Chronic Consumption of a Western Diet causes Perivascular Adipose Tissue (PVAT) Phenotypic Modulation and Increased Macrophages Infiltration
Authors: Lin Zhongqian , Maddie Nicole , Singh Mohnish , Zhang Youhua , Savinova Olga V. , Ramos Raddy , Sepulveda Maria Alicia Carrillo 
Published: April 2020

Background

Obesity has become a prevalent public health issue, increasing the risk of cardiovascular diseases which are the leading cause of death in the US. A major contributor to the obesity epidemic is the chronic consumption of diets rich in saturated fat and sugar, known as western diet (WD). During obesity, PVAT loses its vasculo‐protective properties and becomes inflamed negatively impacting vascular function. Cx3cr1GFP/WT transgenic fluorescent mice that express a GFP reporter in microglia/macrophages, were utilized in this study to visualize macrophage infiltration in the PVAT from mice chronically exposed to a WD.

Methods

Adult homozygous male Cx3cr1GFP/WT mice were randomized to the control group (n=4) fed a regular chow diet (5% fat, 48.7% carbohydrates [3.2% sucrose], and 24.1% protein) and the WD group (n=9) fed a WD (40% fat, 43% carbohydrates [34% sucrose], and 17% protein) for 52 weeks. Metabolic cage studies were performed to determine food and water intake, along with feces and urine output. Glucose metabolism was assessed by intraperitoneal glucose tolerance test (IPGTT). At the terminal experiments, direct measurements of arterial blood pressure were obtained by carotid catheterization, and aortas containing PVAT were collected for further histological analysis. Macrophage labeled by GFP in PVAT was visible by fluorescence microscopy and scored in a blind fashion.

Results

As expected, after over one year under WD conditions, Cx3cr1GFP/WT mice exhibited increased body weight (40.82 ± 2.09 vs. 33.83 ± 1.77g controls, p<0.05) and intolerance to glucose as demonstrated by increased blood glucose area under the curve during IPGTT (51828 ± 4562 vs. 28333 ± 3182 a.u, p<0.05). While the WD group showed decreased daily food consumption (1.36 ± 0.24 vs. 2.17 ± 0.10g controls, p<0.05), no differences in caloric consumption was observed between the groups (5.56 ± 2.78 vs 5.36 ± 1.37 kcals controls). Interestingly, the WD group exhibited decreased water intake (2.90 ± 0.92 vs. 5.13 ± 1.96 mL, p<0.05), urine output (0.56 ± 0.32 vs.1.69 ± 0.63 ml, p<0.01), and feces output (0.34 ± 0.10 vs.1.66 ± 0.30g, p<0.0001) compared to controls. Chronic exposure to WD also resulted in increased systolic blood pressure (119.1 ± 5 vs. 102.9 ± 4 mmHg, p<0.05) along with increased heart rate (481.2 ± 11.7 vs. 429.1 ± 24.6 bpm, p<0.05). Interestingly, PVAT from the WD group exhibited a white‐like adipose tissue feature comprising enlarged adipocytes, in contrast to their native brown‐like adipose tissue, characterizing a phenotypic modulation. Strikingly, GFP signal in the PVAT from the WD group was significantly augmented by 70% compared to controls (Figure
), showing a robust infiltration of macrophages in the PVAT.

Conclusion

Our results suggest that increased infiltration of macrophages in PVAT after chronic consumption of a WD promotes inflamed PVAT which in turn may contribute to dysregulation of blood pressure. Further studies will be needed to fully characterize the negative impact of a WD in the PVAT and its consequence in the development of obesity‐related cardiovascular complications.

Support or Funding Information

NIH R56HL131547

Representative photomicrography of aortic PVAT. Green fluorescence showing macrophage infiltration on PVAT from WD group.

Figure 1