Impairment of sterol biosynthesis leads to phosphorus and calcium accumulation in Leishmania acidocalcisomes

Laboratório de Biologia Celular Parasitária, Programa de Biologia Celular e Parasitologia, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, CCS, Bloco G, Ilha do Fundão, Rio de Janeiro, 21949-900, Brazil 1 Setor de Microscopia Eletrônica e Departamento de Microbiologia Geral, Instituto de Microbiologia Professor Paulo de Góes, Universidade Federal do Rio de Janeiro, Brazil 2 Laboratório de Química Biológica, Instituto Venezoelano de Investigaciones Científicas-IVIC, Venezuela 3 Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Brazil 4 Author for correspondence: Marcos A. Vannier-Santos. Tel: +55 21 260 6963. Fax: +55 21 280 8193. e-mail: vannier{at}biof.ufrj.br The induction of the formation of inclusion vesicles in Leishmania amazonensis by the sterol biosynthesis inhibitors (SBI) ketoconazole and terbinafine has been reported previously. These compartments were recently identified as acidocalcisomes. By the use of electron spectroscopic imaging and energy loss spectroscopy, the presence of calcium, phosphorus and oxygen in the electron-dense inclusions located within the acidocalcisomes has been demonstrated. Endoplasmic reticulum cisternae formed membrane whorls which enclosed large portions of the cytoplasm and sometimes circumscribed acidocalcisomes. In addition, acid phosphatase activity, as well as the endocytic tracers horseradish peroxidase and gold-labelled transferrin and cystatin C were detected within these organelles in both SBI-treated and untreated parasites. These data suggest that impairment of sterol biosynthesis induces the biogenesis of acidocalcisomes and triggers an autophagic process that leads to intersection of the endosomal/lysosomal system with the acidocalcisomes. Keywords: sterol biosynthesis inhibitors, ketoconazole, terbinafine, acidocalcisome, Leishmania Abbreviations: ER, endoplasmic reticulum; ESI, electron spectroscopic imaging; SBI, sterol biosynthesis inhibitors