Bone Marrow Connexin-43 Expression Is Critical for Hematopoietic Regeneration After Chemotherapy

Abstract

Contact between bone marrow (BM) hematopoietic stem cells (HSC) and osteoblast/stromal (OS) cells has been shown to be crucial in the regulation of hematopoiesis. However, very little is known about the regulatory mechanisms of direct cell-to-cell communication in the hematopoietic microenvironment. Gap junction channels (connexons) are formed by polypeptides (connexins) arranged in hexamers and represent the best described intercellular communication system. Connexin-43 (Cx43) is expressed by BM OS cells and has been associated with the cadherin/beta -catenin signaling pathway, recently reported as relevant in the OS/HSC interaction at the stem cell niche. Here, we employed an inducible gene-targeted murine approach to study the role of Cx43 in HSC proliferation and differentiation in vivo. Mx-Cre/Cx43+/+ and Mx-Cre/Cx43flox/flox littermates have been analyzed after gene deletion induced in vivo by the interferon-inducer poly (I)-poly (C), generating control (Cx43+) and Cx43-deficient (Cx43-/-) mice. After one week, Cx43+ and Cx43-/- mice were treated with 5-fluorouracil (5-FU). Cx43 expression in Cx43-/- BM was markedly reduced (> 90%) as analyzed on day +14 post-5-FU treatment. Cx43 deficiency did not induce a significant change in peripheral blood counts before 5-FU treatment, but the hematopoiesis recovery after 5-FU treatment was severely impaired as demonstrated by absence of recovery of peripheral blood counts, including profound neutropenia, anemia with reticulocytopenia, thrombocytopenia and a 5- to 8-fold decrease of cellularity and hematopoietic progenitor content (granulomacrophagic colony-forming-units (CFU-GM-), erythroid burst forming units (BFU-E) and mixed colony forming units (CFU-mix-) in BM and spleen on day +14 post-5-FU treatment. However, the femoral content of Lin-/c-kit+/Sca1+ cells in Cx43-/- BM was maintained when compared to Cx43+ BM. Short-term competitive repopulation ability of Cx43-/- BM cells was diminished as compared to Cx43+ mice, specifically for myeloid and B lymphoid cells, but showed spared long-term competitive repopulation ability with roughly normal hematopoietic differentiation. These data suggest that hematopoietic regeneration after cycle-specific chemotherapy is blocked in Cx43-deficient mice at the long-term HSC repopulating level. Cx43 expression within the BM appears to be crucial in the development of an efficient response to hematopoietic stress.

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

“…Mimicking the situation in aged individuals, the HSC BM content of H-Cx43-deficient old mice is increased over aged-matched controls (47), whereas their ability to regenerate after 5-FU administration is diminished (Ref. 10 and Fig. 1 J and K).…”

“…The reintroduction of Cx43 also rescues the ROS transfer from ROS high HSC/P cells to BM stromal cells, confirming the expected role of HSC Cx43 in ROS scavenging by the HM. Finally, the deficiency of Cx43 in the HM in chimeric mice generated by transplanting WT hematopoiesis (>90%) into an inducible murine model of Cx43 deficiency (10) significantly phenocopies the deficiency of Cx43 in HSCs.…”

Gap junction remodeling and cardiac arrhythmogenesis in a murine model of oculodentodigital dysplasia

“…Site-directed mutagenesis was performed to introduce the disease-causing I130T point mutation into the same gene-targeting vector used to conditionally inactivate Cx43 in the heart and other lineages (23)(24)(25). Targeting was performed in the 129/Sv-derived ES cell line R1 (23,26).…”

ASXL1 mutations identify a high-risk subgroup of older patients with primary cytogenetically normal AML within the ELN Favorable genetic category

“…Among the genes most strongly up-regulated in ASXL1-mut patients were LRP6 (a WNT signaling pathway coreceptor 30 ), cytochrome P450 CYP1B1 (associated with chemotherapy resistance 31 ), and gap junction protein ␣ 1 (GJA1, connexin 43). GJA1 couples early hematopoietic and stromal cells in the BM, is important for regeneration of hematopoiesis after chemotherapy, 32 and mediates secretion of stroma-derived factor 1 (CXCL12), a chemokine essential for hematopoietic stem cell homing and function. 33 On the other hand, KISS1R (a G-protein-coupled receptor suppressing CXCL12-CXCR4 signaling 34 ) was down-regulated in ASXL1-mut CN-AML.…”