BRCC36 prevents vascular calcification in chronic kidney disease through the β-catenin signalling pathway

BRCC36 regulates β-catenin ubiquitination to alleviate vascular calcification in chronic kidney disease

BACKGROUND

The prevalence of vascular calcification (VC) in chronic kidney disease (CKD) patients remains substantial, but currently, there are no effective pharmaceutical therapies available. BRCA1/BRCA2-containing complex subunit 36 (BRCC36) has been implicated in osteoblast osteogenic conversion; however, its specific role in VC remains to be fully elucidated. The aim of this study was to investigate the role and underlying mechanisms of BRCC36 in VC.

METHODS

The association between BRCC36 expression and VC was examined in radial arteries from patients with CKD, high-adenine-induced CKD mice, and vascular smooth muscle cells (VSMCs). Western blotting, real-time polymerase chain reaction, immunofluorescence, and immunohistochemistry were used to analyse gene expression. Gain- and loss-of-function experiments were performed to comprehensively investigate the effects of BRCC36 on VC. Coimmunoprecipitation and TOPFlash luciferase assays were utilized to further investigate the regulatory effects of BRCC36 on the Wnt/β-catenin pathway.

RESULTS

BRCC36 expression was downregulated in human calcified radial arteries, calcified aortas from CKD mice, and calcified VSMCs. VSMC-specific BRCC36 overexpression alleviated calcium deposition in the vasculature, whereas BRCC36 depletion aggravated VC progression. Furthermore, BRCC36 inhibited the osteogenic differentiation of VSMCs in vitro. Rescue experiments revealed that BRCC36 exerts the protective effects on VC partly by regulating the Wnt/β-catenin signalling pathway. Mechanistically, BRCC36 inhibited the Wnt/β-catenin pathway by decreasing the K63-linked ubiquitination of β-catenin. Additionally, pioglitazone attenuated VC partly through upregulating BRCC36 expression.

CONCLUSIONS

Our research results emphasize the critical role of the BRCC36-β-catenin axis in VC, suggesting that BRCC36 or β-catenin may be promising therapeutic targets to prevent the progression of VC in CKD patients.

BRCC3 Regulation of ALK2 in Vascular Smooth Muscle Cells: Implication in Pulmonary Hypertension

BACKGROUND

An imbalance of antiproliferative BMP (bone morphogenetic protein) signaling and proliferative TGF-β (transforming growth factor-β) signaling is implicated in the development of pulmonary arterial hypertension (PAH). The posttranslational modification (eg, phosphorylation and ubiquitination) of TGF-β family receptors, including BMPR2 (bone morphogenetic protein type 2 receptor)/ALK2 (activin receptor-like kinase-2) and TGF-βR2/R1, and receptor-regulated Smads significantly affects their activity and thus regulates the target cell fate. BRCC3 modifies the activity and stability of its substrate proteins through K63-dependent deubiquitination. By modulating the posttranslational modifications of the BMP/TGF-β-PPARγ pathway, BRCC3 may play a role in pulmonary vascular remodeling, hence the pathogenesis of PAH.

METHODS

Bioinformatic analyses were used to explore the mechanism by which BRCC3 deubiquitinates ALK2. Cultured pulmonary artery smooth muscle cells (PASMCs), mouse models, and specimens from patients with idiopathic PAH were used to investigate the rebalance between BMP and TGF-β signaling in regulating ALK2 phosphorylation and ubiquitination in the context of pulmonary hypertension.

RESULTS

BRCC3 was significantly downregulated in PASMCs from patients with PAH and animals with experimental pulmonary hypertension. BRCC3, by de-ubiquitinating ALK2 at Lys-472 and Lys-475, activated receptor-regulated Smad1/5/9, which resulted in transcriptional activation of BMP-regulated PPARγ, p53, and Id1. Overexpression of BRCC3 also attenuated TGF-β signaling by downregulating TGF-β expression and inhibiting phosphorylation of Smad3. Experiments in vitro indicated that overexpression of BRCC3 or the de-ubiquitin-mimetic ALK2-K472/475R attenuated PASMC proliferation and migration and enhanced PASMC apoptosis. In SM22α-BRCC3-Tg mice, pulmonary hypertension was ameliorated because of activation of the ALK2-Smad1/5-PPARγ axis in PASMCs. In contrast, Brcc3-/- mice showed increased susceptibility of experimental pulmonary hypertension because of inhibition of the ALK2-Smad1/5 signaling.

CONCLUSIONS

These results suggest a pivotal role of BRCC3 in sustaining pulmonary vascular homeostasis by maintaining the integrity of the BMP signaling (ie, the ALK2-Smad1/5-PPARγ axis) while suppressing TGF-β signaling in PASMCs. Such rebalance of BMP/TGF-β pathways is translationally important for PAH alleviation.

Methionine Promotes Milk Synthesis through the BRCC36-BRG1-mTOR Signaling Axis in Mammary Epithelial Cells

Methionine (Met) functions as a key stimulator on the mTOR signaling pathway and milk synthesis, but the molecular mechanism remains incompletely understood. We investigated the regulatory roles of BRCC36 in Met-stimulated milk lipid and protein synthesis, cell proliferation, and the mTOR signaling pathway. Knockdown of BRCC36 promoted milk lipid and protein synthesis in HC11 cells as well as cell proliferation by increasing the levels of mTOR gene transcription and protein phosphorylation. Conversely, the gene activation of BRCC36 had opposite effects. Furthermore, BRCC36 gene activation completely blocked Met stimulation on the BRG1 protein level and mTOR mRNA level and protein phosphorylation. BRCC36 bound to BRG1, and BRCC36 and BRG1 bound to the same region on the mTOR promoter. BRCC36 inhibited the BRG1 protein level and the binding of BRG1 to the mTOR promoter. Met decreased the BRCC36 protein level, and this effect was significantly attenuated by MG132 but not affected by cycloheximide or chloroquine. We further showed that Met increased BRCC36 ubiquitination degradation. Our findings reveal that Met promotes milk lipid and protein synthesis in MECs through the BRCC36-BRG1-mTOR signaling axis.

Vascular, valvular and kidney calcification manifested in mouse models of adenine-induced chronic kidney disease

BACKGROUND

Ectopic calcification (EC) involves multiple organ systems in chronic kidney disease (CKD). Previous CKD-animal models primarily focused on a certain histological abnormality but did not show the correlation with calcified development among various tissues. This study compared calcified deposition in various tissues during CKD progression in mice.

METHODS

Male 8-week-old C57BL/6J mice were randomly allocated to the seven groups: a basic, adenine, high-phosphorus, or adenine and high-phosphorus diet for 12-16 weeks (Ctl16, A12, P16, or AP16, respectively); an adenine diet for 4-6 weeks; and a high-phosphorus or adenine and high-phosphorus diet for 10-12 weeks (A6 + P10, A4 + P12, or A4 + AP12, respectively).

RESULTS

Compared to the Ctl16 mice, the P16 mice only displayed a slight abnormality in serum calcium and phosphorus; the A12 mice had the most serious kidney impairment; the A4 + P12 and A6 + P10 mice had similar conditions of CKD, mineral abnormalities, and mild calcification in the kidney and aortic valves; the A4 + AP12 and AP16 groups had severe kidney impairment, mineral abnormalities and calcification in the kidneys, aortic valves and aortas. Furthermore, calcium-phosphate particles were deposited not only in the tubulointerstitial compartment but in the glomerular and tubular basement membrane. The elemental composition of EC in various tissues matched the calcification of human cardiovascular tissue as determined by energy dispersive spectroscopy.

CONCLUSIONS

The severity of CKD was unparalleled with the progression of mineral metabolism disorder and EC. Calcification was closely related in different tissues and observed in the glomerular and tubular basement membranes.

Vascular calcification: Molecular mechanisms and therapeutic interventions

Vascular calcification (VC) is recognized as a pathological vascular disorder associated with various diseases, such as atherosclerosis, hypertension, aortic valve stenosis, coronary artery disease, diabetes mellitus, as well as chronic kidney disease. Therefore, it is a life-threatening state for human health. There were several studies targeting mechanisms of VC that revealed the importance of vascular smooth muscle cells transdifferentiating, phosphorous and calcium milieu, as well as matrix vesicles on the progress of VC. However, the underlying molecular mechanisms of VC need to be elucidated. Though there is no acknowledged effective therapeutic strategy to reverse or cure VC clinically, recent evidence has proved that VC is not a passive irreversible comorbidity but an active process regulated by many factors. Some available approaches targeting the underlying molecular mechanism provide promising prospects for the therapy of VC. This review aims to summarize the novel findings on molecular mechanisms and therapeutic interventions of VC, including the role of inflammatory responses, endoplasmic reticulum stress, mitochondrial dysfunction, iron homeostasis, metabolic imbalance, and some related signaling pathways on VC progression. We also conclude some recent studies on controversial interventions in the clinical practice of VC, such as calcium channel blockers, renin-angiotensin system inhibitions, statins, bisphosphonates, denosumab, vitamins, and ion conditioning agents.