UC Merced

The need for non-invasive therapies to address longstanding healthcare challenges is ever-present. Every year, cancer patients undergo harsh radiation therapies to combat the growth of aggressive tumors. Improving recovery periods of these patients is a challenge faced by healthcare professionals at large. Using the planarian model, we developed techniques to isolate adult planarian stem cells in-vivo and used this method to study the effects of steady-state direct current (DCSS) in the complexities of the adult model organism. We discovered that exposure of transplanted planaria to DCSS resulted in an overall resurgence of stem cell populations within distal irradiated tissues in manner which is sensitive to cytosolic Ca2+ influx. Within minutes of DCSS exposure, planarian stem cell-specific gene expression can be seen returning to lethally irradiated tissue. Moreover, DCSS activates DNA repair mechanisms leading to improved DNA integrity within cells exposed to γ-irradiation. However, the effects of DCSS on planarian stem cells are not restricted to irradiated tissues as they were found to significantly impact planarian stem cell-specific gene expression and mitotic distribution within unirradiated planaria. This work demonstrates the capacity for DCSS to effectively repopulate damaged irradiated tissues with cycling stem cells through mechanisms which are sensitive to Ca2+ regulation.

Bioelectric governance of stem cells using DCSS is made possible by existing networks within stem cells which are designed to respond to naturally occurring bioelectric signals. A common endogenous steady-state electrical signal occurs during tissue injury by which the introduction of epithelial lesions consequently establishes a steady-state electric current. Thus, we sought to better understand the still obscure role of injury induced currents in the initiation and establishment of well-known wound response characteristics. To simulate injury induced currents without introducing physical injury, we developed new techniques to precisely expose planarian epithelial tissues to doses of the nonionic detergent, triton X-100 (trtx), resulting in local tissue depolarization. As a result, trtx-mediated tissue depolarization induced systemic mitotic responses from planarian stem cells while simultaneously generating transcriptomic responses of known planarian wound response genes, many of which closely resemble temporal patterns previously reported during actual tissue injury.

In contrast to DCSS, whose cellular interactions are restricted to the outer cell membrane, pulsed direct current stimulation (DCSP) is a common technique whose current effectively bypasses the highly resistive cell membrane and has been used by researchers as a tool to influence the behavior of cells. Exposure of planaria to DCSP lead to dramatic changes in stem cell proliferation dynamics and strongly impacted the large-scale morphology of differentiated neural tissues. In addition, planarian DCSP effectively reprogrammed tissue identity during planaria regeneration, resulting in complete anterior-posterior (AP) reversal. Surprisingly, signs of AP reprograming caused by DCSP can be seen in the initial stages of planarian regeneration, where expression of anterior specific gene smed-notum is missing in the anterior and inappropriately expressed in the posterior of regenerating DCSP planaria. In summary, we implemented a multifaceted approach that utilizes in-vivo techniques to demonstrate the potential for bioelectric signaling to mediate stem cell-related functions within the adult planaria model organism.