Role of PTP1B/Ptpn1 and TCPTP/Ptpn2 in sepsis-induced cardiomyopathy

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Septic patients often develop an impairment of cardiac function, a condition known as septic cardiomyopathy (SICM) which leads to higher short- and long-term mortality.

Cardiac function hinges on the intricate balance between phosphorylation and dephosphorylation of cell surface receptors and intracellular proteins. Protein tyrosine phosphatases (PTP) like PTP1B/Ptpn1 and TC-PTP/Ptpn2 serve as critical regulators of tyrosine phosphorylation and are involved in signal transduction. We hypothesized that PTP1B and TC-PTP play a protective role in sepsis-induced cardiomyopathy through modulation of intracellular tyrosine phosphorylation.

We first investigated if Ptpn1 and Ptpn2 are regulated in heart and skeletal muscle in response to sepsis and if interleukin (IL6) signaling via its receptor glycoprotein 130 (gp130) contributes to this regulation. Wildtype and cardiomyocyte-specific gp130 knockout mice (gp130^{loxP/loxP;αMHC-CRE}) mice were subjected to cecal ligation and puncture (CLP) surgery to induce polymicrobial sepsis. Sham operated mice were used as controls. qRT-PCR analyses revealed an increased Ptpn1/PTP1B and Ptpn2/TC-PTP mRNA expression in heart and skeletal muscle of CLP compared to sham mice, this increase was also observable in neonatal rat ventricular cardiomyocytes (NRVCM) which were treated with the proinflammatory cytokines sIL6Rα/IL-6 and IL1β. Treatment with Il6st/gp130-siRNA and the JAK2 and STAT3 inhibitors AG490 and C188-9 showed that the increase of Ptpn1/PTP1B and Ptpn2/TC-PTP was mediated by the gp130/IL-6R/JAK2/STAT3 pathway. Knockdown of Ptpn1/PTP1B or Ptpn2/TC-PTP via siRNA augmented sIL6Rα/IL-6-induced increase in STAT3 tyrosine phosphorylation in NRVCM. To investigate the role of PTP1B and TC-PTP in SICM we subjected cardiomyocyte-specific Ptpn1 and Ptpn2 double knockout (Ptpn1+2^{loxP/loxP loxP/loxP; MHC-cre}; cDKO) and wildtype mice (Ptpn1+2^{loxP/loxP loxP/loxP}) to CLP surgery and used sham operated mice as controls. Septic WT mice developed SICM indicated by reduced left-ventricular ejection fraction, while cDKO mice were protected from SICM.

Western Blot analysis of left ventricular tissue revealed an increased phosphorylation of endothelial nitric oxide synthase (eNOS) at baseline as well as under septic conditions in cDKO mice. qRT-PCR showed decreased levels of endoplasmatic reticulum stress markers (Atf6, Perk, Ire1a) in cDKO mice on baseline and in response to CLP compared to their respective WT controls. Expression of interferon-γ dependent genes was higher upregulated in hearts of septic wildtype than in DKO mice compared to their respective controls.

To conclude, proinflammatory cytokines, like sIL6Rα/IL-6, increase Ptpn1 and Ptpn2 gene expression in NRVCM. IL-6 via gp130, JAK2 and STAT3 mediates Ptpn1 and Ptpn2 gene expression in heart in vivo. Sepsis-induced cardiomyopathy is attenuated in cardiomyocyte-specific Ptpn1/Ptpn2 cDKO mice. This protective phenotype can be attributed to increased eNOS phosphorylation, reduced expression of ER stress markers and increased interferon signaling.