TGFβ Decreases Soluble Guanylate Cyclase subunit mRNA Expression in Pulmonary Artery Smooth Muscle Cells via MEK/ERK Signaling
Authors: Du Lili , Roberts Jesse 
Published: June 2021

Lung injury leads to important morbidity and mortality in newborns by disrupting lung development and causing pulmonary vascular disease. Previously we showed that pulmonary artery smooth muscle cell (PASMC) nitric oxide (NO)/cGMP signaling is disrupted in animal models of newborn lung injury. We found that newborn lung injury decreases the expression of soluble guanylate cyclase (sGC), a critical NO receptor that produces cGMP. In part, this decreased sGC expression causes PASMC dedifferentiation, hyperplasia, and muscularization of lung arteries, pulmonary hypertension, and decreased lung alveolarization. Moreover, we determined that sGC expression down‐regulation in the injured newborn lung is directly mediated by TGFβ activation. TGFβ activation was observed to decrease sGC subunit expression in the injured newborn lung as well as in cultured PASMC from a variety of sources. However, the mechanism by which TGFβ decreases sGC expression is unknown.We used a rat pulmonary artery smooth muscle cell line (CS54 cells) to identify the mechanisms by which TGFβ down‐regulates sGC expression by examining the mRNA levels of the sGCα1 subunit. TGFβ was determined to regulate sGC expression through receptor‐mediated mechanisms because treatment of CS54 cells with SB 505125 and SD 208, TGFβ type I receptor inhibitors, prevented TGFβ1‐mediated decrease in sGCα1 mRNA levels. However, TGFβ did not evoke canonical mechanisms in regulating sGC expression; knock‐down of Smad2 and Smad3 expression, individually or together, did not inhibit TGFβ‐mediated sGCα1 mRNA reduction although it inhibited the activity of other TGFβ‐receptor Smad‐dependent genes. Small molecule inhibitor experiments that screened non‐canonical TGFβ signaling pathways (e.g., TAK1, P38, JNK, IKKβ, PI3K/Akt, and MEK/ERK signaling) suggested that MEK1/2 might regulate sGCα1 mRNA expression in TGFβ‐treated PASMC. TGFβ was observed to regulate MEK/ERK signaling in PASMC because physiologic levels of TGFβ1 were found to increase MEK1/2 and ERK1/2 phosphorylation in a dose‐ and bimodal time‐dependent manner in the CS54 cells. Moreover, this pathway was determined to mediate TGFβ regulation of NO/cGMP signaling in PASMC because TGFβ‐mediated sGCα1 mRNA down‐regulation was found to be prevented by treatment with AZD6244 and SCH772984, MEK1/2 and ERK1/2 inhibitors respectively. Finally, nuclear ERK signaling was determined to be sufficient for sGC gene regulation. This is because whereas over‐expression of a constitutively active ERK2‐MEK1 transgene that is retained within the nucleus decreased sGCα1 mRNA levels, in a manner that was inhibited by SCH772984, over‐expression of an ERI2‐MEK1 transgene that is retained in the cytoplasm did not modulate sGCα1 mRNA expression.These studies detail for the first time the intracellular mechanism through which TGFβ downregulates sGC expression in PASMC. It suggests that targeting MEK/ERK signaling might provide a strategy to protect the NO/cGMP signaling system during pathological states characterized by excessive TGFβ activation.Support or Funding InformationNIH R01HL096779 supported this work.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.