Reversible differentiation of immortalized human bladder smooth muscle cells accompanied by actin bundle reorganization

Previous studies have shown that phenotypic modulation of smooth muscle cells (SMCs) plays a pivotal role in human diseases. However, the molecular mechanisms underlying the reversible differentiation of SMCs remain elusive particularly because cultured SMCs that reproducibly exhibit bidirectional phenotypic modulation have not been established. Here we established an immortalized human bladder SMC line designated as hBS11. Under differentiation-inducing conditions, hBS11 cells underwent smooth muscle differentiation accompanied by the robust expression of smooth muscle differentiation markers and isoform-dependent reorganization of actin bundles. The cholinergic receptor agonist carbachol increased intracellular calcium in differentiated hBS11 cells in an acetylcholine muscarinic receptor-dependent manner. Differentiated hBS11 cells displayed contractile properties depending on the elevation in the levels of intracellular calcium. Depolarization of membrane potential triggered inward sodium current in differentiated hBS11 cells. However, differentiated hBS11 cells lost the differentiated phenotype and resumed mitosis when re-fed with growth medium. Our study provides direct evidence pertaining to the human bladder SMCs being able to retain the capacity of reversible differentiation and that the reorganization of actin bundles is involved in the reinstatement of contractility. Moreover, we have established a human SMC line retaining high proliferating potential without compromising differentiation potential.