Proteomic Analysis of Highly Prevalent Amyloid A Amyloidosis Endemic to Endangered Island Foxes

Abstract

Amyloid A (AA) amyloidosis is a debilitating, often fatal, systemic amyloid disease associated with chronic inflammation and persistently elevated serum amyloid A (SAA). Elevated SAA is necessary but not sufficient to cause disease and the risk factors for AA amyloidosis remain poorly understood. Here we identify an extraordinarily high prevalence of AA amyloidosis (34%) in a genetically isolated population of island foxes (Urocyon littoralis) with concurrent chronic inflammatory diseases. Amyloid deposits were most common in kidney (76%), spleen (58%), oral cavity (45%), and vasculature (44%) and were composed of unbranching, 10 nm in diameter fibrils. Peptide sequencing by mass spectrometry revealed that SAA peptides were dominant in amyloid-laden kidney, together with high levels of apolipoprotein E, apolipoprotein A-IV, fibrinogen-α chain, and complement C3 and C4 (false discovery rate ≤0.05). Reassembled peptide sequences showed island fox SAA as an 111 amino acid protein, most similar to dog and artic fox, with 5 unique amino acid variants among carnivores. SAA peptides extended to the last two C-terminal amino acids in 5 of 9 samples, indicating that near full length SAA was often present in amyloid aggregates. These studies define a remarkably prevalent AA amyloidosis in island foxes with widespread systemic amyloid deposition, a unique SAA sequence, and the co-occurrence of AA with apolipoproteins.

Longitudinal study of experimental induction of AA amyloidosis in mice seeded with homologous and heterologous AA fibrils

“…Systemic AA amyloidosis harms various organs, in particular the kidneys [28]. In the present study, the order of severity of AA deposition (from highest to lowest) was spleen, liver, kidney, and intestine.…”

Systemic Amyloid A Amyloidosis in Island Foxes (Urocyon littoralis)

“…The overall prevalence of amyloidosis in this population was previously estimated at 34% (109/321). 11 Prevalence among each island subspecies was further evaluated in the present study and ranged from approximately 23 – 50% [San Nicolas (22.6%), Santa Catalina (29.5%), Santa Cruz (33.3%), Santa Rosa (36.4%), San Clemente (38.9%), and San Miguel (50.0%)] (Table 1). The prevalence of amyloidosis in the San Clemente subspecies was significantly higher than in the San Nicolas subspecies (p = 0.02).…”

“…The amyloidogenic SAA1.1 isoform in humans and island fox SAA both have a high predicted aggregation potential at amino acid segment 2–7. 11,25 An SAA promoter mutation is also a possibility, as described in the cheetah. 59 …”

“…Positive controls included a Shar Pei dog kidney with amyloid and an island fox kidney with AA amyloid confirmed by mass spectrometry. 11 Additional controls included (i) rabbit IgG isotype substitution of the primary antibody on island fox tissues containing amyloid and (ii) primary antibody on island fox tissues lacking congophilic deposits.…”

“…2 Recent catastrophic population declines due to non-native predators 7,40 and canine distemper 47 left some islands with as few as 15 individuals. Disease surveillance through post-mortem examination revealed a high prevalence of systemic amyloid A (AA) amyloidosis, 11 which poses a threat to species recovery.…”