The IGF-I receptor in cell growth, transformation and apoptosis.

Human onchocerciasis is a serious neglected tropical disease caused by the filarial nematode Onchocerca volvulus that can lead to blindness and chronic disability. Control of the disease relies largely on mass administration of a single drug, and the development of new drugs and vaccines depends on a better knowledge of parasite biology. Here, we describe the chromosomes of O. volvulus and its Wolbachia endosymbiont. We provide the highest-quality sequence assembly for any parasitic nematode to date, giving a glimpse into the evolution of filarial parasite chromosomes and proteomes. This resource was used to investigate gene families with key functions that could be potentially exploited as targets for future drugs. Using metabolic reconstruction of the nematode and its endosymbiont, we identified enzymes that are likely to be essential for O. volvulus viability. In addition, we have generated a list of proteins that could be targeted by Federal-Drug-Agency-approved but repurposed drugs, providing starting points for anti-onchocerciasis drug development.

/pdf/the-genome-of-onchocerca-volvulus-agent-of-river-blindness-16b95mpig3.pdf

The genome of Onchocerca volvulus, agent of river blindness

Litomosoides sigmodontis is the only filaria which develops from infective larvae into adults in immunocompetent laboratory mice. Depletion of CD4+ T cells from infected BALB/c mice resulted in worm and microfilarial burdens significantly higher than those of infected controls. Th2 cytokines, eosinophilia, and immunoglobulin E, which were strongly induced in infected controls, were diminished in CD4-depleted mice.

Infection of BALB/c mice with the filarial nematode Litomosoides sigmodontis: role of CD4+ T cells in controlling larval development.

To identify potential vaccine candidates for the prevention of infection with the filarial nematode Onchocerca volvulus, we screened an O. volvulus L3 stage cDNA library with sera from putatively immune (PI) subjects, and a prominent immunogenic clone of 1,184 nucleotides was identified. It contained an open reading frame of 363 amino acids encoding the glycolytic enzyme fructose 1,6 bisphosphate aldolase (Ov-fba-1). Immunolocalization experiments demonstrated that the protein was most abundantly expressed in metabolically active tissues, including body wall muscle and the reproductive tract of adult female worms. Immunoelectron microscopy of L3 demonstrated binding in the region where the cuticle separates during molting, in the channels connecting the esophagus to the cuticle, and in the basal lamina surrounding the esophagus and the body cavity. Among subjects from areas where this organism is endemic specific humoral and cellular immune responses to recombinant protein were observed in both PI and infected subjects, whereas responses were not observed among subjects who had not been exposed to O. volvulus. Despite the absence of differential responsiveness in parasite-exposed human populations, when the recombinant was tested for protective efficacy in a mouse chamber model, a reduction in survival of larvae by ca. 50% was seen. This observation provides support for the further study of this parasite enzyme as a vaccine candidate in larger animal models.

Onchocerca volvulus glycolytic enzyme fructose-1,6-bisphosphate aldolase as a target for a protective immune response in humans

Publisher Summary This chapter examines the role of the insulin-like growth factor-I receptor (IGF-IR) in apoptosis. As cellular proliferation and transformation are clearly related to apoptosis, the role of the IGF-IR in mitogenesis is examined and in transformation, and its role in apoptosis is also focused. The IGF-IR is a tyrosine kinase receptor with a 70% homology to the insulin receptor (IR). It is synthesized as a single precursor polypeptide of 1367 amino acids, including a 30-amino-acid signal peptide. The organization of the preproreceptor is NH2–signal peptide–α subunit–β subunit–COOH. After removal of the signal peptide, the proreceptor is cleaved at the tetrapeptide RKRR after residue 706, to form the α and β subunits, linked by disulfide bonds. The α subunit, entirely extracellular, is involved in ligand binding; the transmembrane β subunit has a tyrosine kinase domain that is entirely intracellular. When activated by its ligands, the IGF-IR transmits a signal to its major substrates, insulin receptor substrate-1 (IRS-11, insulin receptor substrate-2 (IRS-2), and Shc, a signal that is subsequently transduced by the common signal-transducing pathway, through Ras and Raf, all the way to the nucleus.

The Role of the IGF-I Receptor in Apoptosis

Third-stage larvae (L3) of Onchocerca volvulus were implanted in diffusion chambers in chimpanzees, mangabey monkeys, rhesus monkeys, squirrel monkeys, and inbred strains of mice, jirds, and rats for 3-63 days. At different times during the experimental period, larvae were recovered and assessed for their viability and development. Survival and growth rates were equal regardless of whether the implanted larvae were fresh or cryopreserved. Survival and growth rates of the larvae did not differ among the primate and rodent hosts tested, with the exception of squirrel monkeys and rats, which were resistant to infection. Molting from L3 to fourth-stage larvae began on day 3 and continued through day 14 in the primates and rodents. The primate and rodent models developed in the present study will be useful for the study of the immunology and chemotherapy of onchocerciasis.

Anna Marie Lange

Papers

Survival and development of larval Onchocerca volvulus in diffusion chambers implanted in primate and rodent hosts.