Mechanism of Green Tea Peptides in Lowering Blood Pressure and Alleviating Renal Injury Induced by Hypertension Through the Ang II/TGF-β1/SMAD Signaling Pathway

Abstract

Background/Objectives: The kidney plays a crucial role in regulating normal blood pressure and is one of the major organs affected by hypertension. The present study aimed to investigate the hypotensive and renoprotective effects of four specific green tea peptides extracted from green tea dregs on spontaneously hypertensive rats (SHRs) and to investigate the underlying mechanisms. Methods: Four specific green tea peptides (40 mg/kg) were gavaged to SHRs for 4 weeks, and blood pressure, renal function, renal pathological changes, renal tissue fibrosis indexes, and inflammation indexes were examined in SHRs to analyze the role of the four green tea peptides in alleviating hypertension and its renal injury. Results: The results showed that the four TPs significantly reduced systolic and diastolic blood pressure (20-24% and 18-28%) in SHR compared to the model group. Meanwhile, gene levels and protein expression of renal fibrosis-related targets such as phospho-Smad2/3 (p-Smad2/3) (26-47%), Sma- and Mad-related proteins 2/3 (Smad2/3) (19-38%), transforming growth factor-β1 (TGF-β1) (36-63%), and alpha-smooth muscle actin (alpha-SMA) (58-86%) were also significantly reduced. In addition, the reduced expression levels of medullary differentiation factor 88 (MyD88) (14-36%), inducible nitric oxide synthase (iNOS) (58-73%), and nuclear factor-κB p65 (NF-kB p65) (35-78%) in kidneys also confirmed that TPs attenuated renal inflammation in SHR. Therefore, green tea peptides could attenuate the fibrosis and inflammatory responses occurring in hypertensive kidneys by inhibiting the Ang II/TGF-β1/SMAD signaling pathway and MyD88/NF-κB p65/iNOS signaling pathway. Conclusions: The results showed that green tea peptides may be effective candidates for lowering blood pressure and attenuating kidney injury.

Keywords: TGF-β/Smad signaling; hypertension; renal injury; tea polypeptide.

Figure 1

Comparative analysis of green tea peptides on reducing blood pressure, heart rate, and Ang I, Ang II, and ACE levels in kidneys of SHRs (n = 5). Levels of (A) SBP, (B) DBP, and (C) HR at weeks 0–4. Comparative analysis of (D) SBP difference (ΔSBP), (E) DBP difference (ΔDBP), and (F) HR difference (ΔHR) in green tea peptide gavaged rats at week 4 versus week 0. Changes in levels of (G) Ang I, (H) Ang II, and (I) ACE in kidneys of rats after four weeks of continuous gavage. Means denoted by different letter indicate significant differences between groups (p < 0.05).

Figure 2

Comparative analysis of green tea peptides in attenuating renal tubular dilatation, glomerular fibrosis injury, and serum CRE and BUN levels in SHRs. (A) H&E staining of cortical region of kidney showing tubular damage (black arrow), exposed nuclei (green arrow), and thickened basement membrane (red arrow) (200× and 400×) (n = 3). (B) Masson’s trichrome staining of renal cortex shows areas of fibrosis (blue) (200× and 400×) (n = 3). (C) Grading of renal injury (0–4) according to H&E staining results. Scale bar = 20 μm. (D) Masson’s trichrome-stained fibrosis area was quantified by ImageJ software. Levels of (E) CRE and (F) BUN in serum of rats were used to assess degree of renal injury (n = 5). Means denoted by different letter indicate significant differences between groups (p < 0.05).

Figure 3

Comparative analysis of green tea peptides on reduction in renal ACE, Ang II, TGF-β1, p-Smad2/3, Smad2/3, and a-SMA expression in SHRs (n = 3). (A) Protein immunoblotting of ACE, Ang II, TGF-β1, p-Smad2/3, Smad2/3, and α-SMA in rat kidney tissues. Image J quantified protein expression of (B) ACE, (C) Ang II, (D) TGF-β1, (E) p-Smad2/3, (F) Smad2/3, and (G) α-SMA. RT-qPCR analysis of mRNA levels of (H) ACE, (I) Ang II, (J) TGF-β1, (K) Smad2, (L) Smad3, and (M) α-SMA. Means denoted by different letter indicate significant differences between groups (p < 0.05).

Figure 4

Comparative analysis of green tea peptides on reducing MyD88, iNOS, and NF-kB p65 expression in SHR kidneys (n = 3). (A) Protein expression levels of MyD88, iNOS, and NF-κB p65 in rat kidneys. ImageJ quantified protein levels of (B) MyD88, (C) iNOS, and (D) NF-κB p65, and mRNA levels of renal (E) iNOS and (F) NF-κB p65 were analyzed by RT-qPCR. Means denoted by different letter indicate significant differences between groups (p < 0.05).