3.6 Isorhamnetin reversed AngII-induced atrial fibrosis and
related gene expression in AF model mice
Histological analysis was performed to confirm the inhibitory effect of
isorhamnetin on atrial fibrosis. Images obtained from Masson trichome
staining showed more disarray fibrosis in the AngII group (Fig. 6A).
Furthermore, the quantitative ratio of the fibrotic area to the total
area in the AngII group was significantly higher than that in the
control group. However, isorhamnetin markedly suppressed AngII-induced
atrial fibrosis (Fig. 6B).
Tissue
fibrosis normally involves the activation of the TGF-β pathway, which
promotes collagen deposition. As a result, in the left atrium, two weeks
of AngII infusion increased the gene expression of Tgfβ andCol1a1 (collagen type I alpha 1) compared to the controls.
However, isorhamnetin diminished the expression of these genes (Fig.
6C-D). These results demonstrate that isorhamnetin has inhibitory
effects on fibrosis in the atria.
3.7 Effect of isorhamnetinon
AF-related protein expression in atrial
tissues
The pathogenesis of AF is a complex process involving not only
Ca2+ channels, but also a variety of other molecules
(Nattel et al., 2020). CaMKII oxidation usually contributes to diastolic
SR Ca2+ leakage and Ca2+ loading
(Wang et al., 2018). Cav1.2, a subunit of the L-type voltage-gated
calcium channel, is encoded by the calcium voltage-gated channel subunit
alpha1 C (CACNA1C) and is involved in the formation of AP and the
regulation of blood pressure. TRPC3 and TRPC6 are closely related to AF
by promoting myofibroblast formation (Rose et al., 2012). In addition,
JNK, ERK, and nuclear factor kappa-light-chain-enhancer of activated B
cells (NF-κB) activate oxidation, hypertrophy, fibrosis, and
inflammation (Nattel et al., 2020). The mRNA expression level
of Camkii was not significantly increased in the AngII group
compared to the control group (Fig. 7.1A). On the other hand, the mRNA
expression levels of Cacna1c and Ryr2 were increased in
the AngII group and decreased in the AngII +isorhamnetin group (Fig.
7.1B-C). The results of western blotting for
Ca2+-handling-related molecules and TRPCs are shown in
Fig. 7.1D. The protein expression levels of ox-CaMKII and p-RyR2 at Ser
2814 were significantly increased in the AngII group and were
significantly decreased in the AngII +isorhamnetin group (Fig. 7.1E-F).
The elevated expression levels of TRPC3/6 and CACNA1C induced by AngII
were also decreased in the AngII +isorhamnetin group (Fig. 7.1G-I).
Finally, the results of western blotting for the structural
remodeling-related signaling pathways are shown in Fig. 7.2A. The
protein expression levels of p-ERK, p-JNK, and p-NF-κB were remarkably
enhanced in the AngII group and notably diminished in the
AngII+isorhamnetin groups (Fig. 7.2B-D). These results suggest that
suppressing the overexpression of Ca2+-handling and
morphology-related molecules using isorhamnetin treatment may contribute
to the prevention of AF vulnerability.