Response of amputated rat limbs to fetal nerve tissue implants and direct current

Aging as a loss of morphostatic information: A developmental bioelectricity perspective

Maintaining order at the tissue level is crucial throughout the lifespan, as failure can lead to cancer and an accumulation of molecular and cellular disorders. Perhaps, the most consistent and pervasive result of these failures is aging, which is characterized by the progressive loss of function and decline in the ability to maintain anatomical homeostasis and reproduce. This leads to organ malfunction, diseases, and ultimately death. The traditional understanding of aging is that it is caused by the accumulation of molecular and cellular damage. In this article, we propose a complementary view of aging from the perspective of endogenous bioelectricity which has not yet been integrated into aging research. We propose a view of aging as a morphostasis defect, a loss of biophysical prepattern information, encoding anatomical setpoints used for dynamic tissue and organ homeostasis. We hypothesize that this is specifically driven by abrogation of the endogenous bioelectric signaling that normally harnesses individual cell behaviors toward the creation and upkeep of complex multicellular structures in vivo. Herein, we first describe bioelectricity as the physiological software of life, and then identify and discuss the links between bioelectricity and life extension strategies and age-related diseases. We develop a bridge between aging and regeneration via bioelectric signaling that suggests a research program for healthful longevity via morphoceuticals. Finally, we discuss the broader implications of the homologies between development, aging, cancer and regeneration and how morphoceuticals can be developed for aging.

Morphoceuticals: perspectives for discovery of drugs targeting anatomical control mechanisms in regenerative medicine, cancer and aging

Morphoceuticals are a new class of interventions that target the setpoints of anatomical homeostasis for efficient, modular control of growth and form. Here, we focus on a subclass: electroceuticals, which specifically target the cellular bioelectrical interface. Cellular collectives in all tissues form bioelectrical networks via ion channels and gap junctions that process morphogenetic information, controlling gene expression and allowing cell networks to adaptively and dynamically control growth and pattern formation. Recent progress in understanding this physiological control system, including predictive computational models, suggests that targeting bioelectrical interfaces can control embryogenesis and maintain shape against injury, senescence and tumorigenesis. We propose a roadmap for drug discovery focused on manipulating endogenous bioelectric signaling for regenerative medicine, cancer suppression and antiaging therapeutics. Teaser: By taking advantage of the native problem-solving competencies of cells and tissues, a new kind of top-down approach to biomedicine becomes possible. Bioelectricity offers an especially tractable interface for interventions targeting the software of life for regenerative medicine applications.

Bioelectric signaling in regeneration: Mechanisms of ionic controls of growth and form

The ability to control pattern formation is critical for the both the embryonic development of complex structures as well as for the regeneration/repair of damaged or missing tissues and organs. In addition to chemical gradients and gene regulatory networks, endogenous ion flows are key regulators of cell behavior. Not only do bioelectric cues provide information needed for the initial development of structures, they also enable the robust restoration of normal pattern after injury. In order to expand our basic understanding of morphogenetic processes responsible for the repair of complex anatomy, we need to identify the roles of endogenous voltage gradients, ion flows, and electric fields. In complement to the current focus on molecular genetics, decoding the information transduced by bioelectric cues enhances our knowledge of the dynamic control of growth and pattern formation. Recent advances in science and technology place us in an exciting time to elucidate the interplay between molecular-genetic inputs and important biophysical cues that direct the creation of tissues and organs. Moving forward, these new insights enable additional approaches to direct cell behavior and may result in profound advances in augmentation of regenerative capacity.

Genome-wide analysis reveals conserved transcriptional responses downstream of resting potential change in Xenopus embryos, axolotl regeneration, and human mesenchymal cell differentiation

Endogenous bioelectric signaling via changes in cellular resting potential (V_mem) is a key regulator of patterning during regeneration and embryogenesis in numerous model systems. Depolarization of V_mem has been functionally implicated in dedifferentiation, tumorigenesis, anatomical re‐specification, and appendage regeneration. However, no unbiased analyses have been performed to understand genome‐wide transcriptional responses to V_mem change in vivo. Moreover, it is unknown which genes or gene networks represent conserved targets of bioelectrical signaling across different patterning contexts and species. Here, we use microarray analysis to comparatively analyze transcriptional responses to V_mem depolarization. We compare the response of the transcriptome during embryogenesis (Xenopus development), regeneration (axolotl regeneration), and stem cell differentiation (human mesenchymal stem cells in culture) to identify common networks across model species that are associated with depolarization. Both subnetwork enrichment and PANTHER analyses identified a number of key genetic modules as targets of V_mem change, and also revealed important (well‐conserved) commonalities in bioelectric signal transduction, despite highly diverse experimental contexts and species. Depolarization regulates specific transcriptional networks across all three germ layers (ectoderm, mesoderm, and endoderm) such as cell differentiation and apoptosis, and this information will be used for developing mechanistic models of bioelectric regulation of patterning. Moreover, our analysis reveals that V_mem change regulates transcripts related to important disease pathways such as cancer and neurodegeneration, which may represent novel targets for emerging electroceutical therapies.

Effects of electromagnetic field (PEMF) exposure at different frequency and duration on the peripheral nerve regeneration: in vitro and in vivo study

PURPOSE

The purpose was to clarify the influence of frequency and exposure time of pulsed electromagnetic fields (PEMF) on the peripheral nerve regeneration.

MATERIALS AND METHODS

Immortalized rat Schwann cells (iSCs) (1 × 10(2)/well) were exposed at four different conditions in 1 mT (50 Hz 1 h/d, 50 Hz 12 h/d, 150 Hz 1 h/d and 150 Hz 12h/d). Cell proliferation, mRNA expression of S100 and brain-derived neurotrophic factor (BDNF) were analyzed. Sprague-Dawley rats (200-250 g) were divided into six groups (n = 10 each): control, sham, 50 Hz 1 h/d, 50 Hz 12 h/d, 150 Hz 1 h/d and 150 Hz 12 Hr/d. Mental nerve was crush-injured and exposed at four different conditions in 1 mT (50 Hz 1 Hr/d, 50 Hz 12 Hr/d, 150 Hz 1 h/d and 150 Hz 12 h/d). Nerve regeneration was evaluated with functional test, histomorphometry and retrograde labeling of trigeminal ganglion.

RESULTS

iSCs proliferation with 50 Hz, 1 h/d was increased from fourth to seventh day; mRNA expression of S100 and BDNF was significantly increased at the same condition from first week to third week (p < .05 vs. control); difference score was increased at the second and third week, and gap score was increased at the third under 50 Hz 1 h PEMF compared with control while other conditions showed no statistical meaning. Axon counts and retrograde labeled neurons were significantly increased under PEMF of four different conditions compared with control. Although there was no statistical difference, 50 Hz, 1 h PEMF showed highest regeneration ability than other conditions.

CONCLUSION

PEMF enhanced peripheral nerve regeneration, and that it may be due to cell proliferation and increase in BDNF and S100 gene expression.

The strategy and method in modulating finger regeneration

The tip of the human finger can regenerate if the amputation is distal to the nail bed, usually in young children. Studies in regeneration of rodent digits have shown that regeneration occurs if the amputation is distal to the mid-third phalanx for certain ages. The digit contains many different components, such as muscle, tendon, bone, skin, nerves and blood vessels, which must all be regrown in the proper location in order to restore functionality. The mechanism behind the complex healing/regeneration processes is still under investigation; however, improvements in injured finger regeneration have been gradually developing in animal models over the past few years. This review discusses a few strategies and methods to possibly enhance digit regeneration beyond current natural limits, focusing on aspects including scarless wound healing, cell-based treatments, tissue engineering and electrical stimulation.

BioDome regenerative sleeve for biochemical and biophysical stimulation of tissue regeneration

Previous research on vertebrate limb regeneration indicates there are several mediating factors involved during the re-growth process. These factors are both biochemical and biophysical. While the phenomenon of adult limb regeneration does not occur naturally in mammalian species, prior research has focused mainly on biochemical modes of stimulating tissue growth and regeneration. The BioDome was aimed at developing a new experimental tool to permit the more systematic study of the impact of biophysical and biochemical factors on mammalian tissue regeneration. The BioDome is a multi-component sleeve assembly that encompasses the wound site of an amputated murine digit and provides an environment conducive to tissue regeneration. The studies showed that the BioDome was effective in supporting early stages of murine digit tip regeneration when combined with a porcine urinary bladder matrix (UBM) pepsin digest and electrical stimulation. The hydrated inner environment of the BioDome influenced regeneration, with additional effects seen with the application of electrical stimulation and pharmacological treatments.

Bioelectric mechanisms in regeneration: Unique aspects and future perspectives

Regenerative biology has focused largely on chemical factors and transcriptional networks. However, endogenous ion flows serve as key epigenetic regulators of cell behavior. Bioelectric signaling involves feedback loops, long-range communication, polarity, and information transfer over multiple size scales. Understanding the roles of endogenous voltage gradients, ion flows, and electric fields will contribute to the basic understanding of numerous morphogenetic processes and the means by which they can robustly restore pattern after perturbation. By learning to modulate the bioelectrical signals that control cell proliferation, migration, and differentiation, we gain a powerful set of new techniques with which to manipulate growth and patterning in biomedical contexts. This chapter reviews the unique properties of bioelectric signaling, surveys molecular strategies and reagents for its investigation, and discusses the opportunities made available for regenerative medicine.

Large-scale biophysics: ion flows and regeneration

Regeneration requires exquisite orchestration of growth and morphogenesis. A powerful but still largely mysterious system of biophysical signals functions during regeneration, embryonic development and neoplasm. Ion transporters generate pH and voltage gradients, as well as ion fluxes, regulating proliferation, differentiation and migration. Endogenous bioelectrical signals are implicated in the control of wound healing, limb development, left-right patterning and spinal cord regeneration. Recent advances in molecular biology and imaging technology have allowed unprecedented insight into the sources and downstream consequences of ion flows. In complement to the current focus on molecular genetics and stem cell biology, artificial modulation of bioelectrical signals in somatic tissues is a powerful modality that might result in profound advances in understanding and augmentation of regenerative capacity.

Weak electric current accelerates motoneuron regeneration in the sciatic nerve of ten-month-old rats

When a weak direct current (DC) of 10 microA driven by an implantable device was applied to a crushed sciatic nerve in 9-10-month-old rats, regeneration was accelerated as assessed electrophysiologically. Rats underwent a sciatic nerve crush of the right leg and were randomly assigned to one of three groups: (i) Cathode Distal (CD); (ii) Sham Implant (SI); or (iii) No Implant (NI). On post-operative days 25-39 each rat received a measurement of evoked electromyograms (EMG) in the foot. In addition each rat received a behavioural test score (BTS). This BTS correlated well with the evoked EMG results showing the behavioural relevance of the EMG results. NI rats performed the same as SI in the evoked EMG procedure, but CD rats performed significantly better than both the control groups. The recovery period in the CD rats was 21% shorter than in either the sham-treated or untreated controls showing that weak DC can greatly enhance nerve regeneration in adult rats. This result was in contrast to previous work in younger rats where DC treatments had no effects. The discrepancy is discussed in relation to the slowing of regeneration in older rats.

Epidermis, basement membrane, and connective-tissue healing after amputation of mouse digits: implications for mammalian appendage regeneration

Soft tissues from amputation sites of mice were examined at both light and electron microscope levels to determine whether features of growth buds (blastemas), which are necessary for amphibian limb regeneration, exist in nonregenerating mice. Several such features were found. A small area of the wound bed was covered by wound epithelium which, as in regenerating newt limbs, initially lacked an underlying basement membrane. Serially sectioned digits revealed blastemalike growth in the subdermal layer surrounding periosteal chondrogenic cells. Mesenchymelike cells were seen among the fibroblasts and leucocytes within the proliferating tissues. However, no evidence of dedifferentiation was seen in the dermis, which persisted as an apparent intact obstruction to growth bud formation. Existence of the essential ingredients of growth buds and soft-tissue proliferation adjacent to chondrogenic cells proximally suggest that the tissues of mammalian healing may differ quantitatively rather than qualitatively from tissues of appendage regeneration. This premise is encouraging for efforts at growth enhancement in mammals.

Responses of host motor and sensory neurons to a neural tube implant in amputated chick limbs

The right wingbuds of stage 23-25 chick embryos were amputated at the future elbow region and a segment of 2-day neural tube was implanted longitudinally into the limb stump of experimental embryos to induce limb regeneration. Control embryos had no implant in the amputated limb stump. To analyze effects of the neural tube implant (NTI) upon the host nervous system, quantitative determinations were made of the peripheral limb field (PLF), dorsal root ganglia (DRG) and spinal cord lateral motor column (LMC) of the amputated side for comparison with similar determinations of the unamputated side in all embryos. The PLF was estimated by determining the area of the skeletal elements of the amputated and unamputated limb of each embryo. The size of the DRG was estimated by determining the sectional-profile area of a pair of ganglia; the LMC was determined by counting the neurons on both sides of a single spinal cord segment. The PLF was less on the amputated than on the unamputated side but was significantly greater in amputated limbs that received a NTI. The size of the DRG was positively correlated with the size of the PLF in all groups, indicating the DRG was not directly affected by the NTI but did respond to target structures. The number of neurons in the LMC was not positively correlated with the PLF and was not reduced by limb amputation in embryos with a NTI. The data suggest that the NTI may have protected host spinal cord cells from the induced-cell death expected to follow limb amputation; perhaps the implant produces a neuronal survival factor.