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Janus kinase-2 signaling mediates apoptosis in rat cardiomyocytes

Eduardo Mascareno1, Daniel L Beckles, M A Q Siddiqui

  • 1Center for Cardiovascular and Muscle Research, Department of Anatomy and Cell Biology, State University of New York Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, N.Y. 11203, USA.

Vascular Pharmacology
|November 5, 2005
PubMed

Insights

Janus kinase 2 (Jak2) signaling mediates cardiac myocyte apoptosis induced by Angiotensin II and hypoxia/reoxygenation. Inhibiting Jak2 with Tyrphostin AG490 blocked these apoptotic pathways, suggesting Jak2 as a therapeutic target.

Area of Science:

  • Cardiovascular Biology
  • Molecular Cardiology
  • Cell Death Signaling

Background:

  • The renin-angiotensin system (RAS) plays a crucial role in cardiovascular regulation.
  • Angiotensin II (Ang II) and oxidative stress contribute to cardiac myocyte apoptosis.
  • Janus kinase 2 (Jak2) is implicated in signaling pathways relevant to cardiovascular disease.

Purpose of the Study:

  • To investigate the role of Jak2 activation in mediating apoptosis of cardiac myocytes induced by Angiotensin II (Ang II) and hypoxia/reoxygenation.
  • To determine if Jak2 acts as a central mediator for signals leading to enhanced cardiomyocyte susceptibility to cell death.
  • To explore the impact of Jak2 inhibition on pro-apoptotic and anti-apoptotic signaling pathways in cardiomyocytes.

Main Methods:

  • Adult rat cardiomyocytes were treated with Ang II or subjected to hypoxia/reoxygenation.
  • Western blotting was used to assess protein phosphorylation and expression (Jak2, Stat1, JNK, Bax, S6 ribosomal protein, HSP27).
  • Caspase-1 and caspase-3 activities were measured.
  • Pharmacological inhibitors (Tyrphostin AG490 for Jak2, Losartan for AT1 receptor) were employed.

Main Results:

  • Ang II treatment induced cardiomyocyte apoptosis, increased pro-apoptotic markers (phosphorylated Jak2, Stat1, JNK, Bax), and activated caspases.
  • Hypoxia/reoxygenation also triggered apoptosis dependent on Jak2 activation.
  • The Jak2 inhibitor Tyrphostin AG490 significantly reduced apoptosis and downstream signaling in both models.
  • Losartan also attenuated the apoptotic response to hypoxia/reoxygenation.
  • Cardioprotective pathways involving S6 ribosomal protein and HSP27 were concurrently activated.

Conclusions:

  • Jak2 signaling is a critical mediator of Angiotensin II- and hypoxia/reoxygenation-induced apoptosis in cardiac myocytes.
  • Pharmacological inhibition of Jak2 effectively blocks these apoptotic pathways, highlighting its potential as a therapeutic target.
  • While Jak2 activation promotes apoptosis, there is a concurrent activation of cytoprotective signaling pathways that may serve as a negative feedback mechanism.

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