Needle-shaped amyloid deposition in rat mammary gland: evidence of a novel amyloid fibril protein

Amyloidosis is an extremely rare event in rats. In this study, we report that lipopolysaccharide binding protein (LBP) is the most likely amyloidogenic protein in rat mammary amyloidosis. Histologically, corpora amylacea (CA) and stromal amyloid (SA) were observed in rat mammary glands, and needle-shaped amyloid (NA) was also observed on the surface or gap of CA and SA. Following surveillance in aged rats, NA was observed in 62% of mammary tumours, 25% of male mammary glands and 83% of female mammary glands. Proteomic analysis showed that lactadherin was a major constitutive protein of CA and SA, and both were positive following immunohistochemistry with anti-lactadherin antibodies. In the same analysis, LBP was detected as a prime candidate protein in NA, and NA was positive following immunohistochemistry and immunoelectron microscopy with anti-LBP antibody. Furthermore, synthetic peptides derived from rat LBP formed amyloid fibrils <i>in vitro</i>. Overall, these results provide evidence that LBP is an amyloid precursor protein of NA in rat mammary glands.