Interleukin-5: an indicator of mild cognitive impairment in patients with type 2 diabetes mellitus - a comprehensive investigation ranging from bioinformatics analysis to clinical research

Abstract

Purpose: Neuroinflammation constitutes an underlying mechanism for cognitive impairment. Here, we endeavor to scrutinize the potential contribution of interleukin-5 (IL-5) towards mild cognitive impairment (MCI), and to assess its diagnostic value for MCI in patients with type 2 diabetes mellitus (T2DM).

Methods: RNA-seq was used to explore the potential neuroinflammation factors in the hippocampus of diabetic mice with cognitive decline. Additionally, the promising risk factor was verified in animals. Finally, the association between IL-5 levels and cognitive function and its diagnostic value for MCI were assessed.

Results: In animals, up-regulated IL-5 mRNA and protein levels were detected by RNA-seq and (or) verified experiments in the hippocampus of diabetic db/db mice with cognitive decline, compared to those of db/m mice without diabetes. In human, compared to diabetic patients without MCI, those with MCI demonstrate elevated levels of IL-5. It is natively associated with Montreal Cognitive Assessment (MoCA) scores, reflecting global cognitive function, and positively correlated with Trail Making Test A (TMTA) scores, reflecting information processing speed. Furthermore, an elevated level of IL-5 is identified as a risk factor for MCI, and a factor that influences TMTA scores. Finally, it is recommended that the cut-off value for IL-5 in the diagnosis of MCI is 22.98 pg/mL, with a sensitivity of 68.6% and specificity of 72.9%.

Conclusions: IL-5 is considered a risk factor for MCI in T2DM patients and is associated with their performance in information processing speed. Moreover, an elevated level of IL-5 is a plausible biomarker for MCI in T2DM patients.

Keywords: Interleukin-5; Mild cognitive impairment; Neuroinflammation; Type 2 diabetes mellitus.

Fig. 1

Cognitive performance and RNA-seq results of mice with and without diabetes. Notes for Fig. 1: ^*P < 0.05, ^**P < 0.01; Fig. 1A and B showed the difference of body weight and fasting plasma glucose of db/db mice and db/m mice. Figure 1 C and 1D showed the difference of escape latency and path length of db/db mice and db/m mice. Figure 1E showed the trajectory of movement in water maze of db/db mice and db/m mice. Figure 1 F and 1G showed the difference of frequency of crossing the platform area and percentage of the time spent in the target quadrant of db/db mice and db/m mice. Figure 1 H showed the difference of swimming speed of db/db mice and db/m mice. Figure 1I showed the heatmap of RNA-seq results of db/db mice and db/m mice. Figue 1 J and 1 K showed the scatter plot and volcano plot of db/db mice VS db/m mice

Fig. 2

KEGG pathway analysis of DEGs in db/db mice and db/m mice. Notes for Fig. 2: The size of bubbles represents the number of genes in the pathway, while the color of bubbles represents P-value

Fig. 3

GO pathway analysis of DEGs in db/db mice and db/m mice. Notes for Fig. 3: The red bars represent the Biological Process (BP). The green bars represent the Cellular Component (CC) while the blue represent the Molecular Function (MF)

Fig. 4

IL-5 levels and neuroinflammation of mice with and without diabetes. Notes for Fig. 4: ^*P < 0.05, ^**P < 0.01; Fig. 4A showed the IL-5 mRNA levels in db/db mice and db/m mice. Figure 4B showed the image of western blotting for IL-5, while Fig. 4C represent results of western blotting showed in Fig. 4B. Figure 4D showed levels of IL-5 in plasma of db/db mice and db/m mice. Figure 4E F showed the association between IL-5 levels in plasma and frequency of crossing the platform area (or percentage of time spent in the target quadrant) in mice. Figure 4G showed the correlation between IL-5 levels in plasma and swimming speed in mice. Figure 4 H showed the co-location of IBA-1 and CD68 in hippocampus of db/db mice and db/m mice. Figure 4I, 4 J, 4 K and 4 L showed TNF-ɑ, IL-6, IL-1β, and IL-10 levels in hippocampus of db/db mice and db/m mice

Fig. 5

ROC curve of IL-5 for the sensitivity and specificity of MCI. Notes for Fig. 5: It is determined that the diagnostic cut-off value for IL-5 to be 22.98 pg/ml, revealed a sensitivity of 68.6% and specificity of 72.90%. The area under the curve is 0.711. The highest J point of Youden’s index is 0.415. Abbreviations: ROC, receiver operating characteristic; IL-5, interleukin-5; MCI, mild cognitive impairment

Fig. 6

The main content of the research. Notes for Fig. 6: In this study, we first compared the RNA-seq results between diabetic mice (db/db mice) and control mice (db/dm mice). We then validated these sequencing results at both the mRNA and protein levels. Finally, we conducted clinical results to confirm the correlation between IL-5 and cognitive impairment and assessed the diagnostic value of IL-5 for MCI in patients with T2DM