Role for myeloid nuclear differentiation antigen in the regulation of neutrophil apoptosis during sepsis.
BACKGROUND
Suppressed neutrophil apoptosis, a hallmark of sepsis, perpetuates inflammation and delays resolution. Myeloid nuclear differentiation antigen (MNDA) is expressed only in myeloid cells and has been implicated in cell differentiation; however, its function in mature neutrophils is not known.


OBJECTIVE
We studied whether MNDA could contribute to regulation of apoptosis of neutrophils from healthy subjects and patients with sepsis, and investigated the impact of MNDA knockdown on apoptosis.


METHODS
Human neutrophils were challenged with mediators of sepsis and neutrophils from patients with sepsis were cultured to investigate cleavage and cytoplasmic accumulation of MNDA. MNDA was knocked down in myeloid HL-60 cells to investigate development of apoptosis.


RESULTS
During constitutive apoptosis of human neutrophils, MNDA is cleaved by caspases and accumulated in the cytoplasm, where it promotes degradation of the antiapoptotic protein Mcl-1, thereby accelerating collapse of mitochondrial transmembrane potential. Culture of neutrophils with LPS, bacterial DNA, or platelet-activating factor prevented MNDA cleavage and cytoplasmic accumulation. MNDA knockdown with short hairpin RNA markedly attenuated Mcl-1 turnover and conferred resistance to stress-induced apoptosis in HL-60 cells. Neutrophils from patients with severe sepsis exhibited markedly suppressed apoptosis that was associated with impaired cytoplasmic MNDA accumulation, preservation of Mcl-1 expression, and mitochondrial transmembrane potential. Culture of neutrophils of healthy subjects with septic plasma delayed apoptosis and cytoplasmic MNDA accumulation.


CONCLUSIONS
These results indicate that cytoplasmic accumulation of MNDA facilitates progression of apoptosis and suggest that impaired cytoplasmic MNDA accumulation contributes to delayed neutrophil apoptosis in patients with severe sepsis.
Fotouhi-Ardakani
Nasser
N
Maisonneuve-Rosemont Hospital, University of Montreal, Montréal, QC, Canada.
Kebir
Driss El
DE
Pierre-Charles
Natacha
N
Wang
Lili
L
Ahern
Stephane P
SP
Filep
János G
JG
Milot
Eric
E
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015214:Antigens, Differentiation, Myelomonocytic / Q000235:genetics / Q000502:physiology*; D017209:Apoptosis; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D055785:Gene Knockdown Techniques; D006801:Humans; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000502:physiology; D008875:Middle Aged; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009504:Neutrophils / Q000473:pathology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D018805:Sepsis / Q000473:pathology*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
D015214:Antigens, Differentiation, Myelomonocytic; C075373:MNDA protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D014157:Transcription Factors