Production of the yolk protein precursor vitellogenin is mediated by target of rapamycin (TOR) in the soft tick Ornithodoros moubata (Acari: Argasidae)

Initiation of vitellogenesis by blood feeding is essential for egg maturation in ticks. Nutrients derived from the blood meal are utilized by female ticks to synthesize the yolk protein precursor vitellogenin (Vg). Engorged Ornithodoros moubata ticks can synthesize Vg whether mated or virgin, thus O. moubata is an excellent model for studying the relative roles of blood feeding and mating in tick vitellogenesis. Injection of rapamycin into engorged O. moubata resulted in a reduction of ovarian growth and yolk accumulation in the oocytes of mated females. OmVg expression in the midgut and fat body and protein concentrations in the hemolymph significantly decreased in mated ticks after injection with rapamycin, indicating that inhibition of the nutrient-sensing target of rapamycin (TOR) pathway disrupts egg maturation at the levels of Vg expression and synthesis. These results suggest that the TOR-signaling pathway induces vitellogenesis in response to nutritional stimulation after a blood meal in O. moubata and is functionally independent of the mating-induced pathway.

Programmed necrosis, not apoptosis, is a key mediator of cell loss and DAMP-mediated inflammation in dsRNA-induced retinal degeneration

There is no known treatment for the dry form of an age-related macular degeneration (AMD). Cell death and inflammation are important biological processes thought to have central role in AMD. Here we show that receptor-interacting protein (RIP) kinase mediates necrosis and enhances inflammation in a mouse model of retinal degeneration induced by dsRNA, a component of drusen in AMD. In contrast to photoreceptor-induced apoptosis, subretinal injection of the dsRNA analog poly(I : C) caused necrosis of the retinal pigment epithelium (RPE), as well as macrophage infiltration into the outer retinas. In Rip3(-/-) mice, both necrosis and inflammation were prevented, providing substantial protection against poly(I : C)-induced retinal degeneration. Moreover, after poly(I : C) injection, Rip3(-/-) mice displayed decreased levels of pro-inflammatory cytokines (such as TNF-α and IL-6) in the retina, and attenuated intravitreal release of high-mobility group box-1 (HMGB1), a major damage-associated molecular pattern (DAMP). In vitro, poly(I : C)-induced necrosis were inhibited in Rip3-deficient RPE cells, which in turn suppressed HMGB1 release and dampened TNF-α and IL-6 induction evoked by necrotic supernatants. On the other hand, Rip3 deficiency did not modulate directly TNF-α and IL-6 production after poly(I : C) stimulation in RPE cells or macrophages. Therefore, programmed necrosis is crucial in dsRNA-induced retinal degeneration and may promote inflammation by regulating the release of intracellular DAMPs, suggesting novel therapeutic targets for diseases such as AMD.