Effects Of G Protein Inhibitory Polypeptide GCIP-27 On Aortic Vascular Remodeling And Blood Pressure In Spontaneously Hypertensive Rats And Its Mechanism

BACKGROUND: Vascular remodeling, defined as changes in size and/or structure of adult vasculature, not only allows physiological adaptation and healing but also underlines the pathogenesis of major cardiovascular diseases. It is a prime contributor to the pathogenesis of a number of clinical disorders, including hypertension, atherosclerosis and restenosis. Hypertension is a substantial public health problem, and it is an important risk factor for death from stroke, myocardial infarction, congestive heart failure, and renal failure. Vascular remodeling contributes to not only peripheral resistance increase, but also the development and complications. Therefore, to find some new drugs to prevent vascular remodeling is very necessary in the treatment of hypertension and other related diseases. G proteins mediate intracellular responses to extracellular stimuli during cardiac development, adult function, and disease states. It locates at the covergent point in the signal transduction pathway leading to vascular remodeling. G protein inhibitory polypeptide GCIP,which was cloned and expressed in our laboratory previously, could inhibit myocardial hypertrophy induced by norepinephrine (NE). In order to reduce cost and increase activity, GCIP was optimized and a series of candidate polypeptides were synthesized.GCIP-27 was the most optimized one in the candidate polypeptides. Studies in experimental animals suggested that GCIP-27 could prevent the cardiac hypertrophy significantly in vitro and vivo.AIM: This study was designed to observe the effects of G protein inhibitory polypeptide GCIP-27 on the aortic vascular remodeling and blood pressure in spontaneous hypertensive rats (SHR) in vivo, the hyperplasia and hypertrophy in vascular smooth muscle cells (VSMCs) of SHR and the proliferation of rat VSMCs induced by angiotensin II (Ang II), and the potential underlying mechanisms in vitro.METHODS: SHRs were peritoneally injected with GCIP-27 (7, 20, 60μg/kg) in normal saline (3 ml/kg) bis in die (bid), or intragastric administrated with 6 mg/kg Losartan once daily for 8 weeks. Normotensive and age-matched Wistar rats were used as normal control. No treatment SHRs were used as model control. The systolic blood pressure (SBP) and aortic vascular remodeling were measured by the standard tail-cuff technique and pathological method, respectively. VSMCs of rats were isolated from the media of thoracic aorta obtained by explanted method, and identified byα-SM-actin immunocytochemistry assay. The hyperplasia and hypertrophy of SHR VSMCs was determined with the [3H]-Thymidine and [3H]-Leucine incorporation. Cell proliferation was induced with Ang II (1μmol/L). The proliferation rate and protein content were determined with MTT, cells count, and Bradford method, respectively. The level of [Ca²⁺]_i and p-ERK1/2 expression were measured with Fluo-3/AM staining and immunocytochemistry in vitro, respectively.RESULTS: (1) The SBP and the media/lumen ratios (MT/LD) were decreased significantly in GCIP-27 (7, 20, 60μg/kg) treated groups and Losartan (6mg/kg) treated group compared with the control group, respectively (p<0.05 or p<0.01). (2) The decrease degree of blood pressure in the GCIP-27 groups was less than that of the MT/LD ratios by comparison of Losartan group. SBP was decreased 30.1% in Losartan group compared with the control group, at the same time, it was decreased 11.4%, 12.5%, and 18.6% in GCIP-27 (7, 20, 60μg/kg) treated groups respectively. However, the ratios of MT/LD were reduced 13.9% in Losartan group compared with the control group; they were reduced 6.9%, 8.3%, and 13.9% in GCIP-27 (7, 20, 60μg/kg) treated groups respectively. (3) GCIP-27 (3-100μg/L) significantly decreased the incorporation of [3H]-Thymidine and [3H]-Leucine (p<0.05 or p<0.01). (4) Compared with the control group, the VSMCs proliferation activity, protein level, and cell sum (by number) were obviously increased in Ang II group (p<0.05 or p<0.01). (5) GCIP-27 (10μg/L～10mg/L) markedly inhibited the proliferation activity, protein level, and cell sum with a significant difference from Ang II group (p<0.05 or p<0.01). (6) GCIP-27 (3-100μg/L) significantly decreased the level of [Ca²⁺]_i, and the expression of p-ERK1/2 in VSMCs of SHR (p<0.05 or p<0.01).CONCLUSION:(1) GCIP-27 could prevent aortic vascular remodeling and decrease the SBP in SHR. The effect of GCIP-27 on vascular remodeling is not only depended on blood pressure in SHR.(2) GCIP-27 could inhibit the hypertrophy and hyperplasia of SHR VSMCs and the proliferation of VSMCs induced by Ang II.(3) The potential underlying mechanisms of GCIP-27 is the inhibition of G protein, it can induce the decrease of [Ca²⁺]_i and p-ERK1/2 expression in VSMCs.