The proinflammatory cytokine interferon γ (IFNγ ) influences intestinal epithelial cell (IEC) homeostasis in a biphasic manner by acutely stimulating proliferation that is followed by sustained inhibition of proliferation despite continued mucosal injury. β-Catenin activation has been classically associated with increased IEC proliferation. However, we observed that IFNγ inhibits IEC proliferation despite sustained activation of Akt/β-catenin signaling. Here we show that inhibition of Akt/β-catenin-mediated cell proliferation by IFNγ is associated with the formation of a protein complex containing phosphorylated β-catenin 552 (pβ-cat552) and 14.3.3ζ. Akt1 served as a bimodal switch that promotes or inhibits β-catenin transactivation in response to IFNγ stimulation. IFNγ initially promotes β-catenin transactivation through Akt-dependent C-terminal phosphorylation of β-catenin to promote its association with 14.3.3ζ. Augmented β-catenin transactivation leads to increased Akt1 protein levels, and active Akt1 accumulates in the nucleus, where it phosphorylates 14.3.3ζ to translocate 14.3.3ζ/β-catenin from the nucleus, thereby inhibiting β-catenin transactivation and IEC proliferation. These results outline a dual function of Akt1 that suppresses IEC proliferation during intestinal inflammation.
Hemorrhagic strok e is a devastating disease that lacks effective therapies. In the present investigation, we tested 6-bromoindirubin-3¢-oxime (BIO) as a selective glycogen synthase kinase-3b (GSK-3b) inhibitor in a mouse model of intracerebral hemorrhage (ICH). ICH was induced by injection of collagenase IV into the striatum of 8- to 10-week-old C57BL/6 mice. BIO (8 µg/kg, IP) was administered following either an acute delivery (0–2 h delay) or a prolonged regimen (every 48 h starting at 3 days post-ICH). At 2 days post-ICH, the acute BIO treatment significantly reduced the hematoma volume. In the perihematoma regions, BIO administration blocked GSK-3b phosphorylation/activation, increased Bcl-2 and b-catenin levels, and significantly increased viability of neurons and other cell types. The prolonged BIO regimen maintained a higher level of b-catenin, upregulated VEGF and BDNF, and promoted neurogenesis and angiogenesis in peri-injury zones at 14 days after ICH. The BIO treatment also promoted proliferation of neural stem cells (NSCs) and migration of nascent DCX + neuroblasts from the subventricular zone (SVZ) to the lesioned cortex. BIO improved functional outcomes on both the neurological severity score and rotarod tests. The findings of this study corroborate the neuroprotective and regenerative effects of BIO and suggest that the Wnt/GSK-3b/b-catenin pathway may be explored for the treatment of acute or chronic ICH.
by
Xi Feng;
Frank Szulzewsky;
Alexan Yerevanian;
Zhihong Chen;
David Heinzmann;
Rikke Darling Rasmussen;
Virginia Alvarez-Garcia;
Yeonghwan Kim;
Bingcheng Wang;
Ilaria Tamagno;
Hao Zhou;
Xiaoxia Li;
Helmut Kettenmann;
Richard M. Ransohoff;
Dolores Hambardzumyan
The most abundant populations of non-neoplastic cells in the glioblastoma (GBM) microenvironment are resident microglia, macrophages and infiltrating monocytes from the blood circulation. The mechanisms by which monocytes infiltrate into GBM, their fate following infiltration, and their role in GBM growth are not known. Here we tested the hypothesis that loss of the fractalkine receptor CX3CR1 in microglia and monocytes would affect gliomagenesis. Deletion of Cx3cr1 from the microenvironment resulted in increased tumor incidence and shorter survival times in glioma-bearing mice. Loss of Cx3cr1 did not affect accumulation of microglia/ macrophages in peri-tumoral areas, but instead indirectly promoted the trafficking of CD11b+CD45hiCX3CR1lowLy-6ChiLy-6G-F4/80-/low circulating inflammatory monocytes into the CNS, resulting in their increased accumulation in the perivascular area. Cx3cr1- deficient microglia/macrophages and monocytes demonstrated upregulation of IL1β expression that was inversely proportional to Cx3cr1 gene dosage. The Proneural subgroup of the TCGA GBM patient dataset with high IL1β expression showed shorter survival compared to patients with low IL1β. IL1β promoted tumor growth and increased the cancer stem cell phenotype in murine and human Proneural glioma stem cells (GSCs). IL1β activated the p38 MAPK signaling pathway and expression of monocyte chemoattractant protein (MCP-1/CCL2) by tumor cells. Loss of Cx3cr1 in microglia in a monocyte-free environment had no impact on tumor growth and did not alter microglial migration. These data suggest that enhancing signaling to CX3CR1 or inhibiting IL1β signaling in intra-tumoral macrophages can be considered as potential strategies to decrease the tumor-promoting effects of monocytes in Proneural GBM.