Connexin-43 prevents hematopoietic stem cell senescence through transfer of reactive oxygen species to bone marrow stromal cells

Abstract

Hematopoietic stem cell (HSC) aging has become a concern in chemotherapy of older patients. Humoral and paracrine signals from the bone marrow (BM) hematopoietic microenvironment (HM) control HSC activity during regenerative hematopoiesis. Connexin-43 (Cx43), a connexin constituent of gap junctions (GJs) is expressed in HSCs, down-regulated during differentiation, and postulated to be a self-renewal gene. Our studies, however, reveal that hematopoietic-specific Cx43 deficiency does not result in significant long-term competitive repopulation deficiency. Instead, hematopoietic Cx43 (H-Cx43) deficiency delays hematopoietic recovery after myeloablation with 5-fluorouracil (5-FU). 5-FU-treated H-Cx43-deficient HSC and progenitors (HSC/P) cells display decreased survival and fail to enter the cell cycle to proliferate. Cell cycle quiescence is associated with down-regulation of cyclin D1, up-regulation of the cyclin-dependent kinase inhibitors, p21 cip1. and p16 INK4a , and Forkhead transcriptional factor 1 (Foxo1), and activation of p38 mitogen-activated protein kinase (MAPK), indicating that H-Cx43-deficient HSCs are prone to senescence. The mechanism of increased senescence in H-Cx43-deficient HSC/P cells depends on their inability to transfer reactive oxygen species (ROS) to the HM, leading to accumulation of ROS within HSCs. In vivo antioxidant administration prevents the defective hematopoietic regeneration, as well as exogenous expression of Cx43 in HSC/P cells. Furthermore, ROS transfer from HSC/P cells to BM stromal cells is also rescued by reexpression of Cx43 in HSC/P. Finally, the deficiency of Cx43 in the HM phenocopies the hematopoietic defect in vivo. These results indicate that Cx43 exerts a protective role and regulates the HSC/P ROS content through ROS transfer to the HM, resulting in HSC protection during stress hematopoietic regeneration.

Cell-Cell Communication in the Tumor Microenvironment, Carcinogenesis, and Anticancer Treatment

“…Connexin-43 (Cx43)-deficient hematopoietic stem cells (HSCs) exhibit an increased senescence that is dependent on their ability to transfer ROS to the hematopoietic microenvironment, and ROS accumulate in the HSCs. Thus, Cx43 has a protective effect on HSCs, which is exerted through their transfering the ROS to the hematopoietic microenvironment [100]. …”

Adhesion in the stem cell niche: biological roles and regulation

“…Connexin 43 (also known as gap junction protein alpha 1) was first shown to be required in stromal cells to support mouse HSCs in culture (Cancelas et al, 2000), and was later shown to be important for CXCL12 secretion from the stromal cells to control HSC self-renewal (Schajnovitz et al, 2011). Most recently, connexin 43 was shown to prevent HSC senescence by transferring reactive oxygen species into the supporting stromal cells, thus reducing their damage to HSCs (Taniguchi Ishikawa et al, 2012). In the mouse subventricular NSC niche, the gap junction-mediated calcium transfer between supporting astrocytes and NSCs is important for NSC proliferation (Lacar et al, 2011).…”

Until Death Do Us Part: Necrosis and Oxidation Promote the Tumor Microenvironment

“…- scavenging ROS [28] which are provided by inflammatory cells migrating into sites of damage [29,30],…”