Heparan Sulfate Proteoglycan: An Arbovirus Attachment Factor Integral to Mosquito Salivary Gland Ducts

Abstract

Variants of the prototype Alphavirus, Sindbis (SINV), were used in per os infections of adult female mosquitoes to investigate arbovirus interaction with the salivary gland (SG). Infection of Aedine mosquitoes with AR339, a heparan sulfate proteoglycan (HSPG)-dependent variant, resulted in gross pathology in the SG lateral lobes while infection with TR339, a HSPG-independent variant, resulted in minimal SG pathology. HSPG was detected in the internal ducts of the SG lateral lobes by immunolabeling but not in the median lobe, or beyond the triad structure and external ducts. Reports that human lactoferrin interacts with HSPG, suggested an interference with virus attachment to receptors on vertebrate cells. Pre-incubation of Aedes albopictus cultured C7-10 cells with bovine lactoferrin (bLF) followed by adsorption of SINV resulted in earlier and greater intensity of cytopathic response to TR339 compared with AR339. Following pre-treatment of C7-10 cells with bLF, plaques from tissue culture-adapted high-titer SINVTaV-GFP-TC were observed at 48 h post-infection (p.i.), while plaques from low-titer SINVTaV-GFP-TC were not observed until 120 h p.i. Confocal optics detected this reporter virus at 30 days p.i. in the SG proximal lateral lobe, a region of HSPG-immunolocalization. Altogether these data suggest an association between SINV and HSPG in the host mosquito.

Infection pattern and transmission potential of chikungunya virus in two New World laboratory-adapted Aedes aegypti strains

“…In contrast, the CHIKV infection pattern of ORL salivary glands, in which the medial lobe did not contain detectable viral antigen, was similar to that of SINV in Ae. aegypti 42 43 . Around one third of the mosquitoes of both strains did not contain detectable quantities of CHIKV in their saliva at 7 dpi, even though 100% of salivary glands were infected with median virus titres in ORL salivary glands being 1.7x higher than in those of HWE.…”

“…albopictus and Ae. aegypti , which had been intrathoracically injected with SINV or fed with SINV-containing bloodmeals, respectively 42 43 . Salivary ducts of SINV-infected and non-infected salivary glands stained positive in TUNEL assays.…”

Tissue Barriers to Arbovirus Infection in Mosquitoes

“…albopictus or Ae. aegypti [ 40 , 41 , 45 , 46 ]. Thus, Salazar and colleagues speculated that the distal lateral lobes of salivary glands in aedine mosquitoes are the site containing receptors to enable endocytosis of arboviruses [ 41 ].…”

“…The authors speculated that the differences in transcription profiles of lateral and median lobes account for the difference in susceptibility to virus infection. In the internal ducts of the lateral lobes, cuticular filamentous membrane extensions were detected, which are absent in the median lobe of the salivary glands [ 46 ]. These membranous extensions contained heparan-sulfate proteoglycan (HSPG).…”

“…It was concluded that HSPG might act as an attachment factor for certain arboviruses within the salivary gland ducts. Ciano and colleagues suggested that prominent cytopathic effects in the lateral lobes allows for virus release [ 46 ], whereas HSPG could act as a sponge to retain virus in the lateral lobes. Earlier, it was hypothesized that transmissible virus originates in the duct wall of mosquito salivary glands [ 114 ].…”