T18/S19 diphosphorylation of myosin regulatory light chain impairs pulmonary artery relaxation in monocrotaline-induced pulmonary hypertensive rats

Pflugers Arch. 2023 Sep;475(9):1097-1112. doi: 10.1007/s00424-023-02836-6. Epub 2023 Jul 8.


Phosphorylation of Ser19 (S19-p) on the myosin regulatory light chain (MLC2) is critical for arterial contraction. It has been shown that elevated RhoA-dependent kinase (ROCK) activity or decreased MLC phosphatase (MLCP) activity leads to further phosphorylation of Thr18 (T18/S19-pp), which has been linked to vasospastic diseases. However, this phenomenon has not yet been studied in the context of pulmonary arterial hypertension (PAH). In the monocrotaline-induced PAH (PAH-MCT) rat model, we observed a significant delay in pulmonary artery (PA) relaxation following high potassium-induced contraction, which persisted even with the use of an L-type calcium channel blocker or in a calcium-free solution. Immunoblot analysis showed increased levels of both S19-p and T18/S19-pp in unstimulated PAs from PAH-MCT rats. Proteomics analysis revealed a reduction in soluble guanylate cyclase (sGC) and protein kinase G (PKG) levels, and immunoblotting confirmed decreased levels of MYPT1 (a component of MLCP) and increased ROCK in PAH-MCT. In the control PAs, the pharmacological inhibition of sGC with ODQ resulted in a prominent delay of relaxation and increased T18/S19-pp as in PAH-MCT. The delayed relaxation and the T18/S19-pp in PAH-MCT were reversed by ROCK inhibitor, Y27632, while not by membrane permeable 8-Br-cGMP. The delayed relaxation and T18/S19-diP in the ODQ-treated control PA were also reversed by Y27632. Taken together, the decreased sGC and MLCP, and increased ROCK increased T18/S19-pp, which leads to the decreased ability of PA to relax in PAH-MCT rats. PA specific inhibition of ROCK or activation of MLCP are expected to serve as potential drugs in the treatment of PAH.

Keywords: Myosin light chain phosphatase; Myosin regulatory light chain; Pulmonary arterial hypertension; RhoA-dependent kinase; Soluble guanylate cyclase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Hypertension*
  • Monocrotaline
  • Myosin Light Chains / metabolism
  • Pulmonary Artery* / metabolism
  • Rats
  • rho-Associated Kinases / metabolism


  • Myosin Light Chains
  • Y 27632
  • Monocrotaline
  • rho-Associated Kinases