Megakaryocytic hyperplasia in myeloproliferative neoplasms is driven by disordered proliferative, apoptotic and epigenetic mechanisms.
OBJECTIVE
Myeloproliferative neoplasms (MPN) are a heterogeneous group of clonal proliferative bone marrow diseases characterised by extensive megakaryocytic hyperplasia and morphological atypia. Despite knowledge of genomic defects, the pathobiological processes driving these megakaryocytic abnormalities in MPN remain poorly explained. We have explored the proliferative, apoptotic and epigenetic profiles of megakaryocytes in human MPN.


METHODS
Immunohistochemical staining was performed on bone marrow trephine biopsies of 81 MPN (with and without JAK2(V617F) and CALR mutations) and 15 normal controls to assess the megakaryocytic expression of biomarkers associated with proliferation (Ki67), apoptosis (Bcl-XL, BNIP-3) and epigenetic regulation (EZH2, SUZ12).


RESULTS
Myeloproliferative megakaryocytes showed significantly greater expression of proliferative Ki67 and anti-apoptotic Bcl-XL, reduced pro-apoptotic BNIP-3 and increased SUZ12 compared with controls. In essential thrombocythaemia, large-giant megakaryocytes with hyperlobated nuclei showed a trend towards a proliferative signature. In contrast, myelofibrotic megakaryocytes with condensed nuclear chromatin, and cases with CALR mutations, had significant reductions in pro-apoptotic BNIP-3.


CONCLUSIONS
Uncontrolled megakaryocytic expansion in MPN results from a combination of increased proliferation, attenuated apoptosis and defective epigenetic regulation with CALR mutations favouring apoptotic failure. The higher platelet counts reported to be seen in MPN with CALR mutations may be due to greater dysregulation of megakaryocyte apoptosis.
School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia.
Jacques A J
JA
Malherbe
School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia.
Kathryn A
KA
Fuller
School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia.
Ayesha
A
Arshad
Cambridge Institute for Medical Research and Wellcome Trust/MRC Stem Cell Institute, University of Cambridge, Cambridge, UK.
Jyoti
J
Nangalia
School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia PathWest Laboratory Medicine, Western Australia, Australia.
Giuliana
G
Romeo
School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia PathWest Laboratory Medicine, Western Australia, Australia.
Sara L
SL
Hall
School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia.
Katie S
http://orcid.org/0000-0002-9179-4592
KS
Meehan
School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia.
Belinda
B
Guo
School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia PathWest Laboratory Medicine, Western Australia, Australia.
Rebecca
R
Howman
School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia PathWest Laboratory Medicine, Western Australia, Australia.
Wendy N
WN
Erber
D017209:Apoptosis; D014408:Biomarkers, Tumor / Q000032:analysis / Q000235:genetics; D001706:Biopsy; D001856:Bone Marrow Examination; D037282:Calreticulin / Q000235:genetics; D016022:Case-Control Studies; D049109:Cell Proliferation; D004252:DNA Mutational Analysis; D000071221:Enhancer of Zeste Homolog 2 Protein; D044127:Epigenesis, Genetic; D006801:Humans; D006965:Hyperplasia; D007150:Immunohistochemistry; D053614:Janus Kinase 2 / Q000235:genetics; D019394:Ki-67 Antigen / Q000032:analysis; D008533:Megakaryocytes / Q000737:chemistry / Q000473:pathology*; D008565:Membrane Proteins / Q000032:analysis; D009154:Mutation; D009196:Myeloproliferative Disorders / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D009363:Neoplasm Proteins; D063151:Polycomb Repressive Complex 2 / Q000032:analysis; D011518:Proto-Oncogene Proteins / Q000032:analysis; D046888:Tissue Array Analysis; D014157:Transcription Factors; D051020:bcl-X Protein / Q000032:analysis
C494811:BCL2L1 protein, human; C090121:BNIP3 protein, human; D014408:Biomarkers, Tumor; C576483:CALR protein, human; D037282:Calreticulin; D019394:Ki-67 Antigen; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; C430461:SUZ12 protein, human; D014157:Transcription Factors; D051020:bcl-X Protein; C498409:EZH2 protein, human; D000071221:Enhancer of Zeste Homolog 2 Protein; D063151:Polycomb Repressive Complex 2; C507924:JAK2 protein, human; D053614:Janus Kinase 2
APOPTOSIS; BONE MARROW; PROLIFERATION; fibrosis