Trending toward gero‐electroceuticals that target membrane potential for reprogramming aging and lifespan

Ion gradients across cell membranes generate voltage potentials that are involved in a wide range of biological processes. According to the membrane hypothesis of aging, aging is inextricably linked to a decrease in resting membrane potential (Vmem). Alterations in ion channel activity and membrane fluidity caused by aging disrupt bioelectric homeostasis, increase intracellular calcium and potassium concentrations, induce abnormal mechanistic target of rapamycin (MTOR)‐ and AMPK‐regulated metabolism and energy dissipation, and decrease proliferation and regeneration. Failure to maintain ion channel activity and membrane potential leads to cell senescence or death. There is evidence that by manipulating ion channel activities, a cryptic memory can be recalled to restore lost proliferative or regenerative abilities. Reversal or prevention of senescence, aging phenotypes, and longevity may be achieved by fine‐tuning mitochondrial membrane polarization. Therefore, there is optimism that deciphering the bioelectric codes that govern cell functions will lead to the development of new gero‐electroceuticals that restore cell function and prevent tissue loss during aging.

intracellular chemical signals and signaling cascades.Bioelectric fields drive intricate shape changes during developmental tissue remodeling as well as regulate a host of appropriate responses to unfavorable environmental conditions.
The term "bioelectricity" refers to the endogenous electric currents that are generated by living organisms.Gradients of ions across cell membranes create voltage potentials.The electric potential of membranes (V mem ) is a strong electric field (∼1.0 × 10 6 V/m) of approximately −10 to −90 mV.V mem is established by the coordinate actions of numerous membrane ion channels, transporters, and pumps (Figure 1A). 2 The movement of Inorganic ions and charged molecules across gap junctions enables electrical coupling and the integration of cellular voltage gradients into tissue-wide bioelectric fields (Figure 1B-D).
When the membrane potential rises above the resting V mem threshold, the quiescent normal cells become hyperpolarized, whereas falling membrane potential results in a depolarized state. 3Changes in V mem and dissemination of electrical charges in coupled cell networks enable cells to uniformly and coherently respond to environmental cues. 4Additionally, bioelectricity stores information that can be propagated in cell collectives or be disseminated horizontally by somatic-to-germline transfer. 5his review discusses the importance of bioelectric code dysfunctions that are permissive to the development of an aging phenotype.We propose that deciphering the bioelectric codes that are corrupted in aging can be used to create novel gero-electroceuticals for treatment of aging and associated diseases.

BIOELECTRIC DYNAMICS IN AGING
The membrane potential varies significantly in different cell types, and it is altered during transit through the cell cycle, by mechanical properties of cells, environmental cues, and aging.The membrane hypothesis of aging posits that aging occurs when ionic strength in cellular water content exceeds a critical value beyond 400 mEq/kg.This leads to the condensation of chromatin and loss of activity of DNA-dependent polymerase and other enzymes, and protein synthesis decreases. 6he bioelectric dynamics in cells and whole organisms deteriorate with aging.For example, aging is associated with an increase in total l-type Ca 2+ channel activity and voltage-activated calcium (Ca 2+ ) influx. 7Moreover, changes in lipid membrane fluidity drive down resting potassium permeability and allow the intracellular accumulation of this cation. 6There is evidence that aging and senescence cause changes in the resting membrane potential that can impair cellular functionality, proliferative capacity, regenerative potential, and mitochondrial function, leading to senescence and cell death, and limiting the lifespan.This change might be due to the loss of responsiveness to mechanistic target of rapamycin (mTORC)-1 and autophagy. 8Alterations of membrane polarization in senescent cells, mediated by K + channels, reduces activity of PI3K/Akt pathway and restores sensitivity of mTORC1 in senescent cells to serum starvation. 9Similarly, membrane depolarization of mitochondria and, consequently, mitochondrial dysfunction in senescence and aging is mediated by enhanced activation of the mitochondrial permeability transition pore (mPTP), likely due to ROS overproduction. 10,11These changes do not appear to be tissue specific and occur in diverse cell types that experience senescence such as CD8 + T cells, central nervous system. 12,13atterns of resting potentials within tissues provide mechanistic linkage with molecular genetics and biochemical pathways.Thus, it follows that the modification of the membrane bioelectricity carries the potential to restore pathways that have gone awry in human aging.The electroceutical toolkit for prevention or repair includes neurostimulator medical devices as well as a variety of ion channel drugs, many of which are approved for human use.Some of these pharmaceutical drugs can be repurposed as gero-electroceuticals to address a host of age-related disorders.For example, some of these electroceuticals are tailored to revive lost proliferative or regenerative potentials, some modulate cancer cell proliferative, invasive, or metastatic traits, whereas others show palliative impact on age-related diseases.

Restoring proliferation by modulation of V mem
Senescent and aging stem cells lose their proliferative potential and this results in organ-wide loss of mass and extensive tissue atrophy.Reversal of this loss-of-function is necessary for replenishing tissues that are lost by aging.It appears that altering V mem is quite effective in causing proliferation in both normal and malignant cells.Normal cellular collectives collaborate toward an organ-level structural order, which promotes a default level of cell function and proliferative activity by maintaining a normal electric potential across the networked plasma membranes.V mem fluctuates and appears to be required for G1/S and G2/M transitions during cell proliferation.Changing intracellular ion concentrations is sufficient to activate DNA synthesis and proliferation in otherwise non-proliferating neurons. 14,15Conversely, altering the extracellular ion concentration can stop G1/S progression and proliferation in a variety of cells. 16However, there are a host of other factors that alter the ion transfer and membrane polarization and change the outcome of proliferation.The formation of gap junctions would deplete sodium channels, reduce sodium permeability, and stop DNA synthesis.Growth factors, however, can competitively bind to channel-connexon elements, cleave gap junctions, increase sodium permeability by influencing sodium channels, and trigger DNA synthesis. 3,15Thus, it is expected that the manipulation of V mem , sufficient to induce proliferation, requires a thorough understanding of all the elements that fine-tune the ion transfer and polarization state of cells as they transit through the cell cycle.

The impact of depolarization and hyperpolarization on proliferation
The broad consensus is that rapidly dividing cells, including stem cells and embryonic or cancer cells, are more depolarized than nondividing, differentiated cells. 16,17As a result, a cell-specific V mem threshold may discriminate normal quiescent cells from cells that are in a highly proliferative state. 3There are, however, several caveats to the observation that depolarization is the only bioelectric code necessary for promoting cell division.Hyperpolarization situations, such as those caused by Epidermal Growth Factor (EGF)-mediated Ca 2+ influx and prolonged increases in [Ca 2+ ] i , can promote mitogenesis. 18Rather than being dependent on a crucial V mem value, the effect of hyperpolarization appears to be cell-context sensitive.For example, in the central nervous system of frog embryo, hyperpolarization can induce widespread proliferation or apoptosis depending on the cell type. 19Hyperpolarization itself can change the outcome of cell division by intercepting the Ca 2+ influx by the closure of voltage-gated calcium channels. 20Thus, for induction of cell division, it is expected that the manipulation of V mem must be precisely adjusted based on the target cells with the caveat that the changes in membrane polarization cannot be disentangled from changes which occur in the [Ca 2+ ] i .

Restoring lost regenerative potential
Loss of regenerative capability in stem cells is a welldefined feature of aging.Alteration of the resting membrane potential delivers instructional messages in a variety of settings to promote cell growth and proliferation, including embryogenesis, regeneration, and cancer progression. 21Bioelectric field gradients control proliferation and regeneration, organ development, organ size, left-right patterning, and wound healing by intercepting the default transcriptional responses across cell-collectives or tissue fields by fine-tuning the flow of ions such as Ca 2+ and by altering V mem .In fact, bioelectric memory gradients overlay with transcriptional gradients in the highly regenerative planarian flatworm. 22In these animals, the Wnt-β-catenin signaling inducers are expressed anteriorly, whereas its inhibitors accumulate posteriorly establishing an anteroposterior (AP) gradient. 23This spatial transcriptomic landscape is mirrored by a gradient in the membrane potential, which is equally important for maintaining the AP directionality.
There is a growing optimism that V mem and bioelectric fields can be manipulated to restore lost regenerative potentials.As described in the following section, knowledge of this restoration has been gleaned from examining regeneration in flatworms, and by inducing changes in wound healing and restoring regeneration in severed organs under non-regenerative conditions.

Organ regeneration
In adult flatworms, when the default spatial bioelectric field gradient is disrupted by severing the body of the animal, changes in the bioelectric field drive the rebuilding of the damaged organ and restore the default bioelectric state.After a planarian is cut in half, the headless animal develops a tail, whereas the tailless animal acquires a head.4][25] The importance of bioelectric fields in shaping the morpho-space also has been demonstrated in the development of shape-form mutants (Figure 2B).When the head-tail direction of membrane potential is disrupted by RNAi to H + /K + -ATPase, regeneration fails and results in shrunken heads (Figure 2B).Disrupting this bioelectric memory, for example, by treating headless and tailless planarian trunks with octanol, results in aberrant formation of double-headed animals. 22,23(Figure 2C).7][28] Thus, it seems that planaria successfully repair their cut heads and tails by maintaining A-P directionality in their tissue-wide transcriptional and bioelectric fields.Simulating similar changes in bioelectric fields should open the opportunity to restore tissues that atrophy as a result of aging.

Wound repair
The cellular regeneration potential appears to be preserved by a cryptic memory, which can be activated by manipulating ion channel activities. 22,29Wounds, for example, might be thought of as a disruption of endogenous bioelectric circuits, as evidenced by the formation of depolarization at the wound edge.Along the wound edge, local depolarization causes normally nondividing cells to proliferate and migrate. 27,30Depolarization relays mitogenic signals, causes cytoskeletal alterations required for migration, and induces shape changes essential for wound repair.This concept is validated by nonspecific depolarization of the plasma membrane potential of epithelial cells that triggers distinctive cytoskeletal rearrangements. 27,30owever, when depolarization reaches certain thresholds, such as with V-ATPase loss-of-function, regeneration in severed tail buds in Xenopus halts, leaving them in a nonregenerative' refractory' state. 31An inflow of sodium ions occurs in the regenerative bud 18 h after amputation.This event requires, and does not progress without, the requisite phase of V mem repolarization that is dependent on NaV1.2 sodium channel expression in the mesenchymal cells. 32he available evidence, therefore, provide credence for the idea that simulating the bioelectric code that recalls cell division is an appealing method for inducing tissue repair in non-regenerating aging tissues.

Regeneration in non-regenerative conditions
The feasibility of restoring regeneration has already been validated by effectively regenerating amputated appendages in non-regenerative species such as Xenopus by modifying V mem and bioelectric fields. 33,34The stimulation of H + flux is sufficient to induce axonal patterning and tail extension even under otherwise non-regenerative conditions. 31Hyperpolarization also plays a key role in the control of organ development including formation of the eye in Xenopus. 28Although hyperpolarization does not necessarily interfere with instructional regenerative signals, it can derail the outcome of organ regeneration.
F I G U R E 2 Manipulation of V mem overrides the default cell responses.(A) V mem spatial distribution in planaria (top) and planaria stained with voltage-sensitive reporter dyes (bottom) demonstrates depolarization in the head and hyperpolarization in the tail.These states function as meta-transcriptional memory states, forecasting the future fates of tissues that regenerate in an animal whose head and tail have been severed.(B) Changes in the bioelectric field cause the emergence of shape mutants.The introduction of control RNAi has no effect on regenerative potential, allowing the formation of a head and tail in severed animals.RNAi-mediated inhibition of the H + , K + -ATPase ion pump, on the other hand, causes membrane depolarization, abnormal regeneration, and the development of shrunken heads.(C) Cutting the animal in water allows proper formation of head and tail.However, in presence of octanol, the formation of the tail is inhibited, resulting in the formation of double-headed animals. 22,35Source: Images are created at BioRender.com.
For example, inducing hyperpolarization in planaria after removing their heads results in the production of ectopic heads. 35When the head of the flatworm is severed, depolarization via H,K-ATPase and disruption of V mem result in a small head and large pharynx indicating that membrane polarization must be adjusted as a final brake to ensure that organs do not exceed an ideal size limit. 35he disruption of tissue-wide bioelectric fields also allows for regeneration, even in organisms that have lost the ability to replace a lost organ.4] Ion imaging and molecular-genetic approaches have indicated that, with the exception of a few islands containing depolarized cells, the cells in the uncut tail of Xenopus are polarized under normal conditions.However, 6 h after amputation, V-ATPase activity increases, and by 24 h, the regeneration bud is repolarized, with an island of depolarized cells developing just anterior to this bud. 31,33,34Compared with uncut or regenerating tails, non-regenerative "refractory" tail buds are strongly depolarized.
Thus, V-ATPase and NaV1.2, repolarization of V mem and the activity of H + pump and sodium influx, are considered minimal requirements for regulating regenerative activity for effective wound repair and for activating refractory or non-regenerative tissues.These novel strategies, when combined with existing biochemical approaches, potentially may allow for regeneration under the nonregenerating condition of aging. 34

Depolarization of membranes and hyperproliferation in cancer cells
Cancer, a common aging disease, causes dysregulation of bioelectric fields.Cancer cells decouple from the bioelectric cues that maintain the delicate tissue order and function. 25Cancer cells function as independent autonomous agents, free of the constraints imposed by bioelectric fields in normal tissue networks.Although hyperpolarization reduces the susceptibility to tumorigenesis, the plasma membranes in cancer cells, such as MCF7 or MDA-MB-231, are more depolarized compared to the resting membrane potential maintained by the neighboring and networked normal cells.9][40] Depolarization F I G U R E 3 Regulation of normal and neoplastic growth by modifying V mem .(A) Under normal conditions, the Na + /K + ATPase pump, pumps out 3 Na + ions out of the cell and allows 2 K + ions to enter the cell, generating a Na + and K + concentration and electrostatic gradients that create the polarized membranes.SLC5A8, a member of the sodium/glucose cotransporter family, allows a moderate amount of butyrate to enter the cell at rest, thereby inhibiting histone deacetylase [HDAC], proliferation, and differentiation.(B) Physiological factors or oncogene induction, by inducing membrane depolarization, prevent SLC5A8 from importing butyrate and allow HDAC to induce over-proliferation and tumor-like structures.(C) By hyperpolarizing the membrane, molecular and/or pharmacological targeting of H + , K + , or Cl − ion channels blocks the impact of oncogenes.Hyperpolarized membranes enhance SLC5A8-induced butyrate entry into the cytoplasm.Excess intracellular butyrate completely inhibits HDAC, causing cell cycle arrest and inhibiting tumor formation. 24Source: Images are created at BioRender.com.can even send instructive signals to cancer cells that render them metastatic. 41,42hus, it can be argued that the modification of the polarization state of cancer cells by pharmacological inhibitors of calcium influx pathways can be used to inhibit cancer proliferation and or invasion. 25,35,38Given that depolarization promotes cell division, one expects that hyperpolarization should halt this action.Indeed, hyperpolarization produced through molecular and/or pharmacological targeting of H + , K + , or Cl − ion channels enhances the activities of SLC5A8, a sodium/glucose co-transporter family member.This activation permits excess entry of butyrate into the cytoplasm.By blocking histone deacetylase, excess intracellular butyrate causes cell cycle arrest and inhibits tumor formation (Figure 3A-C). 22,35

Mitochondrial protonmotive force, a key to mitochondrial homeostasis
There is sufficient evidence that support the concept that cellular decline in aging is reliant on changes in mitochondrial protonmotive force (PMF) and loss of lysosomal acidification that likely leads to the failure to remove the damaged mitochondria.
Mitochondrial dysfunction is regarded as one of the nine major contributors to aging and senescence. 43By employ-ing an electrochemical gradient across the inner mitochondrial membrane, the PMF in mitochondria drives generation of ATP.5][46] PMF, lysosomal acidification, and respiration deteriorate with aging in numerous experimental paradigms.5][46] In aged cells, inhibiting adenine nucleotide translocase (which transfers ADP into mitochondria for ATP synthesis) protects the PMF, reverses respiratory failure, and rejuvenates mitochondria. 47Lysosomal acidification appears to be a determinant of lifespan.For example, during natural aging, the vacuolar acidity declines and such an altered vacuolar pH drives mitochondrial dysfunction, whereas preventing this decline is sufficient to extend lifespan in replicatively aged yeast. 459][50] MMD in aging is clearly detrimental as it is associated with a decrease in oxygen consumption, fragmentation of mitochondria, and genome instability. 45,48,49Prior to the onset of age-related MMD, vacuolar pH in yeasts increases due to altered activity of the VMA1 and VPH2 genes.These genes normally work with vacuolar H + -ATPase to acidify vacuoles.In yeasts, life can be extended by mere overexpression of VMA1 and VPH2.These over-expressions maintain adequate amino acid import by the vacuole, prevent the age-associated decline in vacuolar acidity, and protect against the development of MMD.Paradoxically, through as yet unknown mechanisms, reduction of mitochondrial membrane potential has shown life-extension property in yeast. 51Furthermore, MMD is engaged by strategies that extend lifespan including CR or deletion of mtDNA. 45,51A mildly depolarized mitochondrial membrane also has shown antiaging effect in Saccharomyces cerevisiae. 52These beneficial effects can be explained (in part) by the fact that control of mitochondrial permeability is required for autophagydependent lifespan extension. 53Opening of the permeability transition pore (mPTP) by genetic means extinguishes autophagy-dependent lifespan extension by CR or loss of germline stem cells.This suggests that the mPTP can transform the outcome of autophagy to a damaging force in mammals, which also suggests that mPTP is proper target for maximizing the benefits of autophagy in aging. 53PMF may also play a role in the regenerative potential of stem cells that declines with age. 54t appears that mitochondrial membrane potential is involved in cell fitness and that adjusting the decrease in this potential renders cells more robust for sustaining long term in vivo persistence and for maintaining enhanced stemness. 55][58] Moreover, restoring the mitochondrial membrane potential of old hematopoietic stem cells is sufficient to restore their youthful phenotype. 54

Lifespan extension by controlling PMF, energy, and nutritional sensors
Energy balance and homeostasis are maintained by the energy sensor AMP-activated protein kinase (AMPK) and by the nutritional sensor mTORC.Defects in this complex system leads to metabolic disorders including obesity and diabetes. 59There is also an intimate link between metabolism, energy and nutritional availability and lifespan. 60This is quite evident in the case of CR, which is known to increase life-span in yeasts, worms, flies, to rodents.CR exerts its effects by virtue of reducing the activity of TOR driven nutrient sensing and increased AMPK, AMP:ATP, and ADP:ATP ratios. 60More specifically, the transgenic expression of AMPK in fat or muscle extends lifespan, whereas its inhibition by RNAi shortens lifespan. 60The hepatic NADH/NAD + ratio, a latent metabolic measure of oxidative stress, is also an indicator of an unfavorable metabolic characteristic that causes age-related diseases ranging from reduced glucose tolerance and insulin resistance to mitochondrial disease. 61MF must be fine-tuned for healthy lifespan extension and prevention of metabolic diseases associated with aging.There is sufficient evidence to suggest that there is a delicate balance between the PMF, AMPK energy, and mTOR nutritional sensing. 62,63For example, exit from pluripotency and cell fate commitment can be regulated by membrane potential via calcium and mTOR. 64Inhibiting mTOR by genetic or pharmacologic means promotes mitochondrial function by encouraging mitophagy, expression of nuclear mitochondrial proteins, maintenance of mitochondrial protein concentrations, and oxidative function. 65,66The preservation of mitochondrial function increases lifespan in yeasts, fruit flies, worms, and mice. 67Longevity in Caenorhabditis elegans is also dependent on AMP-activated protein kinase (AMPK) by antagonistically controlling metabolism and aging. 68The effects of CR can be replicated by either inhibiting mTOR with rapamycin or by targeting AMPK and mitochondrial respiration with metformin. 65,66Restoring the PMF by the AMPK preserves viability, redox homeostasis, and normal mitochondrial signaling. 69However, counterintuitively, optogenetic photoactivation of PMF in vivo in C. elegans reverses the positive effect of AMPK activation during nutritional restriction, whereas reducing PMF promotes adaptation to hypoxia and the AMPK-mediated starvation response. 70urthermore, in replicatively aged S. cerevisiae, increased vacuolar pH, which leads to mitochondrial dysfunction, also increases life-span. 45Mutation or RNAi knockdowns of the components of the mitochondrial transport chain or PMF dissipation by protonophores have also been shown to extend lifespan in C. elegans. 71imilarly, mild mitochondrial uncoupling in mice that simulates CR enhances tissue respiratory rates, improves blood glucose, triglyceride, and insulin concentrations, decreases ROS and tissue DNA and protein oxidation, and reduces body weight. 57

ELECTROCEUTICALS FOR REROUTING CELL DEATH TO CELL PROLIFERATION
Cell death is one of the most distinctive features of aging.Receiving a death signal has traditionally been thought to send cells onto a path that leads to death.Cell proliferation and death, on the other hand, appear to be inextricably intertwined with escape routes that convert an apoptotic outcome to a proliferative activity.The process "anastasis" hardwires the cellular machinery to escape from death even when cells have endured caspase acti- vation and DNA damage. 72Similarly, identical bioelectric manipulations and V mem changes can promote both proliferation and apoptosis.Additionally, hyperpolarization via K + channel activation, instead of causing proliferation, protects cells against cell death. 20,26,28,73The link between cell proliferation and death can be easily visualized in vivo during eye and limb regeneration in Xenopus. 32aves of membrane hyperpolarization and transcriptome change and proliferation and cell death must be precisely timed throughout embryogenesis to temporally and spatially control organ development and organ size. 74The signature feature of V mem depolarization includes joint enrichment of cell cycle and cell death signals. 73Cell death engages and requires changes in ion flux and specifically Ca 2+ by the activation of transient receptor potential channels, ER stress, or inhibition of voltage-gated Ca 2+ channels. 75,76The cell shrinkage that is associated with apoptosis is also due to net efflux of intracellular K + and Cl − and influx of Na + . 77hus, similar bioelectric codes appear to promote both cell proliferation and death non-exclusively.Decoding these intertwined pathways may lead to new strategies for rejuvenating cells rather than allowing them to commit self-suicide.

CONCLUSIONS
Overall, bioelectricity and bioelectric patterns decay with aging and exert far-reaching influence over a wide range of aging phenotypes.Conversely, cell stress, macromolec-ular damage, aberrant AMPK and mTOR signaling, and senescence derail bioelectrical homeostasis.Deciphering aberrant bioelectric codes that promote aging and elucidating how bioelectrical field changes integrate with signaling pathways and transcriptional responses provide key insights into the aging process.Ion channel regulation and membrane potential homeostasis by mTOR and AMPK exemplify linkages between bioelectricity and signaling pathways. 78It is critical to identify pathways that enable voltage membrane patterns that override transcriptional, genomic, and epigenomic responses and to comprehend how bioelectric memory is written-although this likely occurs by inducing a stable epigenetic imprinting. 34here is a gap in our knowledge concerning how dysregulated bioelectric signaling drives senescence and aging phenotypes.Preliminary data encouragingly suggest that targeted modification of membrane potential may enable tissue/organ repair and regeneration.Theoretically, ion channel modifications and corrupted bioelectric codes could be reprogrammed to spatio-temporally regulate V mem .Elucidating bioelectric patterns of aging may enable innovative therapies for halting or even reversing an aging phenotype, as well as for inducing regeneration, preventing cancer or adopt electroceuticals for cancer treatment that do not require genetic engineering.][81] The non-locality of bioelectric information also offers the possibility of surrogate-site diagnostics and treatment.
Among the potential gero-electroceuticals are ivermectin, which targets glycine-and glutamate-gated chloride channels, and monensin, which acts as a sodium ionophore.These drugs restore regeneration.Capsaicin, a TRPV1 agonist, induces axonal growth; and fluoxetine, a serotonin transporter inhibitor, suppresses melanoma. 81ogether, there is a growing optimism that ion channel drugs might be tailored to generate gero-electroceuticals that alleviate aging and age-related disorders.

A U T H O R C O N T R I B U T I O N S
Siamak Tabibzadeh contributed to funding acquisition, conceptualization, preparing and writing of the paper and generation of figures and Olen R. Brown contributed to writing and editing.

A C K N O W L E D G M E N T S
This work was supported by a grant (FBS-2022) from Frontiers in Bioscience.

C O N F L I C T O F I N T E R E S T S TAT E M E N T
The author does not declare any commercial or financial or any other potential conflicts of interest.

F I G U R E 1
The dynamics of bioelectricity.(A) Ion channels mediate bioelectric dynamics in neural networks allowing neurotransmission via membrane depolarization.(B-D) Na + /K + , and Cl − pumps establish a default V mem in somatic cells, allowing for membrane depolarization that spreads throughout cell collectives via voltage sensitive electric synapses [gap junctions].5HT: 5 hydroxy-tryptamine.Source: Figure is created at BioRender.com.

F I G U R E 4
Cellular senescence as a hallmark of aging.Senescence develops by replication exhaustion, cellular stress, environmental factors, telomere shortening, mitochondrial dysfunction, dysfunction of nutrient sensing, oncogene activation, DNA and macromolecular damage, proteostasis, and inflammaging.Failure to maintain ion channel activity and membrane potential also leads to cell senescence.79,80Source: Figure is created at BioRender.com.