Unique Expression of Suppressor of Cytokine Signaling 3 Is Essential for Classical Macrophage Activation in Rodents In Vitro and In Vivo

Abstract

On infiltrating inflamed tissue, macrophages respond to the local microenvironment and develop one of two broad phenotypes: classically activated (M1) macrophages that cause tissue injury and alternatively activated macrophages that promote repair. Understanding how this polarization occurs in vivo is far from complete, and in this study, using a Th1-mediated macrophage-dependent model of acute glomerulonephritis, nephrotoxic nephritis, we examine the role of suppressor of cytokine signaling (SOCS)1 and SOCS3. Macrophages in normal kidneys did not express detectable SOCS proteins but those infiltrating inflamed glomeruli were rapidly polarized to express either SOCS1 (27 ± 6%) or SOCS3 (54 ± 12%) but rarely both (10 ± 3%). Rat bone marrow-derived macrophages incubated with IFN-γ or LPS expressed SOCS1 and SOCS3, whereas IL-4 stimulated macrophages expressed SOCS1 exclusively. By contrast, incubation with IFN-γ and LPS together suppressed SOCS1 while uniquely polarizing macrophages to SOCS3 expressing cells. Macrophages in which SOCS3 was knocked down by short interfering RNA responded to IFN-γ and LPS very differently: they had enhanced STAT3 activity; induction of macrophage mannose receptor, arginase and SOCS1; restoration of IL-4 responsiveness that is inhibited in M1 macrophages; and decreased synthesis of inflammatory mediators (NO and IL-6) and costimulatory molecule CD86, demonstrating that SOCS3 is essential for M1 activation. Without it, macrophages develop characteristic alternatively activated markers when exposed to classical activating stimuli. Lastly, increased glomerular IL-4 in nephrotoxic nephritis inhibits infiltrating macrophages from expressing SOCS3 and was associated with attenuated glomerular injury. Consequently, we propose that SOCS3 is essential for development of M1 macrophages in vitro and in vivo.

CX3CL1–CX3CR1 Interaction Increases the Population of Ly6C−CX3CR1hi Macrophages Contributing to Unilateral Ureteral Obstruction–Induced Fibrosis

“…These findings advance the findings of a prior study, which showed that Ly6C hi monocytes are selectively recruited to the injured kidney and differentiate into functionally distinct populations (36). Our results showing macrophage phenotypic transition in obstructed kidneys further support previous in vitro evidence that macrophages are capable of rapid adaptation to changing stimulants (37) and in vivo demonstration that macrophages convert their phenotype according to their tissue environment (38).…”

Notch Signaling Determines the M1 versus M2 Polarization of Macrophages in Antitumor Immune Responses

“…In macrophages and dendritic cells, SOCS proteins not only regulate the sensitivity of cells toward cytokines but also modulate signaling through Toll-like receptor. Liu and colleagues (44) showed that unique expression of SOCS3 is essential for classic macrophage activation. Because SOCS3 is a downstream molecule of Notch signaling (41), it is most likely that Notch signaling determines the M1 versus M2 polarization of macrophages through SOCS3.…”

Polarization of Prostate Cancer-associated Macrophages Is Induced by Milk Fat Globule-EGF Factor 8 (MFG-E8)-mediated Efferocytosis

“…SOCS3 deficiency in myeloid lineage cells has been shown to prolong activation of the JAK/ STAT pathway and M1 polarization, suggesting that SOCS3 is required for M1 activation (22,36,48). SOCS3 down-regulation in macrophages by siRNA induced M2 polarization and activation of STAT3 (49). In addition, myeloid cell-specific SOCS3 conditional KO mice had fewer liver and lung metastatic nodules than the wild type in a mouse melanoma metastatic model (35).…”