Thrombospondin 2 is a novel biomarker of essential hypertension and associated with nocturnal Na⁺ excretion and insulin resistance

ABSTRACT

Background

Thrombospondins (TSPs) play important roles in several cardiovascular diseases. However, the association between circulating (plasma) thrombospondin 2 (TSP2) and essential hypertension remains unclear. The present study was aimed to investigate the association of circulating TSP2 with blood pressure and nocturnal urine Na⁺ excretion and evaluate the predictive value of circulating TSP2 in subjects with hypertension.

Methods and Results

603 newly diagnosed essential hypertensive subjects and 508 healthy subjects were preliminarily screened, 47 healthy subjects and 40 newly diagnosed essential hypertensive subjects without any chronic diseases were recruited. The results showed that the levels of circulating TSP2 were elevated in essential hypertensive subjects. The levels of TSP2 positively associated with systolic blood pressure (SBP), diastolic blood pressure (DBP), and other clinical parameters, including homeostasis model assessment of insulin resistance (HOMA-IR), brachial-ankle pulse wave velocity, and serum triglycerides, but negatively associated with nocturnal urine Na⁺ concentration and excretion and high-density lipoprotein cholesterol. Results of multiple linear regressions showed that HOMA-IR and nocturnal Na⁺ excretion were independent factors related to circulating TSP2. Mantel–Haenszel chi-square test displayed linear relationships between TSP2 and SBP (χ² = 35.737) and DBP (χ² = 26.652). The area under receiver operating characteristic curve (AUROC) of hypertension prediction was 0.901.

Conclusion

Our study suggests for the first time that the circulating levels of TSP2 may be a novel potential biomarker for essential hypertension. The association between TSP2 and blood pressure may be, at least in part, related to the regulation of renal Na⁺ excretion, insulin resistance, and/or endothelial function.

GRAPHICAL ABSTRACT

KEYWORDS:

• Thrombospondin 2
• hypertension
• renal Na⁺ excretion
• insulin resistance
• endothelial function

Introduction

Thrombospondins (TSPs), a family of secreted extracellular proteins, are matricellular glycoproteins, but not nonstructural extracellular matrix proteins, that participate in cell-to-cell and cell-to-matrix communication (1,2). Based on their domain structure, the human TSP family comprises five members, categorized into two groups: TSP1 and TSP2 comprise trimeric subgroup A, whereas TSP3, TSP4, and TSP5 belong to pentameric subgroup B (3,4). TSPs are widely distributed in many organs and tissues and involved in an extensive range of physiological and pathological processes, including angiogenesis, cell proliferation and migration, platelet aggregation, and inflammatory response (5–9).

Many studies in humans have shown that TSPs increase the risk of some cardiovascular diseases (10). Animal studies further showed that TSPs may participate in the pathogenesis of cardiovascular diseases, including cardiac remodeling and fibrosis, aortic aneurysms, and plaque erosion (11–13). However, the association between TSPs and essential hypertension remains unclear. TSP1 and TSP2 promote arterial remodeling (2), which is closely associated with hypertension (10). TSP1, the most well-studied subtype, regulates blood pressure by inhibiting endothelial nitric oxide synthase activation and endothelial- cell-dependent arterial relaxation (14,15). TSP1 and TSP2, which belong to the same subgroup of TSP family, usually play overlapping roles in the regulation of certain physiological functions. For example, either TSP1 or TSP2 inhibits the proliferation of human microvascular endothelial cells or bovine aortic endothelial cells; the structural motifs common to TSP1 and TSP2 may play a vital role in the regulation of endothelial cell proliferation, which is important in vascular homeostasis and blood pressure regulation (16–18). There is TSP-subtype specificity because TSP2 has been shown to be more potent than TSP1 in some actions, such as inhibiting tumor growth and angiogenesis (19). The latter effect suggests that TSP2 may play an important role in the regulation of blood pressure.

There are very few studies reporting the association between TSP2 and systemic arterial hypertension. The polymorphism of TSP2 gene (3949T > G, THBS2) is associated with the prevalence of hypertension in individuals with chronic kidney disease (20). Another study showed that the same variant allele of THBS2 is a risk factor for thoracic aortic aneurysm in hypertensive patients (21). In addition, the mRNA expression levels of THBS2 are increased in the placenta of preeclamptic patients, which have elevated blood pressure (22). However, the correlation between circulating TSP2 levels and essential hypertension has not been studied.

In our present study, we investigated the association of circulating TSP2 with blood pressure and nocturnal urine Na⁺ concentration and excretion. Moreover, we also determined the correlation between TSP2, and a cluster of parameters related to insulin resistance, arterial stiffness, and endothelial dysfunctions, as well as lipid metabolism. In addition, the linear relationship between hypertension and circulating TSP2 and the predictive value of circulating TSP2 in hypertension were also evaluated.

Methods

Study population

The study was approved by the Ethics Committee of The Third Affiliated Hospital of Chongqing Medical University and registered in the Chinese Clinical Trial Registry (Unique identifier: ChiCTR2300069422). 603 newly diagnosed essential hypertensive subjects and 508 subjects who underwent routine medical checkups aged 18–80 were preliminarily screened. The diagnosis of hypertension was based on the 2018 Chinese Guidelines for Prevention and Treatment of Hypertension, systolic pressure (SBP) ≥140 mmHg and/or diastolic blood pressure (DBP) ≥90 mmHg in the examination room of the hospital (23). Blood pressure was measured three times other than on the same day. Subjects who took any medication known to affect blood pressure and took alcohol or tobacco were excluded. Additional exclusion criteria included patients with secondary hypertension and patients with hypertensive complications, history of chronic endocrine system diseases such as diabetes, history of chronic respiratory and digestive system diseases, infectious diseases, or any disease that required long-term medication. Healthy subjects were recruited from age-matched subjects who underwent routine medical checkups without the above exclusion criteria. According to the above criteria, 47 healthy subjects and 40 patients with newly diagnosed hypertension were finally included.

Measurements of plasma TSP2

Plasma TSP2 concentrations were determined by an ELISA kit (Thermo Fisher, Massachusetts, USA), following the manufacturer’s protocol. The minimum detectable concentration of human TSP2 is 0.68 ng/mL, and intra-assay and inter-assay coefficients of variability (CV) (%) were less than 10% and 12%, respectively.

Measurement of Na⁺ and other indicators in urine

Nocturnal Na⁺ and albumin levels were measured by colorimetry, and nocturnal creatinine level was measured by a microplate method. For at least 7 days before taking the urine samples, 11 hypertensive patients and 11 healthy age-matched subjects, with continuous sleep throughout the night (11:00 pm- 7:00 am), took less than 5 g salt (NaCl) per day (24). One day before the collection of urine, the bladder was emptied before sleeping. After the continuous sleep, the first morning urine was collected. The concentration of urine sodium was measured by a sodium test kit C002-1-1 (Nanjing Jiancheng Bioengineering Institute, Nanjing, China). Total nocturnal sodium excretion was taken as the sodium concentration × nocturnal urine volume. The detection ranges of sodium, albumin, and creatinine were 70–210 mmol/L, 0.1–80 mg/ml, and 5–2000 μmol/L, respectively. The intra-assay CVs were 1.5%, 1.9%, and 3.1%, respectively, while the inter-assay CVs were less than 5.0%, 3.25%, and 5.8%, respectively.

Measurements of clinical parameters

SBP and DBP were measured by the same trained nurse with the same automatic device, kept the upper arm at the heart level, after at least a 5 min rest in a quiet room (23). Serum hepatic and renal function tests, venous blood lipid and fasting venous blood glucose levels were measured by Hitachi LABOSPECT 008 AS (Ibaraki Prefecture, Japan). Serum insulin was measured by using an ELISA kit H203-1-2 (Nanjing Jiancheng Bioengineering Institute, Nanjing, China). The detection range of insulin was 1–300 mIU/L, and intra-assay and inter-assay CVs were less than 10% and 12%, respectively. Triglyceride-glucose index (TyG index) was calculated as = Ln [triglyceride (mg/dl) × glucose (mg/dl)/2] (25). Homeostasis Model of Insulin Resistance (HOMA-IR) was calculated as fasting insulin (μU/mL) × fasting glucose (mmol/L)/22.5 (26). The degree of peripheral arterial arteriosclerosis was estimated by using peripheral arterial hemodynamics BP-203RPE (OMRON, Dalian, China).

Calculation of sample size

There is no published report related to TSP2 in essential hypertension. Thus, six samples in the sample bank were randomly selected for the preliminary experiment. The results showed that the circulating plasma levels of the hypertensive group were 4.81 ± 0.34 ng/mL, which were markedly higher than that measured in the control group (2.95 ± 0.86 ng/mL). The power was set as 0.9 and α as 0.025, calculated by PASS software 15.0. Taking into account a 20% loss of subjects, at least 8 patients had to be recruited in each group.

Statistical analysis

All analyses were performed with SPSS version 20.0 (SPSS, Chicago, USA). Data with normal distribution were expressed as mean ± SE, and data that were not normally distributed were expressed as median (interquartile range). Normal distribution of the data was tested by Shapiro–Wilk test. The square root of a few variables was calculated or logarithmically transformed to obtain a normal distribution. The t test was used to compare two independent normally distributed samples. Three outliers were removed in t test of TSP2. By controlling co-variables, Pearson correlation analysis was used to evaluate the correlation between TSP2 and each variable. Multiple linear regression was used to determine the variables that were independently correlated with TSP2. Mantel–Haenszel chi-square test was used to determine whether there was a linear relationship between plasma TSP2 levels and hypertension. Binary logistic regression was used to explore the association of hypertension with TSP2. ROC was used to evaluate the sensitivity of TSP2 in predicting hypertension. A value of P ＜ 0.05 was considered statistically significant.

Ethics statement

The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of the Chongqing Medical University of China, Poland (protocol code 74/2022, date of approval: 31 December 2022). This study was registered in the Chinese Clinical Trial Registry (Unique identifier: ChiCTR2300069422). Informed consent was obtained from all subjects involved in the study. Written informed consent has been obtained from the patients to publish this paper.

Results

Patient characteristics

The baseline demographic, anthropometric, and metabolic characteristics of 47 healthy subjects and 40 newly-diagnosed hypertensive subjects, which was more than the calculated sample size, are summarized in Table 1. The control and hypertensive groups were similar in sex distribution, age, heart rate, height, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), total bilirubin (TBil), blood urea nitrogen (BUN), creatinine, platelet (PLT) and nocturnal urine albumin creatinine ratio. However, SBP, DBP, weight, body mass index (BMI), brachial-ankle pulse wave velocity (baPWV), serum total glyceride (TG), insulin, TyG index, HOMA-IR, uric acid (UA), alanine aminotransferase (ALT), aspartate transaminase (AST) and albumin were higher in hypertensive subjects, whereas high-density lipoprotein cholesterol (HDL-C) and urine Na⁺ excretion were lower than those in control healthy subjects.

Table 1. Clinical features and plasma TSP2 levels in healthy- and hypertensive subjects.

Feature	Healthy Subjects	Hypertensive Subjects
Male/Female	23/24	26/14
Age (years)	52 (8)	54 (15.25)
SBP (mmHg)	120.809 ± 1.319	156.325 ± 1.912**
DBP (mmHg)	68 (10)	94.5 (15.5)**
HR (bpm)	81.000 ± 1.577	82.775 ± 2.086
Height (cm)	161.000 ± 1.319	164.724 ± 1.459
Weight (kg)	60.983 ± 1.431	7.611 ± 1.988**
BMI (kg/m^2)	23.451 ± 0.373	25.887 ± 0.473**
baPWV right (cm/s)	1364.618 ± 31.208	1812.630 ± 83.931**
baPWV left (cm/s)	1377.677 ± 28.831	1832.926 ± 86.684**
Glucose (mmol/L)	5.010 ± 0.079	5.548 ± 0.241*
TG (mmol/L)	1.323 ± 0.092	2.066 ± 0.187**
TC (mmol/L)	5.135 ± 0.138	5.219 ± 0.136
HDL-C (mmol/L)	1.391 ± 0.044	1.250 ± 0.044*
LDL-C (mmol/L)	3.150 ± 0.118	3.348 ± 0.120
UA (μmol/L)	319 (120)	398 (105.75)**
ALT (U/L)	20 (16)	29.5 (31)*
AST (U/L)	20 (9)	24.5 (14) *
Albumin (g/L)	44.394 ± 0.475	46.343 ± 0.391**
TBil (μmol/L)	13.270 ± 0.867	13.795 ± 0.648
BUN (mmol/L)	4.912 ± 0.187	5.260 ± 0.157
Creatinine (μmoI/L)	63.872 ± 2.071	67.775 ± 2.354
WBC (10^9/L)	5.677 ± 0.262	6.438 ± 0.212*
RBC (10^12/L)	4.72 (0.71)	5.06 (0.68)**
PLT (10^9/L)	216.936 ± 8.746	214.700 ± 7.226
Neu%	54.998 ± 1.224	58.798 ± 1.384*
Lym%	34.6 (12)	31.2 (11.53)*
TyG Index	4.606 ± 0.038	4.888 ± 0.056**
TSP2 (ng/mL)	2.689 ± 0.106	4.349 ± 0.097**
Insulin (mIU/L)	12.357 ± 0.490	25.443 ± 2.400**
HOMA-IR	2.787 ± 0.143	6.383 ± 0.698**
Nocturnal urine Na^+ concentration (mmol/L)	220.759 ± 8.793	14.360 ± 2.725**
Nocturnal urine Volume (L)	0.374 ± 0.015	0.425 ± 0.015*
Nocturnal urine Na^+ excretion (mmol/8 h)	79.46 (32.05)	6.07 (15.82)**
Nocturnal urine albumin concentration (g/L)	0.0167 ± 0.0020	0.0314 ± 0.0104
Nocturnal urine albumin (g/8 h)	0.0061 ± 0.0006	0.0125 ± 0.0039
Nocturnal urine creatinine concentration (μmoI/L)	11262.594 ± 924.657	7091.633 ± 796.257**
Nocturnal urine creatinine (g/8 h)	48.885 ± 5.703	35.068 ± 4.953
Nocturnal urine albumin creatinine ratio (mg/g)	0.152 ± 0.029	0.508 ± 0.199

Normal distribution data were expressed as mean ± SE, and non-normal data were expressed as median (interquartile range). SBP, systolic blood pressure; DBP, diastolic blood pressure; HR, heart rate; BMI, body mass index; baPWV, brachial-ankle pulse wave velocity; TG, total glyceride; TC, total cholesterol; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol; UA, uric acid; ALT, alanine aminotransferase; AST, aspartate transaminase; TBil, total bilirubin; BUN, blood urea nitrogen; WBC, white blood count; RBC, red blood count; PLT, platelet; Neu%, neutrophilic granulocyte percentage; Lym%, Lymphocyte percentage; TyG Index, triglyceride-glucose index; TSP2，thrombospondin 2; HOMA-IR, Homeostatic Model Assessment of Insulin Resistance. *p < .05, **p < .01 vs. controls.

Plasma TSP2 and blood pressure

Our present study showed that the levels of circulating (plasma) TSP2 were much greater in hypertensive patients (4.35 ± 0.10 ng/mL) than healthy subjects (2.69 ± 0.11 ng/mL) (Figure 1). We also found that the levels of plasma TSP2 positively correlated with SBP (r = 0.53) and DBP (r = 0.51) (Table 2, Figures 2a,b).

Figure 1. The levels of circulating TSP2 in healthy subjects (control) and subjects with newly-diagnosed essential hypertension (*P＜0.01 vs. control). TSP2, thrombospondin 2.

Figure 2. Association of circulating TSP2 and clinical parameters, including (a) SBP, (b) DBP, (c) nocturnal urine Na⁺ excretion, (d) nocturnal urine Na⁺ concentration, (e) nocturnal urine albumin/creatinine ratio, (f) HOMA-IR, (g) baPWV left, (h) baPWV right, (i) HDL-C, (j) TG. TSP2, thrombospondin 2; SBP, systolic blood pressure; DBP, diastolic blood pressure; HOMA-IR, homeostatic model assessment of insulin resistance; baPWV, brachial-ankle pulse wave velocity; HDL-C, high-density lipoprotein cholesterol; TG, total glyceride.

Table 2. Correlations of plasma TSP2 with clinical parameters.

Feature	Circulating TSP2
	r	p value
Sex	−0.140	0.195
Age (years)^a	0.007	0.951
SBP (mmHg)	0.529	0.000
DBP (mmHg) ^a	0.511	0.000
HR (bpm)	0.165	0.127
Height (cm)	0.209	0.055
Weight (kg)	0.355	0.001
BMI (kg/m^2)	0.321	0.003
baPWV right (cm/s)	0.293	0.022
baPWV left (cm/s)	0.300	0.019
Glucose (mmol/L)	0.283	0.008
TG (mmol/L)	0.730	0.000
TC (mmol/L)	0.137	0.207
HDL-C (mmol/L)	−0.439	0.000
LDL-C (mmol/L)	0.186	0.094
UA (μmol/L) ^a	0.457	0.000
ALT (U/L) ^a	0.223	0.038
AST (U/L) ^a	0.070	0.520
Albumin (g/L)	0.171	0.114
TBil (μmol/L)	−0.001	0.996
BUN (mmol/L)	−0.152	0.159
Creatinine (μmoI/L)	0.186	0.084
WBC (10^9/L)	0.345	0.001
RBC (10^12/L) ^a	0.215	0.046
PLT (10^9/L)	0.137	0.205
Neu%	0.235	0.028
Lym% ^a	−0.245	0.022
TyG Index	0.808	0.000
Insulin (mIU/L)	0.620	0.000
HOMA-IR	0.591	0.000
Nocturnal urine Na^+ concentration (mmol/L)	−0.735	0.000
Nocturnal urine Volume (L)	−0.174	0.439
Nocturnal urine Na^+ excretion (mmol/8 h) ^a	−0.707	0.000
Nocturnal urine albumin concentration (g/L)	0.520	0.016
Nocturnal urine albumin (g/8 h)	0.512	0.018
Nocturnal urine creatinine concentration (μmoI/L)	−0.615	0.002
Nocturnal urine creatinine (g/8 h)	−0.592	0.004
Nocturnal urine albumin creatinine ratio (mg/g)	0.485	0.026

^atransformed to normal distribution. SBP, systolic blood pressure; DBP, diastolic blood pressure; HR, heart rate; BMI, body mass index; baPWV, brachial-ankle pulse wave velocity; TG, total glyceride; TC, total cholesterol; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol; UA, uric acid; ALT, alanine aminotransferase; AST, aspartate transaminase; TBil, total bilirubin; BUN, blood urea nitrogen; WBC, white blood count; RBC, red blood count; PLT, platelet; Neu%, neutrophilic granulocyte percentage; Lym%, Lymphocyte percentage; TyG Index, triglyceride-glucose index; TSP2，thrombospondin 2; HOMA-IR, Homeostatic Model Assessment of Insulin Resistance.

Plasma TSP2 and clinical parameters

Table 2 and Figure 2 showed the association between increasing plasma TSP2 levels and several parameters in the whole cohort. The long-term control of blood pressure is dependent on sodium homeostasis (27,28). We report for the first time, a negative association between plasma TSP2 levels and nocturnal urine Na⁺ excretion and concentration, but a positive association with nocturnal urine albumin/creatinine ratio (uACR) (Table 2, Figures 2c–e). We next investigated the association between plasma TSP2 and insulin resistance, which plays a vital role in the pathogenesis of hypertension (29). The results showed that plasma TSP2 levels were positively associated with the index and anthropometric parameters of insulin resistance, including TyG index, HOMA-IR (Figure 2f), serum insulin, body weight, and BMI (Table 2). The results also showed that plasma TSP2 positively correlated with baPWV left and baPWV right, an indicator of arterial stiffness and endothelial dysfunction (Table 2, Figures 2g,h), which are present in hypertension (30). We also determined the correlation between plasma TSP2 levels and lipid or purine metabolism, which are also involved in the development of hypertension (31,32). The results showed that plasma TSP2 levels negatively associated with HDL-C but positively associated with serum TG and UA (Table 2, Figures 2i,j).

Clinical parameters independently associated with circulating TSP2

We performed multiple linear regressions to determine clinical parameters that were independently associated with circulating (plasma) TSP2 levels. The results showed that HOMA-IR and nocturnal Na⁺ excretion were independently associated with circulating TSP2. The multiple-regression equation is: Y_THBS2 = 8.301─ 0.604X_{nocturnal Na+ excretion} +0.13X_HOMA-IR.

Binary logistic regression analysis was performed to determine whether TSP2 can predict hypertension

Binary logistic regression analysis was performed, including age, BMI, HDL-C, LDL-C, HOMA-IR, Nocturnal urine Na⁺ excretion, TSP2 level, Grade of TSP2 (divided into 4 grades by quartiles of TSP2), ALT, AST, BUN, creatinine, WBC, neutrophilic granulocyte percentage (Neu%) and insulin. Grade of TSP2 was independently associated with hypertension in two models (odds ratio [OR] 6.132 [95% CI 1.135–33.116], P < .05) (Table 3).

Table 3. Binary logistic regression analysis.

Variable	Model 1		Model 2
	OR (95%CI)	p value	OR (95%CI)	p value
Grade of TSP2	6.132 (1.135–33.116)	0.035	6.132 (1.135–33.116)	0.035
constant	0.006	0.024	0.006	0.024

Model 1: variables included in the analysis were age, body mass index, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, Homeostatic Model Assessment of Insulin Resistance, Nocturnal urine Na⁺ excretion, TSP2 level, Grade of TSP2 (divided into 4 grades by quartiles of TSP2).

Model 2: variables included in the analysis were those in model 1 plus alanine aminotransferase, aspartate transaminase, blood urea nitrogen, white blood count, neutrophilic granulocyte percentage and insulin.

Prediction of circulating TSP2 in hypertension

Mantel–Haenszel chi-square test further showed a linear relationship between circulating TSP2 and SBP and DBP. The χ2 values of systolic- and diastolic blood pressures were 35.737 (P < .001) and 26.652 (P < .001), respectively. Moreover, the Pearson correlation showed that R values of SBP and DBP were 0.645 (P < .001) and 0.557 (P < .001), respectively. These indicated that plasma TSP2 levels increased with the increase levels of SBP and DBP.

We also used plasma TSP2 levels in the form of continuous data instead of applying the cutoff value to predict hypertension. AUROC of plasma TSP2 levels in hypertension prediction was 0.901 (p < .001), rendering its performance comparable to HOMA-IR (AUROC = 0.864, P<0.001) (Figure 3). Previous meta-analyses have shown that an elevated HOMA-IR is independently associated with increased risk of hypertension in the general population (29). These suggest that circulating (plasma) TSP2 may be a biomarker for the presence of hypertension.

Figure 3. The area under ROC curve (AUROC) of circulating TSP2 levels in hypertension prediction was 0.901 (p < .001), and HOMA-IR was 0.864, p < .001). TSP2, thrombospondin 2; HOMA-IR, homeostatic model assessment of insulin resistance.

Discussion

Previous studies have shown that TSPs play an important role in the pathogenesis of cardiovascular diseases, such as myocardial infarction, cardiac hypertrophy, heart failure, atherosclerosis, and aortic valve stenosis (33). However, the association between TSPs and essential hypertension is still unknown. In our present study, we showed that circulating TSP2 levels were significantly elevated in patients with essential hypertension and circulating TSP2 levels significantly correlated with both systolic and diastolic blood pressures. This is the first time that a significant association between TSP2 and hypertension has been shown.

Renal sodium handling plays a vital role in the pathogenesis of hypertension (34). In human protein atlas, single-cell omics data in the kidney showed that TSP2 is mainly distributed in the proximal convoluted tubule, which is the primary segment of the nephron responsible for active transcellular transport of NaCl (35). Our results indicated that circulating TSP2 levels negatively correlated with nocturnal Na⁺ concentration and excretion. These indicated that TSP2 may control blood pressure by regulating Na⁺ excretion. A previous study demonstrated the TSP1 null mice displayed a better circadian rhythm (36). The mRNA and protein expressions of CD36, a TSP2 receptor, were reduced after the knockout of the biological clock Bmal1 in the renal tubule (37). Therefore, we speculated that the diurnal differences in the regulation of sodium excretion by TSP2 may be partly due to the rhythmicity of CD36. In addition, it has been reported that a gene polymorphism of TSP2 (3949T > G, THBS2) is associated with hypertension in patients with chronic kidney disease (20), and the expression of TSP2 is up-regulated in the diabetic patients with nephropathy (38). Lack of TSP2 in mice affects the responses to renal injury; the lack of TSP2 is beneficial for the regeneration process after renal injury as a result of improved endothelial cell proliferation and capillary repair (39). In our current study, we also found that circulating TSP2 levels were significantly correlated with nocturnal urinary albumin and creatinine excretion, suggesting that TSP2 may be associated with renal dysfunction.

Metabolic disturbances, including hyperglycemia, exacerbate high blood pressure and the associated damage of target organs, such as the kidney (40). TSP2 knockout mice fed a standard fat diet had lower body weights than wild-type mice (41). However, the TSP2 deficiency was not compensated by increased expression of TSP1 in TSP2 knockout mice, indicating that the effect of TSP2 on these metabolic disturbances may be independent of TSP1. Our results showed that TSP2 levels were positively associated with HOMA-IR and TyG index. In addition, we observed a strong independent association between HOMA-IR and circulating TSP2 by using multiple linear regression analyses. These suggested that TSP2 may play a key role in the metabolic disturbances in patients with essential hypertension. This is similar to the results in other populations, including individuals with morbid obesity receiving bariatric surgery and subjects with the metabolic syndrome (42).

Endothelial dysfunction plays a vital role in the pathogenesis of hypertension (43). TSP2, an inducible factor of endothelial cell apoptosis (44), also inhibits endothelial cell proliferation (16,45). In this study, we found that TSP2 was associated with baPWV, which raised the possibility that baPWV may link TSP2 with hypertension. However, it should be noted that baPWV has not been found to be a variable that is independently correlated with circulating TSP2 levels.

Our study also found that circulating TSP2 levels were associated with plasma triglycerides and HDL-C, indicating that TSP2 may be involved in the regulation of lipid metabolism. Previous studies have reported that TSP2 is an endogenous adipocyte inhibitor and reduces subcutaneous obesity (46). Thus, further studies should determine the effect of TSP2 in obese subjects and people with abnormal lipid metabolism.

In conclusion, our present study provides evidence of increased circulating TSP2 levels and its mechanism in subjects with essential hypertension. Circulating TSP2 significantly correlated with blood pressure, suggesting that TSP2 may be a biomarker for hypertension. The association between circulating TSP2 and blood pressure may be, at least in part, due to TSP2-mediated regulation of renal Na+ excretion, insulin resistance, and/or endothelial function. These findings provide an insight that a novel extracellular protein may be involved in essential hypertension. Further longitudinal investigations are needed for confirmation.

Limitations

The cross-sectional design of this study does not allow us to determine a causal relationship between circulating TSP2 and hypertension. We also cannot definitively infer the possible mechanisms of TSP2-mediated abnormalities, mentioned above. Another limitation of this study is the number of subjects, although it was more than the calculated sample size. In order to understand completely the role of TSP2 in essential hypertension, large-scale prospective studies are needed.

Author contributions

Conceptualization, Chunyan Deng and Jian Yang; Data curation, Longlong Zhang and Chunyan Deng; Formal analysis, Xiaoxin Zhou, Longlong Zhang and Xun Lei; Investigation, Xiaoxin Zhou and Longlong Zhang; Methodology, Xiaoxin Zhou; Resources, Longlong Zhang, Xiaoqian Lin, Xi Chen, Hong Liu, XiaYuan, Qiuxia Zhao and Weiwei Wang; Software, Xiaoxin Zhou; Supervision, Jian Yang; Validation, Jian Yang; Writing – original draft, Xiaoxin Zhou and Chunyan Deng; Writing – review & editing, Pedro A Jose and Jian Yang.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.

Additional information

Funding

This work was supported in part by grants from the National Natural Science Foundation of China (82100459), the Scientific Research Innovation Project for Postgraduate in Chongqing (CYB22227), Program of Chongqing Medical University for Youth Innovation in Future Medicine (W0085), and Project of Chongqing Medical Talent Studio (2022).