Amyloidosis in transgenic mice expressing murine amyloidogenic apolipoprotein A-II (Apoa2)

Abstract

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.

C-terminal sequence of amyloid-resistant type F apolipoprotein A-II inhibits amyloid fibril formation of apolipoprotein A-II in mice

“…We could not explain the mechanisms underlying the reduced amyloidogenicity of APOA2B from the in vivo polymerization analysis. Genetic analyses suggested that higher levels of cholesterol and larger particles of HDL were present in the plasma of mice with APOA2B compared with mice with APOA2C (15,34) and that it was due to an Ala-to-Val substitution at position 38 (35). In fact, we found that i.v.…”

“…ApoA-II proteins in plasma are primarily distributed in HDL 3 particles (15,32). To determine the effects of the polymorphism of apoA-II protein on lipoprotein distribution, we examined the properties of HDL and levels of ApoAs and cholesterols in B6.SPRET-Apoa2 f mice (Fig.…”

“…We also analyzed the ability of APOA2F peptides to polymerize into amyloid fibrils in vitro. In previous studies, we found that injection of a very small amount of AApoAII amyloid fibrils markedly accelerated amyloid deposition (13)(14)(15). We demonstrated that mice with APOA2F were absolutely resistant against senile amyloidosis, even after induction of amyloidosis by injection with type C AApoAII fibrils.…”

“…Apolipoprotein (apo) A-II is the second most abundant apolipoprotein in human and mouse plasma high-density lipoproteins (HDLs) (11) and the most important protein associated with murine senile amyloidosis because it is the precursor of amyloid fibrils (AApoAII) (12)(13)(14)(15). Seven alleles of the apoA-II gene have been found among inbred strains of mice, with polymorphisms in 15 nucleotide positions comprising eight amino acid positions (16).…”

“…We previously reported a unique mechanism in which N-and C-terminal peptides of apoA-II protein associated into amyloid fibrils in vitro (23) according to the nucleation-dependent polymerization model, which can explain the general mechanisms of amyloid fibril formation (24)(25)(26)(27)(28). The 11-residue amino acid sequence from positions [6][7][8][9][10][11][12][13][14][15][16] in the N terminus of apoA-II protein is critical for polymerization into amyloid fibrils. The 18-residue amino acid sequence from positions 48-65 in the C terminus of apoA-II is also necessary for nucleation, but not for the extension phase.…”