Biology subjects

Mohan, M. L.

Publications and source records attributed to Mohan, M. L..

3 recordsLinked to original sources

bioRxiv2021

Kinase independent function of PI3Kγ modulates calcium re-uptake by regulating phospholamban function

RationaleGenetic deletion of Phosphoinositide 3-kinase (PI3K{gamma}) in mice (PI3K{gamma}-/-) results in increased cAMP levels and enhanced ventricular rate/contractility. Whether PI3K{gamma} plays a role in cardiac contractility by altering intracellular calcium recycling is not known. ObjectiveTo understand the mechanism of PI3K{gamma} mediated regulation of cardiac contractility. Methods and ResultsCaffeine treatment of adult cardiomyocytes from PI3K{gamma}-/- mice showed significantly reduced calcium reuptake by sarcoendoplasmic reticulum (SR) indicating that PI3K{gamma} locally regulates SR function. This resulted in elevated levels of intracellular calcium for prolonged period following caffeine. Our findings show that delayed re-uptake of calcium was caused by changes in phosphorylation of phospholamban (PLN), a major regulator of SR calcium reuptake. PI3K{gamma}-/- cardiomyocytes show significantly reduced PLN phosphorylation due to increase in PLN-associated protein phosphatase (PP) activity as reflected by decreased demethylated-PP2A. Consistently, the altered calcium regulation in the cardiomyocytes of PI3K{gamma}-/- can be restored by inhibition of PP by okadaic acid. Unexpectedly, cardiomyocyate-specific overexpression of kinase-dead PI3K{gamma} PI3K{gamma}inact) in the global PI3K{gamma}-/- cardiomyocytes normalized caffeine induced calcium reuptake, restored PLN phosphorylation, and decreased PLN-associated PP activity reflected by increased demethylated-PP2A. ConclusionsThese studies bring-to-fore an unrecognized regulation of PLN by PI3K{gamma} through PP2A with implications in deleterious cardiac remodeling as PI3K{gamma} is significantly upregulated following cardiac stress.

molecular biology↗

bioRxiv2020

beta-blocker reverses inhibition of beta-2 adrenergic receptor resensitization by hypoxia

Ischemia/hypoxia is major underlying cause for heart failure and stroke. Although beta-adrenergic receptor ({beta}AR) is phosphorylated in response to hypoxia, less is known about the underlying mechanisms. Hypoxia results in robust GRK2-mediated {beta}2AR phosphorylation but does not cause receptor internalization. However, hypoxia leads to significant endosomal-{beta}2AR phosphorylation accompanied by inhibition of {beta}2AR-associated protein phosphatase 2A (PP2A) activity impairing resensitization. Phosphoinositide 3-kinase {gamma} (PI3K{gamma}) impedes resensitization by phosphorylating endogenous inhibitor of protein phosphatase 2A, I2PP2A that inhibits PP2A activity. Hypoxia increased PI3K{gamma} activity leading to significant phosphorylation of I2PP2A resulting in inhibition of PP2A and consequently resensitization. Surprisingly, {beta}-blocker abrogated hypoxia-mediated {beta}2AR phosphorylation instead of phosphorylation in normoxia. Subjecting mice to hypoxia leads to significant cardiac dysfunction and {beta}2AR phosphorylation showing conservation of non-canonical hypoxia-mediated pathway in vivo. These findings provide mechanistic insights on hypoxia-mediated {beta}AR dysfunction which is rescued by {beta}-blocker and will have significant implications in heart failure and stroke.

biochemistry↗

bioRxiv2020

The IgG3 Subclass of β1-adrenergic receptor autoantibody is an endogenous biaser of β1AR signaling

Autoantibodies recognizing human {beta}1ARs generated due to dysregulation in autoimmune response are generally associated with deleterious cardiac outcomes. However, cellular studies show that isolates of {beta}1AR autoantibody from patients differentially modulate {beta}1AR function. {beta}1AR autoantibodies belong to the IgG class of immunoglobulins, however it is not known whether the IgG sub-classes mediate variability in {beta}1AR responses. To determine whether the IgG3 subclass of {beta}1AR autoantibodies uniquely modulate {beta}1AR function, HEK293 cells stably expressing human {beta}1ARs were utilized. Treatment of cells with IgG3(-) serum resulted in significant increase of cAMP compared to IgG3(+) serum. Pre-treatment of cells with IgG3(+) serum impaired dobutamine-mediated Adenylate Cyclase (AC) activity and cAMP generation whereas, it surprisingly increased AC activity and cAMP generation with {beta}-blocker metoprolol. Consistently, purified IgG3(+) {beta}1AR autoantibodies impaired dobutamine-mediated cAMP while elevating metoprolol-mediated AC activity and cAMP. Despite IgG3(+) autoantibodies reducing cAMP response to dobutamine, they mediate significant ERK activation upon dobutamine. IgG3(+) {beta}1AR autoantibodies did not alter {beta}2AR function, reflecting their specificity. The study shows that IgG3(+) {beta}1AR autoantibody impairs agonist-mediated G-protein coupling while preferentially mediating G-protein-independent ERK activation. Furthermore, it uniquely biases {beta}-blocker towards G-protein coupling. This unique biasing capabilities of IgG3(+) {beta}1AR autoantibodies may underlie the beneficial outcomes in patients.

pharmacology and toxicology↗