Rejuvenating Strategies of Tissue-specific Stem Cells for Healthy Aging

Zuogui Pills alleviate cyclophosphamide-induced ovarian aging by reducing oxidative stress and restoring the stemness of oogonial stem cells through the Nrf2/HO-1 signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Zuogui Pill (ZGP) is a traditional herbal formula of Chinese Medicine with a long history of use in alleviating ovarian aging.

AIM OF THE STUDY

To examine the impact of ZGP on oxidative stress and the stemness of oogonial stem cells (OSCs) in cyclophosphamide (CTX)-induced ovarian aging, as well as its molecular mechanisms involving the nuclear factor erythroid 2-related factor 2 (Nrf2, NFE2L2)/heme oxygenase-1 (HO-1, Hmox1) pathway.

MATERIALS AND METHODS

Female Sprague-Dawley (SD) rats were randomly divided into seven groups: control, model (CTX), estradiol valerate (EV, 0.103 mg/kg), ZGP-L (low dose Zuogui Pill, 1.851 g/kg), ZGP-H (high dose Zuogui Pill, 3.702 g/kg), ML385 (30 mg/kg), and ML385+ZGP-L. After CTX modeling, the EV, ZGP-L, ZGP-H, and ML385+ZGP-L groups were treated by gavage for 8 weeks, while the ML385 and ML385+ZGP-L groups were administered the Nrf2 antagonist ML385 twice a week. OSCs were isolated after modeling and then treated with drug serum containing 10% ZGP or 10 μM ML385. The general conditions of the rats, including body weight, ovarian weight/body weight ratio, and estrous cycle, were observed. Ovarian ultrastructure, follicle and corpus luteum counts were assessed via hematoxylin and eosin (H&E) staining. Serum hormone levels were measured using enzyme-linked immunosorbent assay (ELISA). Nrf2/HO-1 pathway, stem cell, germ cell, and cell cycle biomarkers were analyzed by qPCR and Western blot. Cell viability was assessed by cell counting kit-8 (CCK-8) assay. Oxidative stress biomarkers were evaluated using flow cytometry and assay kits. Immunofluorescence was employed to detect and locate OSCs in the ovary, quantify the average fluorescence intensity, and identify OSCs.

RESULTS

After ZGP treatment, rats with CTX-induced ovarian aging exhibited improved general condition, increased body weight, higher total ovarian weight to body weight ratio, and a restoration of the estrous cycle similar to the control group. Serum levels of estradiol (E2) and follicle stimulating hormone (FSH), two sex hormones, were also improved. Ovarian ultrastructure and follicle count at all stages showed improvement. Moreover, the viability and proliferation capacity of OSCs were enhanced following ZGP intervention. The Nrf2/HO-1 pathway was found to be down-regulated in CTX-induced aging ovarian OSCs. However, ZGP reversed this effect by activating the expression of Nrf2, HO-1, and NAD(P)H oxidoreductase 1 (NQO1), increasing the activity of antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX), and reducing the accumulation of malonaldehyde (MDA) and reactive oxygen species (ROS), thus restoring resistance to oxidative stress. Additionally, ZGP improved the cell cycle of OSCs, up-regulated the expression of Cyclin D1 and Cyclin E1, restored cell stemness, promoted proliferation, enhanced the expression of cell stemness markers octamer-binding transcription factor 4 (Oct4) and mouse VASA homolog (MVH), and down-regulated the expression of P21, thereby inhibiting apoptosis. The therapeutic effects of ZGP against oxidative stress and restoration of cell stemness were attenuated following inhibition of the Nrf2 signaling pathway using ML385.

CONCLUSIONS

ZGP protected against CTX-induced ovarian aging by restoring normal ovarian function, alleviating oxidative stress in aging OSCs, promoting OSCs proliferation, and restoring their stemness in rats, possibly through regulating the Nrf2/HO-1 pathway.

Exploring juventology: unlocking the secrets of youthspan and longevity programs

In recent decades, the study of biological aging has evolved from simplistic theories like the free radical theory to more complex and nuanced perspectives. In particular, the identification of evolutionary conserved genes and signaling pathways that can modulate both lifespan but also healthspan has resulted in the expanding understanding of the link between nutrients, signal transduction proteins, and aging along with substantial support for the existence of multiple "longevity programs," which are activated based on the availability of nutrients. Periodic fasting and other dietary restrictions can promote entry into a longevity program characterized by cellular protection and optimized function, and the activation of regenerative processes that lead to rejuvenation. This review discusses the idea of juventology, a novel field proposing the existence of longevity programs that can maintain organisms in a highly functional state for extended periods of time. Drawing upon research on Saccharomyces cerevisiae and other model organisms, the review explores the distinctiveness of juventology from traditional aging-centered views. The focus on the "age of youth" challenges conventional thinking and opens new avenues for understanding and extending the period of peak functionality in organisms. Thus, a "juventology"-based strategy can complement the traditional gerontology approach by focusing not on aging but on the longevity program affecting the life history period in which mortality is very low and organisms remain youthful, healthy, and fully functional.

Targeting the molecular & cellular pillars of human aging with exercise

Biological aging is the main driver of age-associated chronic diseases. In 2014, the United States National Institute of Aging (NIA) sponsored a meeting between several investigators in the field of aging biology, who identified seven biological pillars of aging and a consensus review, "Geroscience: Linking Aging to Chronic Disease," was published. The pillars of aging demonstrated the conservation of aging pathways in diverse model organisms and thus represent a useful framework with which to study human aging. In this present review, we revisit the seven pillars of aging from the perspective of exercise and discuss how regular physical exercise can modulate these pillars to stave off age-related chronic diseases and maintain functional capacity.

Intestinal epithelial stem cell transplants as a novel therapy for cerebrovascular stroke

Almost 2/3rds of stroke survivors exhibit vascular cognitive impairment and a third of stroke patients will develop dementia 1-3 years after stroke. These dire consequences underscore the need for effective stroke therapies. In addition to its damaging effects on the brain, stroke rapidly dysregulates the intestinal epithelium, resulting in elevated blood levels of inflammatory cytokines and toxic gut metabolites due to a 'leaky' gut. We tested whether repairing the gut via intestinal epithelial stem cell (IESC) transplants would also improve stroke recovery. Organoids containing IESCs derived from young rats transplanted into older rats after stroke were incorporated into the gut, restored stroke-induced gut dysmorphology and decreased gut permeability, and reduced circulating levels of endotoxin LPS and the inflammatory cytokine IL-17A. Remarkably, IESC transplants also improved stroke-induced acute (4d) sensory-motor disability and chronic (30d) cognitive-affective function. Moreover, IESCs from older animals displayed senescent features and were not therapeutic for stroke. These data underscore the gut as a critical therapeutic target for stroke and demonstrate the effectiveness of gut stem cell therapy.

Female germline stem cells: aging and anti-aging

The delay of ovarian aging and the fertility preservation of cancer patients are the eternal themes in the field of reproductive medicine. Acting as the pacemaker of female physiological aging, ovary is also considered as the principle player of cancer, cardiovascular diseases, cerebrovascular diseases, neurodegenerative diseases and etc. However, its aging mechanism and preventive measures are still unclear. Some researchers attempt to activate endogenous ovarian female germline stem cells (FGSCs) to restore ovarian function, as the most promising approach. FGSCs are stem cells in the adult ovaries that can be infinitely self-renewing and have the potential of committed differention. This review aims to elucidate FGSCs aging mechanism from multiple perspectives such as niches, immune disorder, chronic inflammation and oxidative stress. Therefore, the rebuilding nichs of FGSCs, regulation of immune dysfunction, anti-inflammation and oxidative stress remission are expected to restore or replenish FGSCs, ultimately to delay ovarian aging.

Role of the mtDNA Mutations and Mitophagy in Inflammaging

Ageing is an unavoidable multi-factorial process, characterised by a gradual decrease in physiological functionality and increasing vulnerability of the organism to environmental factors and pathogens, ending, eventually, in death. One of the most elaborated ageing theories implies a direct connection between ROS-mediated mtDNA damage and mutations. In this review, we focus on the role of mitochondrial metabolism, mitochondria generated ROS, mitochondrial dynamics and mitophagy in normal ageing and pathological conditions, such as inflammation. Also, a chronic form of inflammation, which could change the long-term status of the immune system in an age-dependent way, is discussed. Finally, the role of inflammaging in the most common neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, is also discussed.

OUP accepted manuscript

Stem cell therapies, including stem cell transplantation and rejuvenation of stem cells in situ, are promising avenues for tackling a broad range of diseases. Stem cells can both self-renew and differentiate into other cell types, and play a significant role in the regulation of tissue homeostasis and regeneration after cell degeneration or injury. However, stem cell exhaustion or dysfunction increases with age and impedes the normal function of multiple tissues and systems. Thus, stem cell therapies could provide a solution to aging and age-associated diseases. Here, we discuss recent advances in understanding the mechanisms that regulate stem cell regeneration. We also summarize potential strategies for rejuvenating stem cells that leverage intrinsic and extrinsic factors. These approaches may pave the way toward therapeutic interventions aiming at extending both health and life span.

Opportunities and Challenges in Stem Cell Aging

Studying aging, as a physiological process that can cause various pathological phenotypes, has attracted lots of attention due to its increasing burden and prevalence. Therefore, understanding its mechanism to find novel therapeutic alternatives for age-related disorders such as neurodegenerative and cardiovascular diseases is essential. Stem cell senescence plays an important role in aging. In the context of the underlying pathways, mitochondrial dysfunction, epigenetic and genetic alterations, and other mechanisms have been studied and as a consequence, several rejuvenation strategies targeting these mechanisms like pharmaceutical interventions, genetic modification, and cellular reprogramming have been proposed. On the other hand, since stem cells have great potential for disease modeling, they have been useful for representing aging and its associated disorders. Accordingly, the main mechanisms of senescence in stem cells and promising ways of rejuvenation, along with some examples of stem cell models for aging are introduced and discussed. This review aims to prepare a comprehensive summary of the findings by focusing on the most recent ones to shine a light on this area of research.

Application of mesenchymal stem cell therapy for aging frailty: from mechanisms to therapeutics

Aging frailty is a complex geriatric syndrome that becomes more prevalent with advancing age. It constitutes a major health problem due to frequent adverse outcomes. Frailty is characterized by disruption of physiological homeostasis and progressive decline of health status. Multiple factors contribute to development of frailty with advancing age, including genome instability, DNA damage, epigenetic alternations, stem cell exhaustion, among others. These interrelated factors comprehensively result in loss of tissue homeostasis and diminished reserve capacity in frailty. Therefore, the aged organism gradually represents symptoms of frailty with decline in physiological functions of organs. Notably, the brain, cardiovascular system, skeletal muscle, and endocrine system are intrinsically interrelated to frailty. The patients with frailty may display the diminished reserves capacity of organ systems. Due to the complex pathophysiology, no specific treatments have been approved for prevention of this syndrome. At such, effective strategies for intervening in pathogenic process to improve health status of frail patients are highly needed. Recent progress in cell-based therapy has greatly contributed to the amelioration of degenerative diseases related to age. Mesenchymal stem cells (MSCs) can exert regenerative effects and possess anti-inflammatory properties. Transplantation of MSCs represents as a promising therapeutic strategy to address the pathophysiologic problems of frail syndrome. Currently, MSC therapy have undergone the phase I and II trials in human subjects that have endorsed the safety and efficacy of MSCs for aging frailty. However, despite these positive results, caution is still needed with regard to potential to form tumors, and further large-scale studies are warranted to confirm the therapeutic efficacy of MSC therapy.

"Empowering" Cardiac Cells via Stem Cell Derived Mitochondrial Transplantation- Does Age Matter?

With cardiovascular diseases affecting millions of patients, new treatment strategies are urgently needed. The use of stem cell based approaches has been investigated during the last decades and promising effects have been achieved. However, the beneficial effect of stem cells has been found to being partly due to paracrine functions by alterations of their microenvironment and so an interesting field of research, the “stem- less” approaches has emerged over the last years using or altering the microenvironment, for example, via deletion of senescent cells, application of micro RNAs or by modifying the cellular energy metabolism via targeting mitochondria. Using autologous muscle-derived mitochondria for transplantations into the affected tissues has resulted in promising reports of improvements of cardiac functions in vitro and in vivo. However, since the targeted treatment group represents mainly elderly or otherwise sick patients, it is unclear whether and to what extent autologous mitochondria would exert their beneficial effects in these cases. Stem cells might represent better sources for mitochondria and could enhance the effect of mitochondrial transplantations. Therefore in this review we aim to provide an overview on aging effects of stem cells and mitochondria which might be important for mitochondrial transplantation and to give an overview on the current state in this field together with considerations worthwhile for further investigations.

Extracellular Microvesicles (MV's) Isolated from 5-Azacytidine-and-Resveratrol-Treated Cells Improve Viability and Ameliorate Endoplasmic Reticulum Stress in Metabolic Syndrome Derived Mesenchymal Stem Cells

Extracellular vesicles (EVs), a spherical membrane fragments including exosomes, are released from several cell types, including mesenchymal stromal cells (MSCs), constitutively or under stimulation. As MVs cargo include DNA, RNA, miRNA, lipids and proteins their have gain special attention in the field of regenerative medicine. Depending on the type of transferred molecules, MVs may exert wide range of biological effects in recipient cells including pro-inflammatory and anti-apoptotic action. In presented paper, we isolated MVs form adipose derived mesenchymal stem cells (ASC) which underwent stimulation with 5-azacytydine and resveratrol (AZA/RES) in order to improve their therapeutic potential. Then, isolated MVs were applied to ASC with impaired cytophysiological properties, isolated from equine metabolic syndrome diagnosed animals. Using RT-PCR, immunofluorescence, ELISA, confocal microscopy and western blot, we have evaluated the effects of MVs on recipient cells. We have found, that MVs derived from AZA/RES treated ASC ameliorates apoptosis, senescence and endoplasmic reticulum (ER) stress in deteriorated cells, restoring their proper functions. The work indicates, that cells treated with AZA/RES through their paracrine action can rejuvenate recipient cells. However, further research needs to be performed in order to fully understand the molecular mechanisms of these bioactive factors action. Graphical Abstract Graphical abstract of presented study.

Rejuvenation of mesenchymal stem cells by extracellular vesicles inhibits the elevation of reactive oxygen species

Aging induces numerous cellular disorders, such as the elevation of reactive oxygen species (ROS), in a number type of cells, including mesenchymal stem cells (MSCs). However, the correlation of ROS and impaired healing abilities as well as whether or not the inhibition of elevating ROS results in the rejuvenation of elderly MSCs is unclear. The rejuvenation of aged MSCs has thus recently received attention in the field of regenerative medicine. Specifically, extracellular vesicles (EVs) act as a novel tool for stem cell rejuvenation due to their gene transfer ability with systemic effects and safety. In the present study, we examined the roles of aging-associated ROS in the function and rejuvenation of elderly MSCs by infant EVs. The data clearly showed that elderly MSCs exhibited the downregulation of superoxide dismutase (SOD)1 and SOD3, which resulted in the elevation of ROS and downregulation of the MEK/ERK pathways, which are involved in the impairment of the MSCs’ ability to decrease necrotic area in the skin flap model. Furthermore, treatment with the antioxidant Edaravone or co-overexpression of SOD1 and SOD3 rescued elderly MSCs from the elevation of ROS and cellular senescence, thereby improving their functions. Of note, infant MSC-derived EVs rejuvenated elderly MSCs by inhibiting ROS production and the acceleration of cellular senescence and promoting the proliferation and in vivo functions in both type 1 and type 2 diabetic mice.

Effect of Active Ingredients of Chinese Herbal Medicine on the Rejuvenation of Healthy Aging: Focus on Stem Cells

Stem cells (SCs) are special types of cells with the ability of self-renewal and multidirectional differentiation. As the organism ages, the ability to maintain homeostasis and regeneration deteriorates and the number and activity of stem cells decline. Theoretically, the restoration of stem cells might reverse aging. However, due to their own aging, donor-derived immune rejection, and difficulties in stem cell differentiation control, a series of problems need to be solved to realize the potential for clinical application of stem cells. Chinese herbal medicine is a nature drug library which is suitable for the long-term treatment of aging-related diseases. Modern pharmacological studies have revealed that many active ingredients of Chinese herbal medicines with the effect of promoting stem cells growth and differentiation mainly belong to “reinforcing herbs.” In recent years, exploration of natural active ingredients from Chinese herbal medicines for delaying aging, improving the stem cell microenvironment, and promoting the proliferation and differentiation of endogenous stem cells has attracted substantial attention. This article will focus on active ingredients from Chinese herbs-mediated differentiation of stem cells into particular cell type, like neural cells, endothelial cells, cardiomyocytes, and osteoblasts. We will also discuss the effects of these small molecules on Wnt, Sonic Hedgehog, Notch, eNOS-cGMP, and MAP kinase signal transduction pathways, as well as reveal the role of estrogen receptor α and PPAR γ on selectively promoting or inhibiting stem cells differentiation. This review will provide new insights into the health aging strategies of active ingredients in Chinese herbal medicine in regenerative medicine.

Molecular Insights Into Lysyl Oxidases in Cartilage Regeneration and Rejuvenation

Articular cartilage remains among the most difficult tissues to regenerate due to its poor self-repair capacity. The lysyl oxidase family (LOX; also termed as protein-lysine 6-oxidase), mainly consists of lysyl oxidase (LO) and lysyl oxidase-like 1-4 (LOXL1-LOXL4), has been traditionally defined as cuproenzymes that are essential for stabilization of extracellular matrix, particularly cross-linking of collagen and elastin. LOX is essential in the musculoskeletal system, particularly cartilage. LOXs-mediated collagen cross-links are essential for the functional integrity of articular cartilage. Appropriate modulation of the expression or activity of certain LOX members selectively may become potential promising strategy for cartilage repair. In the current review, we summarized the advances of LOX in cartilage homeostasis and functioning, as well as copper-mediated activation of LOX through hypoxia-responsive signaling axis during recent decades. Also, the molecular signaling network governing LOX expression has been summarized, indicating that appropriate modulation of hypoxia-responsive-signaling-directed LOX expression through manipulation of bioavailability of copper and oxygen is promising for further clinical implications of cartilage regeneration, which has emerged as a potential therapeutic approach for cartilage rejuvenation in tissue engineering and regenerative medicine. Therefore, targeted regulation of copper-mediated hypoxia-responsive signalling axis for selective modulation of LOX expression may become potential effective therapeutics for enhanced cartilage regeneration and rejuvenation in future clinical implications.

Stem Cell Aging in Skeletal Muscle Regeneration and Disease

Skeletal muscle comprises 30-40% of the weight of a healthy human body and is required for voluntary movements in humans. Mature skeletal muscle is formed by multinuclear cells, which are called myofibers. Formation of myofibers depends on the proliferation, differentiation, and fusion of muscle progenitor cells during development and after injury. Muscle progenitor cells are derived from muscle satellite (stem) cells (MuSCs), which reside on the surface of the myofiber but beneath the basement membrane. MuSCs play a central role in postnatal maintenance, growth, repair, and regeneration of skeletal muscle. In sedentary adult muscle, MuSCs are mitotically quiescent, but are promptly activated in response to muscle injury. Physiological and chronological aging induces MuSC aging, leading to an impaired regenerative capability. Importantly, in pathological situations, repetitive muscle injury induces early impairment of MuSCs due to stem cell aging and leads to early impairment of regeneration ability. In this review, we discuss (1) the role of MuSCs in muscle regeneration, (2) stem cell aging under physiological and pathological conditions, and (3) prospects related to clinical applications of controlling MuSCs.

The Danger of Being Too Sympathetic: Norepinephrine in Alzheimer's Disease and Graying of Hair

Although alterations in the sympathetic nervous system (SNS) with age have been reported, and serious degenerative diseases of the autonomic nervous system such as multiple system atrophy are more likely to strike older people, connections between dysregulated adrenergic receptors and age-associated diseases and phenotypes have not been well studied. Two recent reports suggest that SNS may be more closely connected than previously appreciated. First, low nanomolar concentrations of Alzheimer's disease (AD)-associated Aβ42-amyloid oligomers alter signaling by SNS neurotransmitter norepinephrine (NE) to sufficiently activate kinase GSK3β to hyperphosphorylate tau, a key mediator of neurotoxicity in AD. Connecting beta-amyloid to tau in AD has been a key quest in understanding AD and developing therapeutics. The α₂ adrenergic receptor inhibitory drug idazoxan reduces GSK3β activity and tau phosphorylation in AD mice with improved cognitive function, even in the presence of beta-amyloid deposits. In this study, SNS activation in the brain coupled with problematic Aβ42-amyloid oligomers result in serious consequences that can be ameliorated by reducing SNS signaling. A second example of the detrimental effects of increased SNS signaling is the premature graying of hair in response to stress. Secretion of NE resulting from stress causes differentiation of most hair pigment melanocyte stem cells (MeSCs) into melanocytes, rapidly depleting the hair follicle of pigment-producing cells as mature melanocytes undergo apoptosis and MeSCs are eventually eliminated. Blockade of NE SNS signaling preserves hair coloration in stressed animals. Increased SNS activation has serious apparently irreversible effects on homeostasis in both situations. Although neither report directly addresses aging, given that AD and the loss of hair pigmentation have strong age associations, it is of interest to better understand the role that SNS has in promoting age-associated phenotypes generally and determine if tuning the SNS through drug-mediated attenuation of SNS signaling may be of medical benefit.