AA amyloidosis is one of the principal causes of morbidity and mortality in captive cheetahs (Acinonyx jubatus), which are in danger of extinction, but little is known about the underlying mechanisms. Given the transmissible characteristics of AA amyloidosis, transmission between captive cheetahs may be a possible mechanism involved in the high incidence of AA amyloidosis. In this study of animals with AA amyloidosis, we found that cheetah feces contained AA amyloid fibrils that were different from those of the liver with regard to molecular weight and shape and had greater transmissibility. The infectious activity of fecal AA amyloid fibrils was reduced or abolished by the protein denaturants 6 M guanidine⅐HCl and formic acid or by AA immunodepletion. Thus, we propose that feces are a vehicle of transmission that may accelerate AA amyloidosis in captive cheetah populations. These results provide a pathogenesis for AA amyloidosis and suggest possible measures for rescuing cheetahs from extinction.feces ͉ transmissibility

Murine senile [apolipoprotein A-II amyloid (AApoAII)] and reactive [protein A amyloid (AA)] amyloidosis are reported to be transmissible diseases via a seeding mechanism similar to that observed in the prion-associated disorders, although de novo amyloidogenesis and the progression of AApoAII or AA amyloidosis remain unclear. We examined the effect of co-injection of AApoAII and AA fibrils and multiple inflammatory stimuli in R1.P1-Apoa2(c) mice with the amyloidogenic Apoa2(c) allele. Both AApoAII and AA amyloidosis could be induced in this system, but the two types of amyloid fibrils preferentially promote the formation of the same type of fibrils while inhibiting the formation of the other. Furthermore, we demonstrate that AA or AApoAII amyloidosis could be cross-seeded by predeposited AApoAII or AA fibrils and that the predeposited amyloid fibrils were degraded when the fibril formation was reduced or stopped. In addition, a large proportion of the two amyloid fibrils colocalized during the formation of new fibrils in the spleen and liver. Thus, we propose that AApoAII and AA can both cross-seed and cross-compete with regard to amyloid formation, depending on the stage of amyloidogenesis. These results will aid in the clarification of the mechanisms of pathogenesis and progression of amyloid disorders.

In mice, apolipoprotein A-II (apoA-II) self-associates to form amyloid fibrils (AApoAII) in an age-associated manner. We postulated that the two most important factors in apoA-II amyloidosis are the Apoa2 c allele, which codes for the amyloidogenic protein APOA2C (Gln5, Ala38) and transmission of amyloid fibrils. To characterize further the contribution of the Apoa2 c allele to amyloidogenesis and improve detection of amyloidogenic materials, we established transgenic mice that overexpress APOA2C protein under the cytomegalovirus (CMV) immediate early gene (CMV-IE) enhancer/ chicken b promoter. Compared to transgene negative (Tg À/À ) mice that express apoA-II protein mainly in the liver, mice homozygous (Tg þ / þ ) and heterozygous (Tg þ /À ) for the transgene express a high level of apoA-II protein in many tissues. They also have higher plasma concentrations of apoA-II, higher ratios of ApoA-II/apolipoprotein A-I (ApoA-I) and higher concentrations of high-density lipoprotein (HDL) cholesterol. Following injection of AApoAII fibrils into Tg þ / þ mice, amyloid deposition was observed in the testis, liver, kidney, heart, lungs, spleen, tongue, stomach and intestine but not in the brain. In Tg þ / þ mice, but not in Tg À/À mice, amyloid deposition was induced by injection of less than 10 À8 mg AApoAII fibrils. Furthermore, deposition in Tg þ / þ mice occurred more rapidly and to a greater extent than in Tg À/À mice. These studies indicate that increased levels of APOA2C protein lead to earlier and greater amyloid deposition and enhanced sensitivity to the transmission of amyloid fibrils in transgenic mice. This transgenic mouse model should prove valuable for studies of amyloidosis.