RhoA pathway involvement in chronic rejection we generated mice with monocyte/macrophage specific deletion of RhoA. Methods Hearts from BALB/c (H-2d) donors were transplanted into RhoAflox/flox (no Cre) and heterozygous Lyz2Cre+/−RhoAflox/flox recipients treated with CTLA4-Ig to inhibit early T cell response. Allografts were assessed for chronic rejection and monocyte/macrophage functions. Results The deletion of RhoA inhibited macrophage infiltration, neointimal hyperplasia of vasculature and abrogated chronic rejection of the allografts. The RhoA deletion down-regulated G protein-coupled fractalkine receptor CX3CR1, which activates RhoA pathway and controls monocyte/macrophage trafficking into the vascular endothelium. This in turn promotes, through over-proliferation and differentiation of smooth muscle cells in the arterial walls, neointimal hyperplasia. Conclusions Our finding of co-dependence of chronic rejection on monocyte/macrophage CX3CR1/CX3CL1 and RhoA signaling pathways may lead to development of novel anti-chronic rejection therapies.

Magnetic Field Changes Macrophage Phenotype

“…M0 macrophages are naive/unpolarized macrophages. Two of the most common subtypes of activated macrophages are M1 proinflammatory ''killer'' macrophages, which produce damaging reactiveoxygen species and express the nitric oxide synthase iNOS, and M2 antiinflammatory ''repair'' macrophages, which produce the enzyme arginase-1 that depletes L-arginine and deprives iNOS of its substrate (1)(2)(3)(4)(5)(6)(7).…”

Macrophage functions in wound healing

“…Studies in the liver injury mouse model showed that the CCR2 knockout causes impairment in the recruitment of monocytes and collagen production/injury‐related fibrosis (Seki et al, ). Studies from our laboratory showed that the macrophage specific knockout of small GTPase RhoA inhibited expression and recycling of CX3CR1 receptors in the macrophages, which in turn prevented their movement to the transplanted heart and inhibited chronic rejection in mouse transplantation model (Liu, Chen, et al, ). These findings suggest that targeting of CX3CR1/fractalkine via RhoA pathway inhibition may be also useful for the manipulation of macrophage recruitment into the wound site.…”

“…We showed that macrophage‐specific deletion of RhoA, inhibition of ROCK or inhibition of RhoA activator GEFs (Chen, Li, Kubiak, Ghobrial, & Kloc, ), elongates macrophages (they switch into M2 prohealing phenotype), disrupts their Golgi complex and receptor recycling pathway, and influences extracellular matrix degradation. All these changes prevented macrophages from entering the transplanted hearts and inhibited chronic (long term) rejection (Chen, Chen, Chen, et al, ; Chen, Ghobrial, Li, & Kloc, ; Chen, Sandoval, et al, ; Liu, Chen, et al, ; Liu, Kloc, & Li, ; Liu, Minze, et al, ; Liu, Tejpal, et al, ; Liu, Chen, et al, ; Liu, Kubiak, Li, Ghobrial, & Kloc, ; Wu et al, ). We also showed that interference with the RhoA pathway disrupted recycling and expression of CX3CR1 (fractalkine) receptor in monocytes and macrophages and prevented their movement into the graft (Figure ; Liu, Chen, et al, ).…”

“…All these changes prevented macrophages from entering the transplanted hearts and inhibited chronic (long term) rejection (Chen, Chen, Chen, et al, ; Chen, Ghobrial, Li, & Kloc, ; Chen, Sandoval, et al, ; Liu, Chen, et al, ; Liu, Kloc, & Li, ; Liu, Minze, et al, ; Liu, Tejpal, et al, ; Liu, Chen, et al, ; Liu, Kubiak, Li, Ghobrial, & Kloc, ; Wu et al, ). We also showed that interference with the RhoA pathway disrupted recycling and expression of CX3CR1 (fractalkine) receptor in monocytes and macrophages and prevented their movement into the graft (Figure ; Liu, Chen, et al, ). Because CX3CR1 plays an indispensable role in the recruitment of monocytes/macrophages into the wound, these results suggest that RhoA pathway inhibition has a potential to be used for the manipulation of macrophage content/function also in the wound‐healing process.…”

“…The upstream regulators of RhoA are the Guanine nucleotide exchange factors (GEFs). Our studies showed that a deletion of RhoA, inhibition of ROCK, or RhoA specific GEFs disorganize actin, Golgi complex, and disrupts receptor recycling in mouse macrophages (Chen et al, ; Liu, Chen, et al, ; Liu, Kloc, et al, ; Liu, Chen, et al, ; Liu, Kubiak, et al, ) [Colour figure can be viewed at wileyonlinelibrary.com]…”