Growth differentiation factor 15 (GDF15): A survival protein with therapeutic potential in metabolic diseases

A review: hippo signaling pathway promotes tumor invasion and metastasis by regulating target gene expression

BACKGROUND

The Hippo pathway is widely considered to inhibit cell growth and play an important role in regulating the size of organs. However, recent studies have shown that abnormal regulation of the Hippo pathway can also affect tumor invasion and metastasis. Therefore, finding out how the Hippo pathway promotes tumor development by regulating the expression of target genes provides new ideas for future research on targeted drugs that inhibit tumor progression.

METHODS

PubMed, Embase, Web of Science, and the Cochrane Library were systematically searched.

RESULTS

The search strategy identified 1892 hits and 196 publications were finally included in this review. As the core molecule of the Hippo pathway, YAP/TAZ are usually highly expressed in tumors that undergo invasion and migration and are accompanied by abnormally strong nuclear metastasis. Through its interaction with nuclear transcription factors TEADs, it directly or indirectly regulates and the expressions of target genes related to tumor metastasis and invasion. These target genes can induce the formation of invasive pseudopodia in tumor cells, reduce intercellular adhesion, degrade extracellular matrix (ECM), and cause epithelial-mesenchymal transition (EMT), or indirectly promote through other signaling pathways, such as mitogen-activated protein kinases (MAPK), TGF/Smad, etc, which facilitate the invasion and metastasis of tumors.

CONCLUSION

This article mainly introduces the research progress of YAP/TAZ which are the core molecules of the Hippo pathway regulating related target genes to promote tumor invasion and metastasis. Focus on the target genes that affect tumor invasion and metastasis, providing the possibility for the selection of clinical drug treatment targets, to provide some help for a more in-depth study of tumor invasion and migration mechanism and the development of clinical drugs.

NR5A2 transcriptional activation by BRD4 promotes pancreatic cancer progression by upregulating GDF15

NR5A2 is a transcription factor regulating the expression of various oncogenes. However, the role of NR5A2 and the specific regulatory mechanism of NR5A2 in pancreatic ductal adenocarcinoma (PDAC) are not thoroughly studied. In our study, Western blotting, real-time PCR, and immunohistochemistry were conducted to assess the expression levels of different molecules. Wound-healing, MTS, colony formation, and transwell assays were employed to evaluate the malignant potential of pancreatic cancer cells. We demonstrated that NR5A2 acted as a negative prognostic biomarker in PDAC. NR5A2 silencing inhibited the proliferation and migration abilities of pancreatic cancer cells in vitro and in vivo. While NR5A2 overexpression markedly promoted both events in vitro. We further identified that NR5A2 was transcriptionally upregulated by BRD4 in pancreatic cancer cells and this was confirmed by Chromatin immunoprecipitation (ChIP) and ChIP-qPCR. Besides, transcriptome RNA sequencing (RNA-Seq) was performed to explore the cancer-promoting effects of NR5A2, we found that GDF15 is a component of multiple down-regulated tumor-promoting gene sets after NR5A2 was silenced. Next, we showed that NR5A2 enhanced the malignancy of pancreatic cancer cells by inducing the transcription of GDF15. Collectively, our findings suggest that NR5A2 expression is induced by BRD4. In turn, NR5A2 activates the transcription of GDF15, promoting pancreatic cancer progression. Therefore, NR5A2 and GDF15 could be promising therapeutic targets in pancreatic cancer.

Growth Differentiation Factor (GDF)-15 and Cardiometabolic Outcomes among Older Adults: The Atherosclerosis Risk in Communities Study

INTRODUCTION

Laboratory studies suggest an involvement of growth differentiation factor 15 (GDF-15) in metabolic dysregulation. However, the utility of GDF-15 for assessing risk of cardiometabolic outcomes has not been rigorously examined among older adults.

METHODS

We conducted a cross-sectional analysis of older adults who attended visit 6 (2016-2017) of the Atherosclerosis Risk in Communities (ARIC) Study. We used multivariable logistic regression to quantify cross-sectional associations of GDF-15 (in quartiles) with prevalent diabetes, obesity, atherosclerotic cardiovascular disease (ASCVD), subclinical myocardial stress/injury (assessed by NT-proB-type Natriuretic Peptide [NT-proBNP] and high-sensitivity cardiac troponin T [hs-cTnT]), and heart failure (HF).

RESULTS

Among 3792 ARIC study participants (mean age 80 years, 59% women, 23% Blacks and 77% Whites, mean GDF-15: 2094.9 pg/mL [SD: 1395.6]), higher GDF-15 concentrations (highest vs. lowest quartile) were positively associated with diabetes (adjusted odds ratio [aOR]:] : 2.48, 95% CI : 1.89, 3.26), ASCVD (aOR: 1.57, 95% CI: 1.16, 2.11), increased hscTnT (aOR: 2.27, 95%CI: 1.54, 3.34), increased NT-proBNP (aOR: 1.98, 95%CI: 1.46, 2.70), and HF (aOR: 3.22, 95%CI : 2.13, 4.85), in models adjusted for demographics and traditional cardiovascular risk factors.

CONCLUSIONS

In this sample of older US black and whites, increased GDF-15 was positively associated with diabetes, ASCVD, HF, and markers of subclinical myocardial stress or injury. These results illustrate the diverse aspects of the link between GDF-15 and diseases states, and its potential utility as robust biomarker of adverse cardiometabolic outcomes.

ATF4-mediated GDF15 suppresses LPS-induced inflammation and MUC5AC in human nasal epithelial cells through the PI3K/Akt pathway

AIMS

Growth and differentiation factor 15 (GDF15) is a stress-related factor, which implicated in various diseases. This study aimed to investigate the role of GDF15 in LPS-mediated inflammation and to explore the potential underlying molecular mechanisms in human nasal epithelial cells (HNEpCs).

MAIN METHODS

HNEpCs were treated with LPS. GDF15 loss-of-function and gain-of-function experiments were performed. The expression of GDF15 by quantitative real-time PCR (RT-qPCR). The mRNA levels and secretion of inflammatory cytokines and MUC5AC were assessed by RT-qPCR and ELISA kits. LY294002 (PI3K inhibitor) and 740Y-P (PI3K agonist) were utilized to interfere with PI3k/Akt pathway. The relationship between GDF15 and ATF4 was identified by chromatin immunoprecipitation (ChIP) and luciferase reporter assay.

KEY FINDINGS

We observed that LPS triggered GDF15 expression. GDF15 ablation reduced the mRNA levels and secretion of inflammatory cytokines. GDF15 silencing led to the reduction of the MUC5AC mRNA level, protein level and secretion in response to LPS. Enhanced expression of GDF15 showed the opposite results. Furthermore, we found that GDF15 deficiency inhibited activation of the PI3K/Akt pathway, LY294002 treatment further enhanced the role of GDF15 suppression in inflammation and MUC5AC expression, while 740Y-P administration partly reversed the biological activities of GDF15 silencing. ATF4 could bind to the promoter of GDF15 and positively regulate GDF15 expression. Depression of ATF4 diminished the secretion of inflammatory cytokines and MUC5AC via regulation of GDF15.

SIGNIFICANCE

Our data suggest that GDF15 is regulated by ATF4 and suppresses LPS-induced inflammation and MUC5AC in human nasal epithelial cells through the PI3K/Akt pathway.

Elevated circulating growth differentiation factor 15 is related to decreased heart rate variability in chronic kidney disease patients

Background

Growth differentiation factor 15(GDF15) is a distant member of the superfamily of the transforming growth factor beta (TGF-β). It has been established that increased GDF15 levels are associated with an increased risk of cardiovascular disease. However, the detail effect of GDF15 on cardiovascular system in patients with chronic kidney disease (CKD) needs detail analysis.

Methods

Patients with CKD who did not need dialysis were enrolled in the study. Blood pressure (BP), endothelial function, pulse wave velocity (PWV) and heart rate variability (HRV) were taken in all subjects. Plasma GDF15 concentration was measured by an enzyme-linked immunosorbent assay.

Results

Among the 355 participants, the mean age was 57.4 (±14.2) years old and the mean estimated glomerular filtration rate (eGFR) was 50.1 (±33.2) mL/min/1.73m². The average plasma GDF15 level was 1394.7 (±610.1) pg/mL. Higher GDF15 concentrations were significantly associated with decreased eGFR and increased urine protein-to-creatinine ratio (uPCR). In multivariable models, after adjusting for potential confounders, plasma GDF15 has negative concerning with HRV parameters including the standard deviation of the normal-to-normal (NN) interval (SDNN), the square root of the mean of the sum of the squares of differences between adjacent NN intervals (RMSSD) and Triangular Index.

Conclusion

We observed there was a link between increased plasma of GDF15 and decreased HRV. The mechanisms and prediction of GDF15 in the cardiovascular disease with CKD needs further discussion and study.

Hepatokines and metabolism: Deciphering communication from the liver

Background

The liver is a key regulator of systemic energy homeostasis and can sense and respond to nutrient excess and deficiency through crosstalk with multiple tissues. Regulation of systemic energy homeostasis by the liver is mediated in part through regulation of glucose and lipid metabolism. Dysregulation of either process may result in metabolic dysfunction and contribute to the development of insulin resistance or fatty liver disease.

Scope of review

The liver has recently been recognized as an endocrine organ that secretes hepatokines, which are liver-derived factors that can signal to and communicate with distant tissues. Dysregulation of liver-centered inter-organ pathways may contribute to improper regulation of energy homeostasis and ultimately metabolic dysfunction. Deciphering the mechanisms that regulate hepatokine expression and communication with distant tissues is essential for understanding inter-organ communication and for the development of therapeutic strategies to treat metabolic dysfunction.

Major conclusions

In this review, we discuss liver-centric regulation of energy homeostasis through hepatokine secretion. We highlight key hepatokines and their roles in metabolic control, examine the molecular mechanisms of each hepatokine, and discuss their potential as therapeutic targets for metabolic disease. We also discuss important areas of future studies that may contribute to understanding hepatokine signaling under healthy and pathophysiological conditions.

Inflammaging, hormesis and the rationale for anti-aging strategies

We propose in this review that hormesis, a concept profoundly and systematically addressed by Mark Mattson, has to be considered a sort of comprehensive "contact point" capable of unifying several conceptualizations of the aging process, including those focused on the stress response, oxidative stress and chronic inflammation/inflammaging. A major strength of hormesis and inflammaging is that they have a strong evolutionary basis. Moreover, both hormesis and inflammaging frame the aging process within a lifelong perspective of adaptation to different types of stresses. Such adaptation perspective also suggests that the aging process is malleable, and predicts that effective anti-aging strategies should mimic what evolution did in the course of million years and that we have to learn how to exploit the great potential inherent in the hormetic/inflammatory responses. To this regard, new topics such as the production of mitokines to cope with mitochondrial dysfunction are emerging as possible anti-aging target. This approach opens theoretically the door to the possibility of modulating the individual aging rate and trajectory by adopting the most effective scientifically-based lifestyle regarding fundamentally nutrition and physical activity. In this scenario Mark Mattson's lesson and personal example will permanently enlighten the aging field and the quest for a healthy aging and longevity.

Plasma proteomic biomarker signature of age predicts health and life span

Older age is a strong shared risk factor for many chronic diseases, and there is increasing interest in identifying aging biomarkers. Here, a proteomic analysis of 1301 plasma proteins was conducted in 997 individuals between 21 and 102 years of age. We identified 651 proteins associated with age (506 over-represented, 145 underrepresented with age). Mediation analysis suggested a role for partial cis-epigenetic control of protein expression with age. Of the age-associated proteins, 33.5% and 45.3%, were associated with mortality and multimorbidity, respectively. There was enrichment of proteins associated with inflammation and extracellular matrix as well as senescence-associated secretory proteins. A 76-protein proteomic age signature predicted accumulation of chronic diseases and all-cause mortality. These data support the use of proteomic biomarkers to monitor aging trajectories and to identify individuals at higher risk of disease to be targeted for in depth diagnostic procedures and early interventions.

Growth differentiation factor 15 as a potential therapeutic for treating obesity

BACKGROUND

Obesity is rapidly becoming one of the world's most critical health care concerns. Comorbidities accompanying excess weight include cardiovascular disease, diabetes, and certain cancers. These comorbidities result in greater hospitalization and other health care-related costs. Economic impacts are likely to be felt more acutely in developing countries, where obesity rates continue to rise and health care resources are already insufficient. Some of the more effective treatments are invasive and expensive surgeries, which some economies in the world cannot afford to offer to a broad population. Pharmacological therapies are needed to supplement treatment options for patients who cannot, or will not, undergo surgical treatment. However, the few drug therapies currently available have either limited efficacy or safety concerns. A possible exception has been glucagon-like peptide-1 analogs, although these have shown a number of adverse events. New drug therapies that are safe and produce robust weight loss are needed.

SCOPE OF REVIEW

Herein, we review the role of growth differentiation factor 15 (GDF15) in feeding behavior and obesity, summarize some of the new and exciting biological discoveries around signaling pathways and tissue sites of action, and highlight initial efforts to develop GDF15-based therapies suitable for inducing weight loss in humans.

MAJOR CONCLUSIONS

Within the last several years, great strides have been made in understanding the biology of GDF15. Recent developments include identification of an endogenous receptor, biological localization of the receptor system, impact on energy homeostasis, and identification of molecules suitable for administration to humans as anti-obesity treatments. New and exciting research on GDF15 suggests that it holds promise as a novel obesity treatment as new molecules progress toward clinical development.

GDF15 knockdown suppresses cervical cancer cell migration in vitro through the TGF-β/Smad2/3/Snail1 pathway

Growth differentiation factor 15 (GDF15), a member of the transforming growth factor β (TGF-β) superfamily, is a prognostic biomarker of cervical cancer. In addition, GDF15 has been reported to enhance the migration of colorectal cancer cells and liver cancer stem-like cells. However, the mechanism by which GDF15 promotes cervical cancer cell migration is not completely understood. Here, we report that GDF15 expression is enhanced in cervical cancer tissues, as well as in cultured cervical cancer cells. ShGDF15 transfection markedly inhibited expression of Vimentin, N-cadherin and Snail1, and resulted in up-regulation of E-cadherin expression in HT-3 and HeLa cells. Moreover, knockdown of GDF15 suppressed wound healing rate and reduced the number of invasive cells. Furthermore, knockdown of GDF15 significantly suppressed the expression of phosphorylated Smad2 and Smad3. The addition of TGF-β1 partially abolished the inhibitory effects of GDF15 knockdown on the migration and invasion of cervical cancer cells. In summary, we report here that GDF15 knockdown inhibits migration and invasion of cervical cancer cells in vitro through the TGF-β/Smad2/3/Snail1 pathway.

Growth Differentiation Factor 15 Ameliorates Anti-Glomerular Basement Membrane Glomerulonephritis in Mice

Growth differentiation factor 15 (GDF15) is a member of the transforming growth factor-β (TGF-β) cytokine family and an inflammation-associated protein. Here, we investigated the role of GDF15 in murine anti-glomerular basement membrane (GBM) glomerulonephritis. Glomerulonephritis induction in mice induced systemic expression of GDF15. Moreover, we demonstrate the protective effects for GDF15, as GDF15-deficient mice exhibited increased proteinuria with an aggravated crescent formation and mesangial expansion in anti-GBM nephritis. Herein, GDF15 was required for the regulation of T-cell chemotactic chemokines in the kidney. In addition, we found the upregulation of the CXCR3 receptor in activated T-cells in GDF15-deficient mice. These data indicate that CXCL10/CXCR3-dependent-signaling promotes the infiltration of T cells into the organ during acute inflammation controlled by GDF15. Together, these results reveal a novel mechanism limiting the migration of lymphocytes to the site of inflammation during glomerulonephritis.

GDF15, an update of the physiological and pathological roles it plays: a review

Growth differentiation factor 15 (GDF15) is a peptide hormone, and a divergent member of the transforming growth factor beta (TGFβ) superfamily. In normal physiology, GDF15 is expressed in multiple tissues at a low concentration. GDF15 is overexpressed during and following many pathological conditions such as tissue injury and inflammation in order to play a protective role. However, GDF15 appears to promote tumour growth in the later stages of malignant cancer. The recently identified endogenous receptor for GDF15, GDNF family receptor a-like (GFRAL), has allowed elucidation of a physiological pathway in which GDF15 regulates energy homeostasis and body weight, primarily via appetite suppression. The anorectic effect of GDF15 provides some therapeutic potential in management of cancer-related anorexia/cachexia and obesity. Despite the identification of GFRAL as a GDF15 receptor, there appears to be other signalling mechanisms utilized by GDF15 that further increase the possibility of development of therapeutic treatments, should these pathways be fully characterized. In this review, GDF15 function in both physiological and pathological conditions in various tissues will be discussed.

Anti-proliferative activity of A. Oxyphylla and its bioactive constituent nootkatone in colorectal cancer cells

Background

A. oxyphylla extract is known to possess a wide range of pharmacological activites. However, the molecular mechanism of A. oxyphylla and its bioactive compound nootkatone in colorectal cancer is unknown.

Methods

Our study aims to examine the role of A. oxyphylla and its bioactive compound nootkatone, in tumor suppression using several in vitro assays.

Results

Both A. oxyphylla extract and nootkatone exhibited antiproliferative activity in colorectal cancer cells. A. oxyphylla displayed antioxidant activity in colorectal cancer cells, likely mediated via induction of HO-1. Furthermore, expression of pro-apoptotic protein NAG-1 and cell proliferative protein cyclin D1 were increased and decreased respectively in the presence of A. oxyphylla. When examined for anticancer activity, nootkatone treatment resulted in the reduction of colony and spheroid formation. Correspondingly, nootkatone also led to increased NAG-1 expression and decreased cyclin D1 expression. The mechanism by which nootkatone suppresses cyclin D1 involves protein level regulation, whereas nootkatone increases NAG-1 expression at the transcriptional level. In addition to having PPARγ binding activity, nootkatone also increases EGR-1 expression which ultimately results in enhanced NAG-1 promoter activity.

Conclusion

In summary, our findings suggest that nootkatone is an anti-tumorigenic compound harboring antiproliferative and pro-apoptotic activity.

Khademul Islam AB. Perversely expressed long noncoding RNAs can alter host response and viral proliferation in SARS-CoV-2 infection

BACKGROUND

Regulatory roles of long noncoding RNAs (lncRNAs) during viral infection has become more evident in last decade, but are yet to be explored for SARS-CoV-2.

MATERIALS & METHODS

We analyzed RNA-seq dataset of SARS-CoV-2 infected lung epithelial cells to identify differentially expressed genes.

RESULTS

Our analyses uncover 21 differentially expressed lncRNAs broadly involved in cell survival and regulation of gene expression. These lncRNAs can directly interact with six differentially expressed protein-coding genes, and ten host genes that interact with SARS-CoV-2 proteins. Also, they can block the suppressive effect of nine microRNAs induced in viral infections.

CONCLUSION

Our investigation determines that deregulated lncRNAs in SARS-CoV-2 infection are involved in viral proliferation, cellular survival, and immune response, ultimately determining disease outcome.

GDF15: A Hormone Conveying Somatic Distress to the Brain

GDF15 has recently gained scientific and translational prominence with the discovery that its receptor is a GFRAL-RET heterodimer of which GFRAL is expressed solely in the hindbrain. Activation of this receptor results in reduced food intake and loss of body weight and is perceived and recalled by animals as aversive. This information encourages a revised interpretation of the large body of previous research on the protein. GDF15 can be secreted by a wide variety of cell types in response to a broad range of stressors. We propose that central sensing of GDF15 via GFRAL-RET activation results in behaviors that facilitate the reduction of exposure to a noxious stimulus. The human trophoblast appears to have hijacked this signal, producing large amounts of GDF15 from early pregnancy. We speculate that this encourages avoidance of potential teratogens in pregnancy. Circulating GDF15 levels are elevated in a range of human disease states, including various forms of cachexia, and GDF15-GFRAL antagonism is emerging as a therapeutic strategy for anorexia/cachexia syndromes. Metformin elevates circulating GDF15 chronically in humans and the weight loss caused by this drug appears to be dependent on the rise in GDF15. This supports the concept that chronic activation of the GDF15-GFRAL axis has efficacy as an antiobesity agent. In this review, we examine the science of GDF15 since its identification in 1997 with our interpretation of this body of work now being assisted by a clear understanding of its highly selective central site of action.

Associations Between Serum GDF15 Concentrations, Muscle Mass, and Strength Show Sex-Specific Differences in Older Hospital Patients

Aging is accompanied by a progressive decline of muscle mass and strength and also higher levels of circulating cytokines such as growth differentiation factor 15 (GDF15). Studies evaluating the association of GDF15 with muscle mass and strength are rare. In this analysis, we investigated GDF15 concentrations and their relationship with muscle mass and strength in older men compared with women. GDF15 serum concentrations were measured in 103 (60 years and older) hospital patients and an age-matched control group with an immunosorbent assay. Skeletal muscle mass was determined with the bioelectrical impedance analysis. Grip strength and knee extension strength were assessed and normalized for height. Associations between GDF15 concentrations and muscle mass and strength were evaluated with general linear models. Male patients showed higher levels of GDF15 compared with female patients (p = 0.021). Elevated GDF15 concentrations were associated with lower measures of muscle mass, exclusively in men, after adjustment for age and number of drugs per day. Our results indicate sex differences between associations of GDF15 with muscle mass and strength parameters in a cohort of older hospital patients.

Growth Differentiation Factor 15 is a potential biomarker of therapeutic response for TK2 deficient myopathy

GDF-15 is a biomarker for mitochondrial diseases. We investigated the application of GDF-15 as biomarker of disease severity and response to deoxynucleoside treatment in patients with thymidine kinase 2 (TK2) deficiency and compared it to FGF-21. GDF-15 and FGF-21 were measured in serum from 24 patients with TK2 deficiency treated 1–49 months with oral deoxynucleosides. Patients were grouped according to age at treatment and biomarkers were analyzed at baseline and various time points after treatment initiation. GDF-15 was elevated on average 30-fold in children and 6-fold in adults before the start of treatment. There was a significant correlation between basal GDF-15 and severity based on pretreatment distance walked (6MWT) and weight (BMI). During treatment, GDF-15 significantly declined, and the decrease was accompanied by relevant clinical improvements. The decline was greater in the paediatric group, which included the most severe patients and showed the greatest clinical benefit, than in the adult patients. The decline of FGF-21 was less prominent and consistent. GDF-15 is a potential biomarker of severity and of therapeutic response for patients with TK2 deficiency. In addition, we show evidence of clinical benefit of deoxynucleoside treatment, especially when treatment is initiated at an early age.

The Role of Growth Differentiation Factor 15 in Energy Metabolism

Growth differentiation factor 15 (GDF15) is receiving great interest beyond its role as an aging and disease-related biomarker. Recent discovery of its receptor, glial cell line-derived neurotrophic factor (GDNF) family receptor α-like (GFRAL), suggests a central role in appetite regulation. However, there is also considerable evidence that GDF15 may have peripheral activity through an as-of-yet undiscovered mode of action. This raises the question as to whether increased GDF15 induction during pathophysiologic conditions also suppresses appetite. The present review will briefly introduce the discovery of GDF15 and describe the different contexts under which GDF15 is induced, focusing on its induction during mitochondrial dysfunction. We will further discuss the metabolic role of GDF15 under various pathophysiological conditions and conclude with possible therapeutic applications.

Senescent Fibroblast-Derived GDF15 Induces Skin Pigmentation

Senescent fibroblasts play a role in aging pigmentation. In this study, we found that GDF15 expression levels are increased in UV-irradiated senescent fibroblasts and photoaged hyperpigmented skin. To investigate the effects of GDF15 on melanogenesis, normal human melanocytes were cocultured with fibroblasts infected with the GDF15 lentivirus or GDF15 short hairpin RNA. It was found that GDF15 stimulates melanogenesis in melanocytes through MITF/tyrosinase upregulation via β-catenin signaling. The stimulatory action of GDF15 during pigmentation was further confirmed in ex vivo cultured skin and in a reconstituted human skin sample. These results suggest that senescent fibroblast-derived GDF15 stimulates skin pigmentation and may play a role in aging-associated pigmentation.

Functional roles of GDF15 in modulating microenvironment to promote carcinogenesis

Obesity and related metabolic dysregulation are risk factors for many types of cancer. The interactions between a developing tumor and its microenvironment are known to implicate a complex "crosstalk" among the factors produced by the population of cells. Among these factors, Growth and differentiation factor 15 (GDF15) has a functional role in cancer. GDF15 expression is induced in response to the conditions associated with cellular stress and diseases. The GDF15 receptor, a member of the glial-cell-derived neurotropic factor family (GDNF), is a GDNF family receptor α-like (GFRAL) protein. GDF15 induces pro-angiogenic effects in tumors. However, GDF15 could affect tumorigenesis both positively and negatively. With a better understanding of the upstream disease pathways reflected by GDF15, new treatment targets may emerge.

Targeting of Secretory Proteins as a Therapeutic Strategy for Treatment of Nonalcoholic Steatohepatitis (NASH)

Nonalcoholic steatohepatitis (NASH) is defined as a progressive form of nonalcoholic fatty liver disease (NAFLD) and is a common chronic liver disease that causes significant worldwide morbidity and mortality, and has no approved pharmacotherapy. Nevertheless, growing understanding of the molecular mechanisms underlying the development and progression of NASH has suggested multiple potential therapeutic targets and strategies to treat this disease. Here, we review this progress, with emphasis on the functional role of secretory proteins in the development and progression of NASH, in addition to the change of expression of various secretory proteins in mouse NASH models and human NASH subjects. We also highlight secretory protein-based therapeutic approaches that influence obesity-associated insulin resistance, liver steatosis, inflammation, and fibrosis, as well as the gut–liver and adipose–liver axes in the treatment of NASH.

Role of GDF15 in active lifestyle induced metabolic adaptations and acute exercise response in mice

Physical activity is an important contributor to muscle adaptation and metabolic health. Growth differentiation factor 15 (GDF15) is established as cellular and nutritional stress-induced cytokine but its physiological role in response to active lifestyle or acute exercise is unknown. Here, we investigated the metabolic phenotype and circulating GDF15 levels in lean and obese male C57Bl/6J mice with long-term voluntary wheel running (VWR) intervention. Additionally, treadmill running capacity and exercise-induced muscle gene expression was examined in GDF15-ablated mice. Active lifestyle mimic via VWR improved treadmill running performance and, in obese mice, also metabolic phenotype. The post-exercise induction of skeletal muscle transcriptional stress markers was reduced by VWR. Skeletal muscle GDF15 gene expression was very low and only transiently increased post-exercise in sedentary but not in active mice. Plasma GDF15 levels were only marginally affected by chronic or acute exercise. In obese mice, VWR reduced GDF15 gene expression in different tissues but did not reverse elevated plasma GDF15. Genetic ablation of GDF15 had no effect on exercise performance but augmented the post exercise expression of transcriptional exercise stress markers (Atf3, Atf6, and Xbp1s) in skeletal muscle. We conclude that skeletal muscle does not contribute to circulating GDF15 in mice, but muscle GDF15 might play a protective role in the exercise stress response.

Mitochondrial uncoupling and longevity - A role for mitokines?

Aging has been viewed both as a random process due to accumulation of molecular and cellular damage over time and as a programmed process linked to cellular pathway important for growth and maturation. These views converge on mitochondria as both the major producer of damaging reactive oxidant species (ROS) and as signaling organelles. A finite proton leak across the inner mitochondrial membrane leading to a slight uncoupling of oxidative phosphorylation and respiration is an intrinsic property of all mitochondria and according to the "uncoupling to survive" hypothesis it has evolved to protect against ROS production to minimize oxidative damage. This hypothesis is supported by evidence linking an increased endogenous, uncoupling protein (UCP1) mediated, as well as experimentally induced mitochondrial uncoupling to an increased lifespan in rodents. This is possibly due to the synergistic activation of molecular pathways linked to life extending effects of caloric restriction as well as a mitohormetic response. Mitohormesis is an adaptive stress response through mitonuclear signaling which increases stress resistance resulting in health promoting effects. Part of this response is the induction of fibroblast growth factor 21 (FGF21) and growth and differentiation factor 15 (GDF15), two stress-induced mitokines which elicit beneficial systemic metabolic effects via endocrine action.

Competitive inhibition by NAG-1/GDF-15 NLS peptide enhances its anti-cancer activity

Non-steroidal anti-inflammatory drug activated gene-1 (NAG-1), also known as growth differentiation factor 15 (GDF15), is a TGF-β (transforming growth factor beta) superfamily protein with a distinctive secretion pathway. NAG-1 is associated with multiple diseases including cancer, wherein it plays a role in both pro- and anti-cancer activities. We previously reported that NAG-1 is translocated to different subcellular compartments and its activity depends on its localization. In this paper, we report that the transfection of a novel peptide corresponding to the nuclear localization signal (NLS) of NAG-1 blocks its translocation to the nucleus. Further, accumulation of NAG-1 in the cytoplasm decreased mitochondrial membrane potential, thus implying apoptosis induction as a consequence. Overall, our results indicate that the novel peptide derived from NAG-1 NLS sequence is a promising tool for enhancing the anti-tumorigenic activity of NAG-1.