The enzyme encoded by Myrmecia incisa, a green microalga, phospholipase A2 gene preferentially hydrolyzes arachidonic acid at the sn-2 position of phosphatidylcholine.

The enzyme phospholipase A2 (PLA2) plays a crucial role in acyl remodeling of phospholipids via the Lands' cycle, and consequently alters fatty acid compositions in triacylglycerol (TAG). In this study, a full-length cDNA sequence coding Myrmecia incisa phospholipase A2 (MiPLA2) was cloned using the technique of rapid amplification of cDNA ends. Comparison of the 1082-bp cDNA with its corresponding cloned DNA sequence revealed that MiPLA2 contained 3 introns. Mature MiPLA2 (mMiPLA2) had a conserved Ca2+-binding loop and a catalytic site motif that has been recognized in plant secretory PLA2 (sPLA2) proteins. Correspondingly, phylogenetic analysis illustrated that MiPLA2 was clustered within GroupXIA of plant sPLA2 proteins. To ascertain the function of MiPLA2, the cDNA coding for mMiPLA2 was subcloned into the vector pET-32a to facilitate the production of recombinant mMiPLA2 in Escherichia coli. Recombinant mMiPLA2 was purified and used for the in vitro enzyme reaction. Thin-layer chromatography profiles of the catalytic products generated by recombinant mMiPLA2 indicated a specificity for cleaving sn-2 acyl chains from phospholipids, thereby functionally characterizing MiPLA2. Although recombinant mMiPLA2 displayed a strong preference for phosphatidylethanolamine, it preferentially hydrolyzes arachidonic acid (ArA) at the sn-2 position of phosphatidylcholine. Results from the fused expression of p1300-sp-EGFP-mMiPLA2 illustrated that MiPLA2 was localized in the intercellular space of onion epidermis. Furthermore, the positive correlation between MiPLA2 transcription and free ArA levels were established. Consequently, the role of mMiPLA2 in the biosynthesis of ArA-rich TAG was elucidated. This study helps to understand how M. incisa preferentially uses ArA to synthesize TAG.

A Novel NQO1 Enzyme-Responsive Polyurethane Nanocarrier for Redox-Triggered Intracellular Drug Release.

The design of nano-drug delivery vehicles responsive to tumor microenvironment stimuli has become a crucial aspect in developing cancer therapy in recent years. Among them, the enzyme-responsive nano-drug delivery system is particularly effective, as it utilizes tumor-specific and highly expressed enzymes as precise targets, leading to increased drug release at the target sites, reduced nonspecific release, and improved efficacy while minimizing toxic side effects on normal tissues. NAD(P)H:quinone oxidoreductase 1 (NQO1) is an important reductase associated with cancer and is overexpressed in some cancer cells, particularly in lung and breast cancer. Thus, the design of nanocarriers with high selectivity and responsiveness to NQO1 is of great significance for tumor diagnosis and treatment. It has been reported that under physiological conditions, NQO1 can specifically reduce the trimethyl-locked benzoquinone structure through a two-electron reduction, resulting in rapid lactonization via an enzymatic reaction. Based on this, a novel reduction-sensitive polyurethane (PEG-PTU-PEG) block copolymer was designed and synthesized by copolymerizing diisocyanate, a reduction-sensitive monomer (TMBQ), and poly(ethylene glycol). The successful synthesis of monomers and polymers was verified by nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). Then, the PEG-PTU-PEG micelles were successfully prepared by self-assembly, and their reductive dissociation behavior in the presence of Na2S2O4 was verified by dynamic light scattering (DLS), 1H NMR, and GPC. Next, the model drug doxorubicin (DOX) was encapsulated into the hydrophobic core of this polyurethane micelles by microemulsion method. It was observed that the drug-loaded micelles could also achieve a redox response and rapidly release the encapsulated substances. In vitro cell experiments demonstrated that PEG-PTU-PEG micelles had good biocompatibility and a low hemolysis rate (<5%). Furthermore, in the presence of an NQO1 enzyme inhibitor (dicoumarol), lower drug release from micelles was observed in A549 and 4T1 cells by both fluorescence microscopy and flow cytometry assays, but not in NIH-3T3 control cells. Predictably, DOX-loaded micelles also showed lower cytotoxicity in 4T1 cells in the presence of NQO1 enzyme inhibitors. These results indicate that drug-loaded polyurethane micelles could accomplish specific drug release in the reducing environment in the presence of NQO1 enzymes. Therefore, this study provides a new option for the construction of polyurethane nanocarriers for precise targeting and reductive release, which could benefit the intracellular drug-specific release and precision therapy of tumors.

Novel Donor-Acceptor Conjugated Polymer-Based Nanomicelles for Photothermal Therapy in the NIR Window.

In this study, a novel donor-acceptor conjugated polymer PDPPDTP was designed and synthesized by D-A polymerization using 2,6-di(trimethyltin)-N-dithieno[3,2-b:20,30-d]pyrrole as the electron-donating (D) unit and 3,6-bis(5-bromothiophen-2-yl)-2,5-dihexadecylpyrrolo[3,4-c]pyrrole-1,4-dione as the electron-accepting (A) unit. The prepared polymer has strong absorption in the near-infrared (NIR) range of 700-900 nm. Moreover, it shows excellent photothermal performance under irradiation at 808 nm. Next, the biodegradable amphiphilic polymer polyethylene glycol-polycaprolactone was used to encapsulate the new conjugated polymer into nanomicelles by the microemulsion method. The obtained PDPPDTP-loaded micelles exhibited a regular spherical structure, and their hydrodynamic diameter was about 78 nm, characterized by transmission electron microscopy and dynamic light scattering. Notably, the micelles exhibited good stability, and the encapsulation efficiency of the conjugated polymer in the micelles was ∼80%. In vitro cell experiments demonstrated that the nanomicelles not only showed good biocompatibility and low toxicity but also could effectively inhibit the proliferation of breast cancer cells 4T1 under the NIR light irradiation of 808 nm. Furthermore, in vivo studies of photothermal therapy (PTT) efficacy showed that the PDPPDTP-loaded micelles exhibited a remarkable tumor growth inhibition in a syngeneic murine tumor model, indicating that the nanomicelles loaded with this novel conjugated polymer could be further explored as a new type of theranostic agent and applied in the PTT of tumors.

Recent progress of nanomedicine in secreted phospholipase A2 as a potential therapeutic target.

Overexpressed secretory phospholipase A2 (sPLA2) is found in many inflammatory diseases and various types of cancer. sPLA2 can catalyze the hydrolysis of phospholipid sn-2 ester bonds to lysophosphatidylcholine and free fatty acids, and its catalytic substrate and downstream products mediate a series of cascade reactions and inflammatory responses. Furthermore, different subtypes of sPLA2 can participate in different physiological processes by driving unique lipid pathways. Recently, many diseases have not been treated by appropriate chemotherapy methods due to low bioavailability and severe side effects of clinically available small-molecule drugs. Therefore, they have great development prospects of revealing the therapeutic mechanism of sPLA2 and use sPLA2 as a potential therapeutic target for designing and exploring new drugs and their delivery systems. Notably, the emergence of nanomedicines in recent years provides a practical and innovative means for overcoming the challenges associated with chemotherapy. With these considerations in mind, this paper systematically reviews recent studies on nanomedicines targeting sPLA2 overexpression in various diseases during the past few years.

Differential controls of MAIT cell effector polarization by mTORC1/mTORC2 via integrating cytokine and costimulatory signals.

Mucosal-associated invariant T (MAIT) cells have important functions in immune responses against pathogens and in diseases, but mechanisms controlling MAIT cell development and effector lineage differentiation remain unclear. Here, we report that IL-2/IL-15 receptor ß chain and inducible costimulatory (ICOS) not only serve as lineage-specific markers for IFN-γ-producing MAIT1 and IL-17A-producing MAIT17 cells, but are also important for their differentiation, respectively. Both IL-2 and IL-15 induce mTOR activation, T-bet upregulation, and subsequent MAIT cell, especially MAIT1 cell, expansion. By contrast, IL-1ß induces more MAIT17 than MAIT1 cells, while IL-23 alone promotes MAIT17 cell proliferation and survival, but synergizes with IL-1ß to induce strong MAIT17 cell expansion in an mTOR-dependent manner. Moreover, mTOR is dispensable for early MAIT cell development, yet pivotal for MAIT cell effector differentiation. Our results thus show that mTORC2 integrates signals from ICOS and IL-1ßR/IL-23R to exert a crucial role for MAIT17 differentiation, while the IL-2/IL-15R-mTORC1-T-bet axis ensures MAIT1 differentiation.

Negative control of diacylglycerol kinase ζ-mediated inhibition of T cell receptor signaling by nuclear sequestration in mice.

Diacylglycerol kinases (DGKs) play important roles in restraining diacylglycerol (DAG)-mediated signaling. Within the DGK family, the ζ isoform appears to be the most important isoform in T cells for controlling their development and function. DGKζ has been demonstrated to regulate T cell maturation, activation, anergy, effector/memory differentiation, defense against microbial infection, and antitumor immunity. Given its critical functions, DGKζ function should be tightly regulated to ensure proper signal transduction; however, mechanisms that control DGKζ function are still poorly understood. We report here that DGKζ dynamically translocates from the cytosol into the nuclei in T cells after TCR stimulation. In mice, DGKζ mutant defective in nuclear localization displayed enhanced ability to inhibit TCR-induced DAG-mediated signaling in primary T cells, maturation of conventional αßT and iNKT cells, and activation of peripheral T cells compared with WT DGKζ. Our study reveals for the first time nuclear sequestration of DGKζ as a negative control mechanism to spatially restrain it from terminating DAG mediated signaling in T cells. Our data suggest that manipulation of DGKζ nucleus-cytosol shuttling as a novel strategy to modulate DGKζ activity and immune responses for treatment of autoimmune diseases and cancer.

Graded diacylglycerol kinases α and ζ activities ensure mucosal-associated invariant T-cell development in mice.

Mucosal-associated invariant T (MAIT) cells participate in both protective immunity and pathogenesis of diseases. Most murine MAIT cells express an invariant TCRVα19-Jα33 (iVα19) TCR, which triggers signals crucial for their development. However, signal pathways downstream of the iVα19TCR and their regulation in MAIT cells are unknown. Diacylglycerol (DAG) is a critical second messenger that relays the TCR signal to multiple downstream signaling cascades. DAG is terminated by DAG kinase (DGK)-mediated phosphorylation and conversion to phosphatidic acid. We have demonstrated here that downregulation of DAG caused by enhanced DGK activity impairs late-stage MAIT cell maturation in both thymus and spleen. Moreover, deficiency of DGKζ but not DGKα by itself causes modest decreases in MAIT cells, and deficiency of both DGKα and ζ results in severe reductions of MAIT cells in an autonomous manner. Our studies have revealed that DAG signaling is not only critical but also must be tightly regulated by DGKs for MAIT cell development and that both DGKα and, more prominently, DGKζ contribute to the overall DGK activity for MAIT cell development.

Deficiency of Mucosal-Associated Invariant T Cells in TCRJα18 Germline Knockout Mice.

Mucosal-associated invariant T (MAIT) cells and invariant NK T (iNKT) cells account for the major lymphocyte populations that express invariant TCRα-chains. MAIT cells mostly express the TCRVα19-Jα33 TCR in mice and the TCRVα7.2-Jα33 TCR in humans, whereas iNKT cells express the TCRVα14-Jα18 TCR in mice and the TCRVα24-Jα18 TCR in humans. Both MAIT and iNKT cells have the capacity to quickly produce a variety of cytokines in response to agonist stimuli and to regulate both innate and adaptive immunity. The germline TCRJα18 knockout (Traj18-/- ) mice have been used extensively for studying iNKT cells. Although it has been reported that the TCRα repertoire was narrowed and the level of Trav19-ja33 transcript was decreased in this strain of mice, direct assessment of MAIT cells in these mice has not been reported. We demonstrate in this study that this strain of mice is also defective of MAIT T cells, cautioning data interpretation when using this strain of mice.

DGK α and ζ Activities Control TH1 and TH17 Cell Differentiation.

CD4+ T helper (TH) cells are critical for protective adaptive immunity against pathogens, and they also contribute to the pathogenesis of autoimmune diseases. How TH differentiation is regulated by the TCR's downstream signaling is still poorly understood. We describe here that diacylglycerol kinases (DGKs), which are enzymes that convert diacylglycerol (DAG) to phosphatidic acid, exert differential effects on TH cell differentiation in a DGK dosage-dependent manner. A deficiency of either DGKα or ζ selectively impaired TH1 differentiation without obviously affecting TH2 and TH17 differentiation. However, simultaneous ablation of both DGKα and ζ promoted TH1 and TH17 differentiation in vitro and in vivo, leading to exacerbated airway inflammation. Furthermore, we demonstrate that dysregulation of TH17 differentiation of DGKα and ζ double-deficient CD4+ T cells was, at least in part, caused by increased mTOR complex 1/S6K1 signaling.