Follistatin-like 1 protects endothelial function in the spontaneously hypertensive rat by inhibition of endoplasmic reticulum stress through AMPK-dependent mechanism

OBJECTIVE

Endothelial dysfunction is a critical initiating factor in the development of hypertension and related complications. Follistatin-like 1 (FSTL1) can promote endothelial cell function and stimulates revascularization in response to ischemic insult. However, it is unclear whether FSTL1 has an effect on ameliorating endothelial dysfunction in spontaneously hypertensive rats (SHRs).

METHODS

Wistar Kyoto (WKY) and SHRs were treated with a tail vein injection of vehicle (1 mL/day) or recombinant FSTL1 (100 μg/kg body weight/day) for 4 weeks. Blood pressure was measured by tail-cuff plethysmograph, and vascular reactivity in mesenteric arteries was measured using wire myography.

RESULTS

We found that treatment with FSTL1 reversed impaired endothelium-dependent relaxation (EDR) in mesenteric arteries and lowered blood pressure of SHRs. Decreased AMP-activated protein kinase (AMPK) phosphorylation, elevated endoplasmic reticulum (ER) stress markers, increased reactive oxygen species (ROS), and reduction of nitric oxide (NO) production in mesenteric arteries of SHRs were also reversed by FSTL1 treatment. Ex vivo treatment with FSTL1 improved the impaired EDR in mesenteric arteries from SHRs and reversed tunicamycin (ER stress inducer)-induced ER stress and the impairment of EDR in mesenteric arteries from WKY rats. The effects of FSTL1 were abolished by cotreatment of compound C (AMPK inhibitor).

CONCLUSIONS

These results suggest that FSTL1 prevents endothelial dysfunction in mesenteric arteries of SHRs through inhibiting ER stress and ROS and increasing NO production via activation of AMPK signaling.

Serum Fstl1, a novel biomarker screened based on protein array technology, predict acute kidney injury and major renal adverse events after cardiac surgery: A prospective cohort study

BACKGROUND

Acute kidney injury (AKI) is a severe complication after cardiac surgery. The early prediction of AKI can facilitate timely intervention and prevent adverse outcomes. We aimed to identify unique serum biomarker that can be used to facilitate early prediction of AKI after cardiac surgery.

METHODS

A prospective cohort study was performed in cardiac surgery patients, serum samples were collected from 172 patients before surgery, 4 h and 1 day after surgery. We used protein array technology to detect the serum protein expression profile of cardiac surgery-associated AKI (CSA-AKI) patients, and verified the novel biomarker follistatin-like 1 (Fstl1) by expanding the sample size. The primary outcome was AKI, under the definition of Kidney Disease: Improving Global Outcomes (KDIGO).

RESULTS

Patients with AKI had significantly higher serum Fstl1 levels at 4 h after surgery. After multivariate adjustment, the highest quartile of postoperative serum Fstl1 level, compared with the lowest quartile, associated with 56.3-fold higher odds of AKI. Serum Fstl1 at 4 h post-surgery had a high predictive ability for AKI, severe AKI and major renal adverse events(MAKE) (AUC = 0.713, 0.869 and 0.808, respectively). Adding postoperative 4 h serum Fstl1 to the clinical model can significantly improve the predictive performance of the model.

CONCLUSIONS

Higher serum Fstl1 levels at 4 h post-surgery is associated with higher odds of AKI after cardiac surgery, and when added to clinical model and Cleveland Score, serum Fstl1 levels at 4 h after cardiac surgery enhanced early prediction of AKI, severe AKI and MAKE in patients undergoing cardiac surgery.

Follistatin-like 1 ameliorates severe acute pancreatitis associated lung injury via inhibiting the activation of NLRP3 inflammasome and NF-κB pathway

OBJECTIVE

Severe acute pancreatitis (SAP) is one of the most common abdominal conditions of digestive system that usually causes acute lung injury through systemic inflammation. Follistatin-like 1 (FSTL-1) has been reported to have anti-inflammatory and anti-apoptotic effects in a variety of diseases. The aim of this study was to investigate the effects of FSTL-1 on SAP-associated lung injury (SAPALI) and the underlying mechanism.

METHODS

SAP model was induced by intraperitoneal injection of the L-arginine in C57BL/6 mice. The haematoxylin and eosin (H&E) staining was applied to determine the severity of lung and pancreatic injury. ELISA kits were used to determine serum amylase and inflammatory cytokines levels. TUNEL staining was carried out to measure cell apoptosis. Western blotting was applied to analyze the related proteins of NLRP3 inflammasome and NF-κB pathways.

RESULTS

FSTL-1 was significantly increased in the lung of SAP mice. Knockout of FSTL-1 ameliorated pancreatic injury, lung injury, inflammation and apoptosis in mice with SAP. Moreover, the protein levels of NLRP3, ASC, Caspase-1, p-p65 and p-IκBα were obviously reduced in the FSTL-1 KO+SAP group in comparison with SAP group, suggesting that inhibition of FSTL-1 repressed the activation of the NLRP3 inflammasome and NF-κB pathway.

CONCLUSION

This study helps us understand the mechanism of FSTL-1 in SAPALI and might provide a potential new strategy for the treatment of SAPALI.

Follistatin-like 1 promotes proliferation of matured human hypoxic iPSC-cardiomyocytes and is secreted by cardiac fibroblasts

The human heart has limited regenerative capacity. Therefore, patients often progress to heart failure after ischemic injury, despite advances in reperfusion therapies generally decreasing mortality. Depending on its glycosylation state, Follistatin-like 1 (FSTL1) has been shown to increase cardiomyocyte (CM) proliferation, decrease CM apoptosis, and prevent cardiac rupture in animal models of ischemic heart disease. To explore its therapeutic potential, we used a human in vitro model of cardiac ischemic injury with human induced pluripotent stem cell-derived CMs (iPSC-CMs) and assessed regenerative effects of two differently glycosylated variants of human FSTL1. Furthermore, we investigated the FSTL1-mediated interplay between human cardiac fibroblasts (cFBs) and iPSC-CMs in hypoxia. Both FSTL1 variants increased viability, while only hypo-glycosylated FSTL1 increased CM proliferation post-hypoxia. Human fetal cardiac fibroblasts (fcFBs) expressed and secreted FSTL1 under normoxic conditions, while FSTL1 secretion increased by iPSC-cFBs upon hypoxia but decreased in iPSC-CMs. Co-culture of iPSC-CMs and cFBs increased FSTL1 secretion compared with cFB mono-culture. Taken together, we confirm that FSTL1 induces iPSC-CM proliferation in a human cardiac in vitro hypoxia damage model. Furthermore, we show hypoxia-related FSTL1 secretion by human cFBs and indications for FSTL1-mediated intercellular communication between cardiac cell types in response to hypoxic conditions.

Prognostic impact of transcardiac gradient of follistatin-like 1 reflecting hemodynamics in patients with dilated cardiomyopathy

BACKGROUND

Follistatin-like 1 (FSTL1) is a myocyte-secreted glycoprotein that could play a role in myocardial maintenance in response to harmful stimuli. We investigated the association between serum FSTL1 levels, especially focused on transcardiac gradient and the hemodynamics, to explore the prognostic impact of FSTL1 levels in patients with dilated cardiomyopathy (DCM).

METHODS

Thirty-two ambulatory patients with DCM (23 men; mean age 59 years) were prospectively enrolled. Blood samples were simultaneously collected from the aortic root (Ao), coronary sinus (CS), as well as from the peripheral vein during cardiac catheterization in stable conditions. The transcardiac gradient of FSTL1 was calculated by the difference between serum FSTL1 levels of CS and Ao (FSTL1_CS-Ao). Patients were divided into two groups based on the median of FSTL1_CS-Ao: Low FSTL1_CS-Ao group, <0 ng/mL; High FSTL1_CS-Ao group, ≥0 ng/mL. Cardiac events were defined as a composite of cardiac deaths and hospitalizations for worsening heart failure.

RESULTS

Mean left ventricular ejection fraction and median plasma B-type natriuretic peptide levels were 30.9% and 92.3 pg/mL, respectively. FSTL1_CS-Ao was negatively correlated with pulmonary capillary wedge pressure (r = -0.400, p = 0.023). Kaplan-Meier survival analysis showed that event-free survival rate was significantly lower in the Low FSTL1_CS-Ao group than in the High FSTL1_CS-Ao group (p = 0.013). Cox regression analyses revealed that the transcardiac gradient of FSTL1 was an independent predictor for cardiac events. Receiver operating characteristic curve analysis showed that the cut-off value of FSTL1_CS-Ao for the prediction of cardiac events was -4.09 ng/mL with sensitivity of 82% and specificity of 86% (area under the curve, 0.87).

CONCLUSIONS

Fifty percent of patients had negative transcardiac gradient of FSTL1. Reduced transcardiac gradient of FSTL1 might be a novel prognostic predictor in DCM patients with impaired hemodynamics.

Knockdown of Follistatin-like 1 disrupts synaptic transmission in hippocampus and leads to cognitive impairments

Follistatin-like 1 (FSTL1), also named transforming growth factor (TGF)-β1-inducible gene, is a secreted extracellular glycoprotein expressing widely in nervous system. Several recent studies have revealed that FSTL1 plays an essential role in neurological diseases including neuropathic pain and ischemic stroke. It proves that FSTL1 suppresses synaptic transmission by activating Na/K-ATPase in DRG neurons and inhibits neuronal apoptosis by phosphorylation AKT signaling. However, it is not clear whether FSTL1 can play a role in other type of neuron or neurodegenerative diseases. In this study, we found that the mice with Fstl1 genetic knockdown showed not only the impairments of learning and memory abilities, but also abnormal neural oscillations and synaptic plasticity in the hippocampus. Subsequently, we identified broad transcriptional changes including 55 up-regulated and 184 down-regulated genes in Fstl1 knockdown mice by RNA-Seq analysis, as well as neurotransmitter transport, synaptic transmission and disease-related genes. The expression changes of some DEGs were further validated via quantitative Realtime PCR (qRT-PCR). Further patch-clamp whole cell recording showed that Fstl1^+/- mice displayed a significant decrease in glutamatergic synaptic transmission and increase in GABAergic synaptic transmission, which were consistent with the RNA-Seq analysis. Taken together, our results provide an evidence and a possibly underlying mechanism for the critical role of FSTL1 in the hippocampus on learning and memory and normal neural oscillations, suggesting that FSTL1 may plays an important role in neurodegenerative diseases related to cognitive impairments.

Persistent Myocardial Production of Follistatin-like 1 Is Associated With Left Ventricular Adverse Remodeling in Patients With Myocardial Infarction: Myocardial production of FSTL1 in AMI patients

BACKGROUND

Although animal studies showed that Follistatin-like 1 (FSTL1) exerts cardioprotective effects against ischemic injury, little is known in humans. We examined whether FSTL1 is secreted in an infarcted myocardium and whether its production is associated with left ventricular (LV) remodeling in survivors of acute myocardial infarction.

METHODS AND RESULTS

FSTL1 levels were measured by enzyme-linked immunosorbent assay in plasma collected from the aortic root and the anterior interventricular vein in 93 patients with anterior acute myocardial infarction. Measurement of FSTL1 levels and left ventriculography were repeated during the early phase (2 weeks) and the chronic phase (6 months) after MI. A persistent increment in FSTL1 levels from the aortic root to the anterior interventricular vein, reflecting FSTL1 production in the infarcted myocardium at both the early and chronic phases, was seen in 22 patients (24%). A linear regression analysis revealed that a persistent transmyocardial increment in FSTL1 levels was significantly associated with percent changes in LV end-diastolic volume index, LV end-systolic volume index, and LV ejection fraction from the early to the chronic phase (r = 0.44, 0.51, and -0.43, respectively, all P < .001).

CONCLUSIONS

The persistent production of FSTL1 in the infarcted myocardium was associated with adverse LV remodeling in survivors of acute myocardial infarction.

Role of A2B adenosine receptor-dependent adenosine signaling in multi-walled carbon nanotube-triggered lung fibrosis in mice

Background

Multi-walled carbon nanotube (MWCNT)-induced lung fibrosis leads to health concerns in human. However, the mechanisms underlying fibrosis pathogenesis remains unclear. The adenosine (ADO) is produced in response to injury and serves a detrimental role in lung fibrosis. In this study, we aimed to explore the ADO signaling in the progression of lung fibrosis induced by MWCNT.

Results

MWCNT exposure markedly increased A_2B adenosine receptor (A_2BAR) expression in the lungs and ADO level in bronchoalveolar lavage fluid, combined with elevation of blood neutrophils, collagen fiber deposition, and activation of myeloperoxidase (MPO) activity in the lungs. Furthermore, MWCNT exposure elicited an activation of transforming growth factor (TGF)-β1 and follistatin-like 1 (Fstl1), leading to fibroblasts recruitment and differentiation into myofibroblasts in the lungs in an A_2BAR-dependent manner. Conversely, treatment of the selective A_2BAR antagonist CVT-6883 exhibited a significant reduction in levels of fibrosis mediators and efficiently decreased cytotoxicity and inflammatory in MWCNT treated mice.

Conclusion

Our results reveal that accumulation of extracellular ADO promotes the process of the fibroblast-to-myofibroblast transition via A_2BAR/TGF-β1/Fstl1 signaling in MWCNT-induced lung fibrosis.

Follistatin-like 1 protects mesenchymal stem cells from hypoxic damage and enhances their therapeutic efficacy in a mouse myocardial infarction model

BACKGROUND

Cell therapy remains the most promising approach against ischemic heart injury. However, poor survival of engrafted cells in ischemic sites diminishes its therapeutic efficacy. Follistatin-like 1 (Fstl1) is documented as a novel pro-survival cardiokine for cardiomyocytes, and it is protective during ischemic heart injury. In the present study, we characterize the potential of Fstl1 as an effective strategy to enhance hypoxia resistance of donor cells and optimize stem cell-based therapy.

METHODS

Murine bone marrow-derived mesenchymal stem cells (MSCs) were expanded in monolayer culture and characterized by flow cytometry. MSCs were subjected to hypoxia to mimic cardiac ischemic environment. Expression of Fstl1 was monitored 0, 24, and 48 h following hypoxia. Constitutive expression of Fstl1 in MSCs was achieved by lentivirus-mediated Fstl1 overexpression. Genetically modified MSCs were further collected for cell death and proliferation assay following 48 h of hypoxic treatment. Acute myocardial infarction (MI) model was created by ligating the left anterior descending coronary artery, while control MSCs (MSCs-mCherry) or Fstl1-overexpressing MSCs (MSCs-Fstl1) were injected into the peri-infarct zone simultaneously. Subsequently, retention of the donor cells was evaluated on post-therapy 1, 3, & 7 days. Finally, myocardial function, infarct size, inflammation, and neovascularization of the infarcted hearts were calculated thereafter.

RESULTS

Expression of Fstl1 in hypoxic MSCs declines dramatically in a time-dependent manner. In vitro study further demonstrated that Fstl1 promotes survival and proliferation of hypoxic MSCs. Moreover, Fstl1 significantly prolongs MSC survival/retention after implantation. Finally, transplantation with Fstl1-overexpressing MSCs significantly improves post-MI cardiac function by limiting scar formation, reducing inflammatory response, and enhancing neovascularization.

CONCLUSIONS

Our results suggest Fstl1 is an intrinsic cardiokine promoting survival and proliferation of MSCs, thereby optimizing their engraftment and therapeutic efficacy during cell therapy.

Cell type specific expression of Follistatin-like 1 (Fstl1) in mouse embryonic lung development

Follistatin like-1 (Fstl1) is a secreted glycoprotein and can be up-regulated by TGF-β1. To better study the function of Fstl1 in lung development, we examined Fstl1 expression in the developing lung, in a cell type specific manner, using a tamoxifen inducible Fstl1-reporter mouse strain. Our results show that Fstl1 is ubiquitously expressed at saccular stage in the developing lung. At E18.5, Fstl1 expression is robust in most type of mesenchymal cells, including airway smooth muscle cells surrounding airways, vascular smooth muscle cells, endothelial cells, and vascular pericytes from blood vessel, but not PDGFRα⁺ fibroblasts in the distal alveolar sacs. Meanwhile, relative weak and sporadic signals of Fstl1 expression are observed in epithelium, including a subgroup of club cells in proximal airways and a few type II alveolar epithelial cells in distal airways. Our data help to understand the critical role of Fstl1 in lung development and lung disease pathogenesis.

Blocking follistatin-like 1 attenuates liver fibrosis in mice by regulating transforming growth factor-beta signaling

AIM

To elucidate the effect of inhibiting follistatin-like 1 on liver fibrosis and activation of hepatic stellate cells in mice.

METHODS

We generated a follistatin-like 1 neutralizing antibody that can inhibit TGF-β 1-induced expression of collagen1α1 in primary mouse liver fibroblasts. All of the mice in our study were induced with carbon tetrachloride and thioacetamide. In addition, primary hepatic stellate cells from mice were isolated from fresh livers using density gradient separation. The degree and extent of fibrosis in mouse livers from the different groups were evaluated by Sirius Red and Masson staining. The effect of the follistatin-like 1 neutralizing antibody on proliferation and migration of hepatic stellate cells was detected using CCK-8 and Transwell assays, respectively.

RESULTS

Expression of follistatin-like 1 in human cirrhotic liver tissue was higher than that in normal liver tissue. Blocking follistatin-like 1 resulted in a delay of primary hepatic stellate cell activation and down-regulation of the migratory capacity of hepatic stellate cells. Blocking follistatin-like 1 also down-regulated TGF-beta signaling in primary hepatic stellate cells from mice. Finally, inhibition of follistatin-like 1 attenuated liver fibrosis and liver function damage in vivo.

CONCLUSIONS

Inhibiting follistatin-like 1 attenuates liver fibrosis and causes a delay in hepatic stellate cell activation. The effect of follistatin-like 1 on liver fibrosis is mainly attributed to its role in regulating TGF-beta signaling.

Follistatin-like 1 expression is decreased in the alveolar epithelium of hypoplastic rat lungs with nitrofen-induced congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Pulmonary hypoplasia (PH), characterized by incomplete alveolar development, remains a major therapeutic challenge associated with congenital diaphragmatic hernia (CDH). Follistatin-like 1 (Fstl1) is a crucial regulator of alveolar formation and maturation, which is strongly expressed in distal airway epithelium. Fstl1-deficient mice exhibit reduced airspaces, impaired alveolar epithelial cell differentiation, and insufficient production of surfactant proteins similar to PH in human CDH. We hypothesized that pulmonary Fstl1 expression is decreased during alveolarization in the nitrofen-induced CDH model.

METHODS

Timed-pregnant rats received nitrofen or vehicle on gestational day 9 (D9). Fetal lungs were harvested on D18 and D21 and divided into control-/nitrofen-exposed specimens. Alveolarization was assessed using morphometric analysis techniques. Pulmonary gene expression of Fstl1 was determined by qRT-PCR. Immunofluorescence-double-staining for Fstl1 and alveolar epithelial marker surfactant protein C (SP-C) was performed to evaluate protein expression/localization.

RESULTS

Radial alveolar count was significantly reduced in hypoplastic lungs of nitrofen-exposed fetuses with significant down regulation of Fstl1 mRNA expression on D18 and D21 compared to controls. Confocal-laser-scanning-microscopy revealed strikingly diminished Fstl1 immunofluorescence and SP-C expression in distal alveolar epithelium of nitrofen-exposed fetuses with CDH-associated PH on D18 and D21 compared to controls.

CONCLUSIONS

Decreased expression of Fstl1 in alveolar epithelium may disrupt alveolarization and pulmonary surfactant production, thus contributing to the development of PH in the nitrofen-induced CDH model.

LEVEL OF EVIDENCE

2b (Centre for Evidence-Based Medicine, Oxford).