Weak magnetic fields affect reactive oxygen species levels, stem cell proliferation/differentiation, and new tissue growth.

Reactive oxygen species (ROS) signaling regulates cell behaviors and tissue growth in development, regeneration, and cancer. Commonly, ROS are modulated pharmacologically, which while effective comes with potential complications such as off-target effects and lack of drug tolerance. Thus, additional non-invasive therapeutic methods are necessary. Recent advances have highlighted the use of weak magnetic fields (WMFs, <1 mT) as one promising approach. We previously showed that 200 μT WMFs inhibit ROS formation and block planarian regeneration. However, WMF research in different model systems at various field strengths have produced a range of results that do not fit common dose response curves, making it unclear if WMF effects are predictable. Here, we test hypotheses based on spin state theory and the radical pair mechanism, which outlines how magnetic fields can alter the formation of radical pairs by changing electron spin states. This mechanism suggests that across a broad range of field strengths (0–900 μT) some WMF exposures should be able to inhibit while others promote ROS formation in a binary fashion. Our data reveal that WMFs can be used for directed manipulation of stem cell proliferation, differentiation, and tissue growth in predictable ways for both loss and gain of function during regenerative growth. Furthermore, we examine two of the most common ROS signaling effectors, hydrogen peroxide and superoxide, to begin the identification and elucidation of the specific molecular targets by which WMFs affect tissue growth. Together, our data reveal that the cellular effects of WMF exposure are highly dependent on ROS, and we identify superoxide as a specific ROS being modulated. Altogether, these data highlight the possibilities of using WMF exposures to control ROS signaling in vivo and represent an exciting new area of research.

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A key requirement of tissue/organ regeneration is the ability to induce appropriate shape in situ. Regenerated structures need to be integrated with pre-existing ones, through the combined regulation of new tissue growth and the scaling of surrounding tissues. This requires a tightly coordinated control of individual cell functions such as proliferation and stem cell differentiation. While great strides have been made in elucidating cell growth and differentiation mechanisms, how overall shape is generated during regeneration remains unknown. This is because a significant gap remains in our understanding of how cell behaviors are coordinated at the level of tissues and organs. The highly regenerative planarian flatworm has emerged as an important model for defining and understanding regenerative shape mechanisms. This review provides an overview of the main processes known to regulate tissue and animal shape during planarian regeneration: adult stem cell regulation, the reestablishment of body axes, tissue remodeling in pre-existing structures, organ scaling and the maintenance of body proportion, and the bioelectrical regulation of animal morphology. In order for the field to move forward, it will be necessary to identify shape mutants as a means to uncover the molecular mechanisms that synchronize all these separate processes to produce the worm's final regenerative shape. This knowledge will also aid efforts to define the mechanisms that control the termination of regenerative processes.

Reactive oxygen species (ROS), such as hydrogen peroxide, are conserved and critical components of both wound healing and regeneration. Even though millions are affected each year by poor wound healing and an inability to restore functional tissue, how the same ROS-mediated signaling regulates these two different processes is not fully understood. Here, we investigate the role(s) of ROS during planarian wound healing and regeneration. We show ROS accumulate after injury and are required for wound closure (by promoting cytoskeletal movements) and regrowth (by promoting blastema formation). We found that different threshold levels of ROS regulate separate downstream targets to control wound healing (jun-1) versus regeneration (hsp70). By only manipulating ROS levels, we were able to control which injury-induced program was initiated: failure to close (chronic wound), healing only (no blastema), or full regeneration. Our results demonstrate that healing versus regenerative outcomes are based on differential ROS-mediated gene expression soon after injury. This study highlights ROS signaling as a potential therapeutic means to control wound repair mechanisms in multiple contexts. Therefore, investigating the mechanisms by which ROS control different tissue repair processes will be necessary not only for regenerative medicine but to improve clinical outcomes for chronic wounds and fibrosis.

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