Upregulation of OASIS/CREB3L1 in podocytes contributes to the disturbance of kidney homeostasis

Metabolism at the crossroads of inflammation and fibrosis in chronic kidney disease

Chronic kidney disease (CKD), defined as persistent (>3 months) kidney functional loss, has a growing prevalence (>10% worldwide population) and limited treatment options. Fibrosis driven by the aberrant accumulation of extracellular matrix is the final common pathway of nearly all types of chronic repetitive injury in the kidney and is considered a hallmark of CKD. Myofibroblasts are key extracellular matrix-producing cells that are activated by crosstalk between damaged tubules and immune cells. Emerging evidence indicates that metabolic alterations are crucial contributors to the pathogenesis of kidney fibrosis by affecting cellular bioenergetics and metabolite signalling. Immune cell functions are intricately connected to their metabolic characteristics, and kidney cells seem to undergo cell-type-specific metabolic shifts in response to damage, all of which can determine injury and repair responses in CKD. A detailed understanding of the heterogeneity in metabolic reprogramming of different kidney cellular subsets is essential to elucidating communication processes between cell types and to enabling the development of metabolism-based innovative therapeutic strategies against CKD.

CREB3L1/OASIS: cell cycle regulator and tumor suppressor

Cell cycle checkpoints detect DNA errors, eventually arresting the cell cycle to promote DNA repair. Failure of such cell cycle arrest causes aberrant cell proliferation, promoting the pathogenesis of multiple diseases, including cancer. Endoplasmic reticulum (ER) stress transducers activate the unfolded protein response, which not only deals with unfolded proteins in ER lumen but also orchestrates diverse physiological phenomena such as cell differentiation and lipid metabolism. Among ER stress transducers, cyclic AMP-responsive element-binding protein 3-like protein 1 (CREB3L1) [also known as old astrocyte specifically induced substance (OASIS)] is an ER-resident transmembrane transcription factor. This molecule is cleaved by regulated intramembrane proteolysis, followed by activation as a transcription factor. OASIS is preferentially expressed in specific cells, including astrocytes and osteoblasts, to regulate their differentiation. In accordance with its name, OASIS was originally identified as being upregulated in long-term-cultured astrocytes undergoing cell cycle arrest because of replicative stress. In the context of cell cycle regulation, previously unknown physiological roles of OASIS have been discovered. OASIS is activated as a transcription factor in response to DNA damage to induce p21-mediated cell cycle arrest. Although p21 is directly induced by the master regulator of the cell cycle, p53, no crosstalk occurs between p21 induction by OASIS or p53. Here, we summarize previously unknown cell cycle regulation by ER-resident transcription factor OASIS, particularly focusing on commonalities and differences in cell cycle arrest between OASIS and p53. This review also mentions tumorigenesis caused by OASIS dysfunctions, and OASIS's potential as a tumor suppressor and therapeutic target.

Sex-specific molecular signature of mouse podocytes in homeostasis and in response to pharmacological challenge with rapamycin

BACKGROUND

Sex differences exist in the prevalence and progression of major glomerular diseases. Podocytes are the essential cell-type in the kidney which maintain the physiological blood-urine barrier, and pathological changes in podocyte homeostasis are critical accelerators of impairment of kidney function. However, sex-specific molecular signatures of podocytes under physiological and stress conditions remain unknown. This work aimed at identifying sexual dimorphic molecular signatures of podocytes under physiological condition and pharmacologically challenged homeostasis with mechanistic target of rapamycin (mTOR) inhibition. mTOR is a crucial regulator involved in a variety of physiological and pathological stress responses in the kidney and inhibition of this pathway may therefore serve as a general stress challenger to get fundamental insights into sex differences in podocytes.

METHODS

The genomic ROSAmT/mG-NPHS2 Cre mouse model was used which allows obtaining highly pure podocyte fractions for cell-specific molecular analyses, and vehicle or pharmacologic treatment with the mTOR inhibitor rapamycin was performed for 3 weeks. Subsequently, deep RNA sequencing and proteomics were performed of the isolated podocytes to identify intrinsic sex differences. Studies were supplemented with metabolomics from kidney cortex tissues.

RESULTS

Although kidney function and morphology remained normal in all experimental groups, RNA sequencing, proteomics and metabolomics revealed strong intrinsic sex differences in the expression levels of mitochondrial, translation and structural transcripts, protein abundances and regulation of metabolic pathways. Interestingly, rapamycin abolished prominent sex-specific clustering of podocyte gene expression and induced major changes only in male transcriptome. Several sex-biased transcription factors could be identified as possible upstream regulators of these sexually dimorphic responses. Concordant to transcriptomics, metabolomic changes were more prominent in males. Remarkably, high number of previously reported kidney disease genes showed intrinsic sexual dimorphism and/or different response patterns towards mTOR inhibition.

CONCLUSIONS

Our results highlight remarkable intrinsic sex-differences and sex-specific response patterns towards pharmacological challenged podocyte homeostasis which might fundamentally contribute to sex differences in kidney disease susceptibilities and progression. This work provides rationale and an in-depth database for novel targets to be tested in specific kidney disease models to advance with sex-specific treatment strategies.

Metabolism and bioenergetics in the pathophysiology of organ fibrosis

Fibrosis is the tissue scarring characterized by excess deposition of extracellular matrix (ECM) proteins, mainly collagens. A fibrotic response can take place in any tissue of the body and is the result of an imbalanced reaction to inflammation and wound healing. Metabolism has emerged as a major driver of fibrotic diseases. While glycolytic shifts appear to be a key metabolic switch in activated stromal ECM-producing cells, several other cell types such as immune cells, whose functions are intricately connected to their metabolic characteristics, form a complex network of pro-fibrotic cellular crosstalk. This review purports to clarify shared and particular cellular responses and mechanisms across organs and etiologies. We discuss the impact of the cell-type specific metabolic reprogramming in fibrotic diseases in both experimental and human pathology settings, providing a rationale for new therapeutic interventions based on metabolism-targeted antifibrotic agents.

Isorhamnetin inhibits hypertrophic scar formation through TGF-β1/Smad and TGF-β1/CREB3L1 signaling pathways

Background

Hypertrophic scar (HS) is a common fibrotic skin disease that occurs secondary to burns or injuries. The activation of the TGF-β signaling pathway contributes immensely to HS formation. Isorhamnetin (ISO) is a type of flavonoid compound that exerts an antifibrotic effect via TGF-β signaling suppression. However, whether ISO can inhibit HS formation via TGF-β signaling is yet to be elucidated. This study aimed to examine the influence of ISO on HS pathogenesis and TGF-β signaling, especially the downstream molecules and networks of TGF-β signaling that facilitate HS formation.

Methods

Hypertrophic scar fibroblasts (HSFBs) were isolated from human HS tissues. The in vitro proliferation, migration, contractile ability, cell cycle, and apoptosis of HSFBs after ISO treatment were determined using cell viability assay, EdU staining, wound healing assay, collagen gel contraction assay, and flow cytometry. The expressions of genes and proteins involved in TGF-β signaling and its downstream molecules in ISO-treated HSFBs were determined using quantitative PCR (qPCR), immunofluorescence, and western blotting. In vivo, a rabbit HS model was established, and the effects of ISO on rabbit HS formation were investigated using histological analysis, immunohistochemical staining, and qPCR.

Results

In vitro studies indicated that ISO treatment suppressed the proliferation, migration, and contractile ability of HSFBs; attenuated the expressions of COL Ⅰ, COL Ⅲ, and α-SMA; and inhibited TGF-β1 signaling-induced activation of HSFBs by decreasing the levels of phosphorylated Smad2/3 and cleaved CREB3L1 in a dose-dependent manner. Furthermore, ISO augmented apoptosis and G2 phase cell cycle arrest of HSFBs by upregulating the expressions of the proapoptotic proteins Bax and cleaved caspase-3 and downregulating the expression of the antiapoptotic protein Bcl-2. In vivo studies revealed that ISO ameliorated HS formation in the rabbit ear by lowering the scar elevation index, attenuating the collagen density, facilitating the regular arrangement of collagen fibers, and downregulating the expressions of TGF-β1, CREB3L1, COL Ⅰ, COL Ⅲ, and α-SMA.

Conclusions

ISO suppressed HS pathogenesis by dampening TGF-β1/Smad and TGF-β1/CREB3L1 signaling pathways, which suggests that it may serve as a candidate inhibitor of TGF-β1 signaling and a promising anti-HS drug with a high therapeutic potential.

Central role of podocytes in mediating cellular cross talk in glomerular health and disease

Podocytes are highly specialized epithelial cells that surround the capillaries of the glomeruli in the kidney. Together with the glomerular endothelial cells, these postmitotic cells are responsible for regulating filtrate from the circulating blood with their organized network of interdigitating foot processes that wrap around the glomerular basement membrane. Although podocyte injury and subsequent loss is the hallmark of many glomerular diseases, recent evidence suggests that the cell-cell communication between podocytes and other glomerular and nonglomerular cells is critical for the development and progression of kidney disease. In this review, we highlight these key cellular pathways of communication and how they might be a potential target for therapy in glomerular disease. We also postulate that podocytes might serve as a central hub for communication in the kidney under basal conditions and in response to cellular stress, which may have implications for the development and progression of glomerular diseases.

The Regulatory Network of CREB3L1 and Its Roles in Physiological and Pathological Conditions

CREB3 subfamily belongs to the bZIP transcription factor family and comprises five members. Normally they are located on the endoplasmic reticulum (ER) membranes and proteolytically activated through RIP (regulated intramembrane proteolysis) on Golgi apparatus to liberate the N-terminus to serve as transcription factors. CREB3L1 acting as one of them transcriptionally regulates the expressions of target genes and exhibits distinct functions from the other members of CREB3 family in eukaryotes. Physiologically, CREB3L1 involves in the regulation of bone morphogenesis, neurogenesis, neuroendocrine, secretory cell differentiation, and angiogenesis. Pathologically, CREB3L1 implicates in the modulation of osteogenesis imperfecta, low grade fibro myxoid sarcoma (LGFMS), sclerosing epithelioid fibrosarcoma (SEF), glioma, breast cancer, thyroid cancer, and tissue fibrosis. This review summarizes the upstream and downstream regulatory network of CREB3L1 and thoroughly presents our current understanding of CREB3L1 research progress in both physiological and pathological conditions with special focus on the novel findings of CREB3L1 in cancers.

Regulatory mechanisms of the cAMP-responsive element binding protein 3 (CREB3) family in cancers

The CREB3 family of proteins, encompassing CREB3 and its four homologs (CREB3L1, CREB3L2, CREB3L3, and CREB3L4), exerts pivotal control over cellular protein metabolism in response to unfolded protein reactions. Under conditions of endoplasmic reticulum stress, activation of the CREB3 family occurs through regulated intramembrane proteolysis within the endoplasmic reticulum membrane. Perturbations in the function and expression of the CREB3 family have been closely associated with the development of diverse diseases, with a particular emphasis on cancer. Recent investigations have shed light on the indispensable role played by CREB3 family members in modulating the onset and progression of various human cancers. This comprehensive review endeavors to provide an in-depth examination of the involvement of CREB3 family members in distinct human cancer types, accentuating their significance in the pathogenesis of cancer and the manifestation of malignant phenotypes.

From Phenomenon to Essence: A Newly Involved lncRNA Kcnq1ot1 Protective Mechanism of Bone Marrow Mesenchymal Stromal Cells in Liver Cirrhosis

Bone marrow mesenchymal stromal cells (BMSCs) have a protective effect against liver cirrhosis. Long noncoding RNAs (lncRNAs) play crucial roles in the progression of liver cirrhosis. Therefore, it is aimed to clarify the lncRNA Kcnq1ot1 involved protective mechanism of BMSCs in liver cirrhosis. This study found that BMSCs treatment attenuates CCl4 -induced liver cirrhosis in mice. Additionally, the expression of lncRNA Kcnq1ot1 is upregulated in human and mouse liver cirrhosis tissues, in addition to TGF-β1-treated LX2 cells and JS1 cells. The expression of Kcnq1ot1 in liver cirrhosis is reversed with BMSCs treatment. The knockdown of Kcnq1ot1 alleviated liver cirrhosis both in vivo and in vitro. Fluorescence in situ hybridization (FISH) confirms that Kcnq1ot1 is mainly distributed in the cytoplasm of JS1 cells. It is predicted that miR-374-3p can directly bind with lncRNA Kcnq1ot1 and Fstl1, which is verified via luciferase activity assay. The inhibition of miR-374-3p or the overexpression of Fstl1 can attenuate the effect of Kcnq1ot1 knockdown. In addition, the transcription factor Creb3l1 is upregulated during JS1 cells activation. Moreover, Creb3l1 can directly bind to the Kcnq1ot1 promoter and positively regulate its transcription. In conclusion, BMSCs alleviate liver cirrhosis by modulating the Creb3l1/lncRNA Kcnq1ot1/miR-374-3p/Fstl1 signaling pathway.

Arid5a/IL-6/PAI-1 Signaling Is Involved in the Pathogenesis of Lipopolysaccharide-Induced Kidney Injury

A systemic inflammatory response leads to widespread organ dysfunction, such as kidney dysfunction. Plasminogen activator inhibitor-1 (PAI-1) is involved in the pathogenesis of inflammatory kidney injury; however, the regulatory mechanism of PAI-1 in injured kidneys remains unclear. PAI-1 is induced by interleukin (IL)-6 in patients with sepsis. In addition, the stabilization of IL-6 is regulated by the adenine-thymine-rich interactive domain-containing protein 5a (Arid5a). Therefore, the aim of the present study was to examine the involvement of Arid5a/IL-6/PAI-1 signaling in lipopolysaccharide (LPS)-induced inflammatory kidney injury. LPS treatment to C57BL/6J mice upregulated Pai-1 mRNA in the kidneys. Enzyme-linked immunosorbent assay (ELISA) revealed that PAI-1 expression was induced in the culture supernatants of LPS-treated human umbilical vein endothelial cells, but not in those of LPS-treated human kidney 2 (HK-2) cells, a tubular cell line. Combined with single-cell analysis, endothelial cells were found to be responsible for PAI-1 elevation in LPS-treated kidneys. Administration of TM5441, a PAI-1 inhibitor, reduced the urinary albumin/creatinine ratio, concomitant with downregulation of Il-6 and Arid5a mRNA expressions. IL-6 treatment in LPS model mice further upregulated Pai-1 mRNA expression compared with LPS alone, accompanied by renal impairment. Furthermore, the expression of Il-6 and Pai-1 mRNA was lower in Arid5a knockout mice than in wild-type mice after LPS treatment. Taken together, the vicious cycle of Arid5a/IL-6/PAI-1 signaling is involved in LPS-induced kidney injury.