Reprogramming cells and tissue patterning via bioelectrical pathways: molecular mechanisms and biomedical opportunities

Abstract

Transformative impact in regenerative medicine requires more than the reprogramming of individual cells: advances in repair strategies for birth defects or injuries, tumor normalization, and the construction of bioengineered organs and tissues all require the ability to control large-scale anatomical shape. Much recent work has focused on the transcriptional and biochemical regulation of cell behaviour and morphogenesis. However, exciting new data reveal that bioelectrical properties of cells and their microenvironment exert a profound influence on cell differentiation, proliferation, and migration. Ion channels and pumps expressed in all cells, not just excitable nerve and muscle, establish resting potentials that vary across tissues and change with significant developmental events. Most importantly, the spatio-temporal gradients of these endogenous transmembrane voltage potentials (Vmem) serve as instructive patterning cues for large-scale anatomy, providing organ identity, positional information, and prepattern template cues for morphogenesis. New genetic and pharmacological techniques for molecular modulation of bioelectric gradients in vivo have revealed the ability to initiate complex organogenesis, change tissue identity, and trigger regeneration of whole vertebrate appendages. A large segment of the spatial information processing that orchestrates individual cells’ programs towards the anatomical needs of the host organism is electrical; this blurs the line between memory and decision-making in neural networks and morphogenesis in non-neural tissues. Advances in cracking this bioelectric code will enable the rational reprogramming of shape in whole tissues and organs, revolutionizing regenerative medicine, developmental biology, and synthetic bioengineering.

Mechanisms of urodele limb regeneration

“…In a series of papers, Levin and colleagues have described the bioelectric code and provided extensive evidence for its existence and function. In addition, they have provided many examples of manipulation of the code that result in the rearrangement of large‐scale pattern (Levin, 2011, 2013; Mustard & Levin, 2014; Pezzulo & Levin, 2015). For example, a number of cell membrane channels associated with eye formation in Xenopus embryos induced eye formation in the gut, tail, or lateral plate mesoderm when misexpressed in these regions.…”

Local and long-range endogenous resting potential gradients antagonistically regulate apoptosis and proliferation in the embryonic CNS

“…Spatio-temporal gradients of V mem across groups of cells serve as instructive bioelectric signals (Levin, 2013b, Levin, 2014b, Mustard and Levin, 2014. Such patterns of resting potential within living tissues (bioelectric signals) have been studied in the context of their roles in cell migration and wound healing (Cao et al, 2013, Jaffe, 1979, McCaig et al, 2005, Richard B. Borgens, 1989, Zhao et al, 2006 and have long been proposed to direct growth and form in vivo (Burr, 1932).…”

“…Bioelectric signals are implicated in vertebrate appendage regeneration , Tseng et al, 2010, cancer initiation and metastasis (Binggeli and Weinstein, 1986b, Blackiston et al, 2011, Brackenbury, 2012, Chernet and Levin, 2013b, Lobikin et al, 2012b, left-right patterning (Aw et al, 2008, Aw et al, 2010, Levin et al, 2002, planarian head induction (Beane et al, 2011, Beane et al, 2013, Marsh and Beams, 1947, and eye and brain formation (Nuckels et al, 2009, Pai et al, 2015, Pai et al, 2012a, Pai et al, 2012b. Thus bioelectric signals have been shown to be important regulators of large-scale patterning and tissue and organ identity (Levin, 2009, Levin, 2013a, Levin and Stevenson, 2012, Tseng and Levin, 2013a.…”

A linear-encoding model explains the variability of the target morphology in regeneration

“…Importantly, the linear encoding of the target morphology's representation in tissue properties can be very straightforward (such as Hox gene prepatterns that specify underlying tissue fate), or they can be encoded in a more complex manner (linear transformations). For example, a neural network (or a bioelectrical network of non-neural cells [69,150]) could store information that guides growth towards a specifically remembered shape, but the information is not stored in a simple 'image' of the final product but in the distribution of node activation strengths. Either type of encoding can function as target end states of cybernetic goal-seeking mechanisms, such as algorithms that form a shape by comparing the current state with a target state-a novel approach to model a range of regenerative phenomena as discussed above.…”