Bilirubin impacts microglial autophagy via the Akt-mTOR signaling pathway

Potential value of quantitative magnetic susceptibility mapping for the assessment of neonatal hyperbilirubinemic brain injury: A retrospective cohort study based on propensity score matching method

PURPOSE

The aim of the study was to explore the iron contend of patients with neonatal hyperbilirubinemia (NHB) and its correlation with clinical indicators.

METHODS

A total of 34 patients with NHB and 15 subjects in healthy controls (HC) group were included and underwent laboratory examinations and magnetic resonance imaging (MRI) for QSM. The propensity score matching (PSM) method was used to perform 1:1 no-return matching of subjects in the NHB and HC groups, and then the correlation analysis of the susceptibility values of each brain region with the clinical parameter was explored again, as well as the factors influencing the susceptibility values of each brain region were probed by multivariate linear regression analyses. The area under the curve (AUC) for each brain region was obtained via receiver operating characteristic (ROC) curve analysis.

RESULTS

The susceptibility values of the left putamen and left globus pallidum in NHB group were significantly greater than those in the HC group after PSM. And the susceptibility values of the left putamen were significantly positively correlated with serum bilirubin concentrations after PSM. The multiple linear regression analysis revealed that the susceptibility values of the left putamen were influenced by age and serum bilirubin concentrations. According to the ROC curves, the susceptibility values of the left putamen and left globus pallidus has the ability to diagnose NHB.

CONCLUSION

This study revealed that the initial brain damage manifestation in NHB patients may be abnormal iron content in the left putamen and left globus pallidus.

Glycyrrhizin alleviates brain injury in necrotizing enterocolitis model mice by suppressing HMGB1/TLR4 pathway

BACKGROUND

Systemic inflammation from necrotizing enterocolitis (NEC) can adversely affect the developing central nervous system. Evidence indicates that gut-derived high mobility group box 1 (HMGB1) can migrate to the brain and activate microglia.

OBJECTIVE

To determine if glycyrrhizin, an HMGB1 inhibitor, can reduce microglial pyroptosis and neuroinflammatory injury in NEC by modulating the HMGB1/ Toll-like receptor 4 (TLR4) pathway.

METHODS

HMGB1 levels were analyzed in clinical NEC samples. NEC models were induced through hypoxia, cold exposure, and overfeeding. BV2 microglial cells were stimulated with lipopolysaccharide (LPS) to mimic NEC-induced inflammation. Histological assessments were performed on the intestines and brain. Cell proliferation was evaluated employing the cell counting kit-8 (CCK-8) assay. Real-time quantitative polymerase chain reaction (RT-qPCR) quantified mRNA levels of HMGB1, TLR4, nuclear factor kappa B p65 (NF-κB p65), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, IL-6, and IL-18. Protein expression was analyzed using western blotting, ELISA, immunohistochemistry, and immunofluorescence for key markers. Small interfering RNAs (siRNAs) targeted HMGB1 and TLR4.

RESULTS

Elevated levels of HMGB1 were observed in both clinical NEC samples and the NEC mouse model, with higher concentrations detected in feces, cerebrospinal fluid, and brain tissue. In the NEC patients, Spearman analysis revealed a significant correlation between elevated HMGB1 levels in CSF and fecal supernatant. Treatment with glycyrrhizin appeared to mitigate brain damage in the NEC mice and seemed to reduce LPS-induced inflammation in BV2 microglial cells. Additionally, glycyrrhizin enhanced the expression of tight junction protein occludin and myelin basic protein (MBP), which may be associated with improvements in behavioral performance observed in the NEC mice. Furthermore, glycyrrhizin treatment resulted in a reduction of key inflammatory mediators, including NF-κB p65, NOD-like receptor protein 3 (NLRP3), Caspase-1 p20, gasdermin D (GSDMD), IL-1β, and IL-18 in brain tissue and BV2 microglial cells. These results suggest that glycyrrhizin may exert its effects, at least in part, through modulation of the HMGB1/TLR4 signaling pathway.

CONCLUSION

Glycyrrhizin effectively mitigates neuroinflammatory injury in NEC by inhibiting the HMGB1/TLR4 pathway, preserving MBP, protecting the blood-brain barrier, and reducing pyroptosis in BV2 microglial cells. These findings suggest that glycyrrhizin may provide a novel therapeutic approach for improving neurological outcomes in NEC.

TFEB signaling promotes autophagic degradation of NLRP3 to attenuate neuroinflammation in diabetic encephalopathy

Diabetic encephalopathy (DE), a neurological complication of diabetes mellitus, has an unclear etiology. Shreds of evidence show that the nucleotide-binding oligomerization domain-like receptor family protein 3 (NLRP3) inflammasome-induced neuroinflammation and transcription factor EB (TFEB)-mediated autophagy impairment may take part in DE development. The cross talk between these two pathways and their contribution to DE remains to be explored. A mouse model of type 2 diabetes mellitus (T2DM) exhibiting cognitive dysfunction was created, along with high-glucose (HG) cultured BV2 cells. Following, 3-methyladenine (3-MA) and rapamycin were used to modulate autophagy. To evaluate the potential therapeutic benefits of TFEB in DE, we overexpressed and knocked down TFEB in both mice and cells. Autophagy impairment and NLRP3 inflammasome activation were noticed in T2DM mice and HG-cultured BV2 cells. The inflammatory response caused by NLRP3 inflammasome activation was decreased by rapamycin-induced autophagy enhancement, while 3-MA treatment further deteriorated it. Nuclear translocation and expression of TFEB were hampered in HG-cultured BV2 cells and T2DM mice. Exogenous TFEB overexpression boosted NLRP3 degradation via autophagy, which in turn alleviated microglial activation as well as ameliorated cognitive deficits and neuronal damage. In addition, TFEB knockdown exacerbated neuroinflammation by decreasing autophagy-mediated NLRP3 degradation. Our findings have unraveled the pathogenesis of a previously underappreciated disease, implying that the activation of NLRP3 inflammasome and impairment of autophagy in microglia are significant etiological factors in the DE. The TFEB-mediated autophagy pathway can reduce neuroinflammation by enhancing NLRP3 degradation. This could potentially serve as a viable and innovative treatment approach for DE.NEW & NOTEWORTHY This article delves into the intricate connections between inflammation, autophagy, diabetes, and neurodegeneration, with a particular focus on a disease that is not yet fully understood-diabetic encephalopathy (DE). TFEB emerges as a pivotal regulator in balancing autophagy and inflammation in DE. Our findings highlight the crucial function of the TFEB-mediated autophagy pathway in mitigating inflammatory damage in DE, suggesting a new treatment strategy.

[Impact of chaperone-mediated autophagy on bilirubin-induced damage of mouse microglial cells]

OBJECTIVES

To investigate the effect of chaperone-mediated autophagy (CMA) on the damage of mouse microglial BV2 cells induce by unconjugated bilirubin (UCB).

METHODS

The BV2 cell experiments were divided into two parts. (1) For the CMA activation experiment: control group (treated with an equal volume of dimethyl sulfoxide), QX77 group (treated with 20 μmol/L QX77 for 24 hours), UCB group (treated with 40 μmol/L UCB for 24 hours), and UCB+QX77 group (treated with both 20 μmol/L QX77 and 40 μmol/L UCB for 24 hours). (2) For the cell transfection experiment: LAMP2A silencing control group (treated with an equal volume of dimethyl sulfoxide), LAMP2A silencing control+UCB group (treated with 40 μmol/L UCB for 24 hours), LAMP2A silencing group (treated with an equal volume of dimethyl sulfoxide), and LAMP2A silencing+UCB group (treated with 40 μmol/L UCB for 24 hours). The cell viability was assessed using the modified MTT method. The expression levels of p65, nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3), and cysteinyl aspartate specific proteinase-1 (caspase-1) were detected by Western blot. The relative mRNA expression levels of the inflammatory cytokines interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) were determined by real-time quantitative polymerase chain reaction. Levels of IL-6 and TNF-α in the cell culture supernatant were measured using ELISA. The co-localization of heat shock cognate protein 70 with p65 and NLRP3 was detected by immunofluorescence.

RESULTS

Compared to the UCB group, the cell viability in the UCB+QX77 group increased, and the expression levels of inflammation-related proteins p65, NLRP3, and caspase-1, as well as the mRNA relative expression levels of IL-1β, IL-6, and TNF-α and levels of IL-6 and TNF-α decreased (P<0.05). Compared to the control group, there was co-localization of heat shock cognate protein 70 with p65 and NLRP3 in both the UCB and UCB+QX77 groups. After silencing the LAMP2A gene, compared to the LAMP2A silencing control+UCB group, the LAMP2A silencing+UCB group showed increased expression levels of inflammation-related proteins p65, NLRP3, and caspase-1, as well as increased mRNA relative expression levels of IL-1β, IL-6, and TNF-α and levels of IL-6 and TNF-α (P<0.05).

CONCLUSIONS

CMA is inhibited in UCB-induced BV2 cell damage, and activating CMA may reduce p65 and NLRP3 protein levels, suppress inflammatory responses, and counteract bilirubin neurotoxicity.