Upregulation of chemokine (C-C motif) ligand 20 in adult epidermal keratinocytes in direct current electric fields

Bioelectricity in dental medicine: a narrative review

BACKGROUND

Bioelectric signals, whether exogenous or endogenous, play crucial roles in the life processes of organisms. Recently, the significance of bioelectricity in the field of dentistry is steadily gaining greater attention.

OBJECTIVE

This narrative review aims to comprehensively outline the theory, physiological effects, and practical applications of bioelectricity in dental medicine and to offer insights into its potential future direction. It attempts to provide dental clinicians and researchers with an electrophysiological perspective to enhance their clinical practice or fundamental research endeavors.

METHODS

An online computer search for relevant literature was performed in PubMed, Web of Science and Cochrane Library, with the keywords "bioelectricity, endogenous electric signal, electric stimulation, dental medicine."

RESULTS

Eventually, 288 documents were included for review. The variance in ion concentration between the interior and exterior of the cell membrane, referred to as transmembrane potential, forms the fundamental basis of bioelectricity. Transmembrane potential has been established as an essential regulator of intercellular communication, mechanotransduction, migration, proliferation, and immune responses. Thus, exogenous electric stimulation can significantly alter cellular action by affecting transmembrane potential. In the field of dental medicine, electric stimulation has proven useful for assessing pulp condition, locating root apices, improving the properties of dental biomaterials, expediting orthodontic tooth movement, facilitating implant osteointegration, addressing maxillofacial malignancies, and managing neuromuscular dysfunction. Furthermore, the reprogramming of bioelectric signals holds promise as a means to guide organism development and intervene in disease processes. Besides, the development of high-throughput electrophysiological tools will be imperative for identifying ion channel targets and precisely modulating bioelectricity in the future.

CONCLUSIONS

Bioelectricity has found application in various concepts of dental medicine but large-scale, standardized, randomized controlled clinical trials are still necessary in the future. In addition, the precise, repeatable and predictable measurement and modulation methods of bioelectric signal patterns are essential research direction.

Designing a Biomaterial Approach to Control the Adaptive Response to a Skin Injury

The goal of this review is to explain how to design a biomaterial approach to control the adaptive response to injury, with an emphasis on skin wounds. The strategies will be selected based on whether they have a reasonable probability of meeting the desired clinical outcome vs. just comparing the pros and cons of different strategies. To do this, the review will look at the normal adaptive response in adults and why it does not meet the desired clinical outcome in most cases. In addition, the adaptive response will be looked at in cases where it does meet the clinical performance requirements including animals that regenerate and for fetal wound healing. This will lead to how biomaterials can be used to alter the overall adaptive response to allow it to meet the desired clinical outcome. The important message of the review is that you need to use the engineering design process, not the scientific method, to design a clinical treatment. Also, the clinical performance requirements are functional, not structural. The last section will give some specific examples of controlling the adaptive response for two skin injuries: burns and pressure ulcers. For burns, it will cover some preclinical studies used to justify a clinical study as well as discuss the results of a clinical study using this system. For pressure ulcers, it will cover some preclinical studies for two different approaches: electrical stimulation and degradable/regenerative scaffolds. For electrical stimulation, the results of a clinical study will be presented.

Do epidermal keratinocytes have sensory and information processing systems?

It was long considered that the role of epidermal keratinocytes is solely to construct a water-impermeable protective membrane, the stratum corneum, at the uppermost layer of the skin. However, in the last two decades, it has been found that keratinocytes contain multiple sensory systems that detect environmental changes, including mechanical stimuli, sound, visible radiation, electric fields, magnetic fields, temperature and chemical stimuli, and also a variety of receptor molecules associated with olfactory or taste sensation. Moreover, neurotransmitters and their receptors that play crucial roles in the brain are functionally expressed in keratinocytes. Recent studies have demonstrated that excitation of keratinocytes can induce sensory perception in the brain. Here, we review the sensory and information processing capabilities of keratinocytes. We discuss the possibility that epidermal keratinocytes might represent the earliest stage in the development of the brain during the evolution of vertebrates.

Electric Factors in Wound Healing

Significance: Electric factors such as electric charges, electrodynamic field, skin battery, and interstitial exclusion permeate wound healing physiology and physiopathology from injury to re-epithelialization. The understanding of how electric factors contribute to wound healing and how treatments may interfere with them is fundamental for the development of better strategies for the management of pathological scarring and chronic wounds. Recent Advances: Angiogenesis, cell migration, macrophage activation hemorheology, and microcirculation can interfere and be interfered with electric factors. New treatments with various types of electric currents, laser, light emitting diode, acupuncture, and weak electric fields applied directly on the wound have been developed to improve wound healing. Critical Issues: Despite the basic and clinical development, pathological scars such as keloids and chronic wounds are still a challenge. Future Directions: New treatments can be developed to improve skin wound healing taking into account the influence of electrical charges. Monitoring electrical activity during skin healing and the influence of treatments on hemorheology and microcirculation are examples of how to use knowledge of electrical factors to increase their effectiveness.

A pulsed current electric field alters protein expression creating a wound healing phenotype in human skin cells

Aim: Pulsed current (PC) electric field (EF) devices promote healing in chronic wounds but the underpinning mechanisms are largely unknown. The gap between clinical evidence and mechanistic understanding limits device uptake in clinics. Materials & methods: Migration, proliferation and gene/protein expression profiles were investigated in the presence/absence of PCEF, in skin: keratinocytes (NHK); dermal fibroblasts (HDF); dermal microvascular endothelial cells (HDMEC) and macrophages (THP-1). Results: While PCEF had little effect on migration or proliferation, it significantly altered the expression of 31 genes and the secretion of 7 pro-angiogenic and pro-regenerative growth factors using ELISAs. Conclusion: PCEF significantly altered skin cell genomes/proteomes which provides some evidence of how PCEF devices promote healing of chronic wounds.

Hub Proteins Involved in RAW 264.7 Macrophages Exposed to Direct Current Electric Field

At present, studies on macrophage proteins mainly focus on biological stimuli, with less attention paid to the responses of macrophage proteins to physical stimuli, such as electric fields. Here, we exploited the electric field-sensitive hub proteins of macrophages. RAW 264.7 macrophages were treated with a direct current electric field (dcEF) (200 mV/mm) for four hours, followed by RNA-Seq analysis. Differentially expressed genes (DEGs) were obtained, followed by Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) and protein–protein interaction (PPI) analysis. Eight qPCR-verified DEGs were selected. Subsequently, three-dimensional protein models of DEGs were modeled by Modeller and Rosetta, followed by molecular dynamics simulation for 200 ns with GROMACS. Finally, dcEFs (10, 50, and 500 mV/mm) were used to simulate the molecular dynamics of DEG proteins for 200 ns, followed by trajectory analysis. The dcEF has no obvious effect on RAW 264.7 morphology. A total of 689 DEGs were obtained, and enrichment analysis showed that the steroid biosynthesis pathway was most affected by the dcEF. Moreover, the three-dimensional protein structures of hub proteins were constructed, and trajectory analysis suggested that the dcEF caused an increase in the atomic motion of the protein in a dcEF-intensity-dependent manner. Overall, we provide new clues and a basis for investigating the hub proteins of macrophages in response to electric field stimulation.

Biomaterial Enhanced Regeneration Design Research for Skin and Load Bearing Applications

Biomaterial enhanced regeneration (BER) falls mostly under the broad heading of Tissue Engineering: the use of materials (synthetic and natural) usually in conjunction with cells (both native and genetically modified as well as stem cells) and/or biological response modifiers (growth factors and cytokines as well as other stimuli, which alter cellular activity). Although the emphasis is on the biomaterial as a scaffold it is also the use of additive bioactivity to enhance the healing and regenerative properties of the scaffold. Enhancing regeneration is both moving more toward regeneration but also speeding up the process. The review covers principles of design for BER as well as strategies to select the best designs. This is first general design principles, followed by types of design options, and then specific strategies for applications in skin and load bearing applications. The last section, surveys current clinical practice (for skin and load bearing applications) including limitations of these approaches. This is followed by future directions with an attempt to prioritize strategies. Although the review is geared toward design optimization, prioritization also includes the commercializability of the devices. This means a device must meet both the clinical performance design constraints as well as the commercializability design constraints.

The Feasibility of Using Pulsatile Electromagnetic Fields (PEMFs) to Enhance the Regenerative Ability of Dermal Biomaterial Scaffolds

Degradable regenerative scaffolds usually require adjunctive treatment to meet the clinical healing performance requirements. This study was designed to look at pulsatile electromagnetic fields (PEMF) as an adjunctive therapy for these scaffolds in skin wounds; however, no scaffold was used in this study in order to isolate the effects of PEMF alone. In this study, New Zealand rabbits received four full-thickness defects with a size of 3 cm × 3 cm on the dorsolateral aspect. The rabbits in the treatment group were placed in a chamber and subjected to a PEMF at six different predetermined frequency and intensity combinations for 2 h a day for a 2-week period. At the end of the 2-week period, the animals were sacrificed and tissue samples were taken. Half of each tissue sample was used for histomorphometric analysis and the other half was for tensile testing. The study showed an increased healing response by all the PEMF treatments compared to that in the control, although different combinations led to increases in different aspects of the healing response. This suggests that although some treatments are better for the critical clinical parameter—healing rate, it might be beneficial to use treatments in the early stages to increase angiogenesis before the treatment is switched to the one best for the healing rate to get an even better haling rate.

Electric field-induced suppression of PTEN drives epithelial-to-mesenchymal transition via mTORC1 activation

BACKGROUND

Naturally occurring electric fields (EFs) are an intrinsic property of wounds. Endogenous EFs in skin wounds play critical roles in the dynamic and well-ordered biological process of wound healing. The epithelial-to-mesenchymal transition (EMT) allows keratinocytes to transition from sedentary cells to motile cells, facilitating wound healing. However, EMT-related studies have been performed without considering endogenous EFs. Thus, the relationship between electrical signals and the EMT remain elusive.

OBJECTIVE

Phosphatase and tension homolog (PTEN) and mammalian target of rapamycin complex 1 (mTORC1) are key molecules in sensing electrical cues, and they play significant roles in cellular responses to EFs. In addition, these molecules are closely related to the occurrence of the EMT in other cells. We used primary human keratinocytes to investigate the influence of EFs on the EMT as well as the roles of PTEN and mTORC1 in this process.

METHODS

The effects of EFs on the EMT were investigated by analyzing the levels of specific proteins and transcription factors. The roles of mTORC1 and PTEN and their relationship with each other were studied via pharmacological inhibition or genetic knockdown. A Zeiss imaging system and scratch assays were used to study single-cell motility and monolayer cell migration.

RESULTS

EFs induced a range of both biochemical changes (e.g., increased Snail, Slug, vimentin, and N-cadherin expression, decreased E-cadherin expression) and functional changes (e.g., enhanced migratory capacity) that are characteristic of the EMT. EF-stimulated cells exhibited suppressed PTEN expression, and further PTEN downregulation led to the acquisition of more mesenchymal features and the loss of epithelial characteristics, which was accompanied by increased migratory capacity. PTEN overexpression reversed the EF-induced EMT and inhibited the migratory capacity of keratinocytes. EF-induced mTORC1 activation was a required component of the causal relationship between PTEN suppression and the EMT, as mTORC1 inhibition reversed the EMT induced by PTEN downregulation.

CONCLUSIONS

Our data demonstrate that the EF-induced suppression of PTEN drives the EMT via mTORC1 activation, thereby revealing a new and promising role of EFs in facilitating wound reepithelialization. These results provide a novel perspective regarding the significance of EFs in wound healing; therefore, electrical stimulation offers a new avenue of wound management for improved and accelerated wound healing.

Electrical stimulation enhances epidermal proliferation in human cutaneous wounds by modulating p53-SIVA1 interaction

Cutaneous wounds establish endogenous "wound current" upon injury until re-epithelialization is complete. Keratinocyte proliferation, regulated partly by p53, is required for epidermal closure. SIVA1 promotes human double minute 2 homolog (HDM2)-mediated p53 regulation. However, the role of SIVA1 in wound healing is obscure. Here, we report that electrical stimulation (ES) accelerates wound healing by upregulating SIVA1 and its subsequent ability to modulate p53 activities. Cultured donut-shaped human skin explants, subjected to ES, exhibited better epidermal stratification, increased proliferation, and upregulation of gene and protein expression of HDM2/SIVA1, compared with non-ES-treated explants. ES significantly increased in vitro keratinocyte proliferation and phospho-p53-SIVA1 interaction; however, this showed stable expression of phospho-p53, which increased significantly in the absence of SIVA1. Here, HDM2 alone was unable to downregulate nuclear-accumulated phospho-p53, which was evident from decreased proliferation and increased sub-G1 population seen by flow cytometry. Further examination of the epidermis of human cutaneous wounds showed higher p53-SIVA1 coexpression and proliferation 7 days after injury in ES-treated wounds compared with control wounds. In summary, ES-inducible SIVA1 modulates p53 activities in proliferating keratinocytes, and exogenous ES affects p53/HDM2/SIVA1 axis leading to increased proliferation during re-epithelialization. This highlights ES as a potential strategy for enhancing cutaneous repair.

Extracts from Radix Astragali and Radix Rehmanniae promote keratinocyte proliferation by regulating expression of growth factor receptors

Chinese herbal medicine has long been used as a treatment for wounds. However, the underlying cellular and molecular mechanisms remain largely unknown. In this study it was shown that the proliferation of keratinocytes, which is known to play an important role in wound healing as the major cell type in the epidermis, was promoted by three herbal extracts/natural compounds: NF3 (an extract from the mixture of Radix Astragali (RA) and Radix Rehmanniae (RR) in the ratio of 2:1), stachyose (an isolated compound from Radix Rehmanniae) and extract P2-2 (a sub-fraction from the extract of Radix Astragali). The effect of the herbal extracts/natural compounds on the growth of keratinocytes was not influenced by a high glucose level, a condition similar to diabetic patients who usually suffer from diabetic foot ulcers. Real time RT-PCR results showed that the expression of epidermal growth factor (EGF) receptor, but not transforming growth factor-β (TGF-β) receptor, was up-regulated by NF3. Moreover, treatments with the EGF receptor kinase inhibitor AG1478 and the MEK inhibitor U0126 resulted in the diminishment of the effect of the three herbal extracts/natural compounds on keratinocyte proliferation, indicating that EGF receptor might have a significant role in this action. This study has further elucidated the molecular mechanism under which herbal extracts/natural compounds exert their effects on the wound healing process.

Gene expression of human lung cancer cell line CL1-5 in response to a direct current electric field

Background

Electrotaxis is the movement of adherent living cells in response to a direct current (dc) electric field (EF) of physiological strength. Highly metastatic human lung cancer cells, CL1–5, exhibit directional migration and orientation under dcEFs. To understand the transcriptional response of CL1–5 cells to a dcEF, microarray analysis was performed in this study.

Methodology/Principal Findings

A large electric-field chip (LEFC) was designed, fabricated, and used in this study. CL1–5 cells were treated with the EF strength of 0mV/mm (the control group) and 300mV/mm (the EF-treated group) for two hours. Signaling pathways involving the genes that expressed differently between the two groups were revealed. It was shown that the EF-regulated genes highly correlated to adherens junction, telomerase RNA component gene regulation, and tight junction. Some up-regulated genes such as ACVR1B and CTTN, and some down-regulated genes such as PTEN, are known to be positively and negatively correlated to cell migration, respectively. The protein-protein interactions of adherens junction-associated EF-regulated genes suggested that platelet-derived growth factor (PDGF) receptors and ephrin receptors may participate in sensing extracellular electrical stimuli. We further observed a high percentage of significantly regulated genes which encode cell membrane proteins, suggesting that dcEF may directly influence the activity of cell membrane proteins in signal transduction.

Conclusions/Significance

In this study, some of the EF-regulated genes have been reported to be essential whereas others are novel for electrotaxis. Our result confirms that the regulation of gene expression is involved in the mechanism of electrotactic response.

Human keratinocytes' response to injury upregulates CCL20 and other genes linking innate and adaptive immunity

In the early stages of wound healing, keratinocytes become “activated” and release inflammatory molecules such as interleukin-1 and interleukin-8 that are linked to innate immune responses and neutrophil recruitment. It is unclear, however, whether keratinocytes release molecules linked to adaptive immune responses, e.g. CCL20, in their early state of activation without signals from infiltrating T cells. This study aims to isolate the immediate alterations in protective and inflammatory gene expression that occur in epidermal keratinocytes, with a particular focus on molecules associated with cell-mediated immunity. We used dispase-separated epidermis, followed by intercellular disassociation by trypsinization, as a model for epidermal injury. We obtained a pure population of keratinocytes using flow cytometry. As a control for uninjured epidermis, we performed laser capture microdissection on normal human skin. Sorted keratinocytes had an early burst of upregulated gene expression, which included CCL20, IL-15, IL-23A, IFN-κ, and several antimicrobial peptides. Our results provide insight into the potential role of keratinocytes as contributors to cell-mediated inflammation, and expand knowledge about gene modulation that occurs during early wound healing. Our findings may be relevant to cutaneous diseases such as psoriasis, where micro-injury can trigger the formation of psoriatic plaques at the site of trauma.

Extracellular electrical fields direct wound healing and regeneration

Endogenous DC electric fields (EFs) are important, fundamental components of development, regeneration, and wound healing. The fields are the result of polarized ion transport and current flow through electrically conductive pathways. Nullification of endogenous EFs with pharmacological agents or applied EFs of opposite polarity disturbs the aforementioned processes, while enhancement increases the rate of wound closure and the extent of regeneration. EFs are applied to humans in the clinic, to provide an overwhelming signal for the enhancement of healing of chronic wounds. Although clinical trials, spanning a course of decades, have shown that applied EFs enhance healing of chronic wounds, the mechanisms by which cells sense and respond to these weak cues remains unknown. EFs are thought to influence many different processes in vivo. However, under more rigorously controlled conditions in vitro, applied EFs induce cellular polarity and direct migration and outgrowth. Here we review the generation of endogenous EFs, the results of their alteration, and the mechanisms by which cells may sense these weak fields. Understanding the mechanisms by which native and applied EFs direct development and repair will enable current and future therapeutic applications to be optimized.

Gene expression of human lung cancer cell line CL1-5 in response to a direct current electric field

BACKGROUND

Electrotaxis is the movement of adherent living cells in response to a direct current (dc) electric field (EF) of physiological strength. Highly metastatic human lung cancer cells, CL1-5, exhibit directional migration and orientation under dcEFs. To understand the transcriptional response of CL1-5 cells to a dcEF, microarray analysis was performed in this study.

METHODOLOGY/PRINCIPAL FINDINGS

A large electric-field chip (LEFC) was designed, fabricated, and used in this study. CL1-5 cells were treated with the EF strength of 0 mV/mm (the control group) and 300 mV/mm (the EF-treated group) for two hours. Signaling pathways involving the genes that expressed differently between the two groups were revealed. It was shown that the EF-regulated genes highly correlated to adherens junction, telomerase RNA component gene regulation, and tight junction. Some up-regulated genes such as ACVR1B and CTTN, and some down-regulated genes such as PTEN, are known to be positively and negatively correlated to cell migration, respectively. The protein-protein interactions of adherens junction-associated EF-regulated genes suggested that platelet-derived growth factor (PDGF) receptors and ephrin receptors may participate in sensing extracellular electrical stimuli. We further observed a high percentage of significantly regulated genes which encode cell membrane proteins, suggesting that dcEF may directly influence the activity of cell membrane proteins in signal transduction.

CONCLUSIONS/SIGNIFICANCE

In this study, some of the EF-regulated genes have been reported to be essential whereas others are novel for electrotaxis. Our result confirms that the regulation of gene expression is involved in the mechanism of electrotactic response.