TEC regulates macrophage activation dependent on PPARγ
Previous studies have shown that TEC is a partial peroxisome
proliferator-activated receptor-γ (PPARγ) agonist with an
IC50 value of
13.3 µM[31]. PPARγ
activation inhibits the production of TNF-α and IL-1β in monocytes and
macrophages, and promotes alternative macrophage
activation[32].
To confirm the regulation of TEC in KCs, we used primary KCs isolated
from C57BL/6J mice. In vitro, TEC treatment inhibited LPS-induced
activation of KCs, which proved that TEC markedly increased the M2
markers (IL-10, Arg-1, Retnla, CD163 and CD80) and decreased the M1
markers (TNF-α, INF-γ, CCL2, CXCL1 and iNOS) (Figure 4A). Then, GW9662
(PPARγ inhibitor) was used to confirm that TEC regulation of KCs
polarity was dependent on PPARγ. Our results showed that TEC treatment
did not further influence macrophage activation (TNF-α, CXCL1, iNOS and
CCL2) and macrophage alternative activation (IL-10, Arg-1, Retnla,
CD206) when treated with GW9662 in the presence of LPS (Figure 4B).
Analogical results were obtained by
cotreatment with GW1929 (PPARγ agonist) and TEC (Figure S1A and S1B).
Importantly, PPARγ expression deficiency dramatically suppressed
TEC-mediated inhibition of macrophage activation in the presence of LPS
(Figure 4C and 4D).
It is worth noting that BMDMs infiltrated the liver under CLD
conditions. Thus, BMDMs were isolated from mice, and treated with TEC
and/or ILPS. As expected, TEC increased the ratio of CD206/CD80,
decreased M1 marker genes (TNF-α, iNOS, IL-1β and CCL2) and upregulated
the expression of M2 marker genes (IL-10, Arg-1, Retnla and CD163)
(Figure S2A). BMDMs treated with shPPARγ and TEC supported our findings
that TEC did not inhibit LPS-induced macrophage activation when PPARγ
was knocked out (Figure S2B).
Accumulated evidence suggests that PPARγ attenuates inflammation by
suppressing NFκb activity. Mechanically, PPARγ is an E3 ligase that
induces the degradation of NFκb-p65 to terminate NFκB signaling
pathway-elicited
inflammation[33].
In light of this, we further determined whether TEC-regulated macrophage
activation was dependent on the PPARγ/NFκb pathway. BAY 11-7085 (NFκb
inhibitor) and/or TEC were used to treat KCs in the presence of LPS
(Figure S1B). Our results showed that inhibition of NFκb activity
abolished the TEC-mediated regulation of KCs activation.
Taken together, these results indicate that TEC notably inhibited
LPS-induced activation of macrophages. Moreover, TEC regulated
macrophage activation which was dependent on activating PPARγ.