Differential gene transcription and sequence variation in island foxes (Urocyon littoralis) with amyloid A (AA) amyloidosis

The island fox (Urocyon littoralis) is an endangered species that lives exclusively on the California Channel islands and has a high prevalence (34%) of amyloid A (AA) amyloidosis. AA amyloidosis is a fatal misfolded protein... [ view full abstract ]

The island fox (Urocyon littoralis) is an endangered species that lives exclusively on the California Channel islands and has a high prevalence (34%) of amyloid A (AA) amyloidosis. AA amyloidosis is a fatal misfolded protein disease that occurs secondary to chronic infection or inflammation and intermittent or prolonged elevation of the acute phase protein serum amyloid A (SAA). The majority of island foxes die with evidence of chronic infectious diseases (88%), yet not all animals develop AA amyloidosis. The prevalence of AA amyloidosis differs between the six genetically distinct, island-specific subspecies, and amyloidosis is not reported in the island foxes’ nearest genetic relative, the mainland gray fox (Urocyon cinereoargenteus). The objective of this study is to investigate the underlying genetic mechanisms of AA amyloidosis in island foxes. Protein sequencing by mass spectrometry identified an amyloidogenic SAA protein sequence. Gene expression analysis revealed differential upregulation of genes in the SAA transcription pathway in island foxes with AA amyloidosis (n=70 AA pos; n=69 AA neg), including pro-inflammatory cytokines IL-6, IL-1α, and IL-1β, transcription factor cis-enhancing binding protein (C/EBP-δ), and SAA. This suggests an IL-6 mediated pathway driving SAA expression. While SAA gene expression was elevated in diseased individuals, SAA in serum was not elevated, indicating that gene expression more reliably correlates with disease status. Utilizing high through-put gene sequencing, 14 SNPs unique to all island fox subspecies were identified in the region of the SAA gene family, including a SNP in the C/EBP binding site of SAA2. Together, these studies identify key mediators of SAA gene expression in island foxes with AA amyloidosis and a SNP that lies within the SAA transcription pathway. These findings contribute to the understanding of genetic influences on AA amyloidosis in foxes and may help formulate targeted treatment strategies for foxes and other affected wildlife species.