Replication and transcription machinery for ranaviruses: components, correlation, and functional architecture

Background Ranaviruses (family Iridoviridae) are promiscuous pathogens that can infect across species barriers in poikilotherms and can replicate in amphibian and fish cells and even in cultured mammalian cells. However, as nucleocytoplasmic large DNA viruses (NCLDVs), their replication and transcription mechanisms remain largely unknown. Here, we screened and uncovered the replication and transcription machinery of two ranaviruses, Andrias davidianus ranavirus (ADRV) and Rana grylio virus (RGV), by a combination of methods, including the isolation of proteins on nascent DNA, recombinant virus-based affinity, and NanoLuc complementation assay. Results The ranavirus replication and transcription machinery was deeply dissected and identified as a complicated apparatus containing at least 30 viral and 6 host proteins. The viral proteins ADRV-47L/RGV-63R (DNA polymerase, vDPOL), ADRV-23L/RGV-91R (proliferating cell nuclear antigen, vPCNA), ADRV-85L/RGV-27R (single-stranded DNA binding protein, vSSB), ADRV-88L/RGV-24R (vhelicase/primase), etc., constitute the core replisome. Specifically, the core of the transcription complex, the viral RNA polymerase, contain the host RNAPII subunits Rpb3, Rpb6, and Rpb11, which was a first report in NCLDVs. Furthermore, correlations and interactions among these factors in the machinery were described. Significantly, the replisome core protein vDPOL (ADRV-47L) can interact with numerous viral and host proteins and could act as a linker and regulation center in viral DNA replication and transcription. Thus, these results depicted an architecture for ranavirus replication and transcription. Conclusions Up to 36 components from ranavirus and their host were found to form viral replisomes and transcription complexes using a series of precise methods, which further constructed an architecture for ranavirus replication and transcription in which vDPOL was a key central factor and various components correlated and cooperated. Therefore, it provides a cornerstone for further understanding the mechanisms of the replication and transcription of ranaviruses which can ensure the efficient production of progeny virus and adaptation to cross-species infection.

Turning the tide on Alzheimer’s disease: modulation of γ-secretase

Alzheimer’s disease (AD) is the most common type of neurodegenerative disorder. Amyloid-beta (Aβ) plaques are integral to the “amyloid hypothesis,” which states that the accumulation of Aβ peptides triggers a cascade of pathological events leading to neurodegeneration and ultimately AD. While the FDA approved aducanumab, the first Aβ-targeted therapy, multiple safe and effective treatments will be needed to target the complex pathologies of AD. γ-Secretase is an intramembrane aspartyl protease that is critical for the generation of Aβ peptides. Activity and specificity of γ-secretase are regulated by both obligatory subunits and modulatory proteins. Due to its complex structure and function and early clinical failures with pan inhibitors, γ-secretase has been a challenging drug target for AD. γ-secretase modulators, however, have dramatically shifted the approach to targeting γ-secretase. Here we review γ-secretase and small molecule modulators, from the initial characterization of a subset of NSAIDs to the most recent clinical candidates. We also discuss the chemical biology of γ-secretase, in which small molecule probes enabled structural and functional insights into γ-secretase before the emergence of high-resolution structural studies. Finally, we discuss the recent crystal structures of γ-secretase, which have provided valuable perspectives on substrate recognition and molecular mechanisms of small molecules. We conclude that modulation of γ-secretase will be part of a new wave of AD therapeutics.

Offspring production of haploid spermatid-like cells derived from mouse female germline stem cells with chromatin condensation

Background During male meiosis, the Y chromosome can form perfect pairing with the X chromosome. However, it is unclear whether mammalian Female germline stem cells (FGSCs) without a Y chromosome can transdifferentiate into functional haploid spermatid-like cells (SLCs). Results We found that spermatogenesis was restarted by transplanting FGSCs into Kitw/wv mutant testes. Complete meiosis and formation of SLCs was induced in vitro by testicular cells of Kitw/wv mutant mice, cytokines and retinoic acid. Healthy offspring were produced by sperm and SLCs derived from the in vivo and in vitro transdifferentiation of FGSCs, respectively. Furthermore, high-throughput chromosome conformation capture sequencing(Hi-C-seq) and “bivalent” (H3K4me3-H3K27me3) micro chromatin immunoprecipitation sequencing (μChIP-seq) experiments showed that stimulated by retinoic acid gene 8 (STRA8)/protamine 1 (PRM1)-positive transdifferentiated germ cells (tGCs) and male germ cells (mGCs) display similar chromatin dynamics and chromatin condensation during in vitro spermatogenesis. Conclusion This study demonstrates that sperm can be produced from FGSCs without a Y chromosome. This suggests a strategy for dairy cattle breeding to produce only female offspring with a high-quality genetic background.

Ontogeny of RORγt+ cells in the intestine of newborns and its role in the development of experimental necrotizing enterocolitis

Background Neonates possess an immature and plastic immune system, which is a major cause of some diseases in newborns. Necrotizing enterocolitis (NEC) is a severe and devastating intestinal disease that typically affects premature infants. However, the development of intestinal immune cells in neonates and their roles in the pathological process of NEC have not been elucidated. Results We examined the ontogeny of intestinal lamina propria lymphocytes in the early life of mice and found a high percentage of RORγt+ cells (containing inflammatory Th17 and ILC3 populations) during the first week of life. Importantly, the proportion of RORγt+ cells of intestinal lamina propria further increased in both NEC mice and patients tissue than the control. Furthermore, the application of GSK805, a specific antagonist of RORγt, inhibited IL-17A release and ameliorated NEC severity. Conclusions Our data reveal the high proportion of RORγt+ cells in newborn mice may directly contribute to the development of NEC.

Y chromosome is moving out of sex determination shadow

Although sex hormones play a key role in sex differences in susceptibility, severity, outcomes, and response to therapy of different diseases, sex chromosomes are also increasingly recognized as an important factor. Studies demonstrated that the Y chromosome is not a ‘genetic wasteland’ and can be a useful genetic marker for interpreting various male-specific physiological and pathophysiological characteristics. Y chromosome harbors male‑specific genes, which either solely or in cooperation with their X-counterpart, and independent or in conjunction with sex hormones have a considerable impact on basic physiology and disease mechanisms in most or all tissues development. Furthermore, loss of Y chromosome and/or aberrant expression of Y chromosome genes cause sex differences in disease mechanisms. With the launch of the human proteome project (HPP), the association of Y chromosome proteins with pathological conditions has been increasingly explored. In this review, the involvement of Y chromosome genes in male-specific diseases such as prostate cancer and the cases that are more prevalent in men, such as cardiovascular disease, neurological disease, and cancers, has been highlighted. Understanding the molecular mechanisms underlying Y chromosome-related diseases can have a significant impact on the prevention, diagnosis, and treatment of diseases.

The interplay of autophagy and oxidative stress in the pathogenesis and therapy of retinal degenerative diseases

Oxidative stress is mainly caused by intracellular reactive oxygen species (ROS) production, which is highly associated with normal physiological homeostasis and the pathogenesis of diseases, particularly ocular diseases. Autophagy is a self-clearance pathway that removes oxidized cellular components and regulates cellular ROS levels. ROS can modulate autophagy activity through transcriptional and posttranslational mechanisms. Autophagy further triggers transcription factor activation and degrades impaired organelles and proteins to eliminate excessive ROS in cells. Thus, autophagy may play an antioxidant role in protecting ocular cells from oxidative stress. Nevertheless, excessive autophagy may cause autophagic cell death. In this review, we summarize the mechanisms of interaction between ROS and autophagy and their roles in the pathogenesis of several ocular diseases, including glaucoma, age-related macular degeneration (AMD), diabetic retinopathy (DR), and optic nerve atrophy, which are major causes of blindness. The autophagy modulators used to treat ocular diseases are further discussed. The findings of the studies reviewed here might shed light on the development and use of autophagy modulators for the future treatment of ocular diseases.

Intranasal HD-Ad vaccine protects the upper and lower respiratory tracts of hACE2 mice against SARS-CoV-2

Background The ongoing COVID-19 pandemic has resulted in 185 million recorded cases and over 4 million deaths worldwide. Several COVID-19 vaccines have been approved for emergency use in humans and are being used in many countries. However, all the approved vaccines are administered by intramuscular injection and this may not prevent upper airway infection or viral transmission. Results Here, we describe a novel, intranasally delivered COVID-19 vaccine based on a helper-dependent adenoviral (HD-Ad) vector. The vaccine (HD-Ad_RBD) produces a soluble secreted form of the receptor binding domain (RBD) of the SARS-CoV-2 spike protein and we show it induced robust mucosal and systemic immunity. Moreover, intranasal immunization of K18-hACE2 mice with HD-Ad_RBD using a prime-boost regimen, resulted in complete protection of the upper respiratory tract against SARS-CoV-2 infection. Conclusion Our approaches provide a powerful platform for constructing highly effective vaccines targeting SARS-CoV-2 and its emerging variants.

Antioxidant supplements promote tumor formation and growth and confer drug resistance in hepatocellular carcinoma by reducing intracellular ROS and induction of TMBIM1

Background Controversy over the benefits of antioxidants supplements in cancers persists for long. Using hepatocellular carcinoma (HCC) as a model, we investigated the effects of exogenous antioxidants N-acetylcysteine (NAC) and glutathione (GSH) on tumor formation and growth. Methods Multiple mouse models, including diethylnitrosamine (DEN)-induced and Trp53KO/C-MycOE-induced HCC models, mouse hepatoma cell and human HCC cell xenograft models with subcutaneous or orthotopic injection were used. In vitro assays including ROS assay, colony formation, sphere formation, proliferation, migration and invasion, apoptosis, cell cycle assays were conducted. Western blot was performed for protein expression and RNA-sequencing to identify potential gene targets. Results In these multiple different mouse and cell line models, we observed that NAC and GSH promoted HCC tumor formation and growth, accompanied with significant reduction of intracellular reactive oxygen species (ROS) levels. Moreover, NAC and GSH promoted cancer stemness, and abrogated the tumor-suppressive effects of Sorafenib both in vitro and in vivo. Exogenous supplementation of NAC or GSH reduced the expression of NRF2 and GCLC, suggesting the NRF2/GCLC-related antioxidant production pathway might be desensitized. Using transcriptomic analysis to identify potential gene targets, we found that TMBIM1 was significantly upregulated upon NAC and GSH treatment. Both TCGA and in-house RNA-sequence databases showed that TMBIM1 was overexpressed in HCC tumors. Stable knockdown of TMBIM1 increased the intracellular ROS; it also abolished the promoting effects of the antioxidants in HCC cells. On the other hand, BSO and SSA, inhibitors targeting NAC and GSH metabolism respectively, partially abrogated the pro-oncogenic effects induced by NAC and GSH in vitro and in vivo. Conclusions Our data implicate that exogenous antioxidants NAC and GSH, by reducing the intracellular ROS levels and inducing TMBIM expression, promoted HCC formation and tumor growth, and counteracted the therapeutic effect of Sorafenib. Our study provides scientific insight regarding the use of exogenous antioxidant supplements in cancers.

Development of a simple and miniaturized sandwich-like fluorescence polarization assay for rapid screening of SARS-CoV-2 main protease inhibitors

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is highly transmissible and has caused a pandemic named coronavirus disease 2019 (COVID-19), which has quickly spread worldwide. Although several therapeutic agents have been evaluated or approved for the treatment of COVID-19 patients, efficacious antiviral agents are still lacking. An attractive therapeutic target for SARS-CoV-2 is the main protease (Mpro), as this highly conserved enzyme plays a key role in viral polyprotein processing and genomic RNA replication. Therefore, the identification of efficacious antiviral agents against SARS-CoV-2 Mpro using a rapid, miniaturized and economical high-throughput screening (HTS) assay is of the highest importance at the present. Results In this study, we first combined the fluorescence polarization (FP) technique with biotin-avidin system (BAS) to develop a novel and step-by-step sandwich-like FP screening assay to quickly identify SARS-CoV-2 Mpro inhibitors from a natural product library. Using this screening assay, dieckol, a natural phlorotannin component extracted from a Chinese traditional medicine Ecklonia cava, was identified as a novel competitive inhibitor against SARS-CoV-2 Mpro in vitro with an IC50 value of 4.5 ± 0.4 µM. Additionally, dieckol exhibited a high affinity with SARS-CoV-2 Mpro using surface plasmon resonance (SPR) analysis and could bind to the catalytic sites of Mpro through hydrogen-bond interactions in the predicted docking model. Conclusions This innovative sandwich-like FP screening assay enables the rapid discovery of antiviral agents targeting viral proteases, and dieckol will be an excellent lead compound for generating more potent and selective antiviral agents targeting SARS-CoV-2 Mpro.

SIRT6 inhibition delays peripheral nerve recovery by suppressing migration, phagocytosis and M2-polarization of macrophages

Background Silent information regulator 6 (SIRT6) is a mammalian homolog of the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin family. Prior evidences suggested that the anti-inflammatory function of SIRT6 after spinal cord and brain injury, and it plays a crucial role in macrophages polarization of adipose tissue and skin. However, the role of SIRT6 in macrophages involved peripheral nerve injury is still unknown. Given the prominent role of macrophages in peripheral nerve recovery, we aim to investigate the role of SIRT6 in the regulation of phenotypes shift and functions in macrophages after peripheral nerve injury. Results In the present study, we first identified a significant increase of SIRT6 expression during nerve degeneration and macrophages phagocytosis. Next, we found nerve recovery was delayed after SIRT6 silencing by injected shRNA lentivirus into the crushed sciatic nerve, which exhibited a reduced expression of myelin-related proteins (e.g., MAG and MBP), severer myoatrophy of target muscles, and inferior nerve conduction compared to the shRNA control injected mice. In vitro, we found that SIRT6 inhibition by being treated with a selective inhibitor OSS_128167 or lentivirus transfection impairs migration and phagocytosis capacity of bone marrow-derived macrophages (BMDM). In addition, SIRT6 expression was discovered to be reduced after M1 polarization, but SIRT6 was enhanced after M2 polarization in the monocyte-macrophage cell line RAW264.7 and BMDM. Moreover, SIRT6 inhibition increased M1 macrophage polarization with a concomitant decrease in M2 polarization both in RAW264.7 and BMDM via activating NF-κB and TNF-α expression, and SIRT6 activation by UBCS039 treatment could shift the macrophages from M1 to M2 phenotype. Conclusion Our findings indicate that SIRT6 inhibition impairs peripheral nerve repair through suppressing the migration, phagocytosis, and M2 polarization of macrophages. Therefore, SIRT6 may become a favorable therapeutic target for peripheral nerve injury.