TRB3, up-regulated in kidneys of rats with type1 diabetes, mediates extracellular matrix accumulation in vivo and in vitro

Integration of dietary nutrition and TRIB3 action into diabetes mellitus

Despite intensive studies for decades, the common mechanistic correlations among the underlying pathology of diabetes mellitus (DM), its complications, and effective clinical treatments remain poorly characterized. High-quality diets and nutrition therapy have played an indispensable role in the management of DM. More importantly, tribbles homolog 3 (TRIB3), a nutrient-sensing and glucose-responsive regulator, might be an important stress-regulatory switch, linking glucose homeostasis and insulin resistance. Therefore, this review aimed to introduce the latest research progress on the crosstalk between dietary nutrition intervention and TRIB3 in the development and treatment of DM. This study also summarized the possible mechanisms involved in the signaling pathways of TRIB3 action in DM, in order to gain an in-depth understanding of dietary nutrition intervention and TRIB3 in the pathogenesis of DM at the organism level.

Syringin alleviates hepatic fibrosis by enhancing autophagic flux and attenuating ER stress-TRIB3/SMAD3 in diabetic mice

Type 2 diabetes mellitus (T2DM) is a key risk factor for the developing of metabolic liver injury and easily evolving to advanced fibrosis. Syringin (SYR), isolated from Acanthopanax senticosus, has anti-inflammatory, anti-oxidant, and anti-apoptotic properties. However, its hepatoprotective effects and mechanisms in T2DM-induced liver fibrosis remain unclear. Here, we investigated whether syringin (SYR) could serve as a therapeutic agent for liver fibrosis and its mechanism in high-fat diet (HFD)/streptozotocin (STZ)-induced type 2 diabetic mice. C57BL/6 mice were induced with T2DM via HFD and STZ injection and treated with different doses of SYR. Serum lipid parameters and liver function indicators were measured, and hepatic histology and fibrosis were examined. The mechanism of SYR was explored through molecular analyses Results demonstrated SYR improved oral glucose tolerance, decreased the levels of ALT, AST, and AKP, and reduced hepatic lipid deposition in diabetic mice. Moreover, SYR ameliorated epithelial-to-mesenchymal transition to reverse hepatic fibrosis via suppressing TRIB3-SMAD3 interaction to restrain nuclear localization of SMAD3. Strikingly, SYR reversed hyperglycemia-induced deficiency in autophagic flux by regulation of Raptor/mTORC1, triggering nuclear translocation of TFEB to improve autophagosome-lysosomal fusion. In brief, SYR potentially ameliorates hepatic injury and fibrosis by enhancing autophagic flux and inhibing TRIB3 activation in diabetic mice.

TRIB3 Mediates Fibroblast Activation and Fibrosis though Interaction with ATF4 in IPF

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease characterized by fibroblast activation, excessive deposition of extracellular matrix, and progressive scarring; the pathogenesis remains elusive. The present study explored the role of Tribbles pseudokinase 3 (TRIB3), a well-known stress and metabolic sensor, in IPF. TRIB3 is down-regulated in the lungs of IPF patients in comparison to control subjects. Deficiency of TRIB3 markedly inhibited A549 epithelial cells' proliferation and migration, significantly reducing wound healing. Conversely, overexpression of TRIB3 promoted A549 cell proliferation and transmigration while it inhibited its apoptosis. Meanwhile, overexpressed TRIB3 inhibited fibroblast activation and decreased ECM synthesis and deposition in MRC5 cells. TRIB3 attenuated pulmonary fibrosis by negative regulation of ATF4, while TRIB3 expression markedly inhibited ATF4 promoter-driven transcription activity and down-regulated ATF4 expression. A co-culture system showed that TRIB3 is important to maintain the normal epithelial-mesenchymal crosstalk and regulate fibroblast activation. Taken together, our data suggested that an axis of TRIB3-ATF4 is a key mediator in IPF which might be a potential target for fibroproliferative lung disease treatment.

Tribbles 3 deficiency promotes atherosclerotic fibrous cap thickening and macrophage-mediated extracellular matrix remodelling

Tribbles 3 (TRIB3) modulates lipid and glucose metabolism, macrophage lipid uptake, with a gain-of-function variant associated with increased cardiovascular risk. Here we set out to examine the role of this pseudokinase in atherosclerotic plaque development. Human endarterectomy atherosclerotic tissue specimens analysed by immunofluorescence showed upregulated TRIB3 in unstable plaques and an enrichment in unstable regions of stable plaques. Atherosclerosis was induced in full body Trib3^KO and Trib3^WT littermate mice by injecting mPCSK9 expressing adeno-associated virus and western diet feeding for 12 weeks. Trib3^KO mice showed expanded visceral adipose depot while circulatory lipid levels remained unaltered compared to wildtype mice. Trib3^KO mice aortae showed a reduced plaque development and improved plaque stability, with increased fibrous cap thickness and collagen content, which was accompanied by increased macrophage content. Analysis of both mouse and human macrophages with reduced TRIB3 expression showed elongated morphology, increased actin expression and altered regulation of genes involved in extracellular matrix remodelling. In summary, TRIB3 controls plaque development and may be atherogenic in vivo. Loss of TRIB3 increases fibrous cap thickness via altered metalloproteinase expression in macrophages, thus inhibiting collagen and elastic fibre degradation, suggesting a role for TRIB3 in the formation of unstable plaques.

TRAF6 Suppresses the Development of Pulmonary Fibrosis by Attenuating the Activation of Fibroblasts

Pulmonary fibrosis (PF) has a high mortality rate, and its pathogenesis is unknown. TNF receptor-associated factor 6 (TRAF6), a signal transducer for inflammatory signaling, plays crucial roles in the pathogenesis of immune diseases. However, its function in PF remains unknown. Herein, we demonstrated that lungs from mice with bleomycin (BLM)-induced PF were characterized by decreased expression of TRAF6 in lung fibroblasts. Enhancing TRAF6 expression protected mice from BLM-induced PF coupled with a significant reduction in fibroblast differentiation. Furthermore, we demonstrated that overexpression of TRAF6 reversed the activation of myofibroblasts from PF mice by reducing the expression of Wnt3a and subsequently suppressing Wnt/β-catenin signaling. Additionally, the abundance of Tribbles pseudokinase 3 (TRIB3), a stress sensor, was negatively correlated with the abundance of TRAF6 in lung fibroblasts. TRIB3 overexpression decreased TRAF6 abundance by reducing TRAF6 stability in lung fibroblasts during PF. Mechanistic studies revealed that TRIB3 bound to TRAF6 and accelerated basal TRAF6 ubiquitination and degradation. Collectively, our data indicate that reduced TRAF6 expression in fibroblasts is essential for the progression of PF, and therefore, genetically increasing TRAF6 expression or disrupting the TRIB3-TRAF6 interaction could be potential therapeutic strategies for fibroproliferative lung diseases in clinical settings.

Tribbles homolog 3 contributes to high glucose-induced injury in retinal pigment epithelial cells via binding to growth factor receptor-bound 2

Diabetic retinopathy (DR) is the most typical complication of diabetes, which severely threatens sight. Tribbles homolog 3 (TRB3), a kind of pseudokinase, is discovered to be highly expressed in diabetes and retinas after retinal detachment. TRB3 expression in human retinal pigment epithelial (hRPE) cells exposed to different concentrations of glucose was tested by RT-qPCR and western blot. Then, cells were induced with 30 mM high glucose (HG) to establish a DR cell model. Following TRB3 knockdown, cell viability estimation employed CCK-8 assay. The mRNA levels of inflammatory factors were detected by RT-qPCR. Reactive oxygen species (ROS) level was measured by DCFH-DA assay, and levels of oxidative stress markers were evaluated applying corresponding kits. Cell apoptosis was assayed by TUNEL assay and western blot. Following, the growth factor receptor-bound 2 (GRB2) expression was also examined by RT-qPCR and western blot. The interaction between TRB3 and GRB2 was verified by Co-IP assay. After GRB2 was overexpressed in HG-induced hRPE cells transfected with shRNA-TRB3, functional experiments were conducted again. The results manifested that TRB3 expression was elevated under HG conditions. Deficiency of TRB3 enhanced the viability while alleviated inflammation, oxidative stress, and apoptosis in HG-induced hRPE cells. GRB2 was also increased in HG-exposed hRPE cells. Moreover, GRB2 had a strong affinity with TRB3 and positively regulated by TRB3. After GRB2 overexpression, the effects of TRB3 knockdown on HG-stimulated hRPE cells were all reversed. Briefly, this study confirmed the promoting role of TRB3/GRB2 axis in the progression of DR.

Endoplasmic reticulum stress-dependent activation of TRB3-FoxO1 signaling pathway exacerbates hyperglycemic nephrotoxicity: Protection accorded by naringenin

Endoplasmic reticulum (ER) dysfunction contributes greatly to the pathophysiology of hyperglycemic nephrotoxicity. This study unravels the critical role of Tribbles 3 (TRB3)-Forkhead box O1 (FoxO1) signaling pathway during hyperglycemic renal toxicity. It also uncovers the novel role of Naringenin, a flavanone, in regulating ER stress in proximal tubular cells, NRK 52E, and kidneys of streptozotocin/nicotinamide induced experimental diabetic Wistar rats. Results demonstrate that expression of ER stress marker proteins including phosphorylated protein kinase ER like kinase (p-PERK), phosphorylated eukaryotic Initiation Factor 2α (p-eIF2α), X Box Binding Protein 1 spliced (XBP1s), Activating Transcription Factor 4 (ATF4) and C/EBP Homologous Protein (CHOP) were upregulated in diabetic kidneys indicating the activation of ER stress response due to nephrotoxicity. Treatment with Naringenin reduced the expression of TRB3, an ER stress-inducible pseudokinase, both in vitro and in vivo. Gene silencing of TRB3 enhanced Akt and FoxO1 phosphorylation and alleviated FoxO1 mediated apoptosis during hyperglycemic nephrotoxicity. Notably, TRB3 gene silencing effects were comparable to the response with Naringenin treatment. Prevention of nuclear colocalization of ATF4 and CHOP in Naringenin treated cells was evident. Naringenin also reduced insulin resistance, apoptosis and glycogen accumulation along with enhancement of glucose tolerance in diabetic rats. Prevention of ultrastructural aberrations in the ER of hyperglycemic renal cells by Naringenin confirmed its anti-ER stress effects. These findings affirm that activation of TRB3-FoxO1 signaling is critical in the pathogenesis of hyperglycemia-induced renal toxicity and protective effect of Naringenin via modulation of ER stress may be exploited as a novel approach for its management.

TRIB3‒GSK-3β interaction promotes lung fibrosis and serves as a potential therapeutic target

Pulmonary fibrosis (PF) is a chronic, progressive, fatal interstitial lung disease with limited available therapeutic strategies. We recently reported that the protein kinase glycogen synthase kinase-3β (GSK-3β) interacts with and inactivates the ubiquitin-editing enzyme A20 to suppress the degradation of the transcription factor CCAAT/enhancer-binding protein beta (C/EBPβ) in alveolar macrophages (AMs), resulting in a profibrotic phenotype of AMs and promoting the development of PF. Here, we showed that chronic lung injury upregulated the stress response protein tribbles homolog 3 (TRIB3), which interacted with GSK-3β and stabilized GSK-3β from ubiquitination and degradation. Elevated GSK-3β expression phosphorylated A20 to inhibit its ubiquitin-editing activity, causing the accumulation of C/EBPβ and the production of several profibrotic factors in AMs and promoting PF development. Activated C/EBPβ, in turn, increased the transcription of TRIB3 and GSK-3β, thereby establishing a positive feedback loop in AMs. The knockdown of TRIB3 expression or the pharmacologic disruption of the TRIB3‒GSK-3β interaction was an effective PF treatment. Our study reveals an intact profibrotic axis of TRIB3‒GSK-3β‒A20‒C/EBPβ in AMs, which represents a target that may provide a promising treatment strategy for PF.

Sarcopenia is attenuated by TRB3 knockout in aging mice via the alleviation of atrophy and fibrosis of skeletal muscles

BACKGROUND

Sarcopenia causes several adverse events in elderly people. Muscle fibre atrophy and interstitial fibrosis are the main histopathological changes in sarcopenia and account for decreased muscle function. Tribbles homologue 3 (TRB3) was previously reported to exhibit age-related expression and play a vital role in cell proliferation, differentiation, and fibrosis. We aimed to investigate how TRB3 affects sarcopenia.

METHODS

Wild-type and TRB3 knockout C57/BL6J mice were randomly divided into young and old groups. Exercise capacity was evaluated, and single-muscle function was detected by electrophysiological techniques, after which the mice were sacrificed to collect their gastrocnemius muscles for assessment of atrophy and fibrosis by histopathological and molecular biological methods. TRB3 expression, autophagy level, and MAPK signalling pathway activity were evaluated through western blotting. The interaction of TRB3 with P62 and the association between TRB3 and the MAPK signalling pathway were detected by co-immunoprecipitation.

RESULTS

In aged mice, exercise capacity and cross-sectional area of skeletal muscle fibres were decreased significantly, whereas TRB3, atrophy-related markers atrogin 1 and MuRF 1, and interstitial fibrosis, including collagen volume fraction, contents of collagens I and III, and ratio of collagens I to III, were increased significantly (P < 0.05 for all). Following TRB3 knockout, the cross-sectional area of muscle fibres, mainly fast fibres, was elevated (P < 0.05 for both), the atrogin 1 expression was decreased (P = 0.0163), and the corresponding tetanic force of fast muscles was increased (P = 0.0398). Conversely, interstitial fibrosis was substantially decreased and exercise capacity was significantly increased in the knockout mice. In terms of the underlying mechanisms, the autophagy receptor p62 was markedly increased and the MAPK signalling pathway was activated in aged skeletal muscles, which might be attributed to the interaction of TRB3 with p62 and MAPKKs, including MEK1/MEK2, MEK3/MEK6, and MEK4/MKK4. Notably, TRB3 knockout reduced the accumulation of p62 and LC3 (P < 0.05 for both), decreased the phosphorylation of JNK (P = 0.0015), and increased p38 phosphorylation (P = 0.0021).

CONCLUSIONS

TRB3 knockout in mice attenuated muscle fibre atrophy and reduced skeletal muscle fibrosis by increasing autophagy and inhibiting the MAPK signalling pathway. Correspondingly, in aged knockout mice, exercise capacity was improved. Interfering with TRB3 expression in aged skeletal muscles may serve as a target for the prevention and treatment of age-related sarcopenia.

Effects of ATRA on diabetic rats with renal ischemia-reperfusion injury

Purpose

To explore the role of all-trans retinoic acid (ATRA) in renal ischemia/reperfusion injury of diabetic rats.

Methods

Sixty adult male rats were randomly divided into 6 groups, including sham group (S group), ischemia-reperfusion group (I/R group), ischemia-reperfusion+ATRA group (A group), diabetic group (D group), diabetic ischemia-reperfusion group (DI/R group), diabetic ischemia-reperfusion +ATRA group (DA group). The levels of creatinine (Cr), cystatin C (Cys-C) and β2-microglobulin (β2-MG) were measured. Morphology of renal tissue was observed under light microscope.

Results

DJ-1, Nrf2, HO-1 and caspase-3 were detected by western blot. DJ-1, Nrf2, HO-1 and caspase-3 in I/R group, D group and DI/R group was higher than that in S group. Compared with I/R group, Nrf2 and HO-1 in A group was decreased, but caspase-3 was increased. However, Nrf2 in DA group was higher than that in DI/R group, HO-1 and caspase-3 in DA group were lower than that in DI/R group. Compared with group S, Cr, Cys-C and β2-MG in I/R group, A group, D group, and DI/R group were higher. Whereas the levels of Cr, Cys-C, β2-MG and renal injury score in DA group were lower than those in DI/R group.

Conclusion

ATRA has a protective effect on renal ischemia-reperfusion injury in diabetic rats, maybe relating to DJ/Nrf2 pathway.

Expression of TRB3 promotes epithelial‑mesenchymal transition of MLE‑12 murine alveolar type II epithelial cells through the TGF‑β1/Smad3 signaling pathway

The aim of the present study was to investigate whether the expression of tribbles pseudokinase 3 (TRB3) is involved in pulmonary interstitial fibrosis and to examine the possible mechanisms. The expression of TRB3 in murine alveolar type II epithelial cells (MLE‑12 cells) following transforming growth factor β1 (TGF‑β1) stimulation was assessed using various techniques, including western blot and reverse transcription‑quantitative polymerase chain reaction assays. TRB3 overexpression and downregulation models were used to evaluate the impact of TRB3 on the TGF‑β1‑induced epithelial‑mesenchymal transition (EMT) of MLE‑12 cells. The downregulation of TRB3 was induced by RNA interference. The expression of TRB3 was significantly increased in MLE‑12 cells following the activation of TGF‑β1 (P<0.05). The overexpression of TRB3 was found to promote activation of the TGF‑β1/Smad3 signaling pathway, EMT, and the upregulated expression of β‑catenin and EMT‑related genes and proteins (P<0.05), whereas the downregulation of TRB3 attenuated the promoting effect on EMT induced by TGF‑β1. In addition, the overexpression of TRB3 inhibited MLE‑12 cell proliferation by stimulating apoptosis, leading to the formation of pulmonary fibrosis (PF). The positive feedback loop demonstrated that TGF‑β1 induced the expression of TRB3, and TRB3, in turn, stimulated EMT and promoted the onset of PF through activation of the TGF‑β1/Smad3 signaling pathway. Therefore, TRB3 may promote the formation of PF through the TGF‑β1/Smad3 signaling pathway.

Silencing of TRB3 Ameliorates Diabetic Tubule Interstitial Nephropathy via PI3K/AKT Signaling in Rats

Background

Nephropathy, a chronic progressive kidney disease often characterized by glomeruli scarring and sclerosis, is a major complication of diabetes mellitus. Development of nephropathologic lesions has been shown to be associated with suppressed AKT phosphorylation and elevated level of apoptosis. Moreover, it has been established that the TRB3 gene is capable of inhibiting AKT phosphorylation and promoting apoptosis.

Material/Methods

In this study, we injected TRB3 siRNA into Wistar rats with type 1 diabetes, and monitored development of nephropathy in the rats. Urinary albumin excretion and serum creatinine were used as primary indicators, and nephritic histology was also examined. We also measured the serum level of pro-inflammatory cytokines collagen expression, and phosphorylation of PI3K and AKT proteins in the kidneys.

Results

By silencing the TRB3 gene with siRNA, diabetic-induced nephropathy symptoms were alleviated, such as increased serum creatinine level and urinary albumin secretion. Additionally, histological examination showed lower levels of nephropathic lesions, and samples of the kidneys showed less accumulation of collagen proteins. Levels of serum cytokines, including TNF-α, IL-1β, and IL-6, were also lowered, whereas phosphorylation levels of PI3K and AKT were increased. In summary, TRB3 silencing in diabetic rats had a significant ameliorative effect on their nephropathy.

Conclusions

Silencing of TRB3 has a significant ameliorative effect on diabetic nephropathy in rats.