Glioma-mediated microglial activation promotes glioma proliferation and migration: roles of Na⁺/H⁺exchanger isoform 1

Abstract

Microglia play important roles in extracellular matrix remodeling, tumor invasion, angiogenesis, and suppression of adaptive immunity in glioma. Na(+)/H(+) exchanger isoform 1 (NHE1) regulates microglial activation and migration. However, little is known about the roles of NHE1 in intratumoral microglial activation and microglia-glioma interactions. Our study revealed up-regulation of NHE1 protein expression in both glioma cells and tumor-associated Iba1(+) microglia in glioma xenografts and glioblastoma multiforme microarrays. Moreover, we observed positive correlation of NHE1 expression with Iba1 intensity in microglia/macrophages. Glioma cells, via conditioned medium or non-contact glioma-microglia co-cultures, concurrently upregulated microglial expression of NHE1 protein and other microglial activation markers (iNOS, arginase-1, TGF-β, IL-6, IL-10 and the matrix metalloproteinases MT1-MMP and MMP9). Interestingly, glioma-stimulated microglia reciprocally enhanced glioma proliferation and migration. Most importantly, inhibition of microglial NHE1 activity via small interfering RNA (siRNA) knockdown or the potent NHE1-specific inhibitor HOE642 significantly attenuated microglial activation and abolished microglia-stimulated glioma migration and proliferation. Taken together, our findings provide the first evidence that NHE1 function plays an important role in glioma-microglia interactions, enhancing glioma proliferation and invasion by stimulating microglial release of soluble factors. NHE1 upregulation is a novel marker of the glioma-associated microglial activation phenotype. Inhibition of NHE1 represents a novel glioma therapeutic strategy by targeting tumor-induced microglial activation.

The human microglial HMC3 cell line: where do we stand? A systematic literature review

“…All these cell lines were developed through SV40 immortalization of human primary microglial cells, whereas a fraction of SV40-immortalized adult microglial cells were further engineered to express the human telomerase reverse transcriptase (hTERT) and reduce the proliferation rate [19]. To the best of our knowledge, two cell lines are commercially available, the human microglial clone 3 cell line, HMC3 [17,[20][21][22] and the "Immortalized Human Microglia -SV40", developed and distributed by Applied Biological Materials (Vancouver, Canada) [23][24][25][26][27][28]. The HMC3 has been recently authenticated by the American Type Culture Collection (ATCC®), a leading nonprofit organization in the authentication and distribution of biologic material, microorganisms, and standards.…”

Selective role of Na+/H+ exchanger in Cx3cr1+ microglial activation, white matter demyelination, and post‐stroke function recovery

“…NHE1 plays an important role in regulating microglial intracellular pH (pH i ) homeostasis, their activation, and migration (Boscia et al, 2016;Liu et al, 2010;Shi et al, 2013;Zhao et al, 2016;Zhu et al, 2016). In particular, NHE1 maintains optimal pH i to support NADPH oxidase (NOX) function during microglial activation (Lam et al, 2013).…”

Quantitative sodium imaging and gliomas: a feasibility study

“…Upregulation of the Na + /H + exchanger isoform 1 (NHE1), leading to increased intracellular sodium and increased intracellular pH, has been implicated in promoting glioma proliferation, invasion and resistance to temozolomide therapy[24, 25]. Another study demonstrated that in oligodendrogliomas, IDH-mutated and 1p/19q codeleted, the NHE1 on 1p is silenced, and proposes that this could be a major contributor to the low proliferation rates in these tumors[26].…”