Identification of Caspase-6 as a New Regulator of Alternatively Activated Macrophages

Abstract

Alternatively activated macrophages (AAMs) play essential roles in the promotion of tissue remodeling, vasculogenesis, and tumor progression; however, the detailed mechanisms underlying the activation of AAMs remain largely unknown. Here, by using quantitative proteomic analysis, we identified 62 proteins that were up-regulated in IL-4-induced macrophages. Among these, Caspase-6 was increased significantly. Caspase-6 is important in the apoptotic signaling pathway; however, its role in non-apoptosis is also reported. Here, we first examined the non-apoptotic role of Caspase-6 in the alternative activation of macrophages after administration of IL-4, 4T1 tumor conditional medium, or co-culture with 4T1 cells. Both treatments promoted alternative activation of RAW264.7 cells and primary macrophages, whereas disruption of caspase-6 expression and activity could markedly suppress the biomarker levels of AAMs. Overexpression of Caspase-6 could significantly promote the activation of AAMs. Importantly, we further present evidence that caspase-6 could regulate breast cancer cell invasion by modulating MMP-2 and MMP-9 expression in 4T1 tumor-associated macrophages, as ablation of protein levels or activity of caspase-6 suppressed tumor cell invasion in vitro. In conclusion, the observed results markedly expanded our views of the dynamic changes in protein composition during alternative activation of macrophages, and they revealed a critical new role of caspase-6 in regulating this cellular biological process, which suggested that caspase-6 might be a key nod molecule to regulate immunological steady-state and be a therapeutic candidate for tumor immunotherapy.

Caspase-6 Is a Key Regulator of Innate Immunity, Inflammasome Activation, and Host Defense

“…Additionally, Casp6 -/mice showed significantly more lung damage at day 5 post-infection (Figure 4I). It has been shown that caspase-6 promotes the activation of alternatively activated macrophages (AAMs) (Yao et al, 2016). Consistent with this, fewer Arg1 + AAMs were detected in the lungs of Casp6 -/mice after IAV infection compared with WT mice (Figure 4J).…”

The macrophage cytoskeleton acts as a contact sensor upon interaction with Entamoeba histolytica to trigger IL-1β secretion

“…Although caspase-6 is classified as an effector caspase along with caspase-3 and caspase-7, there is increasing evidence that its role extends beyond apoptosis [ 55 ]. A role for caspase-6 in B-cell activation and differentiation, and more recently in macrophage activation, has been shown [ 56 , 57 ]. Moreover, caspase-6 is ubiquitously expressed and the highest levels of pro-caspase-6 are observed in fetal and adult colon [ 58 ].…”

Infective Larvae of Brugia malayi Induce Polarization of Host Macrophages that Helps in Immune Evasion

“…We, therefore, assessed the role of caspases and found reduced expression of caspase 3 ( p ≤ 0.001), and caspase 6 ( p ≤ 0.01) in the cell lysate of FACS-sorted splenic MΦs from Bm-L3-infected mice that received anti-CD25 + anti-GITR treatment as compared to those that received IgG isotypes (Figure 7 ). Notably, no change was observed in the activity of caspase 2, 8, and 9, which not only suggested differential regulation of caspases during Bm-L3 infection, but also underlined reduced caspase activity as one of the reasons that might have prolonged survival of M2 MΦs that lead to enhanced killing of infective larvae ( 16 ).…”