Physical Activity Protects the Pathological Alterations of Alzheimer's Disease Kidneys via the Activation of PACAP and BMP Signaling Pathways

Abstract

Alzheimer's disease (AD) is a neurodegenerative disorder with typical amyloid beta (Aβ) aggregations. Elimination of the Aβ precursors via the kidneys makes the organ a potential factor in the systemic degeneration leading to AD. Pituitary adenylate cyclase-activating polypeptide (PACAP) exerts neuroprotective effects in AD and plays a protective role in kidney pathologies. Increased physical activity is preventive of the formation of AD, but its detailed mechanism and possible connections with PACAP have not been clarified. In the kidneys of AD mice, the effects of physical activity were investigated by comparing wild-type and AD organs. Aβ plaque formation was reduced in AD kidneys after increased training (TAD). Mechanotransduction elevated PACAP receptor expression in TAD mice and normalized the protein kinase A (PKA)-mediated pathways. BMP4/BMPR1 elevation activated Smad1 expression and normalized collagen type IV in TAD animals. In conclusion, our data suggest that elevated physical activity can prevent the AD-induced pathological changes in the kidneys via, at least in part, the activation of PACAP-BMP signaling crosstalk.

Keywords: Alzheimer’s disease; BMP signaling; PACAP; collagen type IV; physical activity.

FIGURE 1

(A) Representative microphotograph of wild-type (WT), Alzheimer’s disease (AD), and trained Alzheimer’s disease (TAD) kidneys stained with hematoxylin and eosin. Overview of the kidney cortex. Original magnification was × 20. Scale bar, 50 μm. Arrows show a representative area for amyloid beta (Aβ) plaque formation. (B) Staining intensity analysis. Representative data of five independent experiments. The staining intensities are presented as bar graphs ± SEM. Asterisks indicate significant (^∗p < 0.05) differences in the staining pixel intensity compared to WT and (^#p < 0.05) compared to AD. (C) Representative microphotographs of WT, AD, and TAD kidneys stained with Congo red. Red colors show Aβ accumulation. Original magnification was × 20. Scale bar, 50 μm.

FIGURE 2

mRNA (A) and protein (B) expressions of pituitary adenylate cyclase-activating polypeptide (PACAP) receptors in the kidneys. The optical density of the signals was measured and the results were normalized to the optical density of the wild type (WT). For (A,B), the numbers below the signals represent the integrated densities of the signals determined by ImageJ software. Asterisks indicate significant (^∗p < 0.05) alterations of expressions as compared to the WT and (^#p < 0.05) compared to Alzheimer’s disease (AD). Representative data of five independent experiments. For reverse transcription PCR (RT-PCR) and for Western blot, actin was used as the control. (C) Statistical analysis of the RT-PCR and Western blot data. All data presented are the averages of at least five different experiments. Statistical analysis was performed with Student’s t-test. All data were normalized on actin and are expressed as the mean ± SEM.

FIGURE 3

mRNA (A) and protein (B) expressions of pituitary adenylate cyclase-activating polypeptide (PACAP) signaling in the kidneys. The optical density of the signals was measured and the results were normalized to the optical density of the controls. For (A,B), the numbers below the signals represent the integrated densities of the signals determined by ImageJ software. Asterisks indicate significant (^∗p < 0.05) alterations of expressions as compared to the wild type (WT) and (^#p < 0.05) compared to Alzheimer’s disease (AD). Representative data of five independent experiments. For reverse transcription PCR (RT-PCR) and for Western blot, actin was used as the control. (C) Statistical analysis of the RT-PCR and Western blot data. All data presented are the averages of at least five different experiments. Statistical analysis was performed with Student’s t-test. All data were normalized on actin and are expressed as the mean ± SEM. (D) Immunohistochemistry of CREB in the cortex of the kidneys. Arrows show the apical part of the proximal tubules. Magnification was made with × 60 objective. Scale bar, 20 μm.

FIGURE 4

mRNA (A) and protein (B) expressions of bone morphogenetic protein (BMP) signaling in the kidneys. For reverse transcription PCR (RT-PCR) and for Western blot, actin was used as the control. The optical density of the signals was measured and the results were normalized to the optical density of the controls. For panels (A) and (B), the numbers below the signals represent the integrated densities of the signals determined by ImageJ software. Asterisks indicate significant (^∗p < 0.05) alterations of expressions as compared to the wild type (WT) and (^#p < 0.05) compared to Alzheimer’s disease (AD). Representative data of five independent experiments. (C) Statistical analysis of the RT-PCR and Western blot data. All data presented are the averages of at least five different experiments. Statistical analysis was performed with Student’s t-test. All data were normalized on actin and are expressed as the mean ± SEM. (D) Immunohistochemistry of Smad1 in the cortex of the kidneys. Magnification was made with × 60 objective. Scale bar, 20 μm.

FIGURE 5

mRNA (A) and protein (B) expressions of collagen type IV in the kidneys. For reverse transcription (RT-PCR) and for Western blot, actin was used as the control. The optical density of the signals was measured and the results were normalized to the optical density of the controls. For (A,B), the numbers below the signals represent the integrated densities of the signals determined by ImageJ software. Asterisks indicate significant (^∗p < 0.05) alterations of expressions as compared to the wild type (WT) and (^#p < 0.05) compared to Alzheimer’s disease (AD). Representative data of five independent experiments. (C) Statistical analysis of the RT-PCR and Western blot data. All data presented are the averages of at least five different experiments. Statistical analysis was performed with Student’s t-test. All data were normalized on actin and are expressed as the mean ± SEM. (D) Immunohistochemistry of collagen type IV in the cortex of the kidneys. Magnification was made with × 20 objective. Scale bar, 50 μm.