Unraveling ferroptosis in osteogenic lineages: implications for dysregulated bone remodeling during periodontitis progression.

Periodontitis is a highly prevalent disease characterized by inflammation and destruction of tooth-supporting tissues that leads to tooth loss in extreme situations. Elucidating the underlying mechanisms of periodontitis pathogenesis and progression will establish the groundwork for developing effective treatment strategies. Recently, evidence concerning the role of ferroptosis in periodontitis progression has emerged. Osteogenic lineage cells are key regulators of bone remodeling. Osteogenic cell death, as observed in experimental periodontitis models, disrupts the balance between bone resorption and bone formation. However, whether the osteogenic lineage undergoes ferroptosis during periodontitis and the corresponding effect on periodontitis progression remain elusive. Here, we investigated cell-specific ferroptosis within the alveolar bone in a murine periodontitis model. Through immunofluorescence double staining and immunohistochemistry, we identified ferroptotic osteocytes and osteoblasts in inflammatory alveolar bone. Next, in vivo administration of erastin or liproxstatin-1 was conducted to either induce or inhibit ferroptosis, respectively. Severe bone resorption and inflammation, accompanied by increased osteoclast formation and impaired osteogenic potential were detected following ferroptosis activation. Subsequently, we carried out in vitro experiments on osteocytes and further verified that ferroptosis enhanced the osteocytic expression of RANKL and IL-6. These findings suggest that ferroptosis occurring within the osteogenic lineage acts as a catalyst in the progression of periodontitis by stimulating osteoclastogenesis through the secretion of inflammatory cytokines and inhibiting osteoblastic function, providing insights into ferroptosis-induced alterations in microenvironment-based intercellular communication. Ferroptosis is a promising target for controlling inflammation and preventing bone resorption in periodontitis.

Structure of the intact tail machine of Anabaena myophage A-1(L).

The Myoviridae cyanophage A-1(L) specifically infects the model cyanobacteria Anabaena sp. PCC 7120. Following our recent report on the capsid structure of A-1(L), here we present the high-resolution cryo-EM structure of its intact tail machine including the neck, tail and attached fibers. Besides the dodecameric portal, the neck contains a canonical hexamer connected to a unique pentadecamer that anchors five extended bead-chain-like neck fibers. The 1045-Å-long contractile tail is composed of a helical bundle of tape measure proteins surrounded by a layer of tube proteins and a layer of sheath proteins, ended with a five-component baseplate. The six long and six short tail fibers are folded back pairwise, each with one end anchoring to the baseplate and the distal end pointing to the capsid. Structural analysis combined with biochemical assays further enable us to identify the dual hydrolytic activities of the baseplate hub, in addition to two host receptor binding domains in the tail fibers. Moreover, the structure of the intact A-1(L) also helps us to reannotate its genome. These findings will facilitate the application of A-1(L) as a chassis cyanophage in synthetic biology.

Interaction between ferroptosis and TNF-α: Impact in obesity-related osteoporosis.

The relationship of obesity and osteoporosis has been widely studied over the past years. However, the implications of obesity for bone health remain controversial, and the underlying molecular mechanism is not yet fully understood. This study demonstrated that high-fat diet-induced obesity leads to significantly decreased bone volume/tissue volume (BV/TV), trabecular number (Tb.N), and cortical thickness (Ct.Th) of male rat femur after mechanical loading effects of body weight were controlled. HFD-induced obese rats exhibited attenuated expression of ferroptosis inhibitory protein SLC7A11 and GPX4 in bone tissues, which was correlated with elevated serum TNF-α concentration. Ferroptosis inhibitor administration could effectively rescue decreased osteogenesis-associated type H vessels and osteoprogenitors, and downregulate serum levels of TNF-α to ameliorate bone loss in obese rats. Since ferroptosis and TNF-α both affect bone and vessel formation, we further investigated the interaction between ferroptosis and TNF-α, and its impact in osteogenesis and angiogenesis in vitro. In human osteoblast-like MG63 and umbilical vein endothelial cells (HUVEC), TNF-α/TNFR2 signaling promoted cystine uptake and GSH biosynthesis to provide protection against low-dose ferroptosis inducer erastin. While, TNF-α/TNFR1 facilitated ferroptosis in the presence of high-dose erastin through ROS accumulation. Moreover, TNF-α regulated ferroptosis-induced osteogenic and angiogenic dysfunctions based on its ferroptosis regulatory role. Meanwhile, ferroptosis inhibitors could reduce intracellular ROS overproduction and enhance osteogenesis and angiogenesis in TNF-α-treated MG63 and HUVECs. This study revealed the interaction between ferroptosis and TNF-α and its impact in osteogenesis and angiogenesis, which provides new insights into the pathogenesis and regenerative therapy of obesity-related osteoporosis.

Fine structure and assembly pattern of a minimal myophage Pam3.

The myophage possesses a contractile tail that penetrates its host cell envelope. Except for investigations on the bacteriophage T4 with a rather complicated structure, the assembly pattern and tail contraction mechanism of myophage remain largely unknown. Here, we present the fine structure of a freshwater Myoviridae cyanophage Pam3, which has an icosahedral capsid of ~680 Å in diameter, connected via a three-section neck to an 840-Å-long contractile tail, ending with a three-module baseplate composed of only six protein components. This simplified baseplate consists of a central hub-spike surrounded by six wedge heterotriplexes, to which twelve tail fibers are covalently attached via disulfide bonds in alternating upward and downward configurations. In vitro reduction assays revealed a putative redox-dependent mechanism of baseplate assembly and tail sheath contraction. These findings establish a minimal myophage that might become a user-friendly chassis phage in synthetic biology.

How Do Extracellular Vesicles Play a Key Role in the Maintenance of Bone Homeostasis and Regeneration? A Comprehensive Review of Literature.

The maintenance of bone homeostasis includes both bone resorption by osteoclasts and bone formation by osteoblasts. These two processes are in dynamic balance to maintain a constant amount of bone for accomplishing its critical functions in daily life. Multiple cell type communications are involved in these two complex and continuous processes. In recent decades, an increasing number of studies have shown that osteogenic and osteoclastic extracellular vesicles play crucial roles in regulating bone homeostasis through paracrine, autosecretory and endocrine signaling. Elucidating the functional roles of extracellular vesicles in the maintenance of bone homeostasis may contribute to the design of new strategies for bone regeneration. Hence, we review the recent understandings of the classification, production process, extraction methods, structure, contents, functions and applications of extracellular vesicles in bone homeostasis. We highlight the contents of various bone-derived extracellular vesicles and their interactions with different cells in the bone microenvironment during bone homeostasis. We also summarize the recent advances in EV-loaded biomaterial scaffolds for bone regeneration and repair.

Comparative genomic analysis of five freshwater cyanophages and reference-guided metagenomic data mining.

BACKGROUND: As important producers using photosynthesis on Earth, cyanobacteria contribute to the oxygenation of atmosphere and the primary production of biosphere. However, due to the eutrophication of urban waterbodies and global warming, uncontrollable growth of cyanobacteria usually leads to the seasonal outbreak of cyanobacterial blooms. Cyanophages, a group of viruses that specifically infect and lyse cyanobacteria, are considered as potential environment-friendly agents to control the harmful blooms. Compared to the marine counterparts, only a few freshwater cyanophages have been isolated and genome sequenced to date, largely limiting their characterizations and applications. RESULTS: Here, we isolated five freshwater cyanophages varying in tail morphology, termed Pam1~Pam5, all of which infect the cyanobacterium Pseudanabaena mucicola Chao 1806 that was isolated from the bloom-suffering Lake Chaohu in Anhui, China. The whole-genome sequencing showed that cyanophages Pam1~Pam5 all contain a dsDNA genome, varying in size from 36 to 142 Kb. Phylogenetic analyses suggested that Pam1~Pam5 possess different DNA packaging mechanisms and are evolutionarily distinct from each other. Notably, Pam1 and Pam5 have lysogeny-associated gene clusters, whereas Pam2 possesses 9 punctuated DNA segments identical to the CRISPR spacers in the host genome. Metagenomic data-based calculation of the relative abundance of Pam1~Pam5 at the Nanfei estuary towards the Lake Chaohu revealed that the short-tailed Pam1 and Pam5 account for the majority of the five cyanophages. Moreover, comparative analyses of the reference genomes of Pam1~Pam5 and previously reported cyanophages enabled us to identify three circular and seven linear contigs of virtual freshwater cyanophages from the metagenomic data of the Lake Chaohu. CONCLUSIONS: We propose a high-throughput strategy to systematically identify cyanophages based on the currently available metagenomic data and the very limited reference genomes of experimentally isolated cyanophages. This strategy could be applied to mine the complete or partial genomes of unculturable bacteriophages and viruses. Transformation of the synthesized whole genomes of these virtual phages/viruses to proper hosts will enable the rescue of bona fide viral particles and eventually enrich the library of microorganisms that exist on Earth. Video abstract.

Capsid Structure of Anabaena Cyanophage A-1(L).

A-1(L) is a freshwater cyanophage with a contractile tail that specifically infects Anabaena sp. PCC 7120, one of the model strains for molecular studies of cyanobacteria. Although isolated for half a century, its structure remains unknown, which limits our understanding on the interplay between A-1(L) and its host. Here we report the 3.35 Å cryo-EM structure of A-1(L) capsid, representing the first near-atomic resolution structure of a phage capsid with a T number of 9. The major capsid gp4 proteins assemble into 91 capsomers, including 80 hexons: 20 at the center of the facet and 60 at the facet edge, in addition to 11 identical pentons. These capsomers further assemble into the icosahedral capsid, via gradually increasing curvatures. Different from the previously reported capsids of known-structure, A-1(L) adopts a noncovalent chainmail structure of capsid stabilized by two kinds of mortise-and-tenon inter-capsomer interactions: a three-layered interface at the pseudo 3-fold axis combined with the complementarity in shape and electrostatic potential around the 2-fold axis. This unique capsomer construction enables A-1(L) to possess a rigid capsid, which is solely composed of the major capsid proteins with an HK97 fold. IMPORTANCE Cyanobacteria are the most abundant photosynthetic bacteria, contributing significantly to the biomass production, O2 generation, and CO2 consumption on our planet. Their community structure and homeostasis in natural aquatic ecosystems are largely regulated by the corresponding cyanophages. In this study, we solved the structure of cyanophage A-1(L) capsid at near-atomic resolution and revealed a unique capsid construction. This capsid structure provides the molecular details for better understanding the assembly of A-1(L), and a structural platform for future investigation and application of A-1(L) in combination with its host Anabaena sp. PCC 7120. As the first isolated freshwater cyanophage that infects the genetically tractable model cyanobacterium, A-1(L) should become an ideal template for the genetic engineering and synthetic biology studies.

Pazopanib, a novel multi-kinase inhibitor, shows potent antitumor activity in colon cancer through PUMA-mediated apoptosis.

Colon cancer is still the third most common cancer which has a high mortality but low five-year survival rate. Novel tyrosine kinase inhibitors (TKI) such as pazopanib become effective antineoplastic agents that show promising clinical activity in a variety of carcinoma, including colon cancer. However, the precise underlying mechanism against tumor is unclear. Here, we demonstrated that pazopanib promoted colon cancer cell apoptosis through inducing PUMA expression. Pazopanib induced p53-independent PUMA activation by inhibiting PI3K/Akt signaling pathway, thereby activating Foxo3a, which subsequently bound to the promoter of PUMA to activate its transcription. After induction, PUMA activated Bax and triggered the intrinsic mitochondrial apoptosis pathway. Furthermore, administration of pazopanib highly suppressed tumor growth in a xenograft model. PUMA deletion in cells and tumors led to resistance of pazopanib, indicating PUMA-mediated pro-apoptotic and anti-tumor effects in vitro and in vivo. Combing pazopanib with some conventional or novel drugs, produced heightened and synergistic antitumor effects that were associated with potentiated PUMA induction via different pathways. Taken together, these results establish a critical role of PUMA in mediating the anticancer effects of pazopanib in colon cancer cells and provide the rationale for clinical evaluation.