Systemic and adipocyte transcriptional and metabolic dysregulation in idiopathic intracranial hypertension

Abstract

BACKGROUNDIdiopathic intracranial hypertension (IIH) is a condition predominantly affecting obese women of reproductive age. Recent evidence suggests that IIH is a disease of metabolic dysregulation, androgen excess, and an increased risk of cardiovascular morbidity. Here we evaluate systemic and adipose specific metabolic determinants of the IIH phenotype.METHODSIn fasted, matched IIH (n = 97) and control (n = 43) patients, we assessed glucose and insulin homeostasis and leptin levels. Body composition was assessed along with an interrogation of adipose tissue function via nuclear magnetic resonance metabolomics and RNA sequencing in paired omental and subcutaneous biopsies in a case-control study.RESULTSWe demonstrate an insulin- and leptin-resistant phenotype in IIH in excess of that driven by obesity. Adiposity in IIH is preferentially centripetal and is associated with increased disease activity and insulin resistance. IIH adipocytes appear transcriptionally and metabolically primed toward depot-specific lipogenesis.CONCLUSIONThese data show that IIH is a metabolic disorder in which adipose tissue dysfunction is a feature of the disease. Managing IIH as a metabolic disease could reduce disease morbidity and improve cardiovascular outcomes.FUNDINGThis study was supported by the UK NIHR (NIHR-CS-011-028), the UK Medical Research Council (MR/K015184/1), Diabetes UK, Wellcome Trust (104612/Z/14/Z), the Sir Jules Thorn Award, and the Midlands Neuroscience Teaching and Research Fund.

Keywords: Neurological disorders; Neuroscience; Obesity; Ophthalmology.

Figure 1. Perturbed metabolic function in IIH.

Histograms of fasted glucose (A), insulin (B), HOMA2-IR (C), HOMA2-%B (D), HOMA2-%S (E), HbA1c (F), cholesterol (G), and triglycerides (H) in control (n = 43) and IIH patients (n = 97). Gray boxes represent healthy clinical reference ranges. (A and F) Dotted lines represent thresholds suggestive of type 2 diabetes mellitus. (C) Dotted line represents HOMA2-IR score 1.8, threshold for insulin resistance. n represents an individual patient. Data presented as mean ± SD, **P < 0.01.

Figure 2. IIH patients have an altered body composition.

IIH and control patient body composition assessed via dual-energy x-ray absorptiometry (DEXA) scanning. Histograms of (A) truncal fat percentage, (B) truncal lean percentage, (C) truncal fat/lean ratio, (D) limb fat percentage, and (E) limb lean percentage. (A–E) n = 27 for control and IIH. Scatter graphs of LP OP versus (F) total body fat (n = 47) and (G) truncal fat mass (n = 47) and (H) HOMA2-IR versus total fat mass (n = 44) in IIH patients. n represents an individual patient. Unpaired t test (B–D). Mann-Whitney U test (A and E). Spearman’s correlations (F–H). Data presented as mean ± SD. *P < 0.05.

Figure 3. IIH patients display an enhanced hyperleptinemia.

Fasted leptin levels assessed by ELISA in IIH and control patients. Serum leptin (A) in control (n = 19) and IIH patients (n = 60). CSF leptin in IIH (n = 87) and control (n = 20) patients (B). Serum/CSF ratio in control (n = 19) and IIH (n = 58) patients (C). Scatter graph of LP OP versus serum leptin (D) and CSF leptin (E). n represents an individual patient. Welch’s t test (A) and Mann-Whitney U test (B and C). Pearson’s correlation (D) and Spearman’s correlation (E). Data presented as mean ± SD, **P < 0.01.

Figure 4. Histomorphometric analysis of IIH adipose tissue.

Micrographs of paired subcutaneous (SC) (A) and omental (OM) (B) adipose tissue from age-, sex-, and BMI-matched control and IIH patients. Mean SC adipocyte area (C) and adipocyte area frequency (D) adipocyte area in control (n = 7) and IIH (n = 8). Mean OM adipocyte area (E) and adipocyte area frequency (F) in control (n = 7) and IIH (n = 11). n represents an individual patient. Scale bar: 100 μm. Unpaired t test (C and E). Two-way ANOVA with Sidak’s multiple-comparison test (D and F). Data presented as mean ± SD (C and E) and mean ± SEM (D and F), *P < 0.05, **P < 0.01, ****P < 0.0001.

Figure 5. Adipocyte leptin hypersecretion in IIH.

Leptin secretion assessed from ex vivo adipose tissue via ELISA in control and IIH patients. (A) Leptin secretion from SC adipose tissue in controls (n = 12) and IIH (n = 11). (B) Leptin secretion from OM adipose tissue in controls (n = 8) and IIH (n = 10). (C) LEP gene expression in subcutaneous adipose tissue. n represents an individual patient. Welch’s t test (A and B), t test (C). Data presented as mean ± SD, *P < 0.05, **P < 0.01. LEP, leptin; FPKM, fragments per kilobase million.

Figure 6. IIH SC adipose tissue displays a distinct transcriptome.

Differential gene expression analysis of SC adipose tissue from control versus IIH patients. (A) Bar plot displaying the number of differentially expressed RefSeq genes at P < 0.05. (B) Gene ontology for significantly downregulated genes in IIH adipose. Gene set enrichment analysis of (C) Ribosomal Subunits, (D) Lipid Biosynthesis, (E) Caloric Intake Up, and (F) Caloric Intake Down against differential expression data from adipose tissue of control versus IIH patients. The green line represents the accumulation of genes in the indicated gene list against the expression pattern in control versus IIH patients (blue, downregulated in samples from IIH; red, upregulated in samples from IIH patients). Control n = 7, IIH n = 13. NES, normalized enrichment score; FDR, false discovery rate.

Figure 7. IIH adipose tissue displays features of altered lipid metabolism.

NMR-based metabolomics on paired SC and OM adipose tissue explants and corresponding media in control and IIH patients. Tissue and media levels of glycerol in SC (n = 10) (A–C) and OM adipose tissue (control n = 9, IIH n = 10) (D–F). Tissue and media levels of leucine and isoleucine in SC (G–J) and OM (K–N) adipose tissue, n = 10. n represents a single patient’s adipose explant or corresponding media. Statistical tests: t tests for A, B, E–G, and I–N and Mann-Whitney U tests for C, D, and H. Data presented as mean ± SD; *P < 0.05, **P < 0.01.

Figure 8. IIH OM adipose tissue displays features of altered nutrient utilization.

NMR-based metabolomics on paired SC and OM adipose tissue explants and corresponding media in control and IIH patients. Tissue concentrations of pyruvate and lactate and pyruvate/lactate ratio in SC (A–C) and OM (D–F) adipose tissue. Media exchange of pyruvate and lactate in SC (G and H) and OM (I and J) adipose tissue. Tissue concentration and media exchange of acetate in SC (K and L) and OM (M and N) adipose tissue. n represents a single patient’s adipose explant or corresponding media. Statistical tests: t tests for A–C and H–N and Mann-Whitney U tests for D–G. Data presented as mean ± SD; *P < 0.05, **P < 0.01.

Figure 9. IIH metabolism concept figure.

IIH patients display systemic and tissue-level metabolic disruption in excess of that conferred by obesity. IIH patients are insulin resistant and display hyperleptinemia, where they have increased abdominal obesity. IIH adipose tissue displays leptin hypersecretion and features of transcriptomic and metabolic dysfunction.