Skeletal muscle-targeted delivery of Fgf6 protects mice from diet-induced obesity and insulin resistance

Fibroblast Growth Factor 6

Fibroblast Growth Factor 6 (FGF6), also referred to as HST2 or HBGF6, is a member of the Fibroblast Growth Factor (FGF), the Heparin Binding Growth Factor (HBGF) and the Heparin Binding Secretory Transforming Gene (HST) families. The genomic and protein structure of FGF6 is highly conserved among varied species, as is its expression in muscle and muscle progenitor cells. Like other members of the FGF family, FGF6 regulates cell proliferation, differentiation, and migration. Specifically, it plays key roles in myogenesis and muscular regeneration, angiogenesis, along with iron transport and lipid metabolism. Similar to others from the FGF family, FGF6 also possesses oncogenic transforming activity, and as such is implicated in a variety of cancers.

Roles of fibroblast growth factors in the treatment of diabetes

Diabetes affects about 422 million people worldwide, causing 1.5 million deaths each year. However, the incidence of diabetes is increasing, including several types of diabetes. Type 1 diabetes (5%-10% of diabetic cases) and type 2 diabetes (90%-95% of diabetic cases) are the main types of diabetes in the clinic. Accumulating evidence shows that the fibroblast growth factor (FGF) family plays important roles in many metabolic disorders, including type 1 and type 2 diabetes. FGF consists of 23 family members (FGF-1-23) in humans. Here, we review current findings of FGFs in the treatment of diabetes and management of diabetic complications. Some FGFs (e.g., FGF-15, FGF-19, and FGF-21) have been broadly investigated in preclinical studies for the diagnosis and treatment of diabetes, and their therapeutic roles in diabetes are currently under investigation in clinical trials. Overall, the roles of FGFs in diabetes and diabetic complications are involved in numerous processes. First, FGF intervention can prevent high-fat diet-induced obesity and insulin resistance and reduce the levels of fasting blood glucose and triglycerides by regulating lipolysis in adipose tissues and hepatic glucose production. Second, modulation of FGF expression can inhibit renal and cardiac fibrosis by regulating the expression of extracellular matrix components, promote diabetic wound healing process and bone repair, and inhibit cancer cell proliferation and migration. Finally, FGFs can regulate the activation of glucose-excited neurons and the expression of thermogenic genes.

Vutiglabridin exerts anti-ageing effects in aged mice through alleviating age-related metabolic dysfunctions

BACKGROUND

Ageing alters the ECM, leading to mitochondrial dysfunction and oxidative stress, which triggers an inflammatory response that exacerbates with age. Age-related changes impact satellite cells, affecting muscle regeneration, and the balance of proteins. Furthermore, ageing causes a decline in NAD+ levels, and alterations in fat metabolism that impact our health. These various metabolic issues become intricately intertwined with ageing, leading to a variety of individual-level diseases and profoundly affecting individuals' healthspan. Therefore, we hypothesize that vutiglabridin capable of alleviating these metabolic abnormalities will be able to ameliorate many of the problems associated with ageing.

METHOD

The efficacy of vutiglabridin, which alleviates metabolic issues by enhancing mitochondrial function, was assessed in aged mice treated with vutiglabridin and compared to untreated elderly mice. On young mice, vutiglabridin-treated aged mice, and non-treated aged mice, the Senescence-associated beta-galactosidase staining and q-PCR for ageing marker genes were carried out. Bulk RNA-seq was carried out on GA muscle, eWAT, and liver from each group of mice to compare differences in gene expression in various gene pathways. Blood from each group of mice was used to compare and analyze the ageing lipid profile.

RESULTS

SA-β-gal staining of eWAT, liver, kidney, and spleen of ageing mice showed that vutiglabridin had anti-ageing effects compared to the control group, and q-PCR of ageing marker genes including Cdkn1a and Cdkn2a in each tissue showed that vutiglabridin reduced the ageing process. In aged mice treated with vutiglabridin, GA muscle showed improved homeostasis compared to controls, eWAT showed restored insulin sensitivity and prevented FALC-induced inflammation, and liver showed reduced inflammation levels due to prevented TLO formation, improved mitochondrial complex I assembly, resulting in reduced ROS formation. Furthermore, blood lipid analysis revealed that ageing-related lipid profile was relieved in ageing mice treated with vutiglabridin versus the control group.

CONCLUSION

Vutiglabridin slows metabolic ageing mechanisms such as decreased insulin sensitivity, increased inflammation, and altered NAD+ metabolism in adipose tissue in mice experiments, while also retaining muscle homeostasis, which is deteriorated with age. It also improves the lipid profile in the blood and restores mitochondrial function in the liver to reduce ROS generation.

Punicalagin protects against impaired skeletal muscle function in high-fat-diet-induced obese mice by regulating TET2

The function of skeletal muscles can be markedly hampered by obesity. Ten-eleven translocation 2 (TET2) is an important therapeutic target for ameliorating skeletal muscle dysfunction. Our previous study revealed that punicalagin (PUN) regulated TET2 in obese mice; however, whether PUN can prevent obesity-induced skeletal muscle dysfunction by regulating TET2 remains unclear. In the present study, 40 male C57BL/6J mice were divided into four groups (n = 10 per group): the control (CON) group, the high-fat-diet (HFD, negative control) group, the resveratrol (positive control) group, and the PUN group. The ratio of gastrocnemius weight to body weight (0.0097 ± 0.0016 vs. 0.0080 ± 0.0011), the grip strength (120.04 g ± 11.10 vs. 98.89 g ± 2.79), and the muscle fiber count (314.56 per visual field ± 92.73 vs. 236.44 per visual field ± 50.58) in the PUN group were higher than those in the HFD group. Moreover, the levels of the TET2 protein, 5-hydroxymethylcytosine (5hmC), and 5-formylcytosine (5fC) in skeletal muscles were significantly lower in the HFD group than those in the CON group; these levels increased after PUN treatment. Compared with the HFD group, the phosphorylation level of AMP-activated protein kinase (AMPK) α in the PUN group was higher, which effectively enhanced the stability of the TET2 protein. Besides, the ratio of (succinic acid + fumaric acid)/α-ketoglutarate in the PUN group was lower than that in the HFD group (43.21 ± 12.42 vs. 99.19 ± 37.07), and a lower ratio led to a higher demethylase activity of TET2 in the PUN group than in the HFD group. This study highlights that PUN supplementation protects against obesity-induced impairment of the skeletal muscle function via regulating the protein stability of TET2 and the enzymatic activity of TET2 demethylation.

Biocompatible Macroion/Growth Factor Assemblies for Medical Applications

Growth factors are a class of proteins that play a role in the proliferation (the increase in the number of cells resulting from cell division) and differentiation (when a cell undergoes changes in gene expression becoming a more specific type of cell) of cells. They can have both positive (accelerating the normal healing process) and negative effects (causing cancer) on disease progression and have potential applications in gene therapy and wound healing. However, their short half-life, low stability, and susceptibility to degradation by enzymes at body temperature make them easily degradable in vivo. To improve their effectiveness and stability, growth factors require carriers for delivery that protect them from heat, pH changes, and proteolysis. These carriers should also be able to deliver the growth factors to their intended destination. This review focuses on the current scientific literature concerning the physicochemical properties (such as biocompatibility, high affinity for binding growth factors, improved bioactivity and stability of the growth factors, protection from heat, pH changes or appropriate electric charge for growth factor attachment via electrostatic interactions) of macroions, growth factors, and macroion-growth factor assemblies, as well as their potential uses in medicine (e.g., diabetic wound healing, tissue regeneration, and cancer therapy). Specific attention is given to three types of growth factors: vascular endothelial growth factors, human fibroblast growth factors, and neurotrophins, as well as selected biocompatible synthetic macroions (obtained through standard polymerization techniques) and polysaccharides (natural macroions composed of repeating monomeric units of monosaccharides). Understanding the mechanisms by which growth factors bind to potential carriers could lead to more effective delivery methods for these proteins, which are of significant interest in the diagnosis and treatment of neurodegenerative and civilization diseases, as well as in the healing of chronic wounds.

Combined analysis of differentially expressed lncRNAs and miRNAs in liver tissues of high-fat fed rabbits by transcriptome sequencing

High-fat diet could lead to a series of metabolic diseases, including obesity, and its mechanism is not clear. In this study, the rabbit individuals were fed with high-fat diet, the liver tissues were collected, high-throughput sequencing technology was used to reveal the expression of lncRNA and miRNA difference, and the molecular regulation mechanism of lncRNA-miRNA. A total of 24,615 DE lncRNAs and 52 DE miRNAs were identified, including 15 novel discovered DE miRNAs (5 upregulated and 10 downregulated). Furthermore, five miRNAs and three mRNAs were verified by qRT-PCR, and the results showed that the expression of the DE miRNAs and DE lncRNAs in the two groups was consistent with our sequencing results. GO and KEGG analyzed 7,57,139 target genes respectively, enriching the pathways related to lipid metabolism, including mucin O-glycan biosynthesis pathway, insulin resistance and glucagon signaling pathway. Moreover, 65 targeting relationships were obtained. Among them, LOC103348122/miR-450a-5p, LOC103350359/miR-450a-3p and LOC103350429/miR-148a-5p were proposed the first time. Significantly, LOC103348122/miR-450a-5p and LOC103350429/miR-148a-5p were related to lipid metabolism in the liver. This study is of great significance to the CeRNA regulatory network related to lipid metabolism in the liver of rabbits, and provides a basis for understanding hepatic steatosis in rabbits.

Severe iatrogenic hypoglycaemia modulates the fibroblast growth factor protein response

INTRODUCTION

There is evidence that fibroblast growth factor (FGF) levels may be implicated in hypoglycaemia, with FGF19 being a potential contributor to insulin-independent pathways driving postprandial hypoglycaemia following bariatric surgery and basic FGF (FGF2) being elevated following mild hypoglycaemia occurring after the glucose tolerance test. However, their response following severe iatrogenic hypoglycaemia is unknown and therefore this pilot exploratory study was undertaken.

METHODS

A case-control study of aged-matched type 2 diabetes (T2D; n = 23) and control (n = 23) subjects who underwent a hyperinsulinaemic clamp, initially to euglycaemia in T2D (5 mmol/L; 90 mg/dl), and then to hypoglycaemia (<2 mmol/L; <36 mg/dl) with subsequent follow-up time course to 24 h. FGF and FGF receptor proteins were determined by Slow Off-rate Modified Aptamer (SOMA)-scan plasma protein measurement.

RESULTS

At baseline, FGF12 (p = .006) was higher and FGF20 (p = .004) was lower in T2D versus controls. At hypoglycaemia, FGF7 was lower in T2D. Post-hypoglycaemic levels of FGF18, FGF19, FGF20 and FGF23 were lower while FGF12 and FGF16 were higher in T2D versus control at different time points. No differences between T2D and controls were seen for FGF1, FGF2, FGF4, FGF6, FGF8, FGF9, FGF10, FGF21 or any of the FGF receptors. At 24 h post-hypoglycaemia, FGF20 (p = .01) differed between controls and T2D, while the levels for the other proteins measured returned to baseline. None of the FGF proteins altered from baseline to euglycaemia when clamped in T2D subjects. FGF23 negatively correlated with fasting blood glucose, but no FGFs correlated with body mass index in T2D.

CONCLUSION

Severe transient hypoglycaemia modulated FGF7, 16, 19, 20 and 23 (known to be associated with diabetes), together with FGF18 and 12, not previously reported to be associated with diabetes but that may be important in the pathophysiology of hypoglycaemia; FGF20 remained low at 24 h. Taken together, these data suggest that recurrent hypoglycaemia may contribute to the development of complications through changes in FGF proteins.

CLSTN3 gene variant associates with obesity risk and contributes to dysfunction in white adipose tissue

Objective

White adipose tissue (WAT) possesses the remarkable remodeling capacity, and maladaptation of this ability contributes to the development of obesity and associated comorbidities. Calsyntenin-3 (CLSTN3) is a transmembrane protein that promotes synapse development in brain. Even though this gene has been reported to be associated with adipose tissue, its role in the regulation of WAT function is unknown yet. We aim to further assess the expression pattern of CLSTN3 gene in human adipose tissue, and investigate its regulatory impact on WAT function.

Methods

In our study, we observed the expression pattern of Clstn3/CLSTN3 gene in mouse and human WAT. Genetic association study and expression quantitative trait loci analysis were combined to identify the phenotypic effect of CLSTN3 gene variant in humans. This was followed by mouse experiments using adeno-associated virus-mediated human CLSTN3 overexpression in inguinal WAT. We investigated the effect of CLSTN3 on WAT function and overall metabolic homeostasis, as well as the possible underlying molecular mechanism.

Results

We observed that CLSTN3 gene was routinely expressed in human WAT and predominantly enriched in adipocyte fraction. Furthermore, we identified that the variant rs7296261 in the CLSTN3 locus was associated with a high risk of obesity, and its risk allele was linked to an increase in CLSTN3 expression in human WAT. Overexpression of CLSTN3 in inguinal WAT of mice resulted in diet-induced local dysfunctional expansion, liver steatosis, and systemic metabolic deficiency. In vivo and ex vivo lipolysis assays demonstrated that CLSTN3 overexpression attenuated catecholamine-stimulated lipolysis. Mechanistically, CLSTN3 could interact with amyloid precursor protein (APP) in WAT and increase APP accumulation in mitochondria, which in turn impaired adipose mitochondrial function and promoted obesity.

Conclusion

Taken together, we provide the evidence for a novel role of CLSTN3 in modulating WAT function, thereby reinforcing the fact that targeting CLSTN3 may be a potential approach for the treatment of obesity and associated metabolic diseases.

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CLSTN3 is expressed in the adipocyte fraction of human adipose tissue and mainly localizes to the plasma membrane.

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SNP rs7296261 in human CLSTN3 locus is associated with obesity risk.

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Overexpression of CLSTN3 leads to adipose tissue dysfunction in mice.

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CLSTN3 can attenuate catecholamine-stimulated lipolysis.

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CLSTN3 overexpression increases mitochondrial APP localization of mouse adipose tissue.

Inhibition of activin A receptor signalling attenuates age-related pathological cardiac remodelling

In the heart, ageing is associated with DNA damage, oxidative stress, fibrosis and activation of the activin signalling pathway, leading to cardiac dysfunction. The cardiac effects of activin signalling blockade in progeria are unknown. This study investigated the cardiac effects of progeria induced by attenuated levels of Ercc1, which is required for DNA excision and repair, and the impact of activin signalling blockade using a soluble activin receptor type IIB (sActRIIB). DNA damage and oxidative stress were significantly increased in Ercc1^Δ/− hearts, but were reduced by sActRIIB treatment. sActRIIB treatment improved cardiac systolic function and induced cardiomyocyte hypertrophy in Ercc1^Δ/− hearts. RNA-sequencing analysis showed that in Ercc1^Δ/− hearts, there was an increase in pro-oxidant and a decrease in antioxidant gene expression, whereas sActRIIB treatment reversed this effect. Ercc1^Δ/− hearts also expressed higher levels of anti-hypertrophic genes and decreased levels of pro-hypertrophic ones, which were also reversed by sActRIIB treatment. These results show for the first time that inhibition of activin A receptor signalling attenuates cardiac dysfunction, pathological tissue remodelling and gene expression in Ercc1-deficient mice and presents a potentially novel therapeutic target for heart diseases.

Summary: Attenuated DNA repair is associated with pathological cardiac remodelling and gene expression. Much of this phenotype is attenuated by inhibition of the activin signalling pathway using soluble activin receptor treatment.