MS80, a novel sulfated oligosaccharide,inhibits pulmonary fibrosis by targeting TGF-β1 both in vitro and in vivo

Aim:

The pro-fibrogenic cytokine transforming growth factor-beta 1 (TGF-β1) has attracted much attention for its potential role in the etiology of idiopathic pulmonary fibrosis (IPF). Here, we demonstrate that MS80, a novel sulfated oligosaccharide extracted from seaweed, can bind TGF-β1. The aim of the present study was to determine whether MS80 is capable of combating TGF-β1-mediated pulmonary fibrotic events both in vitro and in vivo, and to investigate the possible underlying mechanisms.

Methods:

Surface plasmon resonance was used to uncover the binding profiles between the compound and TGF-β. MTT assay, flow cytometry, Western blot analysis, BCA protein assay and SDS-PAGE gelatin zymography were used to probe the antifibrotic mechanisms of MS80. The in vivo fibrotic efficacy was evaluated in a bleomycin instillation-induced rat model.

Results:

We report that MS80, a new kind of sulfated oligosaccharide extracted from seaweed, inhibits TGF-β1-induced pulmonary fibrosis in vitro and bleomycin-induced pulmonary fibrosis in vivo. Our results indicated that MS80 competitively inhibited heparin/HS-TGF-β1 interaction through its high binding affinity for TGF-β1. Moreover, MS80 arrested TGF-β1-induced human embryo pulmonary fibroblast (HEPF) cell proliferation, collagen deposition and matrix metalloproteinase (MMP) activity. Intriguingly, MS80 deactivated both the ERK and p38 signaling pathways. MS80 was also a potent suppressor of bleomycin-induced rat pulmonary fibrosis in vivo, as evidenced by improved pathological settings and decreased lung collagen contents.

Conclusion:

MS80 in particular, and perhaps oligosaccharide in general, offer better pharmacological profiles with appreciably few side effects and represent a promising class of drug candidates for IPF therapy.     

γ-Secretase inhibition promotes fibrotic effects of albumin in proximal tubular epithelial cells

Background and Purpose

Albuminuria is an important biomarker of renal dysfunction and is a major mediator of renal damage and fibrosis during kidney disease. The mechanisms underlying albumin-induced renal fibrosis remain unclear. There has been significant interest in γ-secretase activity in tubular epithelial cells in recent times; however, its potential role in albumin-induced fibrosis has not been investigated.

Experimental Approach

The primary aim of this study was to examine the role of γ-secretase in albumin-induced fibrotic effects in proximal tubular cells. The effects of increasing albumin concentrations on fibrosis indicators and mediators in the human HK-2 cell line were examined in the presence and absence of a γ-secretase inhibitor, compound E.

Key Results

Treatment with albumin resulted in a number of pro-fibrotic effects, including up-regulation of fibronectin, TGF-β1 and the EGF-R. Interestingly, similar effects were observed in response to treatment with the γ-secretase inhibitor, compound E. Co-treatment of cells with albumin and an EGF-R inhibitor, AG-1478, resulted in significant inhibition of the observed pro-fibrotic effects, suggesting a major role for the EGF-R in albumin-induced fibrotic events. Albumin-induced effects on the EGF-R appeared to be mediated through inhibition of γ-secretase activity and were dependent on ERK-MAPK signalling.

Conclusions and Implications

These results provide novel insights into the mechanisms of albumin-induced fibrotic effects in tubular epithelial cells, suggesting important roles for the γ-secretase and the EGF-R. These results suggest that the proposed use of γ-secretase inhibitors as anti-fibrotic agents requires further investigation.     

Moxifloxacin modifies corneal fibroblast-to-myofibroblast differentiation

Background and Purpose

Fibroblast-to-myofibroblast differentiation is associated with scarring, an important issue in corneal surgery. Moxifloxacin (MOX), commonly applied to prevent post-operative infection, would benefit more if it modifies fibroblast-to-myofibroblast differentiation other than antimicrobial activity. Our purpose was to explore whether MOX has anti-fibrotic effect in human corneal fibroblasts (HCFs).

Experimental Approach

HCFs were incubated in MOX-containing medium concurrently with TGF-β1 (co-treatment), before (pretreatment) or after (post-treatment) adding TGF-β1. HCF contractility was evaluated with a type I collagen gel contraction assay. Expression of α-smooth muscle actin (α-SMA), Smad2, phospho-Smad2-Ser467, Smad4 and Smad7 was determined by immunoblotting. Formation of α-SMA-positive filaments and distribution of active Smad2 were observed under confocal microscopy. Expression of TGF-β receptor types I (TGFBR1) and II (TGFBR2) was assessed with flow cytometry.

Key Results

MOX did not affect gel contractility or α-SMA filament formation in HCFs without TGF-β1 stimulation. MOX did, however, retard HCF-containing gel contractility and α-SMA filament formation following TGF-β1 stimulation in the pretreatment and co-treatment groups but not in the post-treatment group. MOX blocked the expression of Smad2, phospho-Smad2-Ser467 and TGFBR1 under TGF-β1 incubation. Additionally, MOX enhanced Smad7 expression in TGF-β1-incubated HCFs, but did not interfere with TGF-β-triggered Smad2 nuclear translocation or Smad4 expression.

Conclusions and Implications

MOX inhibited TGF-β-induced fibroblast-to-myofibroblast differentiation via blocking TGFBR1 and enhancing Smad7 expression. MOX should be used before or during surgery to achieve these effects. These results suggest a de novo mechanism by which MOX participates in corneal wound healing.     

N-Acetylcysteine Effects on Transforming Growth Factor-β and Tumor Necrosis Factor-α Serum Levels as Pro-Fibrotic and Inflammatory Biomarkers in Patients Following ST-Segment Elevation Myocardial Infarction

Background and Aims

Ischemia following acute myocardial infarction (AMI) increases the level of pro-fibrotic and inflammatory cytokines, including transforming growth factor (TGF)-β and tumor necrosis factor (TNF)-α. N-acetylcysteine (NAC) has therapeutic benefits in the management of patients with AMI. To the best of our knowledge, this is the first study that has evaluated the effect of NAC on TNF-α and TGF-β levels in patients with AMI.

Methods

Following confirmation of AMI, 88 patients were randomly administered NAC 600 mg (Fluimucil^®, Zambon, Ticino, Switzerland) or placebo orally twice daily for 3 days. For quantification of TGF-β and TNF-α serum levels after 24 and 72 h of NAC or placebo administration, peripheral venous blood (10 mL) samples were collected at these time points.

Results

Comparisons between levels of TGF-β and TNF-α after 24 and 72 h within the NAC or placebo groups revealed that there was not any significant difference except for TGF-β levels in the placebo group, which increased significantly over time (p = 0.042). Significant relationships existed between patients’ ejection fraction (p = 0.005) and TGF-β levels.

Conclusions

Receiving NAC could prevent TGF-β levels from increasing after 72 h as compared with not receiving NAC. As TGF-β had strong correlations with the ejection fraction, its antagonism seems to be important in the prevention of remodeling.     

The anti-fibrotic effects of epigallocatechin-3-gallate in bile duct-ligated cholestatic rats and human hepatic stellate LX-2 cells are mediated by the PI3K/Akt/Smad pathway

Aim:

(−)-Epigallocatechin-3-gallate (EGCG) is one of the most abundant polyphenols in green tea with strong antioxidant activity and various therapeutic effects. In this study, we investigated the anti-fibrotic effects of EGCG and underlying mechanisms in bile duct-ligated (BDL) rats and a liver fibrosis model in vitro.

Methods:

BDL rats were treated with EGCG (25 mg·kg⁻¹·d⁻¹, po) for 14 d, and then the serum, bile and liver samples were collected. Liver fibrosis was assessed by serum, urine and bile biochemistry analyses and morphological studies of liver tissues. TGF-β1-stimulated human hepatic stellate LX-2 cells were used as a liver fibrosis model in vitro. The expression of liver fibrogenic genes and signaling proteins in the PI3K/Akt/Smad pathway was examined using Western blotting and/or real-time PCR.

Results:

In BDL rats, EGCG treatment significantly ameliorates liver necrosis, inflammation and fibrosis, and suppressed expression of the genes associated with liver inflammation and fibrogenesis, including TNF-α, IL-1β, TGF-β1, MMP-9, α-SMA, and COL1A1. In LX-2 cells, application of EGCG (10, 25 μmol/L) dose-dependently suppressed TGF-β1-stimulated expression of COL1A1, MMP-2, MMP-9, TGF-β1, TIMP1, and α-SMA. Furthermore, EGCG significantly suppressed the phosphorylation of Smad2/3 and Akt in the livers of BDL rats and in TGF-β1-stimulated LX-2 cells. Application of {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002, a specific inhibitor of PI3K, produced similar effects as EGCG did in TGF-β1-stimulated LX-2 cells, but co-application of EGCG and {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 did not produce additive effects.

Conclusion:

EGCG exerts anti-fibrotic effects in BDL rats and TGF-β1-stimulated LX-2 cells in vitro via inhibiting the PI3K/Akt/Smad pathway.     

SAR150640, a selective β3-adrenoceptor agonist,prevents human myometrial remodelling and activation of matrix metalloproteinase in an in vitro model of chorioamnionitis

Background and purpose:

The uterine pathophysiology underlying inflammatory conditions such as chorioamnionitis remains largely unclear. As we have shown that β₃-adrenoceptors act as regulators of myometrial inflammation, we wanted to investigate the potential role of β₃-adrenoceptors in preventing uterine remodelling induced by inflammation.

Experimental approach:

The consequences of human chorioamnionitis on myometrial remodelling were characterized by Sirius Red staining and metalloproteinase (MMP) expression, and compared with the effects of incubating human myometrial samples with Escherichia coli lipopolysaccharide (LPS) in vitro. We also assessed the effect of SAR150640, a selective β₃-adrenoceptor agonist, on the production and activity of MMPs.

Key results:

Chorioamnionitis was associated with a 46% decrease in total collagen, as well as over-expression of MMP2 (+61%) and MMP9 (+84%); both effects were reproduced by incubation with LPS (10 µg·mL⁻¹, 48 h). LPS-induced over-expression of MMP2 and MMP9 in normal human myometrium was paralleled by an overactivity of the proteins. Both over-expression and overactivity were prevented by the β₃-adrenoceptor agonist SAR150640 in a concentration-dependent manner. SAR150640, by itself, did not exhibit any effect on MMP production in control tissues.

Conclusions and implications:

This study shows that inflammation was associated with an intense remodelling of human myometrium, a process likely to be explained by MMP activation. Our study emphasizes the potential therapeutic relevance of β₃-adrenoceptor agonists to the treatment of preterm labour and other uterine inflammatory conditions.     

Glycogen synthase kinase-3 (GSK-3) regulates TGF-β1-induced differentiation of pulmonary fibroblasts

Background

Chronic lung diseases such as asthma, COPD and pulmonary fibrosis are characterized by abnormal extracellular matrix (ECM) turnover. TGF-β is a key mediator stimulating ECM production by recruiting and activating lung fibroblasts and initiating their differentiation process into more active myofibroblasts. Glycogen synthase kinase-3 (GSK-3) regulates various intracellular signalling pathways; its role in TGF-β₁-induced myofibroblast differentiation is currently largely unknown.

Purpose

To determine the contribution of GSK-3 signalling in TGF-β₁-induced myofibroblast differentiation.

Experimental Approach

We used MRC5 human lung fibroblasts and primary pulmonary fibroblasts of individuals with and without COPD. Protein and mRNA expression were determined by immunoblotting and RT-PCR analysis respectively.

Results

Stimulation of MRC5 and primary human lung fibroblasts with TGF-β₁ resulted in time- and dose-dependent increases of α-sm-actin and fibronectin expression, indicative of myofibroblast differentiation. Pharmacological inhibition of GSK-3 by SB216763 dose-dependently attenuated TGF-β₁-induced expression of these myofibroblasts markers. Moreover, silencing of GSK-3 by siRNA or pharmacological inhibition by CT/CHIR99021 fully inhibited the TGF-β₁-induced expression of α-sm-actin and fibronectin. The effect of GSK-3 inhibition on α-sm-actin expression was similar in fibroblasts from individuals with and without COPD. Neither smad, NF-κB nor ERK1/2 were involved in the inhibitory actions of GSK-3 inhibition by SB126763 on myofibroblast differentiation. Rather, SB216763 increased the phosphorylation of CREB, which in its phosphorylated form acts as a functional antagonist of TGF-β/smad signalling.

Conclusion and Implication

We demonstrate that GSK-3 signalling regulates TGF-β₁-induced myofibroblast differentiation by regulating CREB phosphorylation. GSK-3 may constitute a useful target for treatment of chronic lung diseases.     

Evaluation of antitumor activity of a TGF-beta receptor I inhibitor (SD-208) on human colon adenocarcinoma

Background

Transforming growth factor-β (TGF-β) pathway is involved in primary tumor progression and in promoting metastasis in a considerable proportion of human cancers such as colorectal cancer (CRC). Therefore, blockage of TGF-β pathway signaling via an inhibitor could be a valuable tool in CRC treatment.

Methods

To evaluate the efficacy of systemic targeting of the TGF-β pathway for therapeutic effects on CRC, we investigated the effects of a TGβRI (TGF-β receptor 1) or TβRI kinase inhibitor, SD-208, on SW-48, colon adenocarcinoma cells. In this work, in vitro cell proliferation was studied by methyl thiazolyl tetrazolium (MTT) and bromo-2′-deoxyuridine (BrdU) assays. Also, the histopathological and immunohistochemical evaluations were conducted by hematoxylin and eosin, and Ki-67 and CD34 markers were stained, respectively.

Results

Our results showed no significant reduction in cell proliferation and vessel formation (170 ± 70 and 165 ± 70, P > 0.05) in treated SW-48 cells with SD-208 compared to controls.

Conclusion

Our data suggested that SD-208 could not significantly reduce tumor growth and angiogenesis in human colorectal cancer model at least using SW-48 cells.     

Pharmacological inhibition of myostatin/TGF-β receptor/pSmad3 signaling rescues muscle regenerative responses in mouse model of type 1 diabetes

Aim:

To study the influence of acute experimental diabetes on the regenerative potential of muscle stem (satellite) cells in mice.

Methods:

Male C57BL/6 young mice were injected with a single dose of streptozotocin (STZ, 180 mg/kg, ip) to induce diabetes. The diabetic mice were treated with insulin (0.75 U/kg, ip), follistatin (12 μg/kg, im) or Alk5 inhibitor (5 μmol/L per kg, sc) once a day. On the first day when high glucose levels were found, cardiotoxin (CTX) was focally injected into tibialis anterior and gastronemius muscles of the mice. The muscles were harvested 3 d and 5 d after CTX injection, and myofibers and satellite cells were isolated. Quantitative ex-vivo and in-vivo assays of myogenic potential were used to evaluate the muscle regenerative responses.

Results:

The satellite cells from the diabetic mice 3 d after CTX injection fail to activate, and the repair of muscle deteriorates, resembling that observed in old control mice. Furthermore, the satellite cells have excessive levels of myostatin, TGF-β receptor 1, pSmad3 and the cell cycle inhibitor p15, while the level of TGF-β1 remain unchanged. Treatment of the diabetic mice with insulin rescued muscle regenerative responses, and restored the expression levels of myostatin, TGF-β receptor 1, pSmad3, and p15 to those similar of healthy controls. Treatment of the diabetic mice with the myostatin antagonist follistatin, or with the Alk5 inhibitor of TGF-β receptor 1 (which did not diminish the blood glucose levels) rescued muscle regenerative responses and attenuated the myostatin/TGFβ receptor/pSmad3 signaling.

Conclusion:

The muscle regenerative responses are incapacitated and repair of the tissue fails within hours after the initiation of hyperglycemia in a mouse model of type 1 diabetes, but stem cell function is rescued by insulin, as well as follistatin or an Alk5 inhibitor that blocks TGF-β receptor signaling.     

Curcumin attenuates cardiac fibrosis in spontaneously hypertensive rats through PPAR-γ activation

Aim:

To investigate the effects of curcumin (Cur) on cardiac fibrosis in spontaneously hypertensive rats (SHRs) and the mechanisms underlying the anti-fibrotic effect of Cur in rat cardiac fibroblasts (CFs) in vitro.

Methods:

SHRs were orally treated with Cur (100 mg·kg⁻¹·d⁻¹) or Cur (100 mg·kg⁻¹·d⁻¹) plus the PPAR-γ antagonist GW9662 (1 mg·kg⁻¹·d⁻¹) for 12 weeks. Cultured CFs were treated with angiotensin II (Ang II, 0.1 μmol/L) in vitro. The expression of relevant proteins and mRNAs was analyzed using Western blotting and real-time PCR, respectively. The expression and activity of peroxisome proliferator-activated receptor-γ (PPAR-γ) were detected using Western blotting and a DNA-binding assay, respectively.

Results:

Treatment of SHRs with Cur significantly decreased systolic blood pressure, blood Ang II concentration, heart weight/body weight ratio and left ventricle weight/body weight ratio, with concurrently decreased expression of connective tissue growth factor (CTGF), plasminogen activator inhibitor (PAI)-1, collagen III (Col III) and fibronectin (FN), and increased expression and activity of PPAR-γ in the left ventricle. Co-treatment with GW9662 partially abrogated the anti-fibrotic effects of Cur in SHRs. Pretreatment of CFs with Cur (5, 10, 20 μmol/L) dose-dependently inhibited Ang II-induced expression of CTGF, PAI-1, Col III and FN, and increased the expression and binding activity of PPAR-γ. Pretreatment with GW9662 partially reversed anti-fibrotic effects of Cur in vitro. Furthermore, pretreatment of CFs with Cur inhibited Ang II-induced expression of transforming growth factor-β1 (TGF-β1) and phosphorylation of Smad2/3, which were reversed by GW9662.

Conclusion:

Cur attenuates cardiac fibrosis in SHRs and inhibits Ang II-induced production of CTGF, PAI-1 and ECM in CFs in vitro. The crosstalk between PPAR-γ and TGF-β1/Smad2/3 signaling is involved in the anti-fibrotic and anti-proliferative effects of Cur.     

β-Asarone protects PC12 cells against OGD/R-induced injury via attenuating Beclin-1-dependent autophagy

Aim:

To explore the effects of β-asarone from Acorus Tatarinowii Schott on autophagy in an ischemic stroke model of PC12 cells.

Methods:

The ischemic stroke model of PC12 cells was made by OGD/R (2 h oxygen-glucose deprivation followed by 24 h reperfusion). Drug administration was started 1 h before OGD and last for 3 h. Then the cells were incubated in the drug-free and full culture medium under normoxic conditions for 24 h. After the treatments, Beclin-1, intracellular free calcium concentration ([Ca²⁺]_i) and mitochondrial membrane potential (MMP) were analyzed using flow cytometry. Cell viability was measured using MTT assay. Cell morphology was studied under inverted phase contrast microscope, and autophagosomes were observed under transmission electron microscope.

Results:

Pretreatment with β-asarone (20, 30, or 45 μg/mL) or the calcium channel antagonist nimodipine (10 μmol/L) significantly increased the cell viability and MMP, and decreased Beclin-1 expression and [Ca²⁺]_i in OGD/R-treated PC12 cells. Under inverted phase contrast microscope, pretreatment with β-asarone or nimodipine dramatically increase the number of cells and improved the cellular morphology. Autophagosomes were found in OGD/R-treated PC12 cells as well as in drug plus OGD/R-treated PC12 cells.

Conclusion:

β-Asarone protects PC12 cells against OGD/R-induced injury partly due to attenuating Beclin-1-dependent autophagy caused by decreasing [Ca²⁺]_i and increasing MMP.     

Over-production of nitric oxide by oxidative stress-induced activation of the TGF-β1/PI3K/Akt pathway in mesangial cells cultured in high glucose

Aim:

To investigate whether NO over-production in rat mesangial cells cultured in high glucose (HG) is related to activation of the TGF-β1/PI3K/Akt pathway.

Methods:

Rat mesangial cells line (HBZY-1) was exposed to HG (24.44 mmol/L) or H₂O₂ (10 μmol/L) for 16 h. NO release was quantified using the Griess assay. The TGF-β1 level was measured using ELISA. The protein expression of p-Akt, t-Akt, Bim, and iNOS was examined by Western blotting. The mRNA levels of TGF-β1 and Bim were measured using RT-PCR. The cell proliferation rate was estimated using a BrdU incorporation assay.

Results:

Treatment of the cells with HG, H₂O₂, or TGF-β1 (5 ng/mL) significantly increased the NO level that was substantially inhibited by co-treatment with the NADPH oxidase inhibitor diphenylene iodonium (DPI), TGF-β1 inhibitor SB431542, or PI3K inhibitor {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002. Both HG and H₂O₂ significantly increased the protein and mRNA levels of TGF-β1 in the cells, and HG-induced increases of TGF-β1 protein and mRNA were blocked by co-treatment with DPI. Furthermore, the treatment with HG or H₂O₂ significantly increased the expression of phosphorylated Akt and iNOS and cell proliferation rate, which was blocked by co-treatment with DPI, SB431542, or {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002. Moreover, the treatment with HG or H₂O₂ significantly inhibited Bim protein and mRNA expression, which was reversed by co-treatment with DPI, SB431542, or {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002.

Conclusion:

The results demonstrate that high glucose causes oxidative stress and NO over-production in rat mesangial cells in vitro via decreasing Bim and increasing iNOS, which are at least partially mediated by the TGF-β1/PI3K/Akt pathway.     

Amelioration of glomerulosclerosis with all-trans retinoic acid is linked to decreased plasminogen activator inhibitor-1 and α-smooth muscle actin

Aim:

To examine the effects of all-trans retinoic acid (atRA) on renal morphology and function as well as on renal plasminogen activator inhibitor-1 (PAI-1) expression and plasmin activity in rats with 5/6 nephrectomy.

Methods:

Adult male Sprague Dawley rats were given 5/6 nephrectomy or sham operation. Renal function was measured 2 weeks later. The nephrectomized rats were assigned to groups matched for proteinuria and treated with vehicle or atRA (5 or 10 mg/kg by gastric gavage once daily) for the next 12 weeks. Rats with sham operation were treated with vehicle. At the end of the treatments, kidneys were collected for histological examination, Western blot analysis, and enzymatic activity measurements.

Results:

The 5/6 nephrectomy promoted hypertension, renal dysfunction, and glomerulosclerosis. These changes were significantly reduced in the atRA-treated group. The expressions of PAI-1 and α-smooth muscle actin (α-SMA) were significantly increased in the vehicle-treated nephrectomized rats. Treatment with atRA significantly reduced the expressions of PAI-1 and α-SMA. However, plasmin activity remained unchanged following atRA treatment.

Conclusion:

Treatment with atRA ameliorates glomerulosclerosis and improves renal function in rats with 5/6 nephrectomy. This is associated with a decrease in PAI-1 and α-SMA, but not with a change in plasmin activity.     

α-Mangostin suppresses human gastric adenocarcinoma cells in vitro via blockade of Stat3 signaling pathway

Aim:

To investigate the anti-tumor effects of α-mangostin, a major xanthone identified in the pericarp of mangosteen (Garcinia mangostana Linn), against human gastric adenocarcinoma cells in vitro, and the mechanisms of the effects.

Methods:

Human gastric adenocarcinoma cell lines BGC-823 and SGC-7901 were treated with α-mangostin. The cell viability was measured with MTT assay, and cell apoptosis was examined using flow cytometry and TUNEL assay. The expression of the relevant proteins was detected using Western blot.

Results:

Treatment with α-mangostin (3–10 μg/mL) inhibited the viability of both BGC-823 and SGC-7901 cells in dose- and time-manners. Furthermore, α-mangostin (7 μg/mL) time-dependently increased the apoptosis index of the cancer cells, reduced the mitochondrial membrane potential of the cancer cells, and significantly increased the release of cytochrome c and AIF into cytoplasm. Moreover, the α-mangostin treatment markedly suppressed the constitutive Stat3 protein activation, and Stat3-regulated Bcl-xL and Mcl-1 protein levels in the cancer cells.

Conclusion:

The anti-tumor effects of α-mangostin against human gastric adenocarcinoma cells in vitro can be partly attributed to blockade of Stat3 signaling pathway.     

Antidepressant Effects of Abscisic Acid Mediated by the Downregulation of Corticotrophin-Releasing Hormone Gene Expression in Rats

Background:

Corticotrophin-releasing hormone (CRH) is considered to be the central driving force of the hypothalamic-pituitary-adrenal axis, which plays a key role in the stress response and depression. Clinical reports have suggested that excess retinoic acid (RA) is associated with depression. Abscisic acid (ABA) and RA are direct derivatives of carotenoids and share a similar molecular structure. Here, we proposed that ABA also plays a role in the regulation of CRH activity sharing with the RA signaling pathway.

Methods:

[₃H]-ABA radioimmunoassay demonstrated that the hypothalamus of rats shows the highest concentration of ABA compared with the cortex and the hippocampus under basal conditions.

Results:

Under acute stress, ABA concentrations increased in the serum, but decreased in the hypothalamus and were accompanied by increased corticosterone in the serum and c-fos expression in the hypothalamus. Moreover, chronic ABA administration increased sucrose intake and decreased the mRNA expression of CRH and retinoic acid receptor alpha (RARα) in the hypothalamus of rats. Furthermore, ABA improved the symptom of chronic unpredictable mild stress in model rats, as indicated by increased sucrose intake, increased swimming in the forced swim test, and reduced mRNA expression of CRH and RARα in the rat hypothalamus. In vitro, CRH expression decreased after ABA treatment across different neural cells. In BE(2)-C cells, ABA inhibited a series of retinoid receptor expression, including RARα, a receptor that could facilitate CRH expression directly.

Conclusions:

These results suggest that ABA may play a role in the pathogenesis of depression by downregulating CRH mRNA expression shared with the RA signaling pathway.