Nanotube Action between Human Mesothelial Cells Reveals Novel Aspects of Inflammatory Responses

Abstract

A well-known role of human peritoneal mesothelial cells (HPMCs), the resident cells of the peritoneal cavity, is the generation of an immune response during peritonitis by activation of T-cells via antigen presentation. Recent findings have shown that intercellular nanotubes (NTs) mediate functional connectivity between various cell types including immune cells - such as T-cells, natural killer (NK) cells or macrophages - by facilitating a spectrum of long range cell-cell interactions. Although of medical interest, the relevance of NT-related findings for human medical conditions and treatment, e.g. in relation to inflammatory processes, remains elusive, particularly due to a lack of appropriate in vivo data. Here, we show for the first time that primary cultures of patient derived HPMCs are functionally connected via membranous nanotubes. NT formation appears to be actin cytoskeleton dependent, mediated by the action of filopodia. Importantly, significant variances in NT numbers between different donors as a consequence of pathophysiological alterations were observable. Furthermore, we show that TNF-α induces nanotube formation and demonstrate a strong correlation of NT connectivity in accordance with the cellular cholesterol level and distribution, pointing to a complex involvement of NTs in inflammatory processes with potential impact for clinical treatment.

Tumor exosomes induce tunneling nanotubes in lipid raft-enriched regions of human mesothelioma cells

“…[2] Recent studies by other groups have confirmed the ability of an additional mTOR inhibitor (rapamycin) to decrease nanotube formation between benign mesothelial cells, as well as the association of cholesterol/lipid raft microdomains with TnTs. [9, 22, 23] Others have further demonstrated that depletion of cellular cholesterol using agents such as methyl-β-dextrin decreased the density of nanotubes between cells from a urothelial cancer cell line. [23] The same drug effectively reduced cholesterol concentrations and nanotube formation in human mesothelial cells cultivated in vitro .…”

“…[23] The same drug effectively reduced cholesterol concentrations and nanotube formation in human mesothelial cells cultivated in vitro . [9] Paradoxically, the use of the HMG-CoA reductase inhibitor simvastatin - a drug in common medical use for treatment of hypercholesterolemia – led to significant increases in numbers of nanotubes. [9] Nonetheless, as the authors postulate, the distribution of cholesterol across individual cells may account at least in part for this finding.…”

“…[3, 4] TnTs have the ability to directly mediate cell-to-cell communication by serving as long-range conduits for intercellular transfer of proteins, mitochondria, and other subcellular organelles. [1] Much of the work to date on these unique structures has focused on non-cancer cell types including dendritic cells and monocytes,[5] macrophages,[6, 7] T cells,[8, 9] B cells,[10] neutrophils,[11] neurons,[12] kidney cells,[13] endothelial progenitor cells,[14] and mesothelial cells. [9] More recently, we have shown that TnTs connect cells derived from malignant pleural mesothelioma and lung adenocarcinoma, both in vitro [2, 4] and in tumors resected from human patients.…”

“…[21] Furthermore, cholesterol accumulation has been proposed to have a direct effect on TnTs and similar nanotube structures. [9, 22, 23] Most notably, exosomes and lipid rafts appear to facilitate adherence and invasion of malignant cells in vitro [16]. …”

NF-κB-mediated transcriptional upregulation of TNFAIP2 by the Epstein–Barr virus oncoprotein, LMP1, promotes cell motility in nasopharyngeal carcinoma

“…[44][45][46] Moreover, some pathogens have been shown to exploit the related structures to spread among cells, [47][48][49][50] and TNFAIP2 mRNA expression appears to be upregulated under conditions known to enhance nanotube formation. 34,36,51,52 It is not yet clear whether the TNFAIP2-modulated actin protrusions in NPC cells are functionally related to the reported actin-based nanotubes; however, both the actin-based protrusive structures may share the same underlying mechanism that engages the actinremodeling proteins, such as Cdc42. In our previous study, we have revealed that LMP1 is able to activate Cdc42 by directly binding to FGD4, thereby promoting the migration of NPC cells.…”