AA amyloidosis in chinese shar-pei dogs: Immunohistochemical and amino acid sequence analyses

Amyloidosis in Chinese Shar-pei dogs is unique because of certain similarities to familial Mediterranean fever in humans. It is also of interest that renal amyloid deposits in Shar-peis are known to predominate commonly in the medullary interstitium while glomerular amyloidosis is the characteristic clinicopathologic feature in other dog breeds. Our immunohistochemical and biochemical studies confirm that systemic familial amyloidosis occurring in Shar-pei dogs is of the AA-type. The amyloid protein had a blocked N-terminus but deblocking and sequence analysis ofpeptides obtained after cyanogen bromide and BNPS-skctole cleavage provided an amino acid sequence conforming to positions 1 through 91 of dog SAA. The confirmed sequence of Shar-pei protein AA differed from the previously reported dog protein AA sequence by variations present at positions 7 and 17. Specifically, a Ser/Gly variation was present at position 7 and a Leu/Trp variation was not present at position 17 in Shar-pei protein AA (i.e., only Trp was present at position 17). These results thus extend the number of SAA isoforms confirmed to be associated with dog AA amyloidosis from two to three. An insert of eight amino acids (represented by positions 69-76) was confirmed between residues corresponding to positions 69 and 70 of human protein AA, which is consistent with the previously reported sequence in non-Shar-pei breeds. Histones, confirmed by sequence analysis, were present in several SDS-PAGE bands (molecular masses of approximately 18.5, 17.5, and 13 kDa) from purified renal medullary amyloid of one Shar-pei dog. The significance of these histones with respect to the preponderant renal medullary deposition of amyloid in Shar-pei dogs is not known, but similar histone fractions have previously been observed with renal AA amyloid deposits.