Hippocampal damage in mouse and human forms of systemic autoimmune disease

Abstract

Systemic lupus erythematosus (SLE) is frequently accompanied by neuropsychiatric (NP) and cognitive deficits of unknown etiology. By using autoimmune MRL-lpr mice as an animal model of NP-SLE, we examine the relationship between autoimmunity, hippocampal damage, and behavioral dysfunction. Fluoro Jade B (FJB) staining and anti-ubiquitin (anti-Ub) immunocytochemistry were used to assess neuronal damage in young (asymptomatic) and aged (diseased) mice, while spontaneous alternation behavior (SAB) was used to estimate the severity of hippocampal dysfunction. The causal relationship between autoimmunity and neuropathology was tested by prolonged administration of the immunosuppressive drug cyclophosphamide (CY). In comparison to congenic MRL +/+ controls, SAB acquisition rates and performance in the "reversal" trial were impaired in diseased MRL-lpr mice, suggesting limited use of the spatial learning strategy. FJB-positive neurons and anti-Ub particles were frequent in the CA3 region. Conversely, CY treatment attenuated the SAB deficit and overall FJB staining. Similarly to mouse brain, the hippocampus from a patient who died from NP-SLE showed reduced neuronal density in the CA3 region and dentate gyrus, as well as increased FJB positivity in these regions. Gliosis and neuronal loss were observed in the gray matter, and T lymphocytes and stromal calcifications were common in the choroid plexus. Taken together, these results suggest that systemic autoimmunity induces significant hippocampal damage, which may underlie affective and cognitive deficits in NP-SLE.

FIGURE 1

Representative micrographs showing Fluoro Jade B (FJB) and ubiquitin (Ub) labeling in the CA3 region. Numerous FJB-positive cells with neuronal morphology (shown by arrows) were common in brains from MRL-lpr mice (A) in comparison to asymptomatic MRL +/+ controls (B). Intensely immunoreactive Ub-positive spherical particles (shown by arrows) were detected in brains from diseased lupus-prone mice (C), likely reflecting degenerating axon terminals. Such particles were not abundant in the control brains (D). ×400 in A,B; ×1,000 in C,D. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com].

FIGURE 2

Total numbers of Fluoro Jade B (FJB)-positive and ubiquitin (Ub)-positive cells and the immune status in MRL mice at different ages. Cells/particles staining for FJB or Ub significantly increased following the onset of autoimmunity in older MRL-lpr mice (A). Spleen weight (B) and antinuclear antibody (ANA) levels (C) also increased significantly with age, confirming the autoimmune status in the MRL-lpr substrain.

FIGURE 3

Effects of immunosuppressive treatment on brain pathology in MRL mice. Cyclophosphamide (CY) treatment appeared to attenuate the incidence of Fluoro Jade B (FJB)-positive cells in the hippocampus (A) and significantly reduced the staining in other brain regions of MRL-lpr mice (B).

FIGURE 4

Chronic mononuclear inflammatory cells in the human brain. H&E staining showed a cluster of lymphocytes (arrow) in the choroid plexus of the lupus patient (A), but not in the control brain (B). Subsequent immunohistochemical staining for leukocyte common antigen (LCA), CD3, CD4, and CD8 antigens (shown by arrows) confirmed that the cells in the stroma were T lymphocytes (C), while the control brain was negative for the same markers (D). ×100 in A,B; ×200 in C,D; ×600 (inset in A).

FIGURE 5

H&E staining of the parietotemporal cortex and periventricular regions of the human brain. “Dying neurons” (shown by arrows) and satellitosis (Inset) in the gray matter of the lupus patient (A). Normal neurons and resting glial cells in the control brain (B). Numerous particles identified as “brain sand” were common around the ventricles in the patient’s brain (C), and were rarely seen in the control (D). LV, lateral ventricle. ×200 in A,B); ×400 in C,D.

FIGURE 6

Neuronal loss and degeneration in the human hippocampus as revealed by H&E and FJB staining. The brain from the neuropsychiatric-systemic lupus erythematosus (NP-SLE) patient revealed a paucity of neurons and satellitosis (arrow) in the CA3 region (A), while the control brain showed normal neuronal density (B). A patchy area of cell loss was also seen in the dentate gyrus (arrow) of the lupus brain (C), but not in the control (D). Subsequently, bright green Fluoro Jade B (FJB)-positive neurons confirmed a degenerative process in the CA3 region (E), which was not observed in the control brain (F). ×400 in A–D; ×200 in E,F; ×600 (inset in E, under oil immersion). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com].