Protective role of connexin 32 in steady-state hematopoiesis, regeneration state, and leukemogenesis.
The role of gap junctions formed by connexins (Cxs) has been implicated in the homeostatic regulation of multicellular systems. Primitive hematopoietic progenitor cells form a multicellular system, but a previous report states that Cx32 is not expressed in the bone marrow. Thus, a question arises as to why Cx molecules are not detected in the hematopoietic tissue other than in stromal cells. Based on our preliminary study, which suggested a potential impairment of hematopoiesis in Cx32-knockout (KO) mice, the objectives of the present study were to determine whether Cx32 functions in the bone marrow during steady-state hematopoiesis and to examine its possible protective roles during regeneration after chemical abrasions and during leukemogenesis after the administration of a secondary genotoxic chemical, methyl nitrosourea (MNU). As a result, the Cx32 molecule, functioning in the hematopoietic stem cell (HSC) compartment during steady-state hematopoiesis, was observed for the first time; the expressions of Cx32 at the mRNA level, as determined by polymerase chain reaction analysis, and at the protein level, determined using an anti-Cx32 antibody, were observed only in the lin(-)c-kit(+) HSC fraction, using a combination of immunobead-density gradient and immunomagnetic bead separation. Hematopoiesis was impaired in the absence of Cx32, and it was delayed during regeneration after chemical abrasion with 5-fluorouracil at 150 mg/kg body wt in Cx32-KO mice. Cx32-KO mice showed increased leukemogenicity compared with wild-type mice after MNU injection; furthermore, in a competitive assay for leukemogenicity in mice that had been lethally irradiated and repopulated with a mixed population of bone marrow cells from Cx32-KO mice and wild-type mice, the resulting leukemias originated predominantly from Cx32-KO bone marrow cells. In summary, the role of Cx32 in hematopoiesis was not previously recognized, and Cx32 was expressed only in HSCs and their progenitor cells. The results indicate that Cx32 in wild-type mice protects HSCs from chemical abrasion and leukemogenic impacts.
Hirabayashi
Yoko
Y
Division of Cellular and Molecular Toxicology, Center for Biological Safety and Research, National Institute of Health Sciences, Tokyo, Japan.
Yoon
Byung-Il
BI
Tsuboi
Isao
I
Huo
Yan
Y
Kodama
Yukio
Y
Kanno
Jun
J
Ott
Thomas
T
Trosko
James E
JE
Inoue
Tohru
T
D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D016026:Bone Marrow Transplantation; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D017630:Connexins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005260:Female; D005434:Flow Cytometry; D005472:Fluorouracil / Q000494:pharmacology; D020869:Gene Expression Profiling; D005838:Genotype; D006410:Hematopoiesis / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000378:metabolism; D007150:Immunohistochemistry; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007938:Leukemia / Q000139:chemically induced / Q000503:physiopathology*; D008297:Male; D008770:Methylnitrosourea / Q000633:toxicity; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012038:Regeneration / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013154:Spleen / Q000166:cytology / Q000378:metabolism; D000097002:Gap Junction beta-1 Protein
D017630:Connexins; D005472:Fluorouracil; D007166:Immunosuppressive Agents; D008770:Methylnitrosourea; D012333:RNA, Messenger; D000097002:Gap Junction beta-1 Protein