Growth arrest and DNA damage 45γ is required for caspase-dependent renal tubular cell apoptosis

Growth arrest and DNA damage-inducible 45: a new player on inflammatory diseases

Growth arrest and DNA damage-inducible 45 (GADD45) proteins are critical stress sensors rapidly induced in response to genotoxic/physiological stress and regulate many cellular functions. Even though the primary function of the proteins is to block the cell cycle, inhibit cell proliferation, promote cell apoptosis, and repair DNA damage to cope with the damage caused by internal and external stress on the body, evidence has shown that GADD45 also has the function to modulate innate and adaptive immunity and plays a broader role in inflammatory and autoimmune diseases. In this review, we focus on the immunomodulatory role of GADD45 in inflammatory and autoimmune diseases. First, we describe the regulatory factors that affect the expression of GADD45. Then, we introduce its immunoregulatory roles on immune cells and the critical signaling pathways mediated by GADD45. Finally, we discuss its immunomodulatory effects in various inflammatory and autoimmune diseases.

Screening of key genes involved in endometritis in cows and the regulatory role of CD83 in bovine endometrial epithelial cells

Endometritis in dairy cows involves complex molecular regulatory mechanisms. Therefore, uncovering the molecular regulatory mechanisms of endometritis in dairy cows is crucial to understand its development, prevention, and treatment. This study aimed to screen and validate key genes associated with endometritis using transcriptome sequencing of blood samples and previously obtained metabolomic sequencing data. Based on gain-of-function and loss-of-function experiments on the gene, multiple techniques, including qRT-PCR, western blotting, detection of reactive oxygen species (ROS), measurement of mitochondrial membrane potential, EdU assay, flow cytometry, and CCK-8 assay were used to explore the function of the key gene in lipopolysaccharide (LPS)-stimulated bovine endometrial epithelial cells (BEECs). The results identified 536 differentially expressed genes (DEGs) between healthy cows and those with endometritis. These DEGs were significantly enriched in apoptosis and HIF-1 signaling pathways. Weighted gene co-expression network analysis of transcriptomic and metabolomic data identified CD83, CTNNAL1, LRRC25, and NR1H3 as potential key genes for endometritis in dairy cows, with CD83 being more significantly expressed in LPS-induced BEECs. Consequently, in vitro functional studies were performed on CD83. In overexpression experiments, downregulation of the expression of inflammatory markers interleukin (IL)-1β, IL-6, and IL-8 and reduced ROS release primarily indicated the role of CD83 in attenuating the inflammatory response of BEECs. Furthermore, overexpression of CD83 regulated the S/G2 phase transition of BEECs by affecting the mRNA and protein expression of proliferation marker genes, thereby promoting proliferation of BEECs. The increased EdU positivity and the cell proliferation rate further provided evidence for the promotion of cell proliferation after overexpression of CD83. Additionally, overexpression of CD83 attenuated LPS-stimulated mitochondrial damage in BEECs, as well as the downregulation of apoptosis marker gene expression. In contrast, knockdown of CD83 expression showed the opposite trend. In summary, CD83 attenuated the inflammatory response of BEECs, promoted their proliferation, and inhibited apoptosis. This study provided basic data for understanding the mechanisms of endometritis regulation at the gene level in dairy cows.

Urinary GADD45G Protein Excretion Is Associated with IgA Nephropathy Progression

Background: Growth arrest and DNA damage 45G (GADD45G) is a family of proteins involved in DNA damage response and cell growth arrest. In this study, we show evidence that urinary GADD45G protein is associated with the progression of IgA nephropathy. Methods: Patients diagnosed with IgA nephropathy without reversible acute kidney injury at study initiation and with at least one subsequent serum creatinine (SCr) measurement were included. A 50% or greater increase in SCr level was used as an endpoint for the deterioration of renal function. Enzyme-linked immunosorbent assay (ELISA) was performed using a Human GADD45G ELISA kit. Renal biopsy tissues were stained with a monoclonal mouse anti-GADD45G antibody. Results: Forty-five patients whose renal biopsy revealed IgA nephropathy were enrolled. Urinary GADD45G and urinary protein concentrations were 1.26 [0.69-2.20] μg/g creatinine and 0.65 [0.24-1.60] g/g creatinine, respectively. Urinary GADD45G showed significant positive correlations with SCr-slopes and urinary protein. The SCr-slope of the highest tertile group of urinary GADD45G (above 1.95 μg/g creatinine) was significantly higher than that of the lowest tertile group (below 0.90 μg/g). Univariate Cox regression analysis showed that urinary GADD45G was significantly associated with deterioration of renal function. A Kaplan-Meier test showed a significant difference in event-free survival for deterioration of renal function between the highest urinary GADD45G tertile group and other tertile groups. The area under the receiver operating characteristics (ROC) curve indicated urinary GADD45G had a good performance in predicting renal outcome (cut-off point 1.67 μg/g, positive predictive value 36.8%, negative predictive value 100%). Immunohistochemistry showed that GADD45G was expressed across all pathologic grades of IgA nephropathy and mainly detected in the cytoplasm of renal tubules, whereas no staining was noted in normal tissues. Conclusions: Urinary GADD45G excretion was significantly associated with kidney disease progression in patients with IgA nephropathy.

Characterization of circular RNA expression profiles in the age-related thymic involution of Magang goose

The thymus is a vital immune organ, but its function gradually declines with age. Circular RNAs (circRNAs) are related to the development of tissues and organs. In this study, bioinformatics analysis showed that 1329, 755, and 417 circRNAs were differentially expressed between the comparison groups of 6-month age (M6) and 20-embryo age (E20), 3-day post-hatch (P3), and 3-month age (M3) Magang geese, respectively. Among them, 167 circRNAs were differentially co-expressed between thymic development (E20, P3, and M3) and involution (M6). Functional analysis showed significant enrichment of phosphorylation and positive regulation of GTPase activity. Furthermore, pathway analysis has shown that glycerolipid metabolism and the Wnt signaling pathway are critical pathways in the thymic involution process. Finally, we constructed the competitive endogenous RNA (ceRNA) network. The results of this study suggest that circRNAs may be involved in the age-related thymic involution of the Magang goose.

MAGEH1 interacts with GADD45G and induces renal tubular cell apoptosis

BACKGROUND

Melanoma-associated antigen H1 (MAGEH1) is a protein that belongs to melanoma-associated antigen (MAGE) superfamily. Growth arrest and DNA damage 45G (GADD45G) is a member of the DNA damage-inducible gene family which responds to environmental stresses. We have previously shown that GADD45G is a protein that promotes apoptosis of renal tubular cells in response to a nephrotoxic injury. In this study, we show evidence that MAGEH1 interacts with GADD45G and is involved in the induction of nephrotoxin-induced apoptosis of renal tubular cells.

METHODS

Primary human renal tubular epithelial (HRE) cells and human kidney 2 (HK-2) cells were used in this study. To produce stable cell lines in which MAGEH1 expression was silenced, HRE cells were transduced with a lentiviral vector encoding a single guide RNA construct targeting the MAGEH1 gene. To knockdown GADD45G expression in HRE cells, a vector containing short hairpin RNA (shRNA) was used. We used short interfering RNAs (siRNA) to achieve transient silencing of genes in HK-2 cells. Recombinant adenoviruses were synthesized to overexpress MAGEH1 and GADD45G proteins. Human protein microarray was used to identify proteins that binds to GADD45G. Co-immunoprecipitation assays were then performed to confirm microarray results. Cell death was induced by cyclosporine A (CsA). Real-time quantitative PCR assay was used to evaluate gene expression levels. The degree of apoptosis and necrosis of cultured cells was evaluated by flow cytometry. Expression levels of caspases were examined using western blot analysis.

RESULTS

We found that GADD45G bound to one protein spotted in the protein microarray, which was subsequently identified as MAGEH1. We confirmed the interaction between GADD45G and MAGEH1 protein using the co-immunoprecipitation assay. MAGEH1 gene expression was not altered by CsA-induced cytotoxic injury, whereas GADD45G gene expression was increased significantly upon CsA treatment. MAGEH1 expression was significantly downregulated in GADD45G knockdown HRE stable cells suggesting that MAGEH1 expression may be dependent on GADD45G expression. CsA-induced apoptosis was significantly reduced in MAGEH1 knockdown HRE stable cells which led to an increased survival of these cells. Similar results were observed in GADD45G knockdown HRE stable cells. Accordingly, CsA-induced apoptosis was significantly decreased in MAGEH1 siRNA and GADD45G siRNA transfected HK-2 cells. CsA-induced activation of caspase-7 and caspase-9 was inhibited in MAGEH1 knockdown HRE stable cells, and similarly in GADD45G knockdown HRE stable cells.

CONCLUSIONS

To the best of our knowledge, this is the first study to show that MAGEH1 interacts with GADD45G and that MAGEH1 is involved in caspase-dependent apoptosis of renal tubular cells induced by nephrotoxic drugs.

Azacitidine regulates DNA methylation of GADD45γ in myelodysplastic syndromes

Background

Myelodysplastic syndrome (MDS) is a heterogeneous clonal disease originated from hematopoietic stem cells. Epigenetic studies had demonstrated that DNA methylation and histone acetylation were abnormal in MDS. Azacitidine is an effective drug in the treatment of demethylation.

Methods

RT‐PCR was performed to determine GADD45γ in 15 MDS clinical samples. Myelodysplastic syndrome cell lines SKM‐1 and HS‐5 were transfected with GADD45γ eukaryotic expression vector and/or GADD45γ shRNA interference plasmid, and treated with azacitidine. Proliferation and apoptosis were examined by CCK‐8 and Western blot analysis to confirm the function role of GADD45γ and azacitidine. The methylation level of GADD45γ gene was detected by bisulfite conversion and PCR.

Results

This study found that GADD45γ gene was down‐expressed in MDS patients' bone marrow and MDS cell lines, and the down‐regulation of GADD45γ in MDS could inhibit MDS cell apoptosis and promote proliferation. Azacitidine, a demethylation drug, could restore the expression of GADD45γ in MDS cells and inhibit the proliferation of MDS cells by inducing apoptosis, which was related to prognosis and transformation.

Conclusion

This study indicated that GADD45γ was expected to become a new target of MDS‐targeted therapy. The findings of this study provided a new direction for the research and development of new MDS clinical drugs, and gave a new idea for the development of MDS demethylation drug to realize precise treatment.