Thyroid Hormone-Induced Differentiation of Astrocytes is Associated with Transcriptional Upregulation of β-arrestin-1 and β-adrenergic Receptor-Mediated Endosomal Signaling

Role of ARRB1 in prognosis and immunotherapy: A Pan-Cancer analysis

Background: β-arrestin1 (ARRB1), was originally identified as a multifunctional adaptor protein. Although ARRB1 has recently been shown to also play an important role in tumor growth, metastasis, inflammation, and immunity, its relationship with distinct tumor types and the tumor immune microenvironment remains unclear.

Methods: We analyzed the ARRB1 expression profile and clinical characteristics in 33 cancer types using datasets from The Cancer Genome Atlas (TCGA) database. Clinical parameters such as patient survival, tumor stage, age, and gender were used to assess the prognostic value of ARRB1. The Human Protein Atlas (HPA) database was used to explore ARRB1 protein expression data. ESTIMATE and CIBERSORT algorithms were performed to assess immune infiltration. Furthermore, putative correlations between ARRB1 and tumor-infiltrating immune cells, the signatures of T-cell subtypes, immunomodulators, the tumor mutation burden (TMB), Programmed cell death ligand 1 (PD-L1), and microsatellite instability (MSI) were also explored. Gene functional enrichment was determined using GSEA. GSE40435 and GSE13213 cohorts were used to validate the correlation of ARRB1 with KIRC and LUAD clinicopathological parameters. Finally, the relationship between ARRB1 and immunotherapeutic responses was assessed using three independent immunotherapy cohorts, namely, GSE67501, GSE168204, and IMvigor210.

Results: We found that ARRB1 expression levels were lower in 17 tumor tissues than in the corresponding normal tissues. We further found that ARRB1 expression was significantly correlated with tumor stage in BRCA, ESCA, KIRC, TGCT, and THCA, while in some tumors, particularly KIRC and LUAD, ARRB1 expression was associated with better prognosis. ARRB1 expression was also positively correlated with the stromal score or the immune score in some tumors. Regarding immune cell infiltration, ARRB1 expression in DLBC was positively correlated with M1 macrophage content and negatively correlated with B-cell infiltration. Additionally, there was a broad correlation between ARRB1 expression and three classes of immunomodulators. Furthermore, high ARRB1 expression levels were significantly correlated with some tumor immune-related pathways. Finally, ARRB1 expression was significantly associated with MSI, PD-L1, and TMB in some tumors and with the efficacy of immune checkpoint inhibitors (ICIs) in melanoma.

Conclusion: ARRB1 has prognostic value in malignant tumors, especially in KIRC and LUAD. At the same time, ARRB1 was closely correlated with the tumor immune microenvironment and indicators of immunotherapy efficacy, indicating its great potential as a reliable marker for predicting the efficacy of immunotherapy.

Beta-arrestin 2 mediates cardiac hypertrophy induced by thyroid hormones via AT1R

We have previously reported that angiotensin II receptor type 1 (AT1R) contributes to the hypertrophic effects of thyroid hormones (TH) in cardiac cells. Even though evidence indicates crosstalks between TH and AT1R, the underlying mechanisms are poorly understood. Beta-arrestin (ARRB) signaling has been described as noncanonical signal transduction pathway that exerts important effects in the cardiovascular system through G-protein-coupled receptors, as AT1R. Herein, we investigated the contribution of ARRB signaling in TH-induced cardiomyocyte hypertrophy. Primary cardiomyocyte cultures were treated with Triiodothyronine (T3) to induce cell hypertrophy. T3 rapidly activates extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, which was partially inhibited by AT1R blockade. Also, ERK1/2 inhibition attenuated the hypertrophic effects of T3. ARRB2 was upregulated by T3, and small interfering RNA assays revealed the role of ARRB2-but not ARRB1-on ERK1/2 activation and cardiomyocyte hypertrophy. Corroborating these findings, the ARRB2-overexpressed cells showed increased expression of hypertrophic markers, which were attenuated by ERK1/2 inhibition. Immunocytochemistry and immunoprecipitation assays revealed the increased expression of nuclear AT1R after T3 stimulation and the increased interaction of AT1R/ARRB2. The inhibition of endocytosis also attenuated the T3 effects on cardiac cells. Our results evidence the contribution of ARRB2 on ERK1/2 activation and cardiomyocyte hypertrophy induced by T3 via AT1R.

β-Arrestin1-mediated decrease in endoplasmic reticulum stress impairs intestinal stem cell proliferation following radiation

Gastrointestinal toxicity limits the clinical application of abdominal and pelvic radiotherapy and currently has no effective treatment. Intestinal leucine-rich-repeat-containing GPCR 5 (Lgr5)-positive stem cell depletion and loss of proliferative ability due to radiation may be the primary factors causing intestinal injury following radiation. Here, we report the critical role of β-arrestin1 (βarr1) in radiation-induced intestinal injury. Intestinal βarr1 was highly expressed in radiation enteritis and in a radiation model. βarr1 knockout (KO) or knockdown mice exhibited increased proliferation in intestinal Lgr5+ stem cell, crypt reproduction, and survival following radiation. Unexpectedly, the beneficial effects of βarr1 deficiency on intestinal stem cells in response to radiation were compromised when the endoplasmic reticulum stress-related protein kinase RNA-like ER kinase (PERK)/eukaryotic initiation factor-2α (eIF2α) pathway was inhibited, and this result was further supported in vitro. Furthermore, we found that βarr1 knockdown with small interfering RNA significantly enhanced intestinal Lgr5⁺ stem cell proliferation after radiation via directly targeting PERK. βarr1 offers a promising target for mitigating radiation-induced intestinal injury.-Liu, Z., Jiang, J., He, Q., Liu, Z., Yang, Z., Xu, J., Huang, Z., Wu, B. β-Arrestin1-mediated decrease in endoplasmic reticulum stress impairs intestinal stem cell proliferation following radiation.

Docosahexaenoic Acid (DHA) Induced Morphological Differentiation of Astrocytes Is Associated with Transcriptional Upregulation and Endocytosis of β2-AR

Docosahexaenoic acid (DHA), an important ω-3 fatty acid, is abundantly present in the central nervous system and is important in every step of brain development. Much of this knowledge has been based on studies of the role of DHA in the function of the neurons, and reports on its effect on the glial cells are few and far between. We have previously reported that DHA facilitates astrocyte differentiation in primary culture. We have further explored the signaling mechanism associated with this event. It was observed that a sustained activation of the extracellular signal-regulated kinase (ERK) appeared to be critical for DHA-induced differentiation of the cultured astrocytes. Prior exposure to different endocytic inhibitors blocked both ERK activation and differentiation of the astrocytes during DHA treatment suggesting that the observed induction of ERK-2 was purely endosomal. Unlike the β₁-adrenergic receptor (β₁-AR) antagonist, atenolol, pre-treatment of the cells with the β₂-adrenergic receptor (β₂-AR) antagonist, ICI-118,551 inhibited the DHA-induced differentiation process, indicating a downstream involvement of β₂-AR in the differentiation process. qRT-PCR and western blot analysis demonstrated a significant induction in the mRNA and protein expression of β₂-AR at 18-24 h of DHA treatment, suggesting that the induction of β₂-AR may be due to transcriptional upregulation. Moreover, DHA caused activation of PKA at 6 h, followed by activation of downstream cAMP response element-binding protein, a known transcription factor for β₂-AR. Altogether, the observations suggest that DHA upregulates β₂-AR in astrocytes, which undergo endocytosis and signals for sustained endosomal ERK activation to drive the differentiation process.

Regulation of Gene Expression by Thyroid Hormone in Primary Astrocytes: Factors Influencing the Genomic Response

Astrocytes mediate the action of thyroid hormone in the brain on other neural cells through the production of the active hormone triiodothyronine (T3) from its precursor thyroxine. T3 has also many effects on the astrocytes in vivo and in culture, but whether these actions are directly mediated by transcriptional regulation is not clear. In this work, we have analyzed the genomic response to T3 of cultured astrocytes isolated from the postnatal mouse cerebral cortex using RNA sequencing. Cultured astrocytes express relevant genes of thyroid hormone metabolism and action encoding type 2 deiodinase (Dio2), Mct8 transporter (Slc16a2), T3 receptors (Thra1 and Thrb), and nuclear corepressor (Ncor1) and coactivator (Ncoa1). T3 changed the expression of 668 genes (4.5% of expressed genes), of which 117 were responsive to T3 in the presence of cycloheximide. The Wnt and Notch pathways were downregulated at the posttranscriptional level. Comparison with the effect of T3 on astrocyte-enriched genes in mixed cerebrocortical cultures isolated from fetal cortex revealed that the response to T3 is influenced by the degree of astrocyte maturation and that, in agreement with its physiological effects, T3 promotes the transition between the fetal and adult patterns of gene expression.

Thyroid Hormone and Astrocyte Differentiation

Thyroid hormones (THs) have important contributions to the development of the mammalian brain, targeting its actions on both neurons and glial cells. Astrocytes, which constitute about half of the glial cells, characteristically undergo dramatic changes in their morphology during development and such changes become necessary for the proper development of the brain. Interestingly, a large number of studies have suggested that THs play a profound role in such morphological maturation of the astrocytes. This review discusses the present knowledge on the mechanisms by which THs elicit progressive differentiation and maturation of the astrocytes. As a prelude, information on astrocyte morphology during development and its regulations, the role of THs in the various functions of astrocyte shall be dealt with for a thorough understanding of the subject of this review.