Effect Of Transient Receptor Potential Canonical Type1Channels On The Development Of Left Ventricular Hypertrophy In Spontaneously Hypertensive Rats

Left ventricular hypertrophy （LVH） is a common complication of hypertensionand an independent risk factor for cardiovascular death and heart failure. Previousstudies have shown that transient receptor potential canonical type1channels （TRPC₁）was involved in the development of LVH in two rat models: transgenic mice andaortic banding rats. The goal of this present study was to investigate whether TRPC₁correlates with LVH in spontaneously hypertensive rats （SHR）. Firstly, we studied therelationship between the LVH development and the expression of TRPC₁and itsdownstream signal molecule Calcineurin （CaN） and nuclear factor of activated Tcells-3（NFATC₃） in left ventricule of SHR aged from4weeks to18weeks. Secondly,TRPC₁decreased by Telmisartan and CaN inhibited by cyclosporine were respectivelyapplied to8-week-SHR for10weeks to further test if TRPC₁was a role in the processof LVH by detecting the change in LVH and expression of TRPC₁, CaN and NFATC₃on SHR.Part1The dynamic expression of TRPC₁on the left ventricle ofSHR with different weekObjectives: To investigate whether TRPC₁is involved with development of LVH inSHR by determining the expression of TRPC₁on different week of SHR.Methods: Male SHRs were randomly assigned to four groups as experiment groups:4-week-old group,8-week-old group,12-week-old group,18-week-old group（n=8）.Male and age matched Wistar-Kyoto rats （WKY） were served as control grouprespectively （n=8）. At each time point, rats were measured respectively for systolicblood pressure （SBP）, body weight （BW）, inter ventricular septum （IVS） and leftventricular posterior wall （LVPW）. After the rats were sacrificed, the heart mass （HM）, left ventricle mass （LVM） were measured and LVMI were calculatedrespectively. The mRNA transcription and protein expression of TRPC₁, CaN andNFATC₃in LV were determined respectively by real-time PCR, western blot andimmunohistochemistry. The protein expression of p-NFATC₃was examined bywestern blot, and the ratio of p-NFATC₃/NFATC₃was calculated.Results:1SBP: SBP of SHR was markedly increased with age （ρ<0.05）. SBP was similar incomparison to SHR and WKY at4-week-old（ρ>0.05）. The significant increase ofSBP was showed in SHR compared with age-matched WKY from8-week to18-weekof age （ρ<0.05）.2LVH: IVS and LVPW were remarkably increased in SHR with age （ρ<0.05）.There was no significant difference in both SHR and WKY at4-week-old. IVS andLVPW in SHR aged from8-week-old were significantly higher than those inage-matched WKY （ρ<0.05）.The LVMI in SHR was significantly higher than that inage-matched WKY from8-week to18-week of age （ρ<0.05）.3Expression of TRPC₁, CaN and NFATC₃: Both the mRNA transcription andprotein expression of TRPC₁, CaN and NFATC₃on left ventricle in SHR weresignificantly upregulated with age （ρ<0.05）. The ratio of p-NFATC₃/NFATC₃in SHRfrom8-week to18-week was significantly lower than that in age-matched WKY（ρ<0.05）.Conclusions:8–week-old SHR shows LVH and it is aggravated with age. During theprogression of LVH in SHR, the expression of TRPC₁and its downstream signalmolecule CaN and NFATC₃are gradually increased in left ventricle. These resultssuggest that TRPC₁probably associates with the development of LVH in SHR. Part2The influence of LVH by intervening the expressions ofTRPC₁and CaN in SHRObjectives: To study LVH change and the expressions of TRPC₁,CaN and NFATC₃on LV in SHR intervened with Telmisartan and Cyclosporin A respectively for furtherexploring whether TRPC₁participates in the process of LVH in SHR.Methods:8-week-old male SHR were randomized to five groups （n=8）: SHR group,Telmisartan group （8mg/kg.d, T group）, Amlodipine group（10mg/kg.d, A group）, lowdose of Cyclosporin A group （1.25mg/kg.d, LC group）, and high dose of CyclosporinA group（5mg/kg.d, HC group） respectively.8-week-old male WKY was served ascontrol group（n=8）. After10-weeks of administration, all rats were measuredrespectively for SBP, BW and IVS and LVPW. After the rats were sacrificed, the HWand LVW of rats were examined for calculating LVMI. The mRNA transcription andprotein expression of TRPC₁, CaN and NFATC₃in LV were determined by real-timePCR, western blot and immunohistochemistry respectively. The expression ofp-NFATC₃was examined by western blot and the ratio of p-NFATC₃/NFATC₃wascalculated.Results:1SBP: SHR group showed a significantly higher SBP than WKY group （ρ<0.05）.Compared with SHR group, SBP of T group and A group were significantly decreased（ρ<0.05）. SBP of LC group was similar to SBP of SHR group （ρ>0.05）, while SBP ofHC group was significantly increased compared with SBP of SHR group （225.58±6.92mmHg vs.211.65±8.43mmHg, ρ<0.05）.2LVH: Both IVS and LVPW in SHR group were notably higher than those inWKY group （ρ<0.05）. In comparison to SHR group, IVS and LVPW in T group andLC group were significantly decreased respectively （ρ<0.05）, but those in A groupand HC group had no significant change （ρ>0.05）.When compared to SHR group,LVMI of T group and LC group were significantly decreased （ρ<0.05）, but was notdifference in A group and HC group （ρ>0.05）.3Expression of TRPC₁, CaN and NFATC₃: Both the mRNA transcription and protein expression of TRPC₁, CaN and NFATC₃in SHR group were significantlyincreased when compared to those in WKY group （ρ<0.05）, while the ratio ofp-NFATC₃/NFATC₃in SHR group was remarkably lower than that in WKY group（ρ<0.05）. Compared to SHR group, both the mRNA transcription and proteinexpression of TRPC₁, CaN and NFATC₃in T group and LC group were significantlydecreased （ρ<0.05）, but the ratio of p-NFATC₃/NFATC₃in T group and LC group wassignificantly increased （ρ<0.05）. The mRNA transcription and protein expression ofTRPC₁, CaN and NFATC₃and the ratio of p-NFATC₃/NFATC₃in A group and HCgroup were respectively similar to those in SHR group（ρ>0.05）.Conclusions:1Telmisartan not only reduces SBP， but also ameliorates LVH as well asdownregulates expressions of TRPC₁, CaN and NFATC₃in SHR.Amlodipine has anantihypertensive effect on SBP, but has no effect on LVH, and expressions of TRPC₁,CaN and NFATC₃in SHR. These results imply the involvement of TRPC₁in theprogression of LVH in SHR2After CaN is inhibited by low dose of cyclosporin A, LVH is attenuated and theexpression of NFATC₃and TRPC₁on left ventricle in SHR are decreased, whichfurther shows the TRPC₁participation in the development of LVH in SHR.