External bioelectric control of tissue hydrostatic pressure and ion pumping.

Abstract

Direct-Current (DC) currents exist throughout the body and regulate cellular responses spanning directed cell migration (electrotaxis) to transcriptional regulation. New approaches using electrical cues to control biological systems are, therefore, quite exciting, and we have previously demonstrated electrically programmable collective migration in epithelia. Here, we demonstrate those same cues reprogramming 3D growth in lumenized tissues such as hollow kidney spheroids and intestinal organoids. We found that electrical stimulation induces a rapid, powerful, and reversible swelling in these tissues, and we discuss how external electrical stimulation can control the inflation of lumenized structures and cellular mechanisms mediating the response. We first studied hollow kidney spheroids within a hydrogel integrated into our SCHEEPDOG electrobioreactor. This allowed 3D, timelapse imaging during electrical stimulation. Hollow spheroids inflated nearly 3X by volume relative to control spheroids within 4 hrs of stimulation. The rate and magnitude of inflation increased with increasing electric field strength, and overly strong field gradients induced ‘popping’. We hypothesized that the dense actomyosin network at the apical surface of the structures provided a physical limit to the inflation response, and showed that inhibiting actomyosin contractility prevented popping and increased the maximum swelling volume. We used ion channel inhibitors to determine that the majority of the response can be attributed to the CFTR ion channel (apical chloride channel) and NKCC (basal sodium/potassium channel). Our computational model relating direct-current fields, electrochemistry, and hydrostatic pressure capture many of these effects, as well as predicting asymmetric ion distributions around spheroids. Interestingly, 3D cross-sections of inflated tissues reveal asymmetric cell shapes on the anode/cathode cysts of the spheroids. We have recently confirmed that mouse intestinal organoids also inflate upon field stimulation in a CFTR-mediated fashion, and are exploring other lumenized tissues to assess the generality of this phenomenon.