Asprosin-neutralizing antibodies as a treatment for metabolic syndrome

Predictive roles of Asprosin and Gremlin-1 expression in Egyptian pediatric patients with type 1 diabetes

Diabetes mellitus type 1 (insulin-dependent) (T1DM) is characterized by the selective destruction of the insulin-producing pancreatic beta. Asprosin and Gremlin-1 may have roles in T1DM, however these roles are not fully established. The expression of Asprosin and Gremlin-1 genes and their protein levels, was considerably higher in T1DM patients' blood compared to the control group (P < 0.001). The area under the curve of 50 age- and sex-matched control persons was compared to that of serum T1DM patients. Gremlin-1 and Asprosin serum quantities were measured by ELISA, and real-time PCR was used to evaluate the expression of their genes in peripheral blood. Serum Asprosin concentration, Asprosin expression, serum Gremlin-1 concentration, and Gremlin-1 expression were 0.87, 0.997, 0.912, and 0.949, respectively. The Asprosin expression was the best marker for T1DM diagnosis with 96% sensitivity, 92% specificity, and 94% accuracy. Asprosin expression can significantly increase the risk of T1DM by 276 folds, followed by Gremlin-1 expression by 84.33 folds. The best diagnostic for T1DM diagnosis was Asprosin expression, which had 96% sensitivity, 92% specificity, and 94% accuracy. The risk of type 1 diabetes can be raised by 276 times when asprosin expression is present, and by 84.33 times when Gremlin-1 expression is present.

Citronellal Alleviates Insulin Resistance in High-Fat Diet/Streptozocin Model: Role of Asprosin/Olfactory Receptor Axis

Ectopic olfactory receptors are expressed in nonolfactory tissues and perform diverse roles including regulation of glucose homeostasis. We explored the effect of citronellal treatment on olfactory receptor 4M1 subtype (OR4M1) signaling in insulin resistance and Type II diabetes in rats. We aimed to validate the anti-diabetic effect of citronellal through Asprosin/OR4M1 modulation. Exploring new antidiabetics and pharmacological targets is important to improve quality of life and limit complications. The model was established in Sprague-Dawley rats by a high-fat diet for 4 weeks followed by a single low-dose streptozotocin (STZ) (35 mg/kg/ip). One week after STZ injection, oral citronellal (100 mg/kg) was administered for 4 weeks. Citronellal lowered serum glucose and triglycerides and ameliorated OGTT and HOMA-IR results. Docking results revealed that citronellal blocked the Asprosin binding site at OR4M1. The hepatic expression of OR4M1 and Asprosin was reduced. Citronellal lowered cAMP levels causing attenuated levels of protein kinase A and downstream gluconeogenic enzymes: glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. Citronellal also inhibited the expression of hepatic TLR-4 and inhibited JNK phosphorylation. Citronellal attenuated hepatic levels of NF-κB, p-NF-κB, and downstream proteins MCP-1 and TNF-α. These results suggest that citronellal alleviates insulin resistance by mitigating Asprosin/OR4M1 and Asprosin/TLR4/JNK signaling.

Asprosin is a Reliable Predictor of Osteoporosis in Type 2 Diabetic Postmenopausal Women: A Case-Control Study

The study evaluates Asprosin's value in diabetic postmenopausal women, examining its reliability as a predictor for osteoporosis (OP) in the second type of diabetes (T2D) women. A case-control study recruited 255 postmenopausal women attending the geriatric department of the University Hospital. They were grouped into controls (non-OP non-T2D), and study cases. The latter were subdivided into: non-OP T2D, and OP T2D postmenopausal women (85/255) for each. Serum Asprosin level showed a significant increase in postmenopausal T2D women with OP (42.51 ± 2.97 ng/mL, P < 0.001) compared with postmenopausal T2D women without OP and controls. Additionally, there is a significant interrelationship between OP radiological indicators and bone-forming hormone in T2D women, osteocalcin. Moreover, bone resorption and glycemic markers in T2D women correlated significantly and positively with Asprosin. The Receiver operator characteristic curve discriminates OP T2D postmenopausal women from non-OP T2D postmenopausal women by estimating cutoff value (> 39.3 ng/mL) at 90% sensitivity, 63.3% specificity, and P < 0.001.

Comparison of the effects of empagliflozin and sitagliptin, as add-on to metformin, on serum levels of asprosin and metabolic parameters in patients with type 2 diabetes mellitus

The effect of sitagliptin and empagliflozin on serum levels of asprosin and metabolic parameters in patients with type 2 diabetes mellitus (T2DM) was assessed in a non-randomized, prospective observational study. Seventy-nine T2DM patients, without adequate glycemic control with metformin monotherapy, were included in the study. In addition to the ongoing metformin treatment, patients received sitagliptin 100 mg and empagliflozin 10 mg once daily for 12 weeks. Anthropometric parameters, lipid and glycemic profile, insulin resistance (homeostasis model assessment of insulin resistance index [HOMA-IR]), and asprosin serum levels were assessed at baseline and after 12 weeks of therapy. Both empagliflozin and sitagliptin treatments led to similar, significant improvement in fasting blood glucose (FBG) and hemoglobin A1C (HbA1C). Compared to baseline, triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) were improved with both treatments, but empagliflozin led to the more improvement. No significant change of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) were observed in either group. Insulin resistance was significantly attenuated in both groups, but to a greater degree with empagliflozin treatment. The reduction in serum asprosin levels from baseline was significantly higher in patients taking empagliflozin compared to those receiving sitagliptin. Additionally, individuals on empagliflozin exhibited a more decrease in body mass index (BMI) and body weight compared to those on sitagliptin. According to our findings, the addition of empagliflozin to metformin appeared to offer greater benefits compared to the addition of sitagliptin in terms of decreasing asprosin levels and improving certain metabolic parameters in T2DM patients.

The association of plasma asprosin with anthropometric and metabolic parameters in Korean children and adolescents

Background

This study aimed to determine the correlation of plasma asprosin with anthropometric and metabolic parameters in Korean children and adolescents.

Methods

This single-center study included 109 Korean children and adolescents: 62 (56.9%) obese participants with a body mass index (BMI) ≥95th percentile and 47 (43.1%) healthy controls with BMI between the 15th and 85th percentile. Metabolic parameters were measured, including fasting blood glucose, fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), triglyceride and glucose (TyG) index, and lipid profiles.

Results

Plasma asprosin levels were higher in the obese group than in the control group (mean 87.0 vs. 69.3 ng/mL; p = 0.001) and in the IR group than in the non-IR group (mean 98.6 vs. 70.2 ng/mL; p < 0.001). Plasma asprosin levels were not associated with sex or pubertal stage. Plasma asprosin levels were positively correlated with BMI SDS (r = 0.34; p = 0.002), glycated hemoglobin (HbA1c) (r = 0.25; p = 0.02), glucose (r = 0.33; p = 0.002), insulin (r = 0.44; p < 0.001), HOMA-IR (r = 0.47; p < 0.001), triglyceride (TG) (r = 0.33; p = 0.003), high-density lipoprotein (HDL) cholesterol (r = -0.29; p = 0.008), and TyG index (r = 0.38; p < 0.001). Multiple linear regression analysis indicated that plasma asprosin levels were independently associated with HOMA-IR (p < 0.001) and TG/HDL cholesterol ratio (p < 0.001).

Conclusions

This study demonstrated an association between plasma asprosin levels and obesity and insulin resistance in Korean children and adolescents.

Oxidative Stress and Asprosin Levels in Type 2 Diabetic Patients with Good and Poor Glycemic Control

Objectives: HbA1c is the most widely used test as an indicator of glucoregulation in patients with type 2 diabetes mellitus (T2DM). Asprosin and oxidative stress levels can be reduced with good glycemic control (GC) and thus prevented or delayed micro/macro complications in patients with T2DM. The relationship between asprosin, which is thought to affect GC, and oxidative stress parameters such as lipid hydroperoxides (LOOHs), glutathione (GSH), malondialdehyde (MDA), superoxide dismutase (Cu,Zn-SOD), and total antioxidant capacity (TAC) was evaluated in T2DM patients. Materials and Methods: The study was conducted prospectively in 75 healthy people admitted to the hospital for a general health check-up and 150 T2DM patients treated in the diabetes outpatient clinic. The patient's glycemic status measurements were categorized as good glycemic control group (GGC) is defined as HbA1c < 7 and poor glycemic control (PGC) group is defined as HbA1c ≥ 7. Results: The study found a consistent increase in LOOH and MDA levels across the control, GGC, and PGC groups, while GSH, Cu/Zn-SOD, and TAC levels decreased in these respective groups. Additionally, asprosin levels showed a gradual rise in all groups. Positive correlations were observed between asprosin levels and various metabolic and oxidative stress markers, including BMI, WC, FBG, insulin, homeostasis model assessment for insulin resistance (HOMA-IR), DM duration, LOOH, and MDA, while negative correlations were noted with GSH, Cu/Zn-SOD, and TAC specifically in the PGC group. Furthermore, multivariate regression analysis identified HOMA-IR as the primary influencing factor on asprosin levels in PGC patients. Conclusions: Current glycemic dysregulation may lead to increased circulating asprosin and oxidative stress, which cause complications. Since asprosin levels may be an important hormonal factor in determining GC in T2DM, the use of this hormone may be recommended in the future to accelerate therapeutic approaches in T2DM. Early diagnosis and appropriate treatment may delay the development and progression of diabetic complications.

The cerebellum modulates thirst

The cerebellum, a phylogenetically ancient brain region, has long been considered strictly a motor control structure. Recent studies have implicated the cerebellum in cognition, sensation, emotion and autonomic function, making it an important target for further investigation. Here, we show that cerebellar Purkinje neurons in mice are activated by the hormone asprosin, leading to enhanced thirst, and that optogenetic or chemogenetic activation of Purkinje neurons induces rapid manifestation of water drinking. Purkinje neuron-specific asprosin receptor (Ptprd) deletion results in reduced water intake without affecting food intake and abolishes asprosin's dipsogenic effect. Purkinje neuron-mediated motor learning and coordination were unaffected by these manipulations, indicating independent control of two divergent functions by Purkinje neurons. Our results show that the cerebellum is a thirst-modulating brain area and that asprosin-Ptprd signaling may be a potential therapeutic target for the management of thirst disorders.

Effects of atypical antipsychotics on serum asprosin level and other metabolic parameters in patients with schizophrenia

BACKGROUND

In this cross-sectional study, we compared fasting serum asprosin levels and metabolic parameters between patients receiving one of three atypical antipsychotics (olanzapine, risperidone, or aripiprazole) and healthy subjects.

METHODS

The study population included 62 adult outpatients with schizophrenia and 22 healthy controls, matched for age and gender. Patients were in remission and had been on stable monotherapy with one of these atypical antipsychotics for over 6 months. Body Mass Index (BMI) and fasting serum levels of asprosin, glucose, HA1c, insulin, and lipid profile were compared across the investigated groups. Additionally, the number of participants meeting the insulin resistance criterion, defined as homeostasis model assessment for insulin resistance (HOMA-IR) >2.5, as well as the number of participants with elevated BMI levels (men >27 kg/m2, women >25 kg/m2) were compared among the groups.

RESULTS

We observed statistically significant differences in BMI and fasting serum levels of glucose, HA1c, insulin, triglyceride (TG), high-density lipoprotein cholesterol, and asprosin among patients receiving olanzapine or risperidone, as compared to those receiving aripiprazole and healthy subjects. Patients on aripiprazole exhibited values comparable to healthy subjects, whereas those on risperidone or olanzapine showed significantly higher values, with the highest observed in the olanzapine group. Additionally, the prevalence of participants meeting the insulin resistance criterion and those with elevated BMI was also greater in individuals receiving olanzapine or risperidone compared to those on aripiprazole and healthy subjects. Serum asprosin levels showed a significant positive correlation with BMI and several metabolic parameters, including HbA1c, fasting insulin, HOMA-IR, and TG. No significant differences were observed among the investigated groups in terms of serum levels of total cholesterol and low-density lipoprotein cholesterol.

CONCLUSIONS

Our cross-sectional study highlights the association between elevated asprosin levels, weight gain, and metabolic disorders in patients treated with olanzapine and risperidone. Given the bidirectional nature of the relationship between serum asprosin levels and these metabolic disturbances, further research is warranted to elucidate potential causative pathways.

Asprosin: its function as a novel endocrine factor in metabolic-related diseases

BACKGROUND AND PURPOSE

Asprosin was discovered as a new endocrine hormone originating from fibrillin-1 cleavage that plays a crucial role in various metabolic-related diseases, such as obesity, nonalcoholic fatty liver disease (NAFLD), diabetes, polycystic ovary syndrome (PCOS), and cardiovascular diseases. The purpose of this review is to describe the recent advancements of asprosin.

METHOD

Narrative review.

RESULT

This comprehensive review explores its tissue-specific functions, focusing on white adipose tissue, liver, hypothalamus, testis, ovary, heart, pancreas, skeletal muscle, and kidney.

CONCLUSION

Asprosin is a multifaceted protein with tissue-specific roles in various physiological and pathological processes. Further research is needed to fully understand the mechanisms and potential of asprosin as a therapeutic target. These insights could provide new directions for treatments targeting metabolic-related diseases.

Asprosin levels in patients with type 2 diabetes mellitus, metabolic syndrome and obesity: A systematic review and meta-analysis

BACKGROUND & AIMS

Asprosin is a promising candidate for novel treatments for metabolic-endocrine disorders. The objective of this systematic review and meta-analysis was to consolidate the existing evidence regarding asprosin levels in patients diagnosed with type 2 diabetes (T2D), metabolic syndrome (MetS), and obesity.

METHODS

Scopus, Embase, PubMed, Ovid/Medline, and Web of Science were systematically searched without restrictions. We only used the standardized mean differences (SMD) with their 95 % confidence intervals (95 % CI) as the effect measure. A random-effects model (DerSimonian and Laird method) was used for the meta-analysis. Risk of bias was assessed with the Newcastle-Ottawa Scale and Newcastle-Ottawa Scale for Cross-Sectional Studies.

RESULTS

Twenty-six studies (n = 3,787) were included in the meta-analysis. Participants with T2D had higher asprosin values than those without T2D (SMD: 1.64; 95 % CI: 1.08-2.21; I2 = 97 %). Patients with MetS had higher asprosin levels compared to those without MetS (SMD: 0.99; 95 % CI: 0.34-1.64; I2 = 96 %). Patients with obesity had higher asprosin levels than participants without obesity (SMD: 1.49; 95 % CI: 0.23-2.76; I2 = 98 %).

CONCLUSIONS

Asprosin is significantly higher in patients with either T2D, MetS, or obesity, compared with controls.

The secretory function of adipose tissues in metabolic regulation

In addition to their pivotal roles in energy storage and expenditure, adipose tissues play a crucial part in the secretion of bioactive molecules, including peptides, lipids, metabolites, and extracellular vesicles, in response to physiological stimulation and metabolic stress. These secretory factors, through autocrine and paracrine mechanisms, regulate various processes within adipose tissues. These processes include adipogenesis, glucose and lipid metabolism, inflammation, and adaptive thermogenesis, all of which are essential for the maintenance of the balance and functionality of the adipose tissue micro-environment. A subset of these adipose-derived secretory factors can enter the circulation and target the distant tissues to regulate appetite, cognitive function, energy expenditure, insulin secretion and sensitivity, gluconeogenesis, cardiovascular remodeling, and exercise capacity. In this review, we highlight the role of adipose-derived secretory factors and their signaling pathways in modulating metabolic homeostasis. Furthermore, we delve into the alterations in both the content and secretion processes of these factors under various physiological and pathological conditions, shedding light on potential pharmacological treatment strategies for related diseases.

Association of serum asprosin with metabolic dysfunction-associated fatty liver disease in older adult type 2 diabetic patients: a cross-sectional study

BACKGROUND

To explore the association of serum asprosin levels with metabolic dysfunction-associated fatty liver disease (MAFLD) in older adults with type 2 diabetes mellitus (T2DM).

METHODS

The cross-sectional study enrolled patients ≥ 65 years old diagnosed with T2DM at two community health service centers between November 2019 and July 2021. Logistic regression was applied to analyze the influencing factors of MAFLD.

RESULTS

Totally 219 cases were included. Compared with diabetic individuals without MAFLD (n = 105), diabetics with MAFLD (n = 114) had younger ages, higher body mass index values, shorter time from T2DM diagnosis, increased waist-to-hip ratios, elevated triglycerides, reduced high-density lipoprotein cholesterol (HDL-C), elevated alanine aminotransferase (ALT), elevated γ-glutaryl transferase, elevated fasting insulin, and elevated HOMA-IR (all P < 0.05). Serum asprosin levels were elevated in diabetics with MAFLD in comparison with the non-MAFLD group (291.71 ± 73.69 vs. 255.24 ± 82.52 pg/ml, P = 0.001). Multivariable analysis revealed, after adjusted for age, time from T2DM diagnosis, HDL-C, and ALT, serum asprosin level (OR = 1.006, 95%CI: 1.001-1.010, P = 0.014) were independently associated with MAFLD in T2DM.

CONCLUSIONS

High asprosin level are associated with MAFLD in older patients with T2DM, after adjusted for age, time from T2DM diagnosis, WHR, TG, HDL-C, ALT, GGT, FINS, and HOMA-IR.

Asprosin levels in women with and without the polycystic ovary syndrome: a systematic review and meta-analysis

Objective: This systematic review and meta-analysis aimed at summarizing the evidence concerning circulating asprosin, and related endocrine and metabolites in women with and without the polycystic ovary syndrome (PCOS).Method: We performed a comprehensive literature search in Pubmed, Web of Science, Scielo, and Chinese National Knowledge Infrastructure for studies published until May 20, 2022, that evaluated circulating asprosin levels in women with and without PCOS, regardless of language. The quality of studies was assessed with the Newcastle-Ottawa Scale. Random-effects models were used to estimate mean differences (MD) or standardized MD (SMD) and their 95% confidence interval (CI).Results: We evaluated eight studies reporting 1,050 PCOS cases and 796 controls of reproductive age. Participants with PCOS were younger (MD = -2.40 years, 95% CI -2.46 to -2.33), with higher values of asprosin (SMD = 2.57, 95% CI 1.64-3.50), insulin (SMD = 2.73, 95% CI 1.18-4.28), homeostatic model assessment of insulin resistance (SMD = 2.70, 95% CI 0.85-4.55), luteinizing hormone (SMD = 2.33, 95% CI 0.60-4.06), total testosterone (SMD = 4.06, 95% CI 1.89-6.22), dehydroepiandrosterone sulfate (SMD = 2.38, 95% CI 0.37-4.40), and triglycerides (SMD = 1.20, 95% CI 0.13 to 2.27). Moreover, PCOS women had lower circulating levels of sex hormone-binding globulin (SMD = -3.36, 95% CI -4.92 to -1.80), and high-density lipoprotein-cholesterol (SMD = -0.85, 95% CI -1.69 to -0.01); with no significant differences observed for glucose, total cholesterol, and low-density lipoprotein-cholesterol levels.Conclusion: Circulating asprosin levels were significantly higher in women with PCOS as compared to those without the syndrome.

Gonacin: A germ cell-derived hormone with glucogenic, orexigenic, and gonadal activities

Fish require abundant nutrients to generate a large number of eggs for spawning. Based on the evolutionary conservation of human FBN2 and its C-terminal placensin-like sequences in fish, we identified a peptide hormone gonacin (GONAdal Cell placensIN) and found its high expression in early-stage germ cells in the ovary and testis of zebrafish. We demonstrated that gonacin is essential for food intake, glucose release, and ovarian development in zebrafish. Similar expression patterns and functions of gonacin were also demonstrated in rainbow trout. Gonacin represents the first hormone secreted by germ cells with endocrine functions in vertebrates, bridging the energy homeostasis and reproduction.

Asprosin Enhances Cytokine Production by a Co-Culture of Fully Differentiated Mature Adipocytes and Macrophages Leading to the Exacerbation of the Condition Typical of Obesity-Related Inflammation

Asprosin, a fasting-induced, glucogenic, and orexigenic adipokine, has gained popularity in recent years as a potential target in the fight against obesity and its complications. However, the contribution of asprosin to the development of moderate obesity-related inflammation remains still unknown. The present study aimed to evaluate the effect of asprosin on the inflammatory activation of adipocyte–macrophage co-cultures at various stages of differentiation. The study was performed on co-cultures of the murine 3T3L1 adipocyte and the RAW264.7 macrophage cell lines treated with asprosin before, during, and after 3T3L1 cell differentiation, with or without lipopolysaccharide (LPS) stimulation. Cell viability, overall cell activity, and the expression and release of key inflammatory cytokines were analyzed. In the concentration range of 50–100 nM, asprosin increased the pro-inflammatory activity in the mature co-culture and enhanced the expression and release of tumor necrosis factor α (TNF-α), high-mobility group box protein 1 (HMGB1), and interleukin 6 (IL-6). Macrophage migration was also increased, which could be related to the upregulated expression and release of monocyte chemoattractant protein-1 (MCP-1) by the adipocytes. In summary, asprosin exerted a pro-inflammatory effect on the mature adipocyte–macrophage co-culture and may contribute to the spread of moderate obesity-associated inflammation. Nevertheless, further research is needed to fully elucidate this process.

Asprosin promotes feeding through SK channel-dependent activation of AgRP neurons

Asprosin, a recently identified adipokine, activates agouti-related peptide (AgRP) neurons in the arcuate nucleus of the hypothalamus (ARH) via binding to protein tyrosine phosphatase receptor δ (Ptprd) to increase food intake. However, the intracellular mechanisms responsible for asprosin/Ptprd-mediated activation of AgRPARH neurons remain unknown. Here, we demonstrate that the small-conductance calcium-activated potassium (SK) channel is required for the stimulatory effects of asprosin/Ptprd on AgRPARH neurons. Specifically, we found that deficiency or elevation of circulating asprosin increased or decreased the SK current in AgRPARH neurons, respectively. AgRPARH-specific deletion of SK3 (an SK channel subtype highly expressed in AgRPARH neurons) blocked asprosin-induced AgRPARH activation and overeating. Furthermore, pharmacological blockade, genetic knockdown, or knockout of Ptprd abolished asprosin's effects on the SK current and AgRPARH neuronal activity. Therefore, our results demonstrated an essential asprosin-Ptprd-SK3 mechanism in asprosin-induced AgRPARH activation and hyperphagia, which is a potential therapeutic target for the treatment of obesity.

Asprosin in health and disease, a new glucose sensor with central and peripheral metabolic effects

Adipose tissue malfunction leads to altered adipokine secretion which might consequently contribute to an array of metabolic diseases spectrum including obesity, diabetes mellitus, and cardiovascular disorders. Asprosin is a novel diabetogenic adipokine classified as a caudamin hormone protein. This adipokine is released from white adipose tissue during fasting and elicits glucogenic and orexigenic effects. Although white adipose tissue is the dominant source for this multitask adipokine, other tissues also may produce asprosin such as salivary glands, pancreatic B-cells, and cartilage. Significantly, plasma asprosin levels link to glucose metabolism, lipid profile, insulin resistance (IR), and β-cell function. Indeed, asprosin exhibits a potent role in the metabolic process, induces hepatic glucose production, and influences appetite behavior. Clinical and preclinical research showed dysregulated levels of circulating asprosin in several metabolic diseases including obesity, type 2 diabetes mellitus (T2DM), polycystic ovarian syndrome (PCOS), non-alcoholic fatty liver (NAFLD), and several types of cancer. This review provides a comprehensive overview of the asprosin role in the etiology and pathophysiological manifestations of these conditions. Asprosin could be a promising candidate for both novel pharmacological treatment strategies and diagnostic tools, although developing a better understanding of its function and signaling pathways is still needed.

Fibrillin-1 and asprosin, novel players in metabolic syndrome

Fibrillin-1 is a major component of the extracellular microfibrils, where it interacts with other extracellular matrix proteins to provide elasticity to connective tissues, and regulates the bioavailability of TGFβ family members. A peptide consisting of the C-terminal 140 amino acids of fibrillin-1 has recently been identified as a glucogenic hormone, secreted from adipose tissue during fasting and targeting the liver to release glucose. This fragment, called asprosin, also signals in the hypothalamus to stimulate appetite. Asprosin levels are correlated with many of the pathologies indicative of metabolic syndrome, including insulin resistance and obesity. Previous studies and reviews have addressed the therapeutic potential of asprosin as a target in obesity, diabetes and related conditions without considering mechanisms underlying the relationship between generation of asprosin and expression of the much larger fibrillin-1 protein. Profibrillin-1 undergoes obligatory cleavage at the cell surface as part of its assembly into microfibrils, producing the asprosin peptide as well as mature fibrillin-1. Patterns of FBN1 mRNA expression are inconsistent with the necessity for regulated release of asprosin. The asprosin peptide may be protected from degradation in adipose tissue. We present evidence for an alternative possibility, that asprosin mRNA is generated independently from an internal promoter within the 3' end of the FBN1 gene, which would allow for regulation independent of fibrillin-synthesis and is more economical of cellular resources. The discovery of asprosin opened exciting possibilities for treatment of metabolic syndrome related conditions, but there is much to be understood before such therapies could be introduced into the clinic.

Overexpression and ELISA-based detection of asprosin in cultured cells and mice

The unreliability of commercial recombinant asprosin preparations and variability between asprosin detection assays have proven to be a bottleneck in experimental interpretation. This protocol describes the use of viral vectors and expression plasmid for overexpression and secretion of human asprosin to achieve sustained elevation of asprosin protein in mice and HEK293T cells without using recombinant proteins. This protocol also includes a sandwich ELISA using anti-asprosin monoclonal antibodies for detection of asprosin in media from cultured cells and in plasma of mice. For complete details on the use and execution of this protocol, please refer to Duerrschmid et al. (2017), Mishra et al. (2021), and Mishra et al. (2022).

Asprosin, a C-Terminal Cleavage Product of Fibrillin 1 Encoded by the FBN1 Gene, in Health and Disease

BACKGROUND

Asprosin is a novel fasting-induced, glucogenic, and orexigenic protein hormone that is discovered with the help of genetic studies in patients with neonatal progeroid syndrome. Asprosin is encoded by the penultimate 2 exons (65 and 66) of the fibrillin 1 (FBN1) gene. Profibrillin 1 is the unprocessed protein product of FBN1 and undergoes a proteolytic cleavage by furin enzyme to produce mature fibrillin 1 and asprosin. The main organ responsible for the asprosin production seems to be white adipose tissue.

SUMMARY

Asprosin promotes hepatic glucose release in the liver and appetite stimulation in the hypothalamus through activation of the cAMP signaling circuitry through interacting with its G protein-coupled receptor, called OR4M1. Increasing mass of evidence suggests that asprosin is involved in the development and progression of various clinical conditions including diabetes, obesity, cardiomyopathy, cancer, and polycystic ovarian syndrome. It regulates various cellular and physiological processes such as appetite stimulation, glucose release, insulin secretion, apoptotic cell death, and inflammatory response. In this review, we discuss the current literature on asprosin and try to shed light on the yet undiscovered functions of asprosin.

KEY MESSAGE

Asprosin is a key regulatory factor for preserving the homeostasis of energy metabolism.

Protein tyrosine phosphatase receptor δ serves as the orexigenic asprosin receptor

Asprosin is a fasting-induced glucogenic and centrally acting orexigenic hormone. The olfactory receptor Olfr734 is known to be the hepatic receptor for asprosin that mediates its effects on glucose production, but the receptor for asprosin's orexigenic function has been unclear. Here, we have identified protein tyrosine phosphatase receptor δ (Ptprd) as the orexigenic receptor for asprosin. Asprosin functions as a high-affinity Ptprd ligand in hypothalamic AgRP neurons, regulating the activity of this circuit in a cell-autonomous manner. Genetic ablation of Ptprd results in a strong loss of appetite, leanness, and an inability to respond to the orexigenic effects of asprosin. Ablation of Ptprd specifically in AgRP neurons causes resistance to diet-induced obesity. Introduction of the soluble Ptprd ligand-binding domain in the circulation of mice suppresses appetite and blood glucose levels by sequestering plasma asprosin. Identification of Ptprd as the orexigenic asprosin receptor creates a new avenue for the development of anti-obesity therapeutics.

Sensitive asprosin detection in clinical samples reveals serum/saliva correlation and indicates cartilage as source for serum asprosin

The C-terminal pro-fibrillin-1 propeptide asprosin is described as white adipose tissue derived hormone that stimulates rapid hepatic glucose release and activates hunger-promoting hypothalamic neurons. Numerous studies proposed correlations of asprosin levels with clinical parameters. However, the enormous variability of reported serum and plasma asprosin levels illustrates the need for sensitive and reliable detection methods in clinical samples. Here we report on newly developed biochemical methods for asprosin concentration and detection in several body fluids including serum, plasma, saliva, breast milk, and urine. Since we found that glycosylation impacts human asprosin detection we analyzed its glycosylation profile. Employing a new sandwich ELISA revealed that serum and saliva asprosin correlate strongly, depend on biological sex, and feeding status. To investigate the contribution of connective tissue-derived asprosin to serum levels we screened two cohorts with described cartilage turnover. Serum asprosin correlated with COMP, a marker for cartilage degradation upon running exercise and after total hip replacement surgery. This together with our finding that asprosin is produced by primary human chondrocytes and expressed in human cartilage suggests a contribution of cartilage to serum asprosin. Furthermore, we determined asprosin levels in breast milk, and urine, for the first time, and propose saliva asprosin as an accessible clinical marker for future studies.

Caudamins, a new subclass of protein hormones

Hormones have traditionally been classified by their mode of biosynthetic origin. We postulate a mode of hormone biosynthesis that leads to a new subclass of protein hormones. Members of this class are derived from a cleavage event that also generates a much larger, functionally unrelated, nonhormonal protein. Here, we examine four representative members of this group: endostatin, endotrophin, asprosin, and placensin. We have named this subclass of protein hormones caudamins, from the Latin word cauda meaning 'tail'. These four caudamins have shown promise in understanding and treating diseases like metabolic syndrome and cancer. Identification of the rest of the caudamins will likely provide a plethora of drug targets for a variety of diseases.

Role of Vitamin B12 and Folate in Metabolic Syndrome

Metabolic syndrome (MS) is a collection of pathological metabolic conditions that includes insulin resistance, central or abdominal obesity, dyslipidemia, and hypertension. It affects large populations worldwide, and its prevalence is rising exponentially. There is no specific mechanism that leads to the development of MS. Proposed hypotheses range from visceral adiposity being a key factor to an increase in very-low-density lipoprotein and fatty acid synthesis as the primary cause of MS. Numerous pharmaceutical therapies are widely available in the market for the treatment of the individual components of MS. The relationship between MS and vitamin B complex supplementation, specifically folic acid and vitamin B12, has been a subject of investigation worldwide, with several trials reporting a positive impact with vitamin supplementation on MS.

In this study, an all-language literature search was conducted on Medline, Cochrane, Embase, and Google Scholar till September 2021. The following search strings and Medical Subject Headings (MeSH) terms were used: “Vitamin B12,” “Folate,” “Metabolic Syndrome,” and “Insulin Resistance.” We explored the literature on MS for its epidemiology, pathophysiology, newer treatment options, with a special focus on the effectiveness of supplementation with vitamins B9 and B12.

According to the literature, vitamin B12 and folate supplementation, along with a host of novel therapies, has a considerable positive impact on MS. These findings must be kept in mind while designing newer treatment protocols in the future.