Transient receptor potential canonical (TRPC)
proteins play important roles in chronically hypoxic
pulmonary hypertension (
CHPH). Previous results indicated that
sildenafil inhibited TRPC1 and
TRPC6 expression in rat distal pulmonary arteries (PAs). However, the underlying mechanisms remain unknown. We undertook this study to investigate the downstream signaling of
sildenafil's regulation on TRPC1 and
TRPC6 expression in pulmonary arterial smooth muscle cells (PASMCs).
Hypoxia-exposed rats (10% O2 for 21 d) and rat distal PASMCs (4% O2 for 60 h) were taken as models to mimic
CHPH. Real-time PCR, Western blotting, and Fura-2-based fluorescent microscopy were performed for
mRNA,
protein, and Ca(2+) measurements, respectively. The cellular cyclic
guanosine monophosphate (cGMP) analogue 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate
sodium salt (
CPT-cGMP) (100 μM) inhibited TRPC1 and
TRPC6 expression, store-operated Ca(2+) entry (SOCE), and the proliferation and migration of PASMCs exposed to prolonged
hypoxia. The inhibition of
CPT-cGMP on TRPC1 and
TRPC6 expression in PASMCs was relieved by either the inhibition or knockdown of
cGMP-dependent protein kinase (PKG) and
peroxisome proliferator-activated receptor γ (PPARγ) expression. Under hypoxic conditions,
CPT-cGMP increased PPARγ expression. This increase was abolished by the PKG antagonists Rp8 or
KT5823. PPARγ agonist
GW1929 significantly decreased TRPC1 and
TRPC6 expression in PASMCs. Moreover,
hypoxia exposure decreased, whereas
sildenafil treatment increased, PKG and PPARγ expression in PASMCs ex vivo, and in rat distal PAs in vivo. The suppressive effects of
sildenafil on TRPC1 and
TRPC6 in rat distal PAs and on the hemodynamic parameters of
CHPH were inhibited by treatment with the PPARγ antagonist
T0070907. We conclude that
sildenafil inhibits TRPC1 and
TRPC6 expression in PASMCs via cGMP-PKG-PPARγ-dependent signaling during
CHPH.