GDF11 Increases with Age and Inhibits Skeletal Muscle Regeneration

GDF11 Alleviates Vascular Calcification in VitD3-Overloaded Mice Through Inhibition of Inflammatory NF-κB Signal

Vascular calcification, an age-associated disorder, is a highly regulated biological process similar to bone formation. Growth differentiation factor 11 (GDF11), a secreted member of the transforming growth factor beta (TGF-β) superfamily, has been shown to act as an anti-aging factor in the brain, heart, skin, and skeletal muscle. Nevertheless, whether GDF11 affects vascular calcification and the underlying mechanisms remain unclear. In the present study, beta-glycerophosphate and calcium chloride-induced calcification of vascular smooth muscle cells (VSMCs) and a VitD3-overloaded mouse model were used to investigate the role of GDF11 in vascular calcification. Our results revealed that the knockdown of GDF11 by siRNA promoted the calcification of rat VSMCs, whereas GDF11 treatment significantly reduced the calcification of human and rat VSMCs in vitro, as detected by alizarin red staining and calcium content assay. Similarly, GDF11 treatment reduced the expression of bone-related molecules including Runt-related transcription factor 2 (Runx2) and bone morphogenetic protein-2 (BMP2). Furthermore, ex vivo and in vivo studies confirmed the inhibitory effect of GDF11 on vascular calcification. Mechanistically, GDF11 treatment reduced the levels of NF-κB signaling molecules including NLRP3, phosphorylated p65, IL-6, and IL-1β in VSMCs. Additionally, GDF11 siRNA-induced VSMC calcification was repressed by NF-κB inhibitor PDTC treatment. Taken together, these findings suggest that GDF11 alleviates vascular calcification through inhibiting the NF-κB signal. Modulation of GDF11 may represent a therapeutic strategy for vascular calcification.

Age-related declines in niche self-renewal factors controls testis aging and spermatogonial stem cell competition through Hairless, Imp, and Chinmo

Aging is associated with progressive tissue decline and shifts in stem cell clonality. The role of niche signals in driving these processes remains poorly understood. Using the Drosophila testis, we identify a regulatory axis in which age-related decline of niche signals (BMPs) lead to upregulation of the co-repressor Hairless, which downregulates the RNA-binding protein Imp in aged germline stem cells (GSCs). Reduced Imp causes loss of Chinmo, a key factor in GSC aging and competition. Reduced Chinmo causes ectopic Perlecan secretion which accumulates in the testis lumen and causes GSC loss. Aging of the testis is reversed by increasing BMPs in the niche, or by overexpressing Imp or depleting Hairless in GSCs. Furthermore, GSC clones with reduced Imp or increased Hairless are more competitive, expelling wild-type neighbors and monopolizing the niche. Thus, BMPs regulate testicular niche aging through the Hairless-Imp-Chinmo axis and "winning" GSCs usurp these aging mechanisms.

Highlights

Aged niche cells produce less BMPs, resulting in more Hairless (H) in aged GSCs Elevated H represses Imp , resulting in less Chinmo and in ectopic ECM secretion Aging is prevented by higher BMP in niche cells, or by higher Imp or lower H in GSCs GSCs with low Imp or high H exploit these aging mechanisms to colonize the GSC pool.

NaBC1 Boron Transporter Enables Myoblast Response to Substrate Rigidity via Fibronectin-Binding Integrins

Cells are sensitive to the physical properties of their microenvironment and transduce them into biochemical cues that trigger gene expression and alter cell behavior. Numerous proteins, including integrins, are involved in these mechanotransductive events. Here, a novel role for the boron transporter NaBC1 is identified as a mechanotransducer. It is demonstrated that soluble boron ions activate NaBC1 to enhance cell adhesion and intracellular tension in C2C12 myoblasts seeded on fibronectin-functionalized polyacrylamide (PAAm) hydrogels. Retrograde actin flow and traction forces exerted by these cells are significantly increased in vitro in response to both increased boron concentration and hydrogel stiffness. These effects are fibronectin and NaBC1-mediated as they are abrogated in hydrogels coated with laminin-111 in place of fibronectin and in esiRNA NaBC1-silenced cells. These findings thus demonstrate that NaBC1 controls boron homeostasis and also functions as a mechanosensor.

GDF11 Regulates M1 and M2 Polarization of BV2 Microglial Cells via p38 MAPK Signaling Pathway

Growth differentiation factor 11 (GDF11), a member of the transforming growth factor β (TGF-β) superfamily, exhibits great neurological and mental diseases modulating potential. However, its specific effects on microglia, which are the primary immune cells of the nervous system, remain unclear. To investigate the mechanism by which GDF11 affects BV2 microglial cells in vitro and to elucidate its regulatory mechanisms, we carried out a systematic examination of how GDF11 affects the various functions of lipopolysaccharide (LPS)-induced BV2 microglial cells and found that endogenous GDF11 could significantly inhibit cell proliferation, apoptosis, and migration. Specifically, GDF11 inhibited the polarization of BV2 cells to the proinflammatory M1 phenotype and promoted their polarization to the anti-inflammatory M2 phenotype, precipitating a reduction in the expression of CD86 and nitric oxide synthase 2 (NOS2), and an increase in the expression of CD206 and arginase-1. Additionally, RNA-seq and Western blotting experiments revealed that GDF11 activated the p38 MAPK (mitogen-activated protein kinase) pathway, mediating its effects on BV2 cells. Taken together, GDF11 could crucially regulate microglial responses and promote an anti-inflammatory microglial phenotype through the p38 MAPK signaling axis, which may have potential therapeutic implications in neuroinflammatory diseases.

Therapeutic applications and challenges in myostatin inhibition for enhanced skeletal muscle mass and functions

Myostatin, a potent negative regulator of skeletal muscle mass, has garnered significant attention as a therapeutic target for muscle dystrophies. Despite extensive research and promising preclinical results, clinical trials targeting myostatin inhibition in muscle dystrophies have failed to yield substantial improvements in muscle function or fitness in patients. This review details the mechanisms behind myostatin's function and the various inhibitors that have been tested preclinically and clinically. It also examines the challenges encountered in clinical translation, including issues with drug specificity, differences in serum myostatin concentrations between animal models and humans, and the necessity of neural input for functional improvements. Additionally, we explore promising avenues of research beyond muscle dystrophies, particularly in the treatment of metabolic syndromes and orthopedic disorders. Insights from these alternative applications suggest that myostatin inhibition may hold the potential for addressing a broader range of pathologies, providing new directions for therapeutic development.

Infusion of young donor plasma components in older patients modifies the immune and inflammatory response to surgical tissue injury: a randomized clinical trial

BACKGROUND

Preclinical evidence suggests that young plasma has beneficial effects on multiple organ systems in aged mice. Whether young plasma exerts beneficial effects in an aging human population remains highly controversial. Despite lacking data, young donor plasma infusions have been promoted for age-related conditions. Given the preclinical evidence that young plasma exerts beneficial effects by attenuating inflammation, this study examined whether administering a young plasma protein fraction to an elderly population would exert anti-inflammatory and immune modulating effects in humans, using surgery as a tissue injury model.

METHODS

This double-blind, placebo-controlled study enrolled and randomized 38 patients undergoing major joint replacement surgery. Patients received four separate infusions of a plasma protein fraction derived from young donors, or placebo one day before surgery, before and after surgery on the day of surgery, and one day after surgery. Blood specimens for proteomic and immunological analyses were collected before each infusion. Based on the high-content assessment of circulating plasma proteins with single-cell analyses of peripheral immune cells, proteomic signatures and cell-type-specific signaling responses that separated the treatment groups were derived with regression models.

RESULTS

Elastic net regression models revealed that administration a young plasma protein fraction significantly altered the proteomic (AUC = 0.796, p = 0.002) and the cellular immune response (AUC 0.904, p < 0.001) to surgical trauma resulting in signaling pathway- and cell type-specific anti-inflammatory immune modulation. Affected proteomic pathways regulating inflammation included JAK-STAT, NF-kappa B, and MAPK (p < 0.001). These findings were confirmed at the cellular level as the MAPK and JAK/STAT signaling responses were diminished and IkB, the negative regulator of NFkB, was elevated in adaptive immune cells.

CONCLUSION

Reported findings provide a first proof of principle in humans that a young plasma protein fraction actively regulates inflammatory and immune responses in an elderly population. They provide a solid rationale for elucidating active principles in young plasma that may be of therapeutic benefits for a range of age-related pathologies.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03981419.

Geroscience in heart failure: the search for therapeutic targets in the shared pathobiology of human aging and heart failure

Age is a major risk factor for heart failure, but one that has been historically viewed as non-modifiable. Emerging evidence suggests that the biology of aging is malleable, and can potentially be intervened upon to treat age-associated chronic diseases, such as heart failure. While aging biology represents a new frontier for therapeutic target discovery in heart failure, the challenges of translating Geroscience research to the clinic are multifold. In this review, we propose a strategy that prioritizes initial target discovery in human biology. We review the rationale for starting with human omics, which has generated important insights into the shared (patho)biology of human aging and heart failure. We then discuss how this knowledge can be leveraged to identify the mechanisms of aging biology most relevant to heart failure. Lastly, we provide examples of how this human-first Geroscience approach, when paired with rigorous functional assessments in preclinical models, is leading to early-stage clinical development of gerotherapeutic approaches for heart failure.

Reducing functionally defective old HSCs alleviates aging-related phenotypes in old recipient mice

Aging is a process accompanied by functional decline in tissues and organs with great social and medical consequences. Developing effective anti-aging strategies is of great significance. In this study, we demonstrated that transplantation of young hematopoietic stem cells (HSCs) into old mice can mitigate aging phenotypes, underscoring the crucial role of HSCs in the aging process. Through comprehensive molecular and functional analyses, we identified a subset of HSCs in aged mice that exhibit "younger" molecular profiles and functions, marked by low levels of CD150 expression. Mechanistically, CD150low HSCs from old mice but not their CD150high counterparts can effectively differentiate into downstream lineage cells. Notably, transplantation of old CD150low HSCs attenuates aging phenotypes and prolongs lifespan of elderly mice compared to those transplanted with unselected or CD150high HSCs. Importantly, reducing the dysfunctional CD150high HSCs can alleviate aging phenotypes in old recipient mice. Thus, our study demonstrates the presence of "younger" HSCs in old mice, and that aging-associated functional decline can be mitigated by reducing dysfunctional HSCs.

A spontaneously immortalized muscle stem cell line (EfMS) from brown-marbled grouper for cell-cultured fish meat production

Lacking of suitable fish muscle stem cell line has greatly hindered the fabrication of cell-cultured fish meat. Here, we established and characterized a spontaneously immortalized marine fish muscle stem cell line (EfMS) from brown-marbled grouper (Epinephelus fuscoguttatus), which could actively proliferate with good genetic stability and well maintain the stemness of myogenesis potential for over 50 passages. Taurine was found to be able to serve as a substitute of fish muscle extract in maintaining stemness. The EfMS cells could be efficiently induced to myogenic differentiation or adipogenic trans-differentiation in both 2D and 3D culture systems. Using edible 3D microcarriers, we produced 0.65 g fat-free and 1.47 g fat-containing cell-cultured fish meat in 8 days. The scaffold-free cell-cultured fish meat exhibited a much higher content of flavory amino acids than natural fish. Together, EfMS cell line can serve as an ideal seed cell line for the production of cell-cultured fish meat.

Muscle aging and sarcopenia: The pathology, etiology, and most promising therapeutic targets

Sarcopenia is a progressive muscle wasting disorder that severely impacts the quality of life of elderly individuals. Although the natural aging process primarily causes sarcopenia, it can develop in response to other conditions. Because muscle function is influenced by numerous changes that occur with age, the etiology of sarcopenia remains unclear. However, recent characterizations of the aging muscle transcriptional landscape, signaling pathway disruptions, fiber and extracellular matrix compositions, systemic metabolomic and inflammatory responses, mitochondrial function, and neurological inputs offer insights and hope for future treatments. This review will discuss age-related changes in healthy muscle and our current understanding of how this can deteriorate into sarcopenia. As our elderly population continues to grow, we must understand sarcopenia and find treatments that allow individuals to maintain independence and dignity throughout an extended lifespan.

Pathomechanisms of Monoallelic variants in TTN causing skeletal muscle disease

Pathogenic variants in the titin gene (TTN) are known to cause a wide range of cardiac and musculoskeletal disorders, with skeletal myopathy mostly attributed to biallelic variants. We identified monoallelic truncating variants (TTNtv), splice site or internal deletions in TTN in probands with mild, progressive axial and proximal weakness, with dilated cardiomyopathy frequently developing with age. These variants segregated in an autosomal dominant pattern in 7 out of 8 studied families. We investigated the impact of these variants on mRNA, protein levels, and skeletal muscle structure and function. Results reveal that nonsense-mediated decay likely prevents accumulation of harmful truncated protein in skeletal muscle in patients with TTNtvs. Splice variants and an out-of-frame deletion induce aberrant exon skipping, while an in-frame deletion produces shortened titin with intact N- and C-termini, resulting in disrupted sarcomeric structure. All variant types were associated with genome-wide changes in splicing patterns, which represent a hallmark of disease progression. Lastly, RNA-seq studies revealed that GDF11, a member of the TGF-β superfamily, is upregulated in diseased tissue, indicating that it might be a useful therapeutic target in skeletal muscle titinopathies.

Growth Differentiation Factor 11 Evokes Lung Injury, Inflammation, and Fibrosis in Mice through the Activin A Receptor Type II-Like Kinase, 53kDa-Smad2/3 Signaling Pathway

Growth differentiation factor 11 (GDF11) belongs to the transforming growth factor beta superfamily and participates in various pathophysiological processes. Initially, GDF11 was suggested to act as a rejuvenator by improving age-related phenotypes of the heart, brain, and skeletal muscle in aged mice. Recent studies demonstrate that GDF11 also serves as an adverse risk factor for human frailty and diseases. However, the role of GDF11 in pulmonary fibrosis (PF) remains unclear. This study explored the role and signaling mechanisms of GDF11 in PF. GDF11 expression was markedly up-regulated in fibrotic lung tissues of both humans and mice. Intratracheal administration of commercial recombinant GDF11 caused lung injury, inflammation, and fibrogenesis in mice. Furthermore, adenovirus-mediated secretory expression of mature GDF11 was exacerbated, whereas full-length GDF11 or the GDF11 propeptide (GDF111-298) alleviated bleomycin-induced PF in mice. In in vitro experiments, GDF11 suppressed the growth of alveolar and bronchial epithelial cells (A549 and BEAS-2B) and human pulmonary microvascular endothelial cells, promoted fibroblast activation, and induced epithelial/endothelial-mesenchymal transition. These effects corresponded to the phosphorylation of Smad2/3, and blocking activin A receptor type II-like kinase, 53kDa (ALK5)-Smad2/3 signaling abolished the in vivo and in vitro effects of GDF11. In conclusion, these findings provide evidence that GDF11 acts as a potent injurious, proinflammatory, and profibrotic factor in the lungs via the ALK5-Smad2/3 pathway.

Therapeutic targeting of GDF11 in muscle atrophy: Insights and strategies

The exploration of novel therapeutic avenues for skeletal muscle atrophy is imperative due to its significant health impact. Recent studies have spotlighted growth differentiation factor 11 (GDF11), a TGFβ superfamily member, for its rejuvenating role in reversing age-related tissue dysfunction. This review synthesizes current findings on GDF11, elucidating its distinct biological functions and the ongoing debates regarding its efficacy in muscle homeostasis. By addressing discrepancies in current research outcomes and its ambiguous role due to its homological identity to myostatin, a negative regulator of muscle mass, this review aims to clarify the role of GDF11 in muscle homeostasis and its potential as a therapeutic target for muscle atrophy. Through a thorough examination of GDF11's mechanisms and effects, this review provides insights that could pave the way for innovative treatments for muscle atrophy, emphasizing the need and strategies to boost endogenous GDF11 levels for therapeutic potential.

Liver-secreted FGF21 induces sarcopenia by inhibiting satellite cell myogenesis via klotho beta in decompensated cirrhosis

BACKGROUND & AIMS

Sarcopenia, a prevalent condition, significantly impacts the prognosis of patients with decompensated cirrhosis (DC). Serum fibroblast growth factor 21 (FGF21) levels are significantly higher in DC patients with sarcopenia. Satellite cells (SCs) play a role in aging- and cancer-induced sarcopenia. Here, we investigated the roles of FGF21 and SCs in DC-related sarcopenia as well as the underlying mechanisms.

METHODS

We developed two DC mouse models and performed in vivo and in vitro experiments. Klotho beta (KLB) knockout mice in SCs were constructed to investigate the role of KLB downstream of FGF21. In addition, biological samples were collected from patients with DC and control patients to validate the results.

RESULTS

Muscle wasting and impaired SC myogenesis were observed in the DC mouse model and patients with DC. Elevated circulating levels of liver-derived FGF21 were observed, which were significantly negatively correlated with skeletal muscle mass/skeletal muscle index. Liver-secreted FGF21 induces SC dysfunction, contributing to sarcopenia. Mechanistically, FGF21 in the DC state exhibits enhanced interactions with KLB on SC surfaces, leading to downstream phosphatase and tensin homolog upregulation. This inhibits the protein kinase B (PI3K/Akt) pathway, hampering SC proliferation and differentiation, and blocking new myotube formation to repair atrophy. Neutralizing circulating FGF21 using neutralizing antibodies, knockdown of hepatic FGF21 by adeno-associated virus, or knockout of KLB in SCs effectively improved or reversed DC-related sarcopenia.

CONCLUSIONS

Hepatocyte-derived FGF21 mediates liver-muscle crosstalk, which impairs muscle regeneration via the inhibition of the PI3K/Akt pathway, thereby demonstrating a novel therapeutic strategy for DC-related sarcopenia.

Novel insights into the pleiotropic health effects of growth differentiation factor 11 gained from genome-wide association studies in population biobanks

BACKGROUND

Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor-β (TGF-β) superfamily that has gained considerable attention over the last decade for its observed ability to reverse age-related deterioration of multiple tissues, including the heart. Yet as many researchers have struggled to confirm the cardioprotective and anti-aging effects of GDF11, the topic has grown increasingly controversial, and the field has reached an impasse. We postulated that a clearer understanding of GDF11 could be gained by investigating its health effects at the population level.

METHODS AND RESULTS

We employed a comprehensive strategy to interrogate results from genome-wide association studies in population Biobanks. Interestingly, phenome-wide association studies (PheWAS) of GDF11 tissue-specific cis-eQTLs revealed associations with asthma, immune function, lung function, and thyroid phenotypes. Furthermore, PheWAS of GDF11 genetic variants confirmed these results, revealing similar associations with asthma, immune function, lung function, and thyroid health. To complement these findings, we mined results from transcriptome-wide association studies, which uncovered associations between predicted tissue-specific GDF11 expression and the same health effects identified from PheWAS analyses.

CONCLUSIONS

In this study, we report novel relationships between GDF11 and disease, namely asthma and hypothyroidism, in contrast to its formerly assumed role as a rejuvenating factor in basic aging and cardiovascular health. We propose that these associations are mediated through the involvement of GDF11 in inflammatory signaling pathways. Taken together, these findings provide new insights into the health effects of GDF11 at the population level and warrant future studies investigating the role of GDF11 in these specific health conditions.

Ophthalmic acid is a bloodborne metabolite that contributes to age-induced cardiomyocyte hypertrophy

Cardiac aging involves the development of left ventricular hypertrophy alongside a decline in functional capacity. Here, we use neutral blood exchange to demonstrate that the acute removal of age-accumulated blood factors significantly regresses cardiac hypertrophy in aged mice. The reversal of hypertrophy was not attributed to age-associated hemodynamic effects, implicating a role of blood-derived factors. In addition, the overarching paradigm of systemic aging maintains that the age-related overabundance of plasma proteins are largely responsible for causing pathological phenotypes in tissues. Our results suggest that blood metabolites, not proteins, drive cardiac hypertrophy instead. Upon analyzing serum metabolomics data sets, we identified ophthalmic acid as a circulating metabolite whose levels increase with advanced age. Treatment of adult mouse and neonatal rat cardiomyocytes in culture with ophthalmic acid increased their relative surface areas. This study uncovers a non-protein metabolite that may contribute to cardiomyocyte hypertrophy during aging. Identifying a method to counteract ophthalmic acid's hypertrophic effects may reveal novel therapeutic opportunities for cardiac rejuvenation.

Expression profiling by high-throughput sequencing reveals GADD45, SMAD7, EGR-1 and HOXA3 activation in Myostatin (MSTN) and GDF11 treated myoblasts

Growth differentiation factor 11 (GDF11) and myostatin (MSTN/GDF8) are closely related members of the transforming growth factor β (TGFβ) superfamily, sharing structural homology. Despite these structural similarities, recent research has shed light on the distinct roles these ligands play within muscle tissue. This study aims to uncover both the differences and similarities in gene expression at the transcriptome level by utilizing RNA sequencing. We conducted experiments involving five distinct groups, each with three biological replicates, using C2C12 cell cultures. The cells were subjected to high-throughput profiling to investigate disparities in gene expression patterns following preconditioning with either GDF11 or MSTN at concentrations of 1 nM and 10 nM, respectively. In addition, control groups were established. Our research revealed concentration-dependent gene expression patterns, with 38 genes showing significant differences when compared to the control groups. Notably, GADD45, SMAD7, EGR-1, and HOXA3 exhibited significant differential expression. We also conducted an over-representation analysis, highlighting the activation of MAPK and JNK signaling pathways, along with GO-terms related to genes that negatively regulate metabolic processes, biosynthesis, and protein phosphorylation. This study unveiled the activation of several genes not previously discussed in existing literature whose full biological implications are yet to be determined in future research.

Critical signaling molecules in the temporomandibular joint osteoarthritis under different magnitudes of mechanical stimulation

The mechanical stress environment in the temporomandibular joint (TMJ) is constantly changing due to daily mandibular movements. Therefore, TMJ tissues, such as condylar cartilage, the synovial membrane and discs, are influenced by different magnitudes of mechanical stimulation. Moderate mechanical stimulation is beneficial for maintaining homeostasis, whereas abnormal mechanical stimulation leads to degeneration and ultimately contributes to the development of temporomandibular joint osteoarthritis (TMJOA), which involves changes in critical signaling molecules. Under abnormal mechanical stimulation, compensatory molecules may prevent degenerative changes while decompensatory molecules aggravate. In this review, we summarize the critical signaling molecules that are stimulated by moderate or abnormal mechanical loading in TMJ tissues, mainly in condylar cartilage. Furthermore, we classify abnormal mechanical stimulation-induced molecules into compensatory or decompensatory molecules. Our aim is to understand the pathophysiological mechanism of TMJ dysfunction more deeply in the ever-changing mechanical environment, and then provide new ideas for discovering effective diagnostic and therapeutic targets in TMJOA.

The role of TGF-β signaling in muscle atrophy, sarcopenia and cancer cachexia

Skeletal muscle, comprising a significant proportion (40 to 50 percent) of total body weight in humans, plays a critical role in maintaining normal physiological conditions. Muscle atrophy occurs when the rate of protein degradation exceeds protein synthesis. Sarcopenia refers to age-related muscle atrophy, while cachexia represents a more complex form of muscle wasting associated with various diseases such as cancer, heart failure, and AIDS. Recent research has highlighted the involvement of signaling pathways, including IGF1-Akt-mTOR, MuRF1-MAFbx, and FOXO, in regulating the delicate balance between muscle protein synthesis and breakdown. Myostatin, a member of the TGF-β superfamily, negatively regulates muscle growth and promotes muscle atrophy by activating Smad2 and Smad3. It also interacts with other signaling pathways in cachexia and sarcopenia. Inhibition of myostatin has emerged as a promising therapeutic approach for sarcopenia and cachexia. Additionally, other TGF-β family members, such as TGF-β1, activin A, and GDF11, have been implicated in the regulation of skeletal muscle mass. Furthermore, myostatin cooperates with these family members to impair muscle differentiation and contribute to muscle loss. This review provides an overview of the significance of myostatin and other TGF-β signaling pathway members in muscular dystrophy, sarcopenia, and cachexia. It also discusses potential novel therapeutic strategies targeting myostatin and TGF-β signaling for the treatment of muscle atrophy.

Rejuvenation of young blood on aging organs: Effects, circulating factors, and mechanisms

Aging causes degenerative changes in organs, leading to a decline in physical function. Over the past two decades, researchers have made significant progress in understanding the rejuvenating effects of young blood on aging organs, benefiting from heterochronic parabiosis models that connect the blood circulation of aged and young rodents. It has been discovered that young blood can partially rejuvenate organs in old animals by regulating important aging-related signaling pathways. Clinical trials have also shown the effectiveness of young blood in treating aging-related diseases. However, the limited availability of young blood poses a challenge to implementing anti-aging therapies on a large scale for older individuals. As a promising alternative, scientists have identified some specific anti-aging circulating factors in young blood that have been shown to promote organ regeneration, reduce inflammation, and alleviate fibrosis associated with aging in animal experiments. While previous reviews have focused primarily on the effects and mechanisms of circulating factors on aging, it is important to acknowledge that studying the rejuvenating effects and mechanisms of young blood has been a significant source of inspiration in this field, and it will continue to be in the future. In recent years, new findings have emerged, further expanding our knowledge in this area. This review aims to summarize the rejuvenating effects and mechanisms of young blood and circulating factors, discussing their similarities and connections, addressing discrepancies in previous studies, outlining future research directions, and highlighting the potential for clinical translation in anti-aging interventions.

Myokines: metabolic regulation in obesity and type 2 diabetes

Skeletal muscle plays a vital role in the regulation of systemic metabolism, partly through its secretion of endocrine factors which are collectively known as myokines. Altered myokine levels are associated with metabolic diseases, such as type 2 diabetes (T2D). The significance of interorgan crosstalk, particularly through myokines, has emerged as a fundamental aspect of nutrient and energy homeostasis. However, a comprehensive understanding of myokine biology in the setting of obesity and T2D remains a major challenge. In this review, we discuss the regulation and biological functions of key myokines that have been extensively studied during the past two decades, namely interleukin 6 (IL-6), irisin, myostatin (MSTN), growth differentiation factor 11 (GDF11), fibroblast growth factor 21 (FGF21), apelin, brain-derived neurotrophic factor (BDNF), meteorin-like (Metrnl), secreted protein acidic and rich in cysteine (SPARC), β-aminoisobutyric acid (BAIBA), Musclin, and Dickkopf 3 (Dkk3). Related to these, we detail the role of exercise in myokine expression and secretion together with their contributions to metabolic physiology and disease. Despite significant advancements in myokine research, many myokines remain challenging to measure accurately and investigate thoroughly. Hence, new research techniques and detection methods should be developed and rigorously tested. Therefore, developing a comprehensive perspective on myokine biology is crucial, as this will likely offer new insights into the pathophysiological mechanisms underlying obesity and T2D and may reveal novel targets for therapeutic interventions.

Blood-based therapies to combat neurodegenerative diseases

Neurodegeneration, known as the progressive loss of neurons in terms of their structure and function, is the principal pathophysiological change found in the majority of brain-related disorders. Ageing has been considered the most well-established risk factor in most common neurodegenerative diseases, such as Parkinson's disease (PD) and Alzheimer's disease (AD). There is currently no effective treatment or cure for these diseases; the approved therapeutic options to date are only for palliative care. Ageing and neurodegenerative diseases are closely intertwined; reversing the aspects of brain ageing could theoretically mitigate age-related neurodegeneration. Ever since the regenerative properties of young blood on aged tissues came to light, substantial efforts have been focused on identifying and characterizing the circulating factors in the young and old systemic milieu that may attenuate or accentuate brain ageing and neurodegeneration. Later studies discovered the superiority of old plasma dilution in tissue rejuvenation, which is achieved through a molecular reset of the systemic proteome. These findings supported the use of therapeutic blood exchange for the treatment of degenerative diseases in older individuals. The first objective of this article is to explore the rejuvenating properties of blood-based therapies in the ageing brains and their therapeutic effects on AD. Then, we also look into the clinical applications, various limitations, and challenges associated with blood-based therapies for AD patients.

Thbs1 regulates skeletal muscle mass in a TGFβ-Smad2/3-ATF4-dependent manner

Loss of muscle mass is a feature of chronic illness and aging. Here, we report that skeletal muscle-specific thrombospondin-1 transgenic mice (Thbs1 Tg) have profound muscle atrophy with age-dependent decreases in exercise capacity and premature lethality. Mechanistically, Thbs1 activates transforming growth factor β (TGFβ)-Smad2/3 signaling, which also induces activating transcription factor 4 (ATF4) expression that together modulates the autophagy-lysosomal pathway (ALP) and ubiquitin-proteasome system (UPS) to facilitate muscle atrophy. Indeed, myofiber-specific inhibition of TGFβ-receptor signaling represses the induction of ATF4, normalizes ALP and UPS, and partially restores muscle mass in Thbs1 Tg mice. Similarly, myofiber-specific deletion of Smad2 and Smad3 or the Atf4 gene antagonizes Thbs1-induced muscle atrophy. More importantly, Thbs1-/- mice show significantly reduced levels of denervation- and caloric restriction-mediated muscle atrophy, along with blunted TGFβ-Smad3-ATF4 signaling. Thus, Thbs1-mediated TGFβ-Smad3-ATF4 signaling in skeletal muscle regulates tissue rarefaction, suggesting a target for atrophy-based muscle diseases and sarcopenia with aging.

Deletion of TECRL promotes skeletal muscle repair by up-regulating EGR2

Myogenic regeneration relies on the proliferation and differentiation of satellite cells. TECRL (trans-2,3-enoyl-CoA reductase like) is an endoplasmic reticulum protein only expressed in cardiac and skeletal muscle. However, its role in myogenesis remains unknown. We show that TECRL expression is increased in response to injury. Satellite cell-specific deletion of TECRL enhances muscle repair by increasing the expression of EGR2 through the activation of the ERK1/2 signaling pathway, which in turn promotes the expression of PAX7. We further show that TECRL deletion led to the upregulation of the histone acetyltransferase general control nonderepressible 5, which enhances the transcription of EGR2 through acetylation. Importantly, we showed that AAV9-mediated TECRL silencing improved muscle repair in mice. These findings shed light on myogenic regeneration and muscle repair.

Progress in the relationship between GDF11 and depression

Annually, the frequency of morbidity in depression has increased progressively in response to life stressors, and there is an increasing trend toward younger morbidity. The pathogenesis of depression is complicated and includes factors such as genetic inheritance and variations in physiological functions induced by various environmental factors. Currently, drug therapy has wide adaptability in clinical practice and plays an important role in the treatment of patients with mild depression. However, the therapeutic effects of most antidepressants are typically not significant and are associated with considerable adverse effects and addiction. Therefore, it is imperative to identify the deeper mechanisms of depression and search for alternative drug targets. Growth differentiation factor 11 (GDF11) is described as an anti-ageing molecule that belongs to a member of the transforming growth factor β family. Additionally, the latest research findings suggested that GDF11 positively regulates neurogenesis and enhances neuronal activity, thereby attenuating depression-like behaviours. Although an increasing number of studies have focused on the multiple functions of GDF11 in skeletal dysplasia and carcinogenesis, its precise mechanism of action in depression remains unknown. Thus, in this review, we discuss the role of GDF11 and its mechanistic pathways in the pathogenesis of depression to develop novel therapies for depression.

Circulating Growth Differentiation Factors 11 and 8, Their Antagonists Follistatin and Follistatin-Like-3, and Risk of Heart Failure in Elders

BACKGROUND

Heterochronic parabiosis has identified growth differentiation factor (GDF)-11 as a potential means of cardiac rejuvenation, but findings have been inconsistent. A major barrier has been lack of assay specificity for GDF-11 and its homolog GDF-8.

METHODS

We tested the hypothesis that GDF-11 and GDF-8, and their major antagonists follistatin and follistatin-like (FSTL)-3, are associated with incident heart failure (HF) and its subtypes in elders. Based on validation experiments, we used liquid chromatography-tandem mass spectrometry to measure total serum GDF-11 and GDF-8, along with follistatin and FSTL-3 by immunoassay, in 2 longitudinal cohorts of older adults.

RESULTS

In 2 599 participants (age 75.2 ± 4.3) followed for 10.8 ± 5.6 years, 721 HF events occurred. After adjustment, neither GDF-11 (HR per doubling: 0.93 [0.67, 1.30]) nor GDF-8 (HR: 1.02 per doubling [0.83, 1.27]) was associated with incident HF or its subtypes. Positive associations with HF were detected for follistatin (HR: 1.15 [1.00, 1.32]) and FLST-3 (HR: 1.38 [1.03, 1.85]), and with HF with preserved ejection fraction for FSTL-3 (HR: 1.77 [1.03, 3.02]). (All HRs per doubling of biomarker.) FSTL-3 associations with HF appeared stronger at higher follistatin levels and vice versa, and also for men, Blacks, and lower kidney function.

CONCLUSIONS

Among older adults, serum follistatin and FSTL-3, but not GDF-11 or GDF-8, were associated with incident HF. These findings do not support the concept that low serum levels of total GDF-11 or GDF-8 contribute to HF late in life, but do implicate transforming growth factor-β superfamily pathways as potential therapeutic targets.

Aging and age-related diseases with a focus on therapeutic potentials of young blood/plasma

Aging is accompanied by alterations in the body with time-related to decline of physiological integrity and functionality process, responsible for increasing diseases and vulnerability to death. Several ages associated with biomarkers were observed in red blood cells, and consequently plasma proteins have a critical rejuvenating role in the aging process and age-related disorders. Advanced age is a risk factor for a broad spectrum of diseases and disorders such as cardiovascular diseases, musculoskeletal disorders and liver, chronic kidney disease, neurodegenerative diseases, and cancer because of loss of regenerative capacity, correlated to reduced systemic factors and raise of pro-inflammatory cytokines. Most studies have shown that systemic factors in young blood/plasma can strongly protect against age-related diseases in various tissues by restoring autophagy, increasing neurogenesis, and reducing oxidative stress, inflammation, and apoptosis. Here, we focus on the current advances in using young plasma or blood to combat aging and age-related diseases and summarize the experimental and clinical evidence supporting this approach. Based on reports, young plasma or blood is new a therapeutic approach to aging and age-associated diseases.

Circulating GDF11 exacerbates myocardial injury in mice and associates with increased infarct size in humans

AIMS

The heart rejuvenating effects of circulating growth differentiation factor 11 (GDF11), a transforming growth factor-β superfamily member that shares 90% homology with myostatin (MSTN), remains controversial. Here, we aimed to probe the role of GDF11 in acute myocardial infarction (MI), a frequent cause of heart failure and premature death during ageing.

METHODS AND RESULTS

In contrast to endogenous Mstn, myocardial Gdf11 declined during the course of ageing and was particularly reduced following ischaemia/reperfusion (I/R) injury, suggesting a therapeutic potential of GDF11 signalling in MI. Unexpectedly, boosting systemic Gdf11 by recombinant GDF11 delivery (0.1 mg/kg body weight over 30 days) prior to myocardial I/R augmented myocardial infarct size in C57BL/6 mice irrespective of their age, predominantly by accelerating pro-apoptotic signalling. While intrinsic cardioprotective signalling pathways remained unaffected by high circulating GDF11, targeted transcriptomics and immunomapping studies focusing on GDF11-associated downstream targets revealed attenuated Nkx2-5 expression confined to CD105-expressing cells, with pro-apoptotic activity, as assessed by caspase-3 levels, being particularly pronounced in adjacent cells, suggesting an indirect effect. By harnessing a highly specific and validated liquid chromatography-tandem mass spectrometry-based assay, we show that in prospectively recruited patients with MI circulating GDF11 but not MSTN levels incline with age. Moreover, GDF11 levels were particularly elevated in those at high risk for adverse outcomes following the acute event, with circulating GDF11 emerging as an independent predictor of myocardial infarct size, as estimated by standardized peak creatine kinase-MB levels.

CONCLUSION

Our data challenge the initially reported heart rejuvenating effects of circulating GDF11 and suggest that high levels of systemic GDF11 exacerbate myocardial injury in mice and humans alike. Persistently high GDF11 levels during ageing may contribute to the age-dependent loss of cardioprotective mechanisms and thus poor outcomes of elderly patients following acute MI.

The regulatory effect of growth differentiation factor 11 on different cells

Growth differentiation factor 11 (GDF11) is one of the important factors in the pathophysiological process of animals. It is widely expressed in many tissues and organs of animals, showing its wide biological activity and potential application value. Previous research has demonstrated that GDF11 has a therapeutic effect on various diseases, such as anti-myocardial aging and anti-tumor. This has not only sparked intense interest and enthusiasm among academics but also spurred some for-profit businesses to attempt to develop GDF11 as a medication for regenerative medicine or anti-aging application. Currently, Sotatercept, a GDF11 antibody drug, is in the marketing application stage, and HS-235 and rGDF11 are in the preclinical research stage. Therefore, we believe that figuring out which cells GDF11 acts on and its current problems should be an important issue in the scientific and commercial communities. Only through extensive, comprehensive research and discussion can we better understand the role and potential of GDF11, while avoiding unnecessary risks and misinformation. In this review, we aimed to summarize the role of GDF11 in different cells and its current controversies and challenges, providing an important reference for us to deeply understand the function of GDF11 and formulate more effective treatment strategies in the future.

Mutual regulation between GDF11 and TET2 prevents senescence of mesenchymal stem cells

Growth differentiation factor 11 (GDF11) is a putative systemic rejuvenation factor. In this study, we characterized the mechanism by which GDF11 reversed aging of mesenchymal stem cells (MSCs). In culture, aged MSCs proliferate slower and are positive for senescence markers senescence-associated β-galactosidase and P16ink4a . They have shortened telomeres, decreased GDF11 expression, and reduced osteogenic potential. GDF11 can block MSC aging in vitro and reverse age-dependent bone loss in vivo. The antiaging effect of GDF11 is via activation of the Smad2/3-PI3K-AKT-mTOR pathway. Unexpectedly, GDF11 also upregulated a DNA demethylase Tet2, which served as a key mediator for GDF11 to autoregulate itself via demethylation of the GDF11 promoter. Mutation of Tet2 facilitates MSC aging by blocking GDF11 expression. Mutagenesis of Tet2-regulated CpG sites also blocks GDF11 expression, leading to MSC aging. Together, a novel mutual regulatory relationship between GDF11 and an epigenetic factor Tet2 unveiled their antiaging roles.

Cancer Cachexia: New Insights and Future Directions

Cancer remains a major health problem and is associated with cachexia in up to 80% of cases, leading to decreased survival and quality of life. Cachexia involves complex metabolic disturbances in both protein and energy balance, muscle wasting phenomena, weight loss, systemic inflammation, overall decreased performance status, and tolerability to treatment. The clinical impact of cancer cachexia is very complex, with early detection of cachectic patients and identification of predictive biomarkers being two key factors for improving survival. Thus, a better understanding of the complexity of cancer cachexia phenomena and its main pathophysiological mechanism is much needed. Our review highlights the most important information about cancer cachexia, aiming to disseminate updated research findings about this highly deadly condition.

Evaluation of Associations of Growth Differentiation Factor-11, Growth Differentiation Factor-8, and Their Binding Proteins, Follistatin and Follistatin-Like Protein-3, With Measures of Skeletal Muscle Mass, Muscle Strength, and Physical Function in Older Adults

BACKGROUND

Based on studies from animal models, growth differentiation factor-11 (GDF-11) may have rejuvenating effects in humans. GDF-11 has high sequence homology with GDF-8 (also known as myostatin); follistatin and follistatin-like protein-3 (FSTL-3) are inhibitory proteins of both GDF-8 and GDF-11.

METHODS

Using highly specific liquid chromatography with tandem mass spectrometry assays for GDF-11 and GDF-8 and immunoassays for follistatin and FSTL-3, we quantified the association of these factors with muscle size, strength, and physical performance in 2 prospective cohort studies of community-dwelling older adults (Health, Aging, and Body Composition study [Health ABC] and Cardiovascular Health Study [CHS]).

RESULTS

GDF-8 levels were positively associated with thigh muscle cross-sectional area and density in Health ABC (data not available in CHS). GDF-8 levels were positively associated with lean mass (a surrogate of muscle mass) in Health ABC but not CHS, and grip strength in CHS but not Health ABC. FSTL-3 (and perhaps follistatin) was negatively associated with lean mass and had variable associations with other variables. In contrast, GDF-11 was not significantly associated with strength or performance.

CONCLUSIONS

GDF-8 and its binding proteins, follistatin and FSTL-3, may constitute a counterregulatory system (chalones) to restrain age-related loss of muscle mass and strength.

Evaluation of Associations of Growth Differentiation Factor-11, Growth Differentiation Factor-8, and Their Binding Proteins Follistatin and Follistatin-Like Protein-3 With Dementia and Cognition

BACKGROUND

Studies using heterochronic parabiosis discovered that circulating factors mediate brain aging in animal models.

METHODS

We assessed growth differentiation factors (GDF)-11 and GDF-8 using mass spectrometry and inhibitors follistatin and follistatin-like protein-3 (FSTL-3) with ELISA in the Cardiovascular Health Study (CHS; N = 1 506) and the Health, Aging and Body Composition (Health ABC) Study (N = 1 237). CLL-11 and beta-2 microglobulin (β2M) were measured with ELISA in a subset of 400 individuals in Health ABC. Associations were assessed with cognitive function, brain magnetic resonance imaging (MRI) findings (CHS only), and incident dementia using correlations, linear regression, and Cox proportional hazards models.

RESULTS

In CHS, levels of GDF-11, GDF-8, and follistatin were not correlated cross-sectionally with the 3MSE or DSST, brain MRI findings of white matter hyperintensity, atrophy, or small infarcts, nor were they associated with incident dementia. FSTL-3 was modestly correlated with poorer cognitive function, greater white matter hyperintensities, and atrophy on MRI, as well as with incident dementia with an adjusted hazard ratio (HR) of 1.72 (95% CI = 1.13, 2.61) per doubling of FSTL-3. FSTL-3 was not associated with cognition or dementia in Health ABC, but GDF-8 was associated with both. The adjusted HR for incident dementia was 1.50 (95% CI = 1.07, 2.10) per doubling of GDF-8.

CONCLUSIONS

Total GDF-11 level was not related to cognition or dementia in older adults. Associations of GDF-8 with cognitive outcomes in Health ABC were not expected, but consistent with animal models. Associations of FSTL-3 with cognition, brain abnormalities, and incident dementia in CHS implicate TGFβ superfamily inhibition in the pathogenesis of dementia.

Relationships of GDF8 and 11 and Their Antagonists With Decline of Grip Strength Among Older Adults in the Baltimore Longitudinal Study of Aging

Although growth/differentiation factor 11 (GDF11), growth/differentiation factor 8 (GDF8), and their circulating antagonists, which include GDF11 and GDF8 propeptides, follistatin (FST), WAP, Follistatin/Kazal, Immunoglobulin, Kunitz And Netrin Domain Containing (WFIKKN)1, and WFIKKN2, have been shown to influence skeletal muscle and aging in mice, the relationship of these circulating factors with human phenotypes is less clear. This study aimed to characterize the relationship between plasma GDF8, GDF11, FST, WFIKKN1, and WFIKKN2 concentrations with the decline of grip strength in 534 adults, ≥65 years, who participated in the Baltimore Longitudinal Study of Aging and had grip strength measured over time. Plasma GDF8 and GDF11 mature proteins, GDF8 and GDF11 propeptides, FST (isoform FST315 and cleaved form FST303), WFIKKN1, and WFIKKN2 concentrations were measured using selected reaction monitoring-tandem mass spectrometry at baseline. Grip strength was measured at baseline and at follow-up visits (median follow-up 8.87 years). Mean (standard deviation) grip strength declined in men and women by -0.84 (2.45) and -0.60 (1.32) kg/year, respectively. Plasma GDF8 and GDF11 mature proteins, GDF8 and GDF11 propeptides, FST315, FST303, WFIKKN1, and WFIKKN2 concentrations were not independently predictive of the decline of grip strength in men or women in multivariable linear regression analyses that adjusted for potential confounders. In conclusion, circulating GDF8, GDF11, and their antagonists do not appear to influence the decline of grip strength in older men or women.

GDF11 and aging biology - controversies resolved and pending

Since the exogenous administration of GDF11, a TGF-ß superfamily member, was reported to have beneficial effects in some models of human disease, there have been many research studies in GDF11 biology. However, many studies have now confirmed that exogenous administration of GDF11 can improve physiology in disease models, including cardiac fibrosis, experimental stroke, and disordered metabolism. GDF11 is similar to GDF8 (also called Myostatin), differing only by 11 amino acids in their mature signaling domains. These two proteins are now known to be biochemically different both in vitro and in vivo. GDF11 is much more potent than GDF8 and induces more strongly SMAD2 phosphorylation in the myocardium compared to GDF8. GDF8 and GDF11 prodomain are only 52% identical and are cleaved by different Tolloid proteases to liberate the mature signaling domain from inhibition of the prodomain. Here, we review the state of GDF11 biology, highlighting both resolved and remaining controversies.

GDF11 as a friend or an enemy in the cancer biology?

The Growth and Differential Factor 11 (GDF11) is a recently discovered representative of Transforming Growth Factor β superfamily. The highest expression of GDF11 is detected in the nervous system, bladder, seminal vesicles and muscles whereas the lowest in the testis, liver or breast. GDF11 role in physiology is still not clear. GDF11 is a crucial factor in embryogenesis, cell cycle control and apoptosis, inasmuch it mainly targets cell retain stemness features, managing to the cell differentiation and the maturation. GDF11 is entangled in lipid metabolism, inflammatory processes and aging. GDF11 is strongly related to carcinogenesis and its expression in tumors is intruded. GDF11 can promote cancer growth in the colon or inhibit the cell proliferation in breast cancer. The aberrated expression is probably allied with the impaired maturation. In this article we summarized an impact of GDF11 on the tumor cells and review the all attitudes connecting GDF11 with carcinogenesis.

Targeting aging with the healthy skeletal system: The endocrine role of bone

Aging is an inevitable biological process, and longevity may be related to bone health. Maintaining strong bone health can extend one's lifespan, but the exact mechanism is unclear. Bone and extraosseous organs, including the heart and brain, have complex and precise communication mechanisms. In addition to its load bearing capacity, the skeletal system secretes cytokines, which play a role in bone regulation of extraosseous organs. FGF23, OCN, and LCN2 are three representative bone-derived cytokines involved in energy metabolism, endocrine homeostasis and systemic chronic inflammation levels. Today, advanced research methods provide new understandings of bone as a crucial endocrine organ. For example, gene editing technology enables bone-specific conditional gene knockout models, which allows the study of bone-derived cytokines to be more precise. We systematically evaluated the various effects of bone-derived cytokines on extraosseous organs and their possible antiaging mechanism. Targeting aging with the current knowledge of the healthy skeletal system is a potential therapeutic strategy. Therefore, we present a comprehensive review that summarizes the current knowledge and provides insights for futures studies.

Rejuvenating effects of young extracellular vesicles in aged rats and in cellular models of human senescence

Rejuvenation of an old organism was achieved in heterochronic parabiosis experiments, implicating different soluble factors in this effect. Extracellular vesicles (EVs) are the secretory effectors of many cells, including cardiosphere-derived cells (CDCs) with demonstrated anti-senescent effect. 1. To determine the role of EVs (versus other blood fractions) on the rejuvenating effect of the young blood. 2. To evaluate the anti-aging properties of therapeutically administered EVs secreted by young-CDCs in an old organism. Neonatal blood fractioned in 4 components (whole blood, serum, EV-depleted serum and purified EVs) was used to treat old human cardiac stromal cells (CSPCs). CDCs were generated from neonatal rat hearts and the secreted CDC-EVs were purified. CDC-EVs were then tested in naturally-aged rats, using monthly injections over 4-months period. For validation in human samples, pediatric CDC-EVs were tested in aged human CSPCs and progeric fibroblasts. While the purified EVs reproduced the rejuvenating effects of the whole blood, CSPCs treated with EV-depleted serum exhibited the highest degree of senescence. Treatment with young CDC-EVs induce structural and functional improvements in the heart, lungs, skeletal muscle, and kidneys of old rats, while favorably modulating glucose metabolism and anti-senescence pathways. Lifespan was prolonged. EVs secreted by young CDCs exert broad-ranging anti-aging effects in aged rodents and in cellular models of human senescence. Our work not only identifies CDC-EVs as possible therapeutic candidates for a wide range of age-related pathologies, but also raises the question of whether EVs function as endogenous modulators of senescence.

A novel fasting regimen revealed protein reservation and complement C3 down-regulation after 14-day's continual dietary deprivation

Objectives

The aim is to evaluate the effect of a novel 14-day fasting regimen on the balance between skeletal muscle and adipose tissue composition which might associate with inflammatory factors. Our analysis includes basic physical examinations, clinical laboratory analysis, bioelectrical impedance and biochemical analytic assessments of healthy volunteers.

Methods

Eight healthy subjects were randomly selected from a pool of volunteers to undergo a continual dietary deprivation (CDD) regimen. Individuals were assigned to take Flexible Abrosia (FA, prebiotic combination) plus appropriate mineral supplement of potassium and magnesium at 3 mealtime every day to prevent potential injury from starved intestinal flora and avoid spasms of smooth muscle due to hunger. Physical and medical examinations were conducted and blood samples were collected at following timepoints: before CDD as self-control (0D), day 7 and day 14 during fasting, and 7-21days and/or 2~3mo after refeeding.

Results

The combination of FA and mineral supplements significantly decreased self-reported physical response of starvation, with tolerable hunger-mediated sensations experienced during CDD. Bioelectrical and biochemical results indicated significant reduction in both muscle lean and fat mass on day 7. Meanwhile, markers related to fat composition consistently decreased during and after CDD. In addition, most biochemical marker levels, including serum proteins, reached their inflection points at the 7th day of CDD as compared to the control measurements. Levels of these factors started to show a relative plateau, or reversed direction upon the 14th day of CDD. The exceptions of above factors were myostatin and complement protein C3, which remained at lower concentrations in the blood throughout CDD, and were unable to fully recover toward baseline levels even after 3 months' refeeding.

Conclusion

Our results indicated that human subjects undergoing prolonged dietary restriction were well protected by FA and mineral ions from gut injury or physical discomfort of starvation. Most factors showed a relative plateau response at the end of 14D-CDD. The muscle tissues were well preserved during prolonged fasting, and an improved protein/lipid ratio was observed. Upon refeeding, constant lower levels of myostatin and complement C3 were maintained after CDD implies a long-term beneficial effect in dealing with anti-aging and inflammation.

Challenges and Future Prospects of Targeting Myostatin/Activin A Signaling to Treat Diseases of Muscle Loss and Metabolic Dysfunction

Over the past 25 years, considerable progress has been made in terms of elucidating the regulatory and signaling mechanisms underlying the control of skeletal muscle mass by myostatin and other secreted proteins belonging to the transforming growth factor-β superfamily. Preclinical studies demonstrating the potential benefits of targeting the activities of these ligands have fueled the development of numerous biologics capable of perturbing this signaling pathway and increasing muscle mass and function. These biologics have been tested in numerous clinical trials for a wide range of indications characterized by muscle loss and excess adiposity. Here, we review the results of these trials and discuss some of the challenges and future prospects for targeting this signaling pathway to treat muscle and metabolic diseases. Myostatin inhibitors may improve metabolic outcomes by increasing muscle mass, and metabolic disorders may be attractive potential indications for these molecules.

Growth differentiation factor 11: A new hope for the treatment of cardiovascular diseases

Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor-β superfamily that has garnered significant attention due to its anti-cardiac aging properties. Many studies have revealed that GDF11 plays an indispensable role in the onset of cardiovascular diseases (CVDs). Consequently, it has emerged as a potential target and novel therapeutic agent for CVD treatment. However, currently, no literature reviews comprehensively summarize the research on GDF11 in the context of CVDs. Therefore, herein, we comprehensively described GDF11's structure, function, and signaling in various tissues. Furthermore, we focused on the latest findings concerning its involvement in CVD development and its potential for clinical translation as a CVD treatment. We aim to provide a theoretical basis for the prospects and future research directions of the GDF11 application regarding CVDs.

Myogenic differentiation of human myoblasts and Mesenchymal stromal cells under GDF11 on NPoly-ɛ-caprolactone-collagen I-Polyethylene-nanofibers

BACKGROUND

For the purpose of skeletal muscle engineering, primary myoblasts (Mb) and adipogenic mesenchymal stem cells (ADSC) can be co-cultured and myogenically differentiated. Electrospun composite nanofiber scaffolds represent suitable matrices for tissue engineering of skeletal muscle, combining both biocompatibility and stability Although growth differentiation factor 11 (GDF11) has been proposed as a rejuvenating circulating factor, restoring skeletal muscle function in aging mice, some studies have also described a harming effect of GDF11. Therefore, the aim of the study was to analyze the effect of GDF11 on co-cultures of Mb and ADSC on poly-ε-caprolactone (PCL)-collagen I-polyethylene oxide (PEO)-nanofibers.

RESULTS

Human Mb were co-cultured with ADSC two-dimensionally (2D) as monolayers or three-dimensionally (3D) on aligned PCL-collagen I-PEO-nanofibers. Differentiation media were either serum-free with or without GDF11, or serum containing as in a conventional differentiation medium. Cell viability was higher after conventional myogenic differentiation compared to serum-free and serum-free + GDF11 differentiation as was creatine kinase activity. Immunofluorescence staining showed myosine heavy chain expression in all groups after 28 days of differentiation without any clear evidence of more or less pronounced expression in either group. Gene expression of myosine heavy chain (MYH2) increased after serum-free + GDF11 stimulation compared to serum-free stimulation alone.

CONCLUSIONS

This is the first study analyzing the effect of GDF11 on myogenic differentiation of Mb and ADSC co-cultures under serum-free conditions. The results of this study show that PCL-collagen I-PEO-nanofibers represent a suitable matrix for 3D myogenic differentiation of Mb and ADSC. In this context, GDF11 seems to promote myogenic differentiation of Mb and ADSC co-cultures compared to serum-free differentiation without any evidence of a harming effect.

GDF11 promotes wound healing in diabetic mice via stimulating HIF-1ɑ-VEGF/SDF-1ɑ-mediated endothelial progenitor cell mobilization and neovascularization

Non-healing diabetic wounds (DW) are a serious clinical problem that remained poorly understood. We recently found that topical application of growth differentiation factor 11 (GDF11) accelerated skin wound healing in both Type 1 DM (T1DM) and genetically engineered Type 2 diabetic db/db (T2DM) mice. In the present study, we elucidated the cellular and molecular mechanisms underlying the action of GDF11 on healing of small skin wound. Single round-shape full-thickness wound of 5-mm diameter with muscle and bone exposed was made on mouse dorsum using a sterile punch biopsy 7 days following the onset of DM. Recombinant human GDF11 (rGDF11, 50 ng/mL, 10 μL) was topically applied onto the wound area twice a day until epidermal closure (maximum 14 days). Digital images of wound were obtained once a day from D0 to D14 post-wounding. We showed that topical application of GDF11 accelerated the healing of full-thickness skin wounds in both type 1 and type 2 diabetic mice, even after GDF8 (a muscle growth factor) had been silenced. At the cellular level, GDF11 significantly facilitated neovascularization to enhance regeneration of skin tissues by stimulating mobilization, migration and homing of endothelial progenitor cells (EPCs) to the wounded area. At the molecular level, GDF11 greatly increased HIF-1ɑ expression to enhance the activities of VEGF and SDF-1ɑ, thereby neovascularization. We found that endogenous GDF11 level was robustly decreased in skin tissue of diabetic wounds. The specific antibody against GDF11 or silence of GDF11 by siRNA in healthy mice mimicked the non-healing property of diabetic wound. Thus, we demonstrate that GDF11 promotes diabetic wound healing via stimulating endothelial progenitor cells mobilization and neovascularization mediated by HIF-1ɑ-VEGF/SDF-1ɑ pathway. Our results support the potential of GDF11 as a therapeutic agent for non-healing DW.

The correlation between circulating growth differentiation factor 11 and the risk of osteopenia/osteoporosis in men

Our results suggest that the serum GDF11 concentration is significantly associated with the risk of bone metabolism dysfunction in men and may be a useful target for prediction of osteopenia/osteoporosis to enable prompt intervention for this common but invariably under- or misdiagnosed condition in men.

PURPOSE

Male osteopenia/osteoporosis remains a neglected subject or is under- or misdiagnosed. Many studies have confirmed the role of growth differentiation factor 11 (GDF11) in bone metabolism, although its role in bone metabolism remains controversial. In this study, we aimed to investigate the association between serum GDF11 levels and the prevalence of osteopenia/osteoporosis (OP) in a male cohort and explore the possibility of GDF11 to be a useful target for prediction of osteopenia/osteoporosis to enable prompt intervention for this disease.

METHODS

This cross-sectional study included 121 native Chinese men randomly aged 20-87 years, excluded the subjects who had the conditions of bone metabolism-related disease and administration of hormonal drugs, and grouped the subjects to OP and non-OP, based on the WHO definition and latest guidelines of OP. The serum GDF11 concentration was determined using a GDF11-specific immunoassay. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry. Tartrate-resistant acid phosphatase 5b (TRAP-5b) were measured in serum samples with ELISA method.

RESULTS

We observed a negative correlation between serum GDF11 levels and age, a positive correlation between serum GDF11 levels and the femoral neck BMD, and a negative correlation between serum GDF11 levels and TRAP-5b in men. The prevalence and risk of OP were significantly higher in men with low serum GDF11 levels.

CONCLUSIONS

The serum GDF11 concentration is significantly associated with the risk of bone metabolism dysfunction and may be a useful target for prediction of OP in male cohort.

The Role of TGF-β, Activin and Follistatin in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is an immune-mediated inflammatory condition predominantly affecting the gastrointestinal (GI) tract. An increasing prevalence of IBD has been observed globally. The pathogenesis of IBD includes a complex interplay between the intestinal microbiome, diet, genetic factors and immune responses. The consequent imbalance of inflammatory mediators ultimately leads to intestinal mucosal damage and defective repair. Growth factors, given their specific roles in maintaining the homeostasis and integrity of the intestinal epithelium, are of particular interest in the setting of IBD. Furthermore, direct targeting of growth factor signalling pathways involved in the regeneration of the damaged epithelium and the regulation of inflammation could be considered as therapeutic options for individuals with IBD. Several members of the transforming growth factor (TGF)-β superfamily, particularly TGF-β, activin and follistatin, are key candidates as they exhibit various roles in inflammatory processes and contribute to maintenance and homeostasis in the GI tract. This article aimed firstly to review the events involved in the pathogenesis of IBD with particular emphasis on TGF-β, activin and follistatin and secondly to outline the potential role of therapeutic manipulation of these pathways.

In vivo modulation of endogenous gene expression via CRISPR/Cas9-mediated 3'UTR editing

The 3' untranslated regions (UTRs) modulate gene expression levels by regulating mRNA stability and translation. We previously showed that the replacement of the negative regulatory elements from the 3'UTR of glial cell line-derived neurotrophic factor (GDNF) resulted in increased endogenous GDNF expression while retaining its normal spatiotemporal expression pattern. Here, we have developed a methodology for the generation of in vivo hyper- and hypomorphic alleles via 3'UTR targeting using the CRISPR/Cas9 system. We demonstrate that CRISPR/Cas9-mediated excision of a long inhibitory sequence from Gdnf native 3'UTR in mouse zygotes increases the levels of endogenous GDNF with similar phenotypic alterations in embryonic kidney development as we described in GDNF constitutive and conditional hypermorphic mice. Furthermore, we show that CRISPR/Cas9-mediated targeting of 3'UTRs in vivo allows the modulation of the expression levels of two other morphogens, Gdf11 and Bdnf. Together, our work demonstrates the power of in vivo 3'UTR editing using the CRISPR/Cas9 system to create hyper- and hypomorphic alleles, suggesting wide applicability in studies on gene function and potentially, in gene therapy.

Blood-to-brain communication in aging and rejuvenation

Aging induces molecular, cellular and functional changes in the adult brain that drive cognitive decline and increase vulnerability to dementia-related neurodegenerative diseases. Leveraging systemic and lifestyle interventions, such as heterochronic parabiosis, administration of 'young blood', exercise and caloric restriction, has challenged prevalent views of brain aging as a rigid process and has demonstrated that aging-associated cognitive and cellular impairments can be restored to more youthful levels. Technological advances in proteomic and transcriptomic analyses have further facilitated investigations into the functional impact of intertissue communication on brain aging and have led to the identification of a growing number of pro-aging and pro-youthful factors in blood. In this review, we discuss blood-to-brain communication from a systems physiology perspective with an emphasis on blood-derived signals as potent drivers of both age-related brain dysfunction and brain rejuvenation.

Functional substitutions of amino acids that differ between GDF11 and GDF8 impact skeletal development and skeletal muscle

Growth differentiation factor 11 (GDF11) and GDF8 (MSTN) are closely related TGF-β family proteins that interact with nearly identical signaling receptors and antagonists. However, GDF11 appears to activate SMAD2/3 more potently than GDF8 in vitro and in vivo. The ligands possess divergent structural properties, whereby substituting unique GDF11 amino acids into GDF8 enhanced the activity of the resulting chimeric GDF8. We investigated potentially distinct endogenous activities of GDF11 and GDF8 in vivo by genetically modifying their mature signaling domains. Full recoding of GDF8 to that of GDF11 yielded mice lacking GDF8, with GDF11 levels ∼50-fold higher than normal, and exhibiting modestly decreased muscle mass, with no apparent negative impacts on health or survival. Substitution of two specific amino acids in the fingertip region of GDF11 with the corresponding GDF8 residues resulted in prenatal axial skeletal transformations, consistent with Gdf11-deficient mice, without apparent perturbation of skeletal or cardiac muscle development or homeostasis. These experiments uncover distinctive features between the GDF11 and GDF8 mature domains in vivo and identify a specific requirement for GDF11 in early-stage skeletal development.

The Preventive Effect of Specific Collagen Peptides against Dexamethasone-Induced Muscle Atrophy in Mice

Muscle atrophy, also known as muscle wasting, is the thinning of muscle mass due to muscle disuse, aging, or diseases such as cancer or neurological problems. Muscle atrophy is closely related to the quality of life and has high morbidity and mortality. However, therapeutic options for muscle atrophy are limited, so studies to develop therapeutic agents for muscle loss are always required. For this study, we investigated how orally administered specific collagen peptides (CP) affect muscle atrophy and elucidated its molecular mechanism using an in vivo model. We treated mice with dexamethasone (DEX) to induce a muscular atrophy phenotype and then administered CP (0.25 and 0.5 g/kg) for four weeks. In a microcomputed tomography analysis, CP (0.5 g/kg) intake significantly increased the volume of calf muscles in mice with DEX-induced muscle atrophy. In addition, the administration of CP (0.25 and 0.5 g/kg) restored the weight of the gluteus maximus and the fiber cross-sectional area (CSA) of the pectoralis major and calf muscles, which were reduced by DEX. CP significantly inhibited the mRNA expression of myostatin and the phosphorylation of Smad2, but it did not affect TGF-β, BDNF, or FNDC5 gene expression. In addition, AKT/mTOR, a central pathway for muscle protein synthesis and related to myostatin signaling, was enhanced in the groups that were administered CP. Finally, CP decreased serum albumin levels and increased TNF-α gene expression. Collectively, our in vivo results demonstrate that CP can alleviate muscle wasting through a multitude of mechanisms. Therefore, we propose CP as a supplement or treatment to prevent muscle atrophy.