Non-prion-type transmission in A53T α-synuclein transgenic mice: a normal component of spinal homogenates from naïve non-transgenic mice induces robust α-synuclein pathology.

Abstract

identity of the inducing factor(s) in tissue homogenates has not been unequivocally resolved. To determine whether degenerating tissues might contain non-αS components that could induce pathology in M83+/− mice, we conducted brain injections of young M83+/− mice with spinal cord (SC) homogenates prepared from motor-impaired M83+/+ mice, motor-impaired transgenic mice expressing the G93A variant of human superoxide dismutase-1 (hSOD-1), and healthy non-transgenic (NTg) mice. The intracerebral (hippocampal) injection of SC homogenates from affected M83+/+ mice served as a positive control and these mice were sacrificed at 120 days post-injection (DPI), at which time αS pathology was predominantly observed in the forebrain (hippocampus and entorhinal cortex), but also distributed in the midbrain, brainstem, and SC (Supplemental Fig. 1; Table 1). For the intrahippocampal injections of SC homogenates from paralyzed G93A hSOD-1 and NTg mice, the study design was to sacrifice mice at 180 DPI to assess pathology levels. Unexpectedly, two of the M83+/− mice injected with SC homogenate from paralyzed G93A hSOD-1 mice developed motor impairments prior to 180 DPI, leading to complete hind limb paralysis (Table 1). These two mice and the other three asymptomatic mice, sacrificed at 180 DPI, all had prominent αS inclusion pathology with a distribution typical of aged M83 mice, with additional pathology observed in the hippocampus (Fig. 1; Table 1). Even more surprisingly, 4 out of the 5 M83+/− mice injected in the hippocampus with SC homogenates from NTg mice also developed M83-type motor impairment and paralysis (Table 1). M83+/− mice injected with either G93A hSOD-1 or NTg SC homogenates showed similar levels of αS inclusion pathology (Fig. 1; Table 1). One pre-symptomatic mouse from each of these cohorts was sacrificed at 105 DPI to survey for earlier pathologic induction and these also presented with αS inclusion The injection of tissue homogenates from diseased animals into naive animals to induce a neurodegenerative phenotype is a feature that defines “prion-like” transmission. Several recent studies have demonstrated that transgenic mice expressing human A53T-α-synuclein (αS; Line M83), respond to injections of CNS tissue homogenates containing abundant αS pathology by accelerated onset of CNS pathology with concurrent accelerated motor impairment [1, 3–5, 9]. Homozygous line M83+/+ A53T αS mice naturally develop a severe motor phenotype between 8 and 16 months that is associated with the formation of αS inclusions in the spinal cord, brain stem, thalamus, periaqueductal gray, and motor cortex [2]. Hemizygous M83+/− mice do not begin to develop these phenotypes until 21 months or later [2], but disease can be induced earlier by injection of CNS homogenates from affected M83+/+ mice [5, 9]. Although purified αS protein fibrils can reproduce the effects seen with tissue homogenates [1, 3, 6, 8], the