EXTENDED REPORT

Increased expression of humanin peptide in diffuse-type pigmented villonodular synovitis: implication of its mitochondrial abnormality

K Ijiri^1,2, H Tsuruga³, H Sakakima¹, K Tomita⁵, N Taniguchi⁴, K Shimoonoda⁴, S Komiya⁴, M B Goldring², H J Majima⁵, T Matsuyama³

¹ Course of Physiotherapy, School of Health Science, Faculty of Medicine, Kagoshima University, Kagoshima, Japan
² Beth Israel Deaconess Medical Center, New England Baptist Bone and Joint Institute, Boston, MA, USA
³ Immunology and Medical Zoology, Graduate School of Medicine, Kagoshima University, Kagoshima, Japan
⁴ Department of Neuro-Musculoskeletal Disorder, Kagoshima University Graduate School of Medicine and Dentistry, Kagoshima University, Kagoshima, Japan
⁵ Department of Oncology, Kagoshima University Graduate School of Medicine and Dental Science, Kagoshima, Japan

Correspondence to:
Dr K Ijiri
Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine, Room 237, 4 Blackfan, Circle, Boston, MA 02115, USA; kijiri{at}bidmc.harvard.edu

Objectives: To define the pathogenesis of pigmented villonodular synovitis (PVNS), by searching for highly expressed genes in primary synovial cells from patients with PVNS.

Methods: A combination of subtraction cloning and Southern colony hybridisation was used to detect highly expressed genes in PVNS in comparison with rheumatoid synovial cells. Northern hybridisation was performed to confirm the differential expression of the humanin gene in PVNS. Expression of the humanin peptide was analysed by western blotting and immunohistochemistry. Electron microscopic immunohistochemistry was performed to investigate the distribution of this peptide within the cell.

Results: 68 highly expressed genes were identified in PVNS. Humanin genes were strongly expressed in diffuse-type PVNS, but were barely detected in nodular-type PVNS, rheumatoid arthritis, or osteoarthritis. Humanin peptide was identified in synovium from diffuse-type PVNS, and most of the positive cells were distributed in the deep layer of the synovial tissue. Double staining with anti-humanin and anti-heat shock protein 60 showed that humanin was expressed mainly in mitochondria. Electron microscopy disclosed immunolocalisation of this peptide, predominantly around dense iron deposits within the siderosome.

Conclusions: Increased expression of the humanin peptide in mitochondria and siderosomes is characteristic of synovial cells from diffuse-type PVNS. Humanin is an anti-apoptotic peptide which is encoded in the mitochondrial genome. Present findings suggest that mitochondrial dysfunction may be the principal factor in pathogenesis of diffuse-type PVNS and that humanin peptide may play a part in the neoplastic process in this form of PVNS.

Abbreviations: BSA, bovine serum albumin; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; hsp, heat shock protein; IMDM, Iscove modified Dulbecco’s medium; OA, osteoarthritis; PBS, phosphate buffered saline; PCR, polymerase chain reaction; PVNS, pigmented villonodular synovitis; RA, rheumatoid arthritis; RT-PCR, reverse transcriptase-polymerase chain reaction; SDS, sodium dodecyl sulphate; SDS-PAGE, sodium dodecyl sulphate-polyacrylamide gel electrophoresis; SSC, saline sodium citrate

Keywords: humanin; mitochondria; pigmented villonodular synovitis

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