The IP ₃ Receptor Regulates Cardiac Hypertrophy in Response to Select Stimuli

Abstract

Objective: Here, we generated conditional, heart-specific transgenic mice with both gain-and loss-of-function for IP 3 receptor signaling to examine its hypertrophic growth effects following pathological and physiological stimulation. Methods and Results:Overexpression of the mouse type-2 IP 3 receptor (IP 3 R2) in the heart generated mild baseline cardiac hypertrophy at 3 months of age. Isolated myocytes from overexpressing lines showed increased Ca 2؉ transients and arrhythmias in response to endothelin-1 stimulation. Although low levels of IP 3 R2 overexpression failed to augment/synergize cardiac hypertrophy following 2 weeks of pressure-overload stimulation, such levels did enhance hypertrophy following 2 weeks of isoproterenol infusion, in response to G␣q overexpression, and/or in response to exercise stimulation. To inhibit IP 3 signaling in vivo, we generated transgenic mice expressing an IP 3 chelating protein (IP 3 -sponge). IP 3 -sponge transgenic mice abrogated cardiac hypertrophy in response to isoproterenol and angiotensin II infusion but not pressure-overload stimulation. Mechanistically, IP 3 R2-enhanced cardiac hypertrophy following isoproterenol infusion was significantly reduced in the calcineurin-A␤-null background. IP 3 is a second messenger generated by hydrolysis of membrane lipid phosphatidyl-inositol 4,5-bisphosphate by phospholipase (PL)C in response to GPCR activation associated with growth factors and neuroendocrine agonists. 6 Once generated, IP 3 causes Ca 2ϩ release from intracellular stores by binding the IP 3 receptor (IP 3 R), an intracellular Ca 2ϩ release channel embedded in the sarcoplasmic reticulum (SR) and nuclear envelope. Cardiac hypertrophy has been associated with increased PLC activity and increased generation of IP 3 . 7,8 Moreover, expression of IP 3 Rs is increased in both human and animal models of heart failure, suggesting that this form of Ca The IP 3 R family consists of 3 genes 11 : IP 3 R1, IP 3 R2, and IP 3 R3. IP 3 R2 is thought to be the most prominent gene expressed in the heart, 12,13 and its deletion in gene-targeted mice abolished positive inotropy and spontaneous Ca 2ϩ release in atrial myocytes caused by endothelin (ET)-1 stimulation. 13 Even though ventricular myocytes express much lower levels of IP 3 Rs than atrial myocytes, these receptors, in some reports, can alter Ca 2ϩ release and predispose to arrhythmia. 14 -16 Although the IP 3 Rs can affect Ca 2ϩ release, it has not been possible to determine their necessity in regulating the cardiac hypertrophic response because all 3 receptor genes are expressed in the heart, complicating a gene-targeting approach, not withstanding lethality issues in IP 3 R1-null mice. Here, we generated transgenic mice with IP 3 R2 overexpression and the inhibitory IP 3 -sponge protein, demonstrating for the first time that the IP 3 R functions as a hypertrophic effector in vivo. Conclusion Methods Generation of Transgenic MicecDNAs encoding mouse IP 3 R2 and recombinant Flag-tagged IP 3 -sponge protein 17,18 were...

Intracrine endothelin signaling evokes IP3-dependent increases in nucleoplasmic Ca2+ in adult cardiac myocytes

“…IP3R-mediated Ca 2+ -release is involved in hypertrophy induced by isoproterenol and Ang II but not by constriction of the transverse aorta [96]. The increase in [Ca 2+ ] n mediated by IP3R activates CaMKIIδ within the nucleus.…”

Mutual antagonism between IP3RII and miRNA-133a regulates calcium signals and cardiac hypertrophy

“…To this end, we used mice engineered to inducibly express the IP 3 -sponge, a fragment of IP 3 RI spanning its ligand-binding domain that binds free IP 3 with very high affinity (Uchiyama et al, 2002;Nakayama et al, 2010). These mice show blunted hypertrophic responses to systemic infusion with the hypertrophic agonists angiotensin II and isoproterenol (Nakayama et al, 2010).…”

Vascular Endothelial σ₁-Receptor Stimulation With SA4503 Rescues Aortic Relaxation via Akt/eNOS Signaling in Ovariectomized Rats With Aortic Banding

“…34 When mice that overexpressed the IP3 receptor (IP3R) are crossed with calcineurinnull mice, isoproterenol-induced cardiac hypertrophy is inhibited in their offspring. 35 We speculate that increased calcineurin activity is related to an increase in intracellular basal Ca 2+ levels through IP3R-mediated Ca 2+ release from the endoplasmic reticulum. Chronic treatment of OVX-PO rats with SA4503 completely rescued Akt dephosphorylation, suggesting that Ca 2+ leakage from the endoplasmic reticulum is inhibited by σ1R stimulation with SA4503.…”