Involvement of the Notch Pathway in Terminal Astrocytic Differentiation: Role of PKA

Abstract

The Notch pathway is a highly conserved signaling system essential for modulating neurogenesis and promoting astrogenesis. Similarly, the cAMP signaling cascade can promote astrocytic commitment in several cell culture models, such as the C6 glioma cell line. These cells have the capacity to differentiate into oligodendrocytes or astrocytes, characteristics that allow their use as a glial progenitor model. In this context, we explore here the plausible involvement of cAMP in Notch-dependent signal transactions. The exposure of C6 cells to a non-hydrolysable cAMP analogue resulted in a sustained augmentation of Notch activity, as detected by nuclear translocation of its intracellular domain portion (NICD) and transcriptional activity. The cAMP effect is mediated through the activation of the γ-secretase complex, responsible for Notch cleavage and is sensitive to inhibitors of the cAMP-dependent protein kinase, PKA. As expected, Notch cleavage and nuclear translocation resulted in the up-regulation of the mRNA levels of one of its target genes, the transcription factor Hair and enhancer of split 5. Moreover, the glutamate uptake activity, as well as the expression of astrocytic markers such as glial fibrillary acidic protein, S100β protein and GLAST was also enhanced in cAMP-exposed cells. Our results clearly suggest that during the process of C6 astrocytic differentiation, cAMP activates the PKA/γ-secretase/NICD/RBPJκ pathway and Notch1 expression, leading to transcriptional activation of the genes responsible for glial progenitor cell fate decision.

Alterations in cellular metabolome after pharmacological inhibition of Notch in glioblastoma cells

“…40 Moreover, Angulo-Rojo et al found that Notch induces glutamate consumption during terminal differentiation of astrocytes. 41 Glutamate has also been shown to serve as growth stimulus for murine GSCs and that the neocortex, a brain region rich in glutamate, generates a metabolic niche advantageous for the growth of brain tumors. 42 Our findings are consistent with prior studies implicating Notch in glutamate regulation.…”

Notch Signaling in the Astroglial Phenotype: Relevance to Glutamatergic Transmission

“…In the same model, the cAMP-PKA-CREB signaling cascade cross talks with the Notch pathway, and together they act synergistically to reduce the progenitor marker (Nestin) and to induce astrocytic differentiation; measured by induced astrocytic markers (GFAP, S100β, and GLAST) and glutamate uptake. In this context, Notch1 mRNA is up-regulated in a PKA/γ-secretase/NICD/CSL-dependent manner, suggesting the establishment of a feedback loop to keep Notch pathway active until astrocytic differentiation is complete [50]. It is not surprising that the Notch pathway interacts with other signaling cascades to complete astrocytic differentiation.…”

“…In contrast, when the Notch receptor is not activated, PKCζ interacts with the receptor to induce a shift in receptor distribution from the plasma membrane to intracellular vesicles [70]. In C6 glioma cells, increased cAMP levels promote astrocytic commitment with a sustained augmentation of Notch activity, as detected by nuclear translocation of its intracellular domain portion (NICD) and its transcriptional activity [50]. The cAMP effect is mediated through the activation of the γ-secretase complex, responsible for Notch cleavage as demonstrated by its sensitivity to PKA inhibitors.…”

“…As expected, Notch cleavage and nuclear translocation result in the upregulation of the mRNA levels of one of its target genes, the transcription factor Hair, and enhancer of split 5. Moreover, glutamate uptake activity, expression of astrocytic markers (genes responsible for glial progenitor cell fate decision) such as the glial fibrillary acidic protein, the S100beta protein, and GLAST, are also enhanced in cAMP-exposed cells [50]. Interestingly, polychlorinated biphenyls (PCBs) disturb the cAMP-induced astrocytic differentiation of C6 cells via the PKC isoforms γ, β2, δ and ε [58].…”

ZMIZ1 Variants Cause a Syndromic Neurodevelopmental Disorder

“…Through its direct interaction with NOTCH1, ZMIZ1 plays a role in T lymphocyte development. 11,12 As NOTCH1 is directly involved in the regulation of cell fate during both neuronal and glial cell developments, [13][14][15] a role for ZMIZ1 in neural development is equally plausible. Like other PIAS, ZMIZ1 is predicted to function as an E3 SUMO ligase.…”