Abstract
Background
C1q/tumor necrosis factor-related protein 1 (CTRP1) is an adipokine secreted by adipose tissue, related to chondrocyte proliferation, inflammation, and glucose homeostasis. However, the therapeutic effects on metabolic disorders and the underlying mechanism were unclear. Here, we investigated the functions and mechanisms of CTRP1 in treating obesity and diabetes.
Methods
The plasmid containing human CTRP1 was delivered to mice by hydrodynamic injection, which sustained expression of CTRP1 in the liver and high protein level in the blood. High-fat diet (HFD) fed mice and STZ-induced diabetes model were used to study the effects of CTRP1 on obesity, glucose homeostasis, insulin resistance, and hepatic lipid accumulation. The lipid accumulation in liver and adipose tissue, glucose tolerance, insulin sensitivity, food intake, and energy expenditure were detected by H&E staining, Oil-Red O staining, glucose tolerance test, insulin tolerance test, and metabolic cage, respectively. The metabolic-related genes and signal pathways were determined using qPCR and western blotting.
Results
With high blood circulation, CTRP1 prevented obesity, hyperglycemia, insulin resistance, and fatty liver in HFD-fed mice. CTRP1 also improved glucose metabolism and insulin resistance in obese and STZ-induced diabetic mice. The metabolic cage study revealed that CTRP1 reduced food intake and enhanced energy expenditure. The mechanistic study demonstrated that CTRP1 upregulated the protein level of leptin in blood, thermogenic gene expression in brown adipose tissue, and the gene expression responsible for lipolysis and glycolysis in white adipose tissue (WAT). CTRP1 also downregulated the expression of inflammatory genes in WAT. Overexpression of CTRP1 activated AMPK and PI3K/Akt signaling pathways and inhibited ERK signaling pathway.
Conclusion
These results demonstrate that CTRP1 could improve glucose homeostasis and prevent HFD-induced obesity and fatty liver through upregulating the energy expenditure and reducing food intake, suggesting CTRP1 may serve as a promising target for treating metabolic diseases.
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Introduction
C1q/TNF-related proteins (CTRP) are a family of secreted proteins [1]. The protein structures of the CTRP family are similar to that of adiponectin [2]. CTRP1, a 281 amino acids-glycoprotein, is an important adipokine closely related to metabolic and inflammatory pathways [3, 4]. CTRP1 is expressed in adipose, placenta, and many other tissues [2, 5, 6]. In clinical research, serum CTRP1 level was higher in metabolic syndrome and type II diabetes (T2DM) patients [7,8,28], which may cause different effects of CTRP1 on the appetite. More study is needed to investigate the mechanism of CTRP1 in appetite regulation and the causal relation between leptin and obesity after CTRP1 treatment.
CTRP1 significantly prevented the development of adipose hypertrophy and hepatic steatosis in HFD-fed mice (Fig. 2D, 3A), but it did not considerably lose weight in obese mice (Fig. 6G). The phosphorylation of AKT was upregulated in EWAT after CTRP1 treatment but not in the liver (Fig. 10B, E). Previous studies also observed controversial evidence between glucose metabolism and lipid clearance in Ctrp1 KO mice and transgenic mice: Ctrp1 transgenic mice maintained better glucose homeostasis and lipid homeostasis via AMPK and AKT pathways [13, 14]. Knockout of CTRP1 impaired glucose homeostasis and caused liver steatosis in LFD-fed mice [16]. However, the knockout of CTPR1 improved the lipid metabolism of HFD-fed mice, which may result from the up-regulation of Scd1, Cd36, and Pparγ [16]. We also found that some lipogenesis genes (Acly, Fas, Elovl6, and Pparγ1) were up-regulated in our study (Fig. 9A). In addition, the protein level of GLUT4, AMPK, and phosphorylation level of AMPK was decreased in skeletal muscle of LFD-fed CTRP1 KO mice, but phosphorylation level of AMPK was up-regulated in the liver in HFD-fed Ctrp1 KO mice [16]. These results suggested that the functions of CTRP1 in regulating lipid metabolism were various in different animal models and pathological statuses.
Hydrodynamic gene delivery of CTRP1 gene generated long-term anti-diabetic effects and beneficial effects in preventing HFD-induced obesity and fatty liver, indicating that CTRP1 has the therapeutic potential in maintaining glucose homeostasis and treating obesity-related metabolic disorders. However, the molecular mechanisms and clear signaling pathways of CTRP1 in preventing obesity, glucose tolerance, and fatty liver remain unclear, as well as the underlying mechanisms of CTRP1 in regulating food intake, inflammation, and thermogenesis. Further studies are needed to investigate the mechanisms of CTRP1 in regulating metabolic homeostasis and appetite. Moreover, the hydrodynamic injection strategy is a physical method of gene delivery to the liver [13, 14, 29]. The overexpressed CTRP1 protein can secrete into the blood and distribute to multiple tissues. CTRP1 was associated with adverse cardiovascular events [30] and was reported to prevent pathological vascular remodeling [31]. CTRP1 also prevented cardiac and renal disease [32, 33]. Further studies are needed to investigate the function of CTRP1 in different animal models, as well as the long-term effects and side effects of CTRP1 in multiple organs, such as cardiovascular systems, bone, muscle, and neurometabolic systems. This will help us better to understand its mechanism at deeper levels.
Conclusion
This study demonstrates that the hydrodynamic injection of CTRP1 improves glucose homeostasis and prevents HFD-induced obesity, adipose hypertrophy, and fatty liver due to upregulated energy expenditure, thermogenesis, lipolysis, and reduced inflammation and food intake. The beneficial effects of CTRP1 are related to modulation of the activity of AMPK, AKT, and upregulation of leptin, suggesting CTRP1 may serve as a target in treating metabolic diseases, as well as the potential use of CTRP1 by gene transfer for the treatment of metabolic diseases.
Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Abbreviations
- CTRP1:
-
C1q/tumor necrosis factor-related protein 1
- STZ:
-
Streptozotocin
- HFD:
-
High-fat diet
- GTT:
-
Glucose tolerance test
- ITT:
-
Insulin tolerance test
- HOMA-IR:
-
Homeostatic model assessment for insulin resistance
- AST:
-
Aspartate aminotransferase
- ALT:
-
Alanine aminotransferase
- WAT:
-
White adipose tissue
- IWAT:
-
Inguinal white adipose tissue
- EWAT:
-
Epididymal white adipose tissue
- PWAT:
-
Perirenal white adipose tissue
- BAT:
-
Brown adipose tissue
- AUC:
-
Area under the curve
- T2DM:
-
Type II diabetes
- NAFLD:
-
Nonalcoholic fatty liver disease
- LFD:
-
Low-fat diet
- KO:
-
Knockout
- FFA:
-
Free fatty acid
- RER:
-
Respiratory exchange ratio
- EE:
-
Energy expenditure
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Financial support was provided by the National Natural Science Foundation of China (NSFC-81860662, NSFC-82160259, NSFC-31771400, NSFC-81501129, NSFC-81728006), Natural Science Foundation of Jiangxi Province (20212ACB206039, 20171ACB21001, 20171BCB23029, 20161BAB215200).
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Conceptualization, CZ; methodology, MR, JP, XY, KC, and XY; investigation, CZ; writing—original draft, KC and CZ; writing—review & editing, CZ; funding acquisition, CZ; supervision, CZ. All authors read and approved the final manuscript.
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Additional file 1
: Table S1. Primer list. Table S2. Blood index. Figure S1. The map of the constructs. Figure S2. ALT, AST, and food intake in the HFD fed mice. A. ALT and AST in mice serum at the 11th week of the experiment; B. food intake; C. food intake (kcal). Figure S3. Cell viability was detected by CCK8 assay. Figure S5. Full view of H&E staining of WAT and BAT. Figure S5. Full view of H&E staining and Oil-Red O staining of liver tissue. Figure S6. ITT in wight control model on week 8. Figure S7. Glucose-stimulated insulin secretion test in vitro. Figure S8. Body weight, food intake, and fasting blood glucose in STZ-induced T2DM mice. A. The curve of body weight of STZ treated mice; B. Food intake; C. Fasting blood glucose. Figure S9. The expression of appetite related genes in the hypothalamus (A) and intestine (B). Figure S10. The expression level of upstream regulatory genes of AMPK in liver tissue.
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Ren, M., Pan, J., Yu, X. et al. CTRP1 prevents high fat diet-induced obesity and improves glucose homeostasis in obese and STZ-induced diabetic mice. J Transl Med 20, 449 (2022). https://doi.org/10.1186/s12967-022-03672-5
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DOI: https://doi.org/10.1186/s12967-022-03672-5