Proteasome Inhibition Is an Effective Treatment Strategy for Microsporidia Infection in Honey Bees

Abstract

The microsporidia Nosema ceranae is an obligate intracellular parasite that causes honey bee mortality and contributes to colony collapse. Fumagillin is presently the only pharmacological control for N. ceranae infections in honey bees. Resistance is already emerging, and alternative controls are critically needed. Nosema spp. exhibit increased sensitivity to heat shock, a common proteotoxic stress. Thus, we hypothesized that targeting the Nosema proteasome, the major protease removing misfolded proteins, might be effective against N. ceranae infections in honey bees. Nosema genome analysis and molecular modeling revealed an unexpectedly compact proteasome apparently lacking multiple canonical subunits, but with highly conserved proteolytic active sites expected to be receptive to FDA-approved proteasome inhibitors. Indeed, N. ceranae were strikingly sensitive to pharmacological disruption of proteasome function at doses that were well tolerated by honey bees. Thus, proteasome inhibition is a novel candidate treatment strategy for microsporidia infection in honey bees.

Paromomycin Reduces Vairimorpha (Nosema) ceranae Infection in Honey Bees but Perturbs Microbiome Levels and Midgut Cell Function

“…The honey bee experiments were performed as before [10,18]. Source colonies for the bees were outbred colonies in New York, New York, consisting of a typical mix of the Apis mellifera subspecies that is found in North America.…”

“…V. ceranae spores were obtained from infected individuals for use in these infection studies [10]. In addition, an isolate was obtained from this colony and serially passaged through the bees, as performed previously [19].…”

“…At three days post-infection, honey bees in individual cages were fed sucrose solution alone or sucrose solution containing paromomycin (at doses from 0.25 to 1 mg/mL). After 4 days of drug feeding, the honey bee midguts were dissected and crushed in 0.5 mL of water, then the number of mature spores was counted by light microscopy [21], as previously described [10,18]. In parallel, qPCR was used on harvested midgut tissue (pooled from bees in the specific group) to determine the relative amount of V. ceranae genome equivalents versus host genome equivalents.…”

“…DNA extraction was performed using a modified "smash and grab" DNA miniprep protocol, as described previously [10]. The resulting DNA was used as a template for qPCR to determine the levels of infection of Vairimorpha sp.…”

“…Additionally, fumagillin may impact host cell function at high doses, V. ceranae may be able to evade suppression in some circumstance [9], and the future availability of fumagillin is also uncertain. Many promising alternative strategies for the mitigation of V. ceranae infection are now being pursued (see [10] and references therein).…”