Does transmembrane communication through gap junctions enable stem cells to overcome stromal inhibition?

Abstract

ronectin on stromal cells. 11 Lipophilic compounds that do not affect GJIC had no effect onWe asked if the gap junctions which are present in haemo- drugs (Ref. 13 and Krenács and Rosendaal, in preparation).Keywords: blood formation; haemopoietic regulation; gap junctions; Cx43; Amphotericin B; stem cells; stroma Gap junctions are intramembranous channels through the walls of adjacent cells which permit the passage of watersoluble molecules smaller than 1 kDa, which could be messengers. Channels are gated, open when cytosolic [Ca 2+ i ] is Introduction high or pH low and closed when the opposite conditions occur. A single gap junction channel is called a connexon Normally blood cells form only in those parts of the body, and is formed by two hemi-connexons, one in each cell wall. especially bone marrow, where specialised cells calledThe channels group into plaques and these are the functional haemopoietic stromal cells are found. Grafting these cells into gap junctions. Each hemi-connexon is formed by six identical, non-medullary tissues such as the kidney enables such tissues membrane-spanning proteins called connexins. Thirteen conto form blood. 1 We have been able to understand many nexin species have been described and named for their molaspects of lifelong blood formation supported by stromal cells ecular weights in thousands, abbreviated as Cx43, etc. 15 Cerusing long-term bone marrow cultures. 2 tain kinds of stromal cell in haemopoietic tissue are coupled It was thought that long-term cultures required an underlyby Cx43 gap junctions, but we do not know yet if that is the ing monolayer of adherent bone marrow stromal cells to form only connexin species that can form haemopoietic junctions. blood cells for a long time. Bentley 3 indicated that stroma and There are functional gap junctions in long-term cultures stem cells need only be close for the maintenance of spleen between stromal and haemopoietic cells. 12 To investigate a colony-forming units and Brandt and colleagues 4 found that possible role of gap junctions in the regulation of haemopothe underlay could be replaced by adding recombinant iesis we studied the numerical alterations in clone formation interleukins IL-1 alpha, IL-3, IL-6, or granulocyte-macrophage and progenitor cell generation in stroma-supported long-term colony-stimulating factor (GM-CSF) at 2-day intervals. IL-3 cultures 2,[16][17][18] in the presence of lipophilic substances which block GJIC. Absolute numbers of haemopoietic clones were estimated using the cobblestone area forming cell (CAFC) culture carried out in a limited dilution set-up. In the mouse

Bone marrow stroma inhibits proliferation and apoptosis in leukemic cells through gap junction-mediated cell communication

“…Moreover, using radiation chimeras, the authors showed that impaired T-and B-lymphocyte maturation was due to a defect in the stromal cells of both the thymus and BM. This confirms Rosendaal hypothesis 11,15,18 that Cx43 expression in the stroma is critical during early growth and regeneration of the hematopoietic system, but not for maintenance of the steady-state blood cell production.…”

“…18 In contrast, using a direct assay, we have shown that GJs are actually involved in the maintenance of quiescence. We also suggest that such regulation can be achieved through signaling for asymmetric cell division.…”

Hematopoietic capacity of connexin43 wild-type and knock-out fetal liver cells not different on wild-type stroma

“…17 We compared blood formation by WT and KO stems as published. 1 An intracellular injection of lucifer yellow 18 into WT stroma spread over 4 to 5 cell diameters but did not pass from one KO cell to another. KO cells passed neurobiotin to the next cell but no further.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] Gap junctions have been comprehensively reviewed. 13 In 1995 and 1997, we proposed 1,14 that Cx43 gap junctions between stromal and hematopoietic cells determine hematopoiesis. If this were the case, was this effect because of coupling between hematopoietic and stromal cells or between stromal cells alone?…”

Non-classical Signalling Mechanisms in Stem Cells

“…Current knowledge is however sparse. It has been proposed that Cx32, Cx43 and GJIC play a role in HSC maintenance and differentiation (Hirabayashi et al, 2007b;Ploemacher et al, 2000;Rosendaal et al, 1997). Indeed, Cx32 knockout mice exhibit more undifferentiated HSC and fewer progenitor cells, suggesting a role of Cx32 in maturation of HSC to progenitor cells (Hirabayashi et al, 2007a;Hirabayashi et al, 2007b).…”