Dysfunctional pro-ceramide, ER stress, and insulin/IGF signaling networks with progression of Alzheimer's disease - PubMed (original) (raw)

Dysfunctional pro-ceramide, ER stress, and insulin/IGF signaling networks with progression of Alzheimer's disease

Suzanne M de la Monte et al. J Alzheimers Dis. 2012.

Abstract

In Alzheimer's disease (AD), brain insulin and insulin-like growth factor (IGF) resistance and deficiency begin early, and worsen with severity of disease. The factors mediating progression of brain insulin/IGF resistance in AD are not well understood. We hypothesize that AD progression is mediated via negative cross-talk that promotes toxic ceramide generation and endoplasmic reticulum (ER) stress. The rationale is that insulin resistance dysregulates lipid metabolism and promotes ceramide accumulation, and thereby increases inflammation and stress. Consequences include disruption of cytoskeletal function and AβPP-Aβ secretion. The present study correlates AD stage with activation of pro-ceramide genes, ceramide levels, and molecular indices of ER stress in postmortem human brain tissue. The results demonstrated that in AD, brain insulin/IGF resistance was associated with constitutive activation of multiple pro-ceramide genes, increased ceramide levels, and increased expression of pro-ER stress pathway genes and proteins. Expression of several pro-ceramide and pro-apoptotic ER stress pathway molecules increased with AD severity and brain insulin/IGF resistance. In contrast, ER stress molecules that help maintain homeostasis with respect to unfolded protein responses were mainly upregulated in the intermediate rather than late stage of AD. These findings support our hypothesis that in AD, a triangulated mal-signaling network initiated by brain insulin/IGF resistance is propagated by the dysregulation of ceramide and ER stress homeostasis, which themselves promote insulin resistance. Therefore, once established, this reverberating loop must be targeted using multi-pronged approaches to disrupt the AD neurodegeneration cascade.

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Figures

Fig. 1

Fig. 1

Increased pro-ceramide gene expression and ceramide levels in AD brains. RNA extracted from frontal lobes of aged controls (Braak stages 0–1), and subjects with moderate (Braak 3–4) or severe (Braak 6) AD was reverse transcribed, and the cDNAs were used in qPCR reactions. Gene expression was normalized to 18S rRNA measured in the same samples (See Methods and Table 1). Box plots depict medians (horizontal bars), 95% confidence interval limits (tops and bottoms of boxes), and range (stems) corresponding to relative levels of gene expression for (A–C) Ceramide synthases (CERS) 1, 2, 4, (D) UDP glucose ceramide glycosyltransferase (UGCG), (E) serine palmitoyl transferase subunit 1 (SPTLC), (F) GM3-synthase, (G) acid sphingomyelinase (SMPD1). (H) Ceramide immunoreactivity was measured in brain homogenates by ELISA and results were normalized to protein concentration. Inter-group comparisons were made using one-way repeated measures ANOVA with the post hoc Tukey test for significance.

Fig. 2

Fig. 2

ER stress genes are upregulated in AD brains. RNA extracted from brains with normal aging (Braak 0–1), moderate AD (Braak 3–4), or severe AD (Braak 6) (n = 8/group) was reverse transcribed, and the resulting cDNAs were used in qPCR amplification reactions (See Methods and Table 1). Box plots depict medians (horizontal bars), 95% confidence interval limits (tops and bottoms of boxes), and range (stems) corresponding to relative mRNA levels of (A) GRP78, (B) ATF-4, (C) p58IPK, (D) CHOP, (E) BAX, (F) HERPUD, and (G) PDI. Inter-group comparisons were made using one-way repeated measures ANOVA with the post hoc Tukey test for significance.

Fig. 3

Fig. 3

ER stress pathway activation in AD brains. ER stress proteins were measured by ELISA in brains with normal aging (Braak 0–1), moderate AD (Braak 3–4), or severe AD (Braak 6) (n = 8/group). Immunoreactivity was detected with HRP-conjugated secondary antibody and Amplex UltraRed soluble fluorophore. Results were normalized to β-actin immunoreactivity measured in the same samples. The ratios of phosphorylated/total PERK or eIF2-α were calculated. Box plots depict medians (horizontal bars), 95% confidence interval limits (tops and bottoms of boxes), and range (stems) for (A) PERK, (B) p-PERK (Thr980), (C) pPERK/PERK ratio, (D) eIF2-α, (E) p-eIF2-α (Ser51), and (F) p-eIF2-α/eIF2-α immunoreactivity. Fluorescence light units (FLU) were measured (Ex 530 nm/Em 590 nm) in a Spectramax M5 microplate reader. Inter-group comparisons were made using one-way repeated measures ANOVA with the post hoc Tukey test for significance.

Fig. 4

Fig. 4

Increased indices of ER stress in AD brains. Protein homogenates from aged controls (Braak 0–1), and individuals with moderate (Braak 3–4) or advanced (Braak 6) AD were used to measure immunoreactivity to (A) IRE-1, (B) CHOP, (C) GRP-78/BiP, (D) PDI, (E) ERO1, and (F) calnexin. Fluorescence light units (FLU) were measured (Ex 530 nm/Em 590 nm) in a Spectramax M5 microplate reader. Box plots depict medians (horizontal bars), 95% confidence interval limits (tops and bottoms of boxes), and range (stems). Inter-group comparisons were made using one-way repeated measures ANOVA tests with the Tukey post hoc significance test.

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References

    1. de la Monte SM. Therapeutic targets of brain insulin resistance in sporadic Alzheimer’s disease. Front Biosci. 2012;E4:1582–1605. - PMC - PubMed
    1. de la Monte SM, Longato L, Tong M, Wands JR. Insulin resistance and neurodegeneration: Roles of obesity, type 2 diabetes mellitus and non-alcoholic steatohepatitis. Curr Opin Investig Drugs. 2009;10:1049–1060. - PMC - PubMed
    1. Rivera EJ, Goldin A, Fulmer N, Tavares R, Wands JR, de la Monte SM. Insulin and insulin-like growth factor expression and function deteriorate with progression of Alzheimer’s disease: Link to brain reductions in acetyl-choline. J Alzheimers Dis. 2005;8:247–268. - PubMed
    1. Kao Y, Youson JH, Holmes JA, Al-Mahrouki A, Sheridan MA. Effects of insulin on lipid metabolism of larvae and metamorphosing landlocked sea lamprey, Petromyzon marinus. Gen Comp Endocrinol. 1999;114:405–414. - PubMed
    1. Holland WL, Summers SA. Sphingolipids, insulin resistance, and metabolic disease: New insights from in vivo manipulation of sphingolipid metabolism. Endocr Rev. 2008;29:381–402. - PMC - PubMed

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