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Original article
Dysregulation of the intrinsic apoptotic pathway mediates megakaryocytic hyperplasia in myeloproliferative neoplasms
  1. Jacques A J Malherbe1,
  2. Kathryn A Fuller1,2,
  3. Bob Mirzai1,2,
  4. Simon Kavanagh1,2,
  5. Chi-Chiu So3,
  6. Ho-Wan Ip4,
  7. Belinda B Guo1,
  8. Cecily Forsyth5,
  9. Rebecca Howman2,
  10. Wendy N Erber1,2
  1. 1School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, Western Australia, Australia
  2. 2PathWest Laboratory Medicine, Nedlands, Western Australia, Australia
  3. 3Department of Pathology, Faculty of Medicine, University of Hong Kong, Hong Kong, Hong Kong
  4. 4Department of Pathology & Clinical Biochemistry, Queen Mary Hospital, Hong Kong, Hong Kong
  5. 5Jarrett Street Specialist Centre, North Gosford, New South Wales, Australia
  1. Correspondence to Professor Wendy N Erber, School of Pathology and Laboratory Medicine (M504), The University of Western Australia: 35 Stirling Highway, Crawley, Western Australia 6009, Australia; wendy.erber{at}uwa.edu.au

Abstract

Aims Megakaryocyte expansion in myeloproliferative neoplasms (MPNs) is due to uncontrolled proliferation accompanied by dysregulation of proapoptotic and antiapoptotic mechanisms. Here we have investigated the intrinsic and extrinsic apoptotic pathways of megakaryocytes in human MPNs to further define the mechanisms involved.

Methods The megakaryocytic expression of proapoptotic caspase-8, caspase-9, Diablo, p53 and antiapoptotic survivin proteins was investigated in bone marrow specimens of the MPNs (n=145) and controls (n=15) using immunohistochemistry. The megakaryocyte percentage positivity was assessed by light microscopy and correlated with the MPN entity, JAK2V617F/CALR mutation status and platelet count.

Results The proportion of megakaryocytes in the MPNs expressing caspase-8, caspase-9, Diablo, survivin and p53 was significantly greater than controls. A greater proportion of myeloproliferative megakaryocytes expressed survivin relative to its reciprocal inhibitor, Diablo. Differences were seen between myelofibrosis, polycythaemia vera and essential thrombocythaemia for caspase-9 and p53. CALR-mutated cases had greater megakaryocyte p53 positivity compared to those with the JAK2V617F mutation. Proapoptotic caspase-9 expression showed a positive correlation with platelet count, which was most marked in myelofibrosis and CALR-mutated cases.

Conclusions Disruptions targeting the intrinsic apoptotic cascade promote megakaryocyte hyperplasia and thrombocytosis in the MPNs. There is progressive dysfunction of apoptosis as evidenced by the marked reduction in proapoptotic caspase-9 and accumulation of p53 in myelofibrosis. The dysfunction of caspase-9, which is necessary for proplatelet formation, may be the mechanism for the excess thrombocytosis associated with CALR mutations. Survivin seems to be the key protein mediating the megakaryocyte survival signature in the MPNs and is a potential therapeutic target.

  • MYELOPROLIFERATIVE DISEASE
  • APOPTOSIS
  • IMMUNOHISTOCHEMISTRY

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/

https://doi.org/10.1136/jclinpath-2016-203625

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    Footnotes

    • Handling editor Mary Frances McMullin

    • Contributors JAJM, KAF and BM performed the immunohistochemical studies. C-CS, H-WI and BBG conducted the molecular analyses. JAJM, KAF, SK, BM and WNE performed the megakaryocyte enumeration for all cases. JAJM conducted the statistical analyses. C-CS, HWI, CF and WNE undertook the morphological review. RH and WNE initiated the study. All authors contributed to the writing of the manuscript.

    • Funding The study was supported by the Australian Leukaemia and Lymphoma Group and Novartis Pharmaceuticals Australia Pty Ltd, the Cancer Council Western Australia, Perpetual Foundation-Ann Helene Toakley Charitable Endowment and the Royal College of Pathologists of Australasia.

    • Competing interests None declared.

    • Patient consent Obtained.

    • Ethics approval (1) Sir Charles Gairdner Hospital Human Research Ethics Committee (#2012-094). (2) The University of Western Australia Human Research Ethics Committee (#RA/4/1/6566). (3) The Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster (#UW 13-189).

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement Data are available upon request and at the discretion of the authors.