Abstract
Alpha-Gal Syndrome (AGS) is an IgE-mediated delayed-type hypersensitivity reaction to the oligosaccharide galactose-α-1, 3-galactose (α-gal) injected into humans from the lone-star tick (Amblyomma americanum) bite. Indeed, α-gal is discovered in salivary glands of lone-star tick; however, the tick’s specific intrinsic factors involved in endogenous α-gal production and presentation to host during hematophagy are poorly understood. This study aimed to investigate the functional role of two tick enzymes, α-D-galactosidase (ADGal) and β-1,4 galactosyltransferases (β-1,4GalT), in endogenous α-gal production, carbohydrate metabolism, and N-glycan profile in lone-star tick. The ADGal enzyme cleaves terminal α-galactose moieties from glycoproteins and glycolipids, whereas β-1,4GalT transfers α-galactose to a β1,4 terminal linkage acceptor sugars—GlcNAc, Glc, and Xyl—in various processes of glycoconjugate synthesis. An RNA interference approach was utilized to silence ADGal and β-1,4GalT in Am. americanum to examine their function in α-gal metabolism in tick and AGS onset. Silencing of ADGal led to the significant downregulation of genes involved in galactose metabolism and transport in Am. americanum. Immunoblot and N-glycan analysis of the Am. americanum salivary glands showed a significant reduction in α-gal levels in silenced tissues. However, there was no significant difference in the level of α-gal in β-1,4GalT-silenced tick salivary glands. A basophil-activation test showed a decrease in the frequency of activated basophil by ADGal-silenced salivary glands. These results provide an insight into the roles of ADGal and β-1,4GalT in α-gal production and presentation in ticks and the probable involvement in the onset of AGS.
Highlights
Lone-star ticks (Amblyomma americanum) are highly competent arthropod vectors, which transmit a wide variety of viral and bacterial pathogens to mammals (Childs and Paddock, 2003; Goddard and Varela-Stokes, 2009; Sayler et al, 2014)
Transcriptional expression was normalized against the unfed tick salivary gland. b-actin and histone, two housekeeping genes, were used to normalize the gene expression
We investigated the role of differentially expressed tick molecules during prolonged blood-feeding on the host, i.e., aD-galactosidase, an enzyme that catalyzes the breakdown of galactose from glycoproteins or glycolipids, and b-1,4-galactosyltransferase (b-1,4-GalT), an enzyme that is involved in the synthesis of Galb1-4-GlcNacdisaccharide unit of glycoconjugates (Hennet, 2002; Calhoun et al, 1985)
Summary
Lone-star ticks (Amblyomma americanum) are highly competent arthropod vectors, which transmit a wide variety of viral and bacterial pathogens to mammals (Childs and Paddock, 2003; Goddard and Varela-Stokes, 2009; Sayler et al, 2014). Alpha-gal is found in the tissues of most mammals, including cattle, sheep, and swine but notably absent from humans and Great Apes. AGS is already common in several world regions; within 10 years, the US alone has confirmed a spike in cases from 12 in 2009 to >34,000 in 2019 (Binder et al, 2021); most strongly attributed to sensitization to a-gal is Am. americanum (Crispell et al, 2019). Several studies have reported the presence of a-gal in the midguts of Ixodes ricinus, salivary glands of Haemaphysalis longicornis and Am. sculptum, and both the salivary glands and saliva of Ixodes scapularis and Am. americanum (Hamsten et al, 2013a; Hamsten et al, 2013b; Araujo et al, 2016; Chinuki et al, 2016; Crispell et al, 2019; Choudhary et al, 2021)
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