Pharmacology of the Human Fetus: Adrenergic Receptor Function in the Small Intestine

Insulin impairs β2-adrenergic receptor (β2AR) function via trans-phosphorylation through G protein-coupled receptor kinase 2 (GRK2). However, less is known about dephosphorylation mechanisms mediated by protein phosphatase 2A (PP2A) during this insulin-β2AR cross-talk. Pharmacologic or genetic inhibition of phosphoinositide 3-kinase γ (PI3Kγ) unexpectedly resulted in significant reduction of insulin-mediated β2AR phosphorylation. Interestingly, β2AR-associated phosphatase activity was inhibited by insulin but was reversed by knock-down of PI3Kγ showing negative regulation of PP2A by PI3Kγ. Co-immunoprecipitation and surface plasmon resonance studies using purified proteins showed that GRK2 and PI3Kγ form a complex and could be recruited to β2ARs as GRK2 interacts with insulin receptor substrate (IRS) following insulin treatment. Further, co-immunoprecipitation studies showed that PI3Kγ directly interacted with both IRS-1 and IRS-2 but only IRS-2 interaction with PI3Kγ significantly increased following insulin stimulation. These results indicated that PI3Kγ could also be directly recruited to the receptor complex by IRS-2. Consistently, β-blocker pretreatment did not reduce insulin-mediated β2AR phosphorylation indicating agonist- and Gβγ-independent non-canonical regulation of receptor function. Mechanistically, PI3Kγ inhibits PP2A activity at the βAR complex by phosphorylating an intracellular inhibitor of PP2A (I2PP2A). Knock-down or CRISPR ablation of endogenous I2PP2A unlocked PP2A inhibition mediating β2AR dephosphorylation showing an unappreciated acute regulation of PP2A in mediating insulin-β2AR cross-talk.

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Platelet reactivity and its dependence on alpha-adrenergic receptor function in patients with ischaemic heart disease.

Heart ◽

10.1136/hrt.49.1.20 ◽

1983 ◽

Vol 49 (1) ◽

pp. 20-25 ◽

Cited By ~ 12

Author(s):

M Yokoyama ◽

S Kawashima ◽

S Sakamoto ◽

H Akita ◽

T Okada ◽

...

Keyword(s):

Heart Disease ◽

Ischaemic Heart Disease ◽

Adrenergic Receptor ◽

Platelet Reactivity ◽

Receptor Function ◽

Alpha Adrenergic Receptor

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Dexmedetomidine Prevents Excessive γ-Aminobutyric Acid Type A Receptor Function after Anesthesia

Anesthesiology ◽

10.1097/aln.0000000000002311 ◽

2018 ◽

Vol 129 (3) ◽

pp. 477-489 ◽

Cited By ~ 15

Author(s):

Dian-Shi Wang ◽

Kirusanthy Kaneshwaran ◽

Gang Lei ◽

Fariya Mostafa ◽

Junhui Wang ◽

...

Keyword(s):

Problem Solving ◽

Adrenergic Receptor ◽

Hippocampal Neurons ◽

Type A ◽

Surface Expression ◽

Aminobutyric Acid ◽

Cell Surface Expression ◽

Receptor Function ◽

Anesthetic Drugs ◽

Acid Type

Abstract What We Already Know about This Topic What This Article Tells Us That Is New Background Postoperative delirium is associated with poor long-term outcomes and increased mortality. General anesthetic drugs may contribute to delirium because they increase cell-surface expression and function of α5 subunit-containing γ-aminobutyric acid type A receptors, an effect that persists long after the drugs have been eliminated. Dexmedetomidine, an α2 adrenergic receptor agonist, prevents delirium in patients and reduces cognitive deficits in animals. Thus, it was postulated that dexmedetomidine prevents excessive function of α5 γ-aminobutyric acid type A receptors. Methods Injectable (etomidate) and inhaled (sevoflurane) anesthetic drugs were studied using cultured murine hippocampal neurons, cultured murine and human cortical astrocytes, and ex vivo murine hippocampal slices. γ-Aminobutyric acid type A receptor function and cell-signaling pathways were studied using electrophysiologic and biochemical methods. Memory and problem-solving behaviors were also studied. Results The etomidate-induced sustained increase in α5 γ-aminobutyric acid type A receptor cell-surface expression was reduced by dexmedetomidine (mean ± SD, etomidate: 146.4 ± 51.6% vs. etomidate + dexmedetomidine: 118.4 ± 39.1% of control, n = 8 each). Dexmedetomidine also reduced the persistent increase in tonic inhibitory current in hippocampal neurons (etomidate: 1.44 ± 0.33 pA/pF, n = 10; etomidate + dexmedetomidine: 1.01 ± 0.45 pA/pF, n = 9). Similarly, dexmedetomidine prevented a sevoflurane-induced increase in the tonic current. Dexmedetomidine stimulated astrocytes to release brain-derived neurotrophic factor, which acted as a paracrine factor to reduce excessive α5 γ-aminobutyric acid type A receptor function in neurons. Finally, dexmedetomidine attenuated memory and problem-solving deficits after anesthesia. Conclusions Dexmedetomidine prevented excessive α5 γ-aminobutyric acid type A receptor function after anesthesia. This novel α2 adrenergic receptor- and brain-derived neurotrophic factor-dependent pathway may be targeted to prevent delirium.

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Abstract 469: Targeting Beta Adrenergic Receptor Resensitization Aids in Preservation of Receptor Function

Circulation Research ◽

10.1161/res.121.suppl_1.469 ◽

2017 ◽

Vol 121 (suppl_1) ◽

Author(s):

Elizabeth E Martellli ◽

Yu Sun ◽

John George ◽

Maradumane L Mohan ◽

Randall Starling ◽

...

Keyword(s):

Heart Failure ◽

Small Molecule ◽

In Silico ◽

Adrenergic Receptor ◽

Human Heart ◽

Receptor Function ◽

Human Heart Failure ◽

Pp2a Activity ◽

Pi3k Activity ◽

Underlying Mechanisms

Beta adrenergic receptor (βAR) down-regulation and desensitization are hallmarks of heart failure. Traditionally, it has been considered that increased desensitization mechanisms underlie βAR dysfunction in heart failure but it is not known whether resensitization of βARs is altered and is an integral contributor to heart failure. We have previously shown that resensitization is regulated by inhibition of PP2A by I2PP2A via PI3Kγ (Vasudevan et. al., 2011), the underlying mechanisms of I2PP2A binding to PP2A are not well understood. We used PyMOL software to find the binding interaction between PP2A and I2PP2A. Based on in silico predictions, we generated a mutant PP2A that when expressed would compete out I2PP2A and inhibit I2PP2A from binding to endogenous PP2A. Expression of PP2A mutant in β2AR expressing cells showed preservation of β2AR function following stimulation as measured by reduced β2AR phosphorylation, increased cAMP generation and increased phosphatase function. We also generated a small molecule from our in silico predictions that could target the interface of I2PP2A and PP2A binding to find that disruption of the PP2A/I2PP2A interaction underlies receptor function. We will use this small molecule to look at preservation of βAR function and amelioration of cardiac function. To test whether resensitization is altered in heart failure we used plasma membrane and endosomal fractions from non-failing and paired pre- and post-LVAD samples to show PI3K activity, PP2A activity, β2AR phosphorylation and adenylyl cyclase activity as a measure of recovery in βAR function. Our studies showed that endosomal fractions from human heart failure samples had elevated PI3K activity associated with reduced PP2A activity supporting the idea that βAR resensitization is inhibited in human heart failure samples. Since human heart failure samples have inhibited resensitization we tested the underlying mechanisms regulating βAR resensitization. Thus ongoing studies suggest that targeting the resensitization of βAR could provide beneficial cardiac remodeling in conditions of chronic mechanical overload and will be further discussed.

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