Compensatory ion transport buffers daily protein rhythms to regulate osmotic balance and cellular physiology

Alessandra Stangherlin,John S O’Neill,Rachel S Edgar,Andrew D Beale,R.m Voorhees ,Gerben Van Ooijen,Jason Day,Edward A Hayter ,David A Bechtold,Peter Newham,Silvia Barbiero,J P Watson ,Nicolas Lequeux,Emmanuel Derivery,Thomas Pons,Alina Guna,Eline Bartolami,Alison J Inglis,Aiwei Zeng,Stefan Matile,Estere Seinkmane,Sew Peak Chew,David Wong ,Marrit Putker

doi:10.1038/s41467-021-25942-4

Abstract

Between 6–20% of the cellular proteome is under circadian control and tunes mammalian cell function with daily environmental cycles. For cell viability, and to maintain volume within narrow limits, the daily variation in osmotic potential exerted by changes in the soluble proteome must be counterbalanced. The mechanisms and consequences of this osmotic compensation have not been investigated before. In cultured cells and in tissue we find that compensation involves electroneutral active transport of Na+, K+, and Cl− through differential activity of SLC12A family cotransporters. In cardiomyocytes ex vivo and in vivo, compensatory ion fluxes confer daily variation in electrical activity. Perturbation of soluble protein abundance has commensurate effects on ion composition and cellular function across the circadian cycle. Thus, circadian regulation of the proteome impacts ion homeostasis with substantial consequences for the physiology of electrically active cells such as cardiomyocytes.

Highlights

Between 6–20% of the cellular proteome is under circadian control and tunes mammalian cell function with daily environmental cycles
The molecular mechanisms of SLC12A regulation are already well-characterized in the context of Regulatory volume increase/decrease (RVI/D), following extracellular osmotic challenge[17,20,62,67,68,69], we propose that RVI/D regulation of NKCC1 vs. KCC extends to encompass intracellular osmotic challenge over the circadian cycle without significant volume change
We addressed this aspect of cell physiology in mouse fibroblasts, where we identified cell-autonomous rhythms in soluble protein abundance and molecular crowding sustained by daily rhythms of mechanistic target-of-rapamycin complexes (mTORC) activity, in the absence of any corresponding alteration in cell volume

Summary

Introduction

Between 6–20% of the cellular proteome is under circadian control and tunes mammalian cell function with daily environmental cycles. Cells must accommodate any daily variation in cytosolic protein abundance without compromising osmotic homeostasis (osmostasis), which would have deleterious effects on cellular function and viability[17,18,19,20]. Major components of RVI/D are the electroneutral cotransporters of the SLC12A family: ubiquitously-expressed symporters that regulate transmembrane ion gradients and cell volume across a wide variety of tissues[22]. These chloride cotransporters couple ion transport with the respective transmembrane Na+ and K+ gradients that are established by the universal and essential Na/K-ATPase antiporter[17].

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Conclusion