Intraneuronal β-Amyloid Accumulation: Aging HIV-1 Human and HIV-1 Transgenic Rat Brain

Abstract

The prevalence of HIV-1 associated neurocognitive disorders (HAND) is significantly greater in older, relative to younger, HIV-1 seropositive individuals; the neural pathogenesis of HAND in older HIV-1 seropositive individuals, however, remains elusive. To address this knowledge gap, abnormal protein aggregates (i.e., β-amyloid) were investigated in the brains of aging (>12 months of age) HIV-1 transgenic (Tg) rats. In aging HIV-1 Tg rats, double immunohistochemistry staining revealed abnormal intraneuronal β-amyloid accumulation in the prefrontal cortex (PFC) and hippocampus, relative to F344/N control rats. Notably, in HIV-1 Tg animals, increased β-amyloid accumulation occurred in the absence of any genotypic changes in amyloid precursor protein (APP). Furthermore, no clear amyloid plaque deposition was observed in HIV-1 Tg animals. Critically, β-amyloid was co-localized with neurons in the cortex and hippocampus, supporting a potential mechanism underlying synaptic dysfunction in the HIV-1 Tg rat. Consistent with these neuropathological findings, HIV-1 Tg rats exhibited prominent alterations in the progression of temporal processing relative to control animals; temporal processing relies, at least in part, on the integrity of the PFC and hippocampus. In addition, in post-mortem HIV-1 seropositive individuals with HAND, intraneuronal β-amyloid accumulation was observed in the dorsolateral PFC and hippocampal dentate gyrus. Consistent with observations in the HIV-1 Tg rat, no amyloid plaques were found in these post-mortem HIV-1 seropositive individuals with HAND. Collectively, intraneuronal β-amyloid aggregation observed in the PFC and hippocampus of HIV-1 Tg rats supports a potential factor underlying HIV-1 associated synaptodendritic damage. Further, the HIV-1 Tg rat provides a biological system to model HAND in older HIV-1 seropositive individuals.

Keywords: HIV-1; RNAscope; neurodegenerative diseases; prepulse inhibition; β-amyloid.

Figure 1

IHC double staining revealed an abnormal intraneuronal accumulation of β-amyloid in the HIV-1 Tg rat. (A,B) Representative confocal images of β-amyloid expression and co-localization with NeuN (neuronal marker) in the mPFC and CA3 area of hippocampus in F344/N and HIV-1 Tg rats. The Alexa 488 green fluorescence indicates expression of β-amyloid; the Alexa 594 red fluorescence represents NeuN signals. (C) Representative images of amyloid precursor protein (APP) expression in the mPFC and hippocampal CA3 region in HIV-1 Tg and F344/N rats. APP expression is indicated by green fluorescence. (D) HIV-1 Tg rats exhibited abnormal accumulation of β-amyloid in both the mPFC and hippocampal CA3 region relative to control animals. (E) Statistical evaluation of APP in the mPFC and hippocampal CA3 areas compared to control rat. Statistically significant (p ≤ 0.05) differences between HIV-1 Tg and control animals are indicated using an *.

Figure 2

Co-localization of DiOlistically labeled neurons and β-amyloid immunostaining in the hippocampus, cortex, and prefrontal cortex. The yellow circle indicated the DiOlistically labeled neuron co-localizing with β-amyloid immunostaining positive signal.

Figure 3

Neurocognitive assessments of temporal processing were evaluated using gap-prepulse inhibition (gap-PPI). The mean peak ASR amplitude response curve for gap-PPI was used to calculate prepulse inhibition in HIV-1 Tg and control rats from PD 240 to PD 540. (A) At the genotypic level, HIV-1 Tg animals exhibited a profound alteration in the progression of temporal processing relative to control animals. (B,C) Fundamentally, both male (B) and female (C) HIV-1 Tg animals displayed prominent alterations in the progression of temporal processing; the magnitude of these alterations was influenced by biological sex.

Figure 4

β-amyloid accumulation in the dorsolateral PFC (dlPFC) and hippocampal dentate gyrus from human autopsy HIV-infected cases with HAND. (A–F) Representative images of double staining of β-amyloid with NeuN (a neuronal marker) in the dlPFC (A–C), and in the hippocampus from human autopsy (D–F). (G,H) Confocal images of amyloid precursor protein expression in the dlPFC and hippocampus. (I) Quantification of β-amyloid and amyloid precursor protein expression in the dlPFC and hippocampus.