Cytokine expression and microglial activation in progressive supranuclear palsy

Abstract

Although little is known about the etiology of progressive supranuclear palsy (PSP), genetic and epigenetic factors, oxidative injury and inflammation are thought to contribute to its development and/or progression. Evidence for activated glia involvement in PSP has raised the possibility that neuroinflammation may contribute to its pathogenesis. To investigate the correlation between neuroinflammation and PSP, a comparative study was conducted on the patterns of cytokine expression in different regions of the brains of PSP, Alzheimer's disease (AD) patients and normal controls. Our results show different patterns of cytokine expression in each disease, with the expression of IL-1β transcripts being significantly higher in the substantia nigra of PSP than in AD and controls, while AD brains had significantly higher IL-1β expression in the parietal cortex compared to PSP and controls. In addition, expression of TGFβ was significantly higher in the cortical areas (particularly frontal and parietal lobes) of AD compared to PSP and controls. These results show a disease-specific topographical relationship among the expression of certain cytokines (IL-1β and TGFβ), microglial activation and neurodegenerative changes, suggesting that these cytokines may contribute to the pathologic process. If so, the use of cytokine-inhibitors and/or other anti-inflammatory agents may be able to slow disease progression in PSP.

Figure 1

Relative expression of transcripts for IL-1β (A), TGFβ1 (B), TNFα (C) and IL-6 (D) in the subthalamic nucleus (ST), caudate nucleus (CD), substantia nigra (SN), frontal cortex (FC), parietal cortex (PC) and occipital cortex (OC) of post-mortem brains from PSP, AD patients and controls. Transcript expression was measured by real time PCR after reverse transcription of total RNA extracted from the dissected tissues. The relative abundance of each transcript is expressed as its ratio to that of the house-keeping gene, GAPDH. Results represent the mean and standard error (n=5 [PSP and AD]; n= 4 [controls]). Statistically-significant differences, * (p < 0.05) and ** (p<0.01), over the corresponding groups are indicated.

Figure 2

Micrographs of representative LN3-staining (HLA-DR) used for assessment of microglial burden in the subthalamic nucleus (a,b), substantia nigra (c,d) and mid-frontal cortex (e,f) of PSP (a, c & e) and AD brains (b, d & f). Insets in Figures 2b and 2c show ramified and a phagocytic (ameboid) microglial cells, respectively. Inset in Figure 2f shows activated microglia associated with a senile plaque. HLA-DR staining was performed by immunohistochemistry on paraffin-embeded tissue from the contralateral areas of the same brains used for cytokine analyses.

Figure 3

A. Microglial burden in the subthalamic nucleus (SN), caudate nucleus (CD), substantia nigra (SN), frontal cortex (FC), parietal cortex (PC) and occipital cortex (OC) of post-mortem brains from PSP and AD patients. Microglial burden was measured after staining for HLA-DR expression by immunohistochemistry with the LN3 antibody followed by image analysis and expressed as the percent of the total area occupied by the LN3 label (LN3 %-area). Scores represent the mean and standard error (n=5). B-E. Linear regression analysis of the correlation between cytokine transcript expression and the microglial burden (MB). Expression of transcripts for IL-1β (B), TGFβ1 (C), TNFα (D) and IL-6 (E) in all six brain areas examined were plotted against the microglial burden scores. Pearson correlation coefficients (r) are indicated in each graph. Statistically significant correlations, * (p < 0.05) and ** (p<0.01), are indicated.