Transforming growth factor β1 +869T/C gene polymorphism and essential hypertension: a meta-analysis involving 2708 participants in the Chinese population

Transforming growth factor beta1 and aldosterone

PURPOSE OF REVIEW

It is well established that blocking the renin-angiotensin-aldosterone system (RAAS) is effective for the treatment of cardiovascular and renal complications in hypertension and diabetes mellitus. Although the induction of transforming growth factor beta1 (TGFbeta1) by components of the RAAS mediates the hypertrophic and fibrogenic changes in cardiovascular-renal complications, it is still controversial as to whether TGFbeta1 can be a target to prevent such complications. Here, we review recent findings on the role of TGFbeta1 in fluid homeostasis, focusing on the relationship with aldosterone.

RECENT FINDINGS

TGFbeta1 suppresses the adrenal production of aldosterone and renal tubular sodium reabsorption. We have generated mice with TGFbeta1 mRNA expression graded in five steps, from 10 to 300% of normal, and found that blood pressure and plasma volume are negatively regulated by TGFbeta1. Notably, the 10% hypomorph exhibits primary aldosteronism and sodium and water retention due to markedly impaired urinary excretion of water and electrolytes.

SUMMARY

These results identify TGFbeta signalling as an important counterregulatory system against aldosterone. Understanding the molecular mechanisms for the suppressive effects of TGFbeta1 on adrenocortical and renal function may further our understanding of primary aldosteronism, as well as assist in the development of novel therapeutic strategies for hypertension.

Association of a Large Panel of Cytokine Gene Polymorphisms with Complications and Comorbidities in Type 2 Diabetes Patients

AIMS

The polymorphisms of pro- and anti-inflammatory cytokines may be involved in type 2 diabetes (T2D) pathogenesis and its complications.

METHODS

We investigated in 102 T2D patients the association of the cytokine polymorphisms in the TNF-α, IL-10, IL-6, TGF-β1, and IFN-γ genes with the T2D microvascular complications and comorbidities (hypertension, dyslipidemia, and obesity). Cytokine genotypes were determined by PCR using Cytokine Genotyping Tray kit.

RESULTS

Diabetic retinopathy was associated with GG genotype and G allele in TGF-β1 codon 25C/G polymorphism (p = 0.004 and p = 0.018) and the nephropathy was associated the lower frequency of GG genotype in IL-10 -1082G/A polymorphism (p = 0.049). Hypertension was associated with the CC genotype and C allele for IL-10 -592C/A polymorphism (p = 0.013 and p = 0.009) and higher frequencies of T (p = 0.047) and C (p = 0.033) alleles of the TGF-β1 codon 10T/C and IL-10 -819T/C polymorphisms, respectively. The TGF-β1 codon 10T/C polymorphism was associated with the BMI groups (p = 0.026): the CC genotype was more frequent in the group with BMI < 25 Kg/m(2), while the TC genotype was more frequent in the group with BMI = 30 Kg/m(2).

CONCLUSIONS

Our findings suggest that TGF-β1 and IL-10 polymorphisms are involved in complications and comorbidities in T2D patients.

The role of transforming growth factor β1 in the regulation of blood pressure

Although human association studies suggest a link between polymorphisms in the gene encoding transforming growth factor (TGF) β1 and differing blood pressure levels, a causative mechanism for this correlation remains elusive. Recently we have generated a series of mice with graded expression of TGFβ1, ranging from approximately 10% to 300% compared to normal. We have found that blood pressure and plasma volume are negatively regulated by TGFβ1. Of note, the 10% hypomorph exhibits primary aldosteronism and markedly impaired urinary excretion of water and electrolytes. We here review previous literature highlighting the importance of TGFβ signaling as a natriuretic system, which we postulate is a causative mechanism explaining how polymorphisms in TGFβ1 could influence blood pressure levels.

Primary aldosteronism and impaired natriuresis in mice underexpressing TGFβ1

To uncover the potential cardiovascular effects of human polymorphisms influencing transforming growth factor β1 (TGFβ1) expression, we generated mice with Tgfb1 mRNA expression graded in five steps from 10% to 300% normal. Adrenal expression of the genes for mineralocorticoid-producing enzymes ranged from 50% normal in the hypermorphs at age 12 wk to 400% normal in the hypomorphs accompanied with proportionate changes in plasma aldosterone levels, whereas plasma volumes ranged from 50% to 150% normal accompanied by marked compensatory changes in plasma angiotensin II and renin levels. The aldosterone/renin ratio ranged from 0.3 times normal in the 300% hypermorphs to six times in the 10% hypomorphs, which have elevated blood pressure. Urinary output of water and electrolytes are markedly decreased in the 10% hypomorphs without significant change in the glomerular filtration rate. Renal activities for the Na(+), K(+)-ATPase, and epithelial sodium channel are markedly increased in the 10% hypomorphs. The hypertension in the 10% hypomorphs is corrected by spironolactone or amiloride at doses that do not change blood pressure in wild-type mice. Thus, changes in Tgfb1 expression cause marked progressive changes in multiple systems that regulate blood pressure and fluid homeostasis, with the major effects being mediated by changes in adrenocortical function.

A Hypertension Gene: Are We There Yet?

Cardiovascular diseases are the leading cause of death worldwide. Essential hypertension is a major risk factor for the development of other cardiovascular diseases and is caused by a combination of environmental and genetic factors, with up to 50% of blood pressure variance currently attributed to an individual's genetic makeup. By studying genes that cause monogenic forms of hypertension and pathways relevant to blood pressure control, a number of polymorphisms have been identified that increase an individual's risk of developing high blood pressure. We report on candidate gene association studies and genome-wide association studies that have been performed to date in the field of hypertension research. It is becoming clear that for the majority of people there is no single gene polymorphism that causes hypertension, but rather a number of common genetic variants, each having a small effect. Using pharmacogenomics to personalize the treatment of hypertension holds promise for achieving and sustaining normotensive pressures quickly, while minimizing the risk of adverse reactions and unwanted side-effects. This will decrease the risk of stroke and myocardial infarction in individuals and lead to a reduced burden of disease upon society as a whole.

Transforming growth factor-β1 gene +869T/C, but not +915G/C polymorphism is associated with essential hypertension in a Chinese patient cohort

Many studies have suggested that transforming growth factor-β1 (TGF-β1) gene might be involved in the development of hypertension. However, results have been inconsistent. In this study, the authors performed a meta-analysis to investigate the associations of +869T/C and +915G/C polymorphisms in TGF-β1 gene with hypertension risk in Chinese. Published literature from PubMed, EMBASE, CNKI, CBM, and Wanfang Data were searched. Pooled odds ratio (OR) and 95% confidence interval (CI) were calculated using fixed or random-effects model. Nine studies (1,995 cases/1,840 controls) for +869T/C polymorphism and seven studies (1,547 cases/1,577 controls) for +915G/C polymorphism were included in the meta-analysis. The overall result showed that there was a statistically significant association between +869T/C polymorphism and hypertension risk (CC vs. TT: OR = 1.80, 95% CI 1.34-2.44). Similar results were found among two geographic locations and two subgroups with different sample size. However, no significant association was found for +915G/C polymorphism with the risk of hypertension (CC vs. GG: OR = 1.66, 95% CI 0.74-3.74). The meta-analysis indicated the significant association of +869T/C, but not +915G/C polymorphism with hypertension susceptibility. However, given the limited sample size, the associations warrant further investigation.