A fatty acid ordered plasma membrane environment is critical for Ebola virus matrix protein assembly and budding.

Plasma membrane (PM) domains and order phases have been shown to play a key role in the assembly, release, and entry of several lipid-enveloped viruses. In the present study, we provide a mechanistic understanding of the Ebola virus (EBOV) matrix protein VP40 interaction with PM lipids and their effect on VP40 oligomerization, a crucial step for viral assembly and budding. VP40 matrix formation is sufficient to induce changes in the PM fluidity. We demonstrate that the distance between the lipid headgroups, the fatty acid tail saturation and the PM order are important factors for the stability of VP40 binding and oligomerization at the PM. Use of FDA-approved drugs to fluidize the PM, destabilizes the viral matrix assembly leading to a reduction in budding efficiency. Overall, these findings support an EBOV assembly mechanism that reaches beyond lipid headgroup specificity by using ordered PM lipid regions independent of cholesterol.

Biochemistry and Diseases Related to the Interconversion of Phosphatidylcholine, Phosphatidylethanolamine, and Phosphatidylserine.

Phospholipids are crucial structural components of cells. Phosphatidylcholine and phosphatidylethanolamine (both synthesized via the Kennedy pathway) and phosphatidylserine undergo interconversion. The dysregulation of this process is implicated in various diseases. This paper discusses the role of enzymes involved in the interconversion of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine, specifically phosphatidylethanolamine N-methyltransferase (PEMT), phosphatidylserine synthases (PTDSS1 and PTDSS2), and phosphatidylserine decarboxylase (PISD), with a focus on their biochemical properties. Additionally, we describe the effects of the deregulation of these enzymes and their roles in both oncological and non-oncological diseases, including nonalcoholic fatty liver disease (NAFLD), Alzheimer's disease, obesity, insulin resistance, and type II diabetes. Current knowledge on inhibitors of these enzymes as potential therapeutic agents is also reviewed, although in most cases, inhibitors are yet to be developed. The final section of this article presents a bioinformatic analysis using the GEPIA portal to explore the significance of these enzymes in cancer processes.

Phosphatidylserine-mediated uptake of extracellular vesicles by hepatocytes ameliorates liver ischemia-reperfusion injury.

Compelling evidence suggests that mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) promote regeneration in animal models of liver injury by delivering signaling molecules. However, their target cells and uptake mechanism remain elusive. In this study, MSC-EVs were intravenously administered in a mouse model of liver ischemia-reperfusion injury (IRI). Our results revealed that MSC-EVs exhibit enhanced liver targeting in IRI mice, and injured hepatocytes display a greater capacity for MSC-EV uptake. We found that phosphatidylserine (PS) displayed on the exterior of injured hepatocytes promotes MSC-EV internalization, possibly by binding to MFGE8, a protein expressed on the MSC-EV membrane. Furthermore, the therapeutic effect of MSC-EVs on liver IRI is highly dependent on this PS-mediated uptake pathway. Our findings provide evidence that MSC-EVs preferentially target injured hepatocytes, relying on a PS-dependent uptake route to exert hepatoprotective effects, which are critical for the future design of EV-based therapeutic strategies for liver IRI.

Phase-Specific Immobilization of Phospholipase D as an Efficient Pickering Emulsion Interfacial Catalyst for Converting Antarctic Krill Oil Phospholipid.

Phosphatidylserine (PS), a rare phospholipid in Antarctic krill oil (AKO) critical for brain development, can be produced from the abundant phosphatidylcholine (PC) using phospholipase D (PLD) in Pickering emulsion interfacial catalysis (PIC) systems. However, the exposure of PLD to organic solvent around the emulsion interface diminished PLD activity, limiting the conversion efficiency of PS. In this study, we proposed a strategy to fabricate a PIC system with high efficiency and stability by immobilizing PLD in a specific phase on the emulsion interface, based on investigating the effect of the interfacial microenvironment on PLD activity. Janus-poly(acrylic acid)/polystyrene (JPP) and Janus-polyethylenimine/octadecane (JPO) particles were fabricated as carriers to realize the specific-phase immobilization of PLD. The highest activity was observed when PLD was immobilized on the hydrophilic side of JPP (PLD@JPP(W)), 1.9-fold that of free PLD. The catalytic efficiency of PLD@JPP(W) was 1.7-fold that of free PLD, confirmed by the kcat/Km value enhancement. Immobilization on the hydrophilic side also enhanced the thermal stability of PLD. The half-lives of PLD were extended from 4 to 36 h at 40 °C and from 6 to 28 days at 4 °C. Importantly, PLD@JPP(W) showed excellent catalytic efficiency as a PIC system, achieving a PS productivity of 93% within a short time of 2 h at an enzyme dosage of 0.05 mg. PLD@JPP(W) exhibited a 3.6 times higher yield than free PLD in the production of PS from PC rich in Antarctic krill oil. The strategy in this work could also be applied to other lipases, providing a promising method for the efficient conversion of functional lipids.

Phosphatidylserine liposomes induce a phagosome acidification-dependent and ROS-mediated intracellular killing of Mycobacterium abscessus in human macrophages.

Mycobacterium abscessus (Mab) is an opportunistic nontuberculous mycobacterium responsible of difficult-to-treat pulmonary infections in vulnerable patients, such as those suffering from Cystic Fibrosis (CF), where it represents a major cause of morbidity and mortality. Additionally, due to the intrinsic extensive antimicrobial resistance spectrum displayed by this species and the side effects reported for some available antibiotics, the therapeutic management of such infections remains extremely difficult. In the present study, we show that phosphatidylserine liposomes (PS-L) enhance intracellular mycobacterial killing of Mab infected human macrophages with functional or pharmacologically inhibited cystic fibrosis conductance regulator (CFTR), by a mechanism involving phagosome acidification and reactive oxygen species (ROS) production. Additionally, PS-L significantly reduce proinflammatory response of Mab infected macrophages in terms of NF-kB activation and TNF-α production, irrespective of CFTR inhibition. Altogether, these results represent the proof of concept for a possible future development of PS-L as a therapeutic strategy against difficult-to-treat Mab infection.

Engineering Phosphatidylserine Containing Asymmetric Giant Unilamellar Vesicles.

The plasma membrane lipid distribution is asymmetric, with several anionic lipid species located in its inner leaflet. Among these, phosphatidylserine (PS) plays a crucial role in various important physiological functions. Over the last decade several methods have been developed that allow for the fabrication of large or giant unilamellar vesicles (GUVs) with an asymmetric lipid composition. Investigating the physicochemical properties of PS in such asymmetric lipid bilayers and studying its interactions with proteins necessitates the reliable fabrication of asymmetric GUVs (aGUVs) with a high degree of asymmetry that exhibit PS in the outer leaflet so that the interaction with peptides and proteins can be studied. Despite progress, achieving aGUVs with well-defined PS asymmetry remains challenging. Recently, a Ca2+-initiated hemifusion method has been introduced, utilizing the fusion of symmetric GUVs (sGUVs) with a supported lipid bilayer (SLB) for the fabrication of aGUVs. We extend this approach to create aGUVs with PS in the outer bilayer leaflet. Comparing the degree of asymmetry between aGUVs obtained via Ca2+ or Mg2+ initiated hemifusion of a phosphatidylcholine (PC) sGUVwith a PC/PS-supported lipid bilayer, we observe for both bivalent cations a significant number of aGUVs with near-complete asymmetry. The degree of asymmetry distribution is narrower for physiological salt conditions than at lower ionic strengths. While Ca2+ clusters PS in the SLB, macroscopic domain formation is absent in the presence of Mg2+. However, the clustering of PS upon the addition of Ca2+ is apparently too slow to have a negative effect on the quality of the obtained aGUVs. We introduce a data filtering method to select aGUVs that are best suited for further investigation.

Electronic detection of apoptotic cells on a microchip.

Robust and rapid detection of apoptosis in cells is crucially needed for diagnostics, drug discovery, studying pathogenic mechanisms and tracking patient response to medical interventions and treatments. Traditionally, the methods employed to detect apoptosis rely on complex instrumentation like flow cytometers and fluorescence microscopes, which are both expensive and complex-to-operate except in centralized laboratories with trained labor. In this work, we introduce a microfluidic device that can screen cells in a suspension for apoptosis markers and report the assays results as electronic data. Specifically, our device identifies apoptotic cells by detecting externalized phosphatidylserine on a cell membrane - a well-established biomarker that is also targeted by fluorophore-based labeling in conventional assays. In our device, apoptotic cells are discriminated from others through biochemical capture followed by transduction of individual capture events into electrical signals via integrated electrical sensors. The developed technology was tested on simulated samples containing controlled amounts of cells with artificially-induced apoptosis and validated by benchmarking against conventional flow cytometry. Combining sample manipulation and electronic detection on a disposable microfluidic chip, our cell apoptosis assay is amenable to be implemented in a variety of settings and therefore has the potential to create new opportunities for cell-based diagnostics and therapeutics and contribute to improved healthcare outcomes on a large scale.

Phosphatidylserine synthase plays a critical role in the utilization of n-alkanes in the yeast Yarrowia lipolytica.

The yeast Yarrowia lipolytica can assimilate n-alkane as a carbon and energy source. To elucidate the significance of phosphatidylserine (PS) in the utilization of n-alkane in Y. lipolytica, we investigated the role of the Y. lipolytica ortholog (PSS1) of Saccharomyces cerevisiae PSS1/CHO1, which encodes a PS synthase. The PSS1 deletion mutant (pss1Δ) of Y. lipolytica could not grow on minimal medium in the absence of ethanolamine and choline but grew when either ethanolamine or choline was supplied to synthesize phosphatidylethanolamine and phosphatidylcholine. The pss1Δ strain exhibited severe growth defects on media containing n-alkanes even in the presence of ethanolamine and choline. In the pss1Δ strain, the transcription of ALK1, which encodes a primary cytochrome P450 that catalyses the hydroxylation of n-alkanes in the endoplasmic reticulum, was upregulated by n-alkane as in the wild-type strain. However, the production of functional P450 was not detected, as indicated by the absence of reduced CO-difference spectra in the pss1Δ strain. PS was undetectable in the lipid extracts of the pss1Δ strain. These results underscore the critical role of PSS1 in the biosynthesis of PS, which is essential for the production of functional P450 enzymes involved in n-alkane hydroxylation in Y. lipolytica.

Unveiling the reaction mechanism of arginine decarboxylase in Aspergillus oryzae: Insights from crystal structure analysis.

Agmatine, a natural polyamine also known as 4-aminobutyl-guanidine, is biosynthesized from arginine by decarboxylation. Aspergillus oryzae contains high amounts of agmatine, suggesting highly active arginine decarboxylase (ADC) in this organism. However, genome analysis revealed no ADC homolog in A. oryzae. A. oryzae strain RIB40 has six homologs of phosphatidylserine decarboxylase (PSD), an enzyme that synthesizes phosphatidyl ethanolamine from phosphatidylserine. We previously discovered that one of these homologs, AO090102000327, encodes arginine decarboxylase, which we named ADC1. In the present study, we determined the crystal structures of ligand-free, arginine-treated, and agmatine-treated ADC1 each at 1.9-2.15 Å resolution. Each structure contained four ADC1 molecules (chains A-D) in the asymmetric unit of the cell. Each ADC1 molecule is a heterodimer consisting of the N-terminal region (Asn60-Gly441) and C-terminal region (Ser442-Thr482). In the ligand-free ADC1, the N-terminus of Ser442 was modified to form a pyruvoyl group. In the arginine-treated ADC1, arginine was converted to agmatine, with the pyruvoyl group covalently bound to agmatine by forming a Schiff base. The same structure was observed in agmatine-treated ADC1. These results indicate that ADC1 is a pyruvoyl-dependent decarboxylase and unveils the reaction mechanism of ADC from A. oryzae.

Exposed Phosphatidylserine as a Biomarker for Clear Identification of Breast Cancer Brain Metastases in Mouse Models.

Brain metastasis is the most common intracranial malignancy in adults. The prognosis is extremely poor, partly because most patients have more than one brain lesion, and the currently available therapies are nonspecific or inaccessible to those occult metastases due to an impermeable blood-tumor barrier (BTB). Phosphatidylserine (PS) is externalized on the surface of viable endothelial cells (ECs) in tumor blood vessels. In this study, we have applied a PS-targeting antibody to assess brain metastases in mouse models. Fluorescence microscopic imaging revealed that extensive PS exposure was found exclusively on vascular ECs of brain metastases. The highly sensitive and specific binding of the PS antibody enables individual metastases, even micrometastases containing an intact BTB, to be clearly delineated. Furthermore, the conjugation of the PS antibody with a fluorescence dye, IRDye 800CW, or a radioisotope, 125I, allowed the clear visualization of individual brain metastases by optical imaging and autoradiography, respectively. In conclusion, we demonstrated a novel strategy for targeting brain metastases based on our finding that abundant PS exposure occurs on blood vessels of brain metastases but not on normal brain, which may be useful for the development of imaging and targeted therapeutics for brain metastases.

Effects of a food supplement containing phosphatidylserine on cognitive function in Chinese older adults with mild cognitive impairment: A randomized double-blind, placebo-controlled trial.

BACKGROUND: Phosphatidylserine (PS) and α-Linolenic acid (ALA), are positively associated with cognitive function, but their combination effects and possible mechanisms remain unclear. We aimed to explore the effects on cognition and potential mechanism of the supplements. METHODS: This randomized, double-blind, placebo-controlled trial recruited 190 MCI patients in Tianjin, China, and randomly assigned in intervention group and placebo group. Each group consumed two capsules every day for 12 months. Each capsule for intervention group contains 144 mg ALA, 31.5 mg PS and 3.6 mg Ginkgo total flavonoids as main functional components, with 0.48 mg Vitamin B1 (as thiamine hydrochloride), 0.48 mg Vitamin B6 (as pyridoxine hydrochloride) and 90 µg folic acid as supplement. Capsules for placebo group were identical but contain no active ingredients. Cognitive function, serum n-3 polyunsaturated fatty acids (PUFAs) and neurotransmitters were assessed at baseline and 12 months. Linear mixed effects model and causal mediation analysis were conducted to explore the effects and potential mechanism of the intervention. RESULTS: A total of 190 participants (mean [SD] age, 67.95 [5.62] years; 70 (36.8 %) male and 120 (63.2 %) female) were randomized to the placebo group (n = 95) and intervention group (n = 95). Compared with placebo group, the intervention group had statistically significant improvements in arithmetic testing (ß, 0.688; 95 % CI, 0.103-1.274), the similarity test (ß, 1.070; 95 % CI, 0.472-1.667) and short-term memory (ß, 0.600; 95 % CI, 0.399-0.800). Besides, the intervention group had statistically significant increases in serum ALA (ß, 1.620; 95 % CI, 0.967-2.265), DHA (ß, 2.797; 95 % CI, 1.075-4.532), EPA (ß, 1.472; 95 % CI, 0.296-2.643), acetylcholine (ß, 0.441; 95 % CI, 0.415-0.468), GABA (ß, 0.009; 95 % CI, 0.001-0.016) and 5-HT (ß, 0.160; 95 % CI, 0.081-0.238) compared to the placebo group. And the intervention may improve short-term memory by increasing serum ALA levels (average causal mediation effect = 0.132, 95 % CI, 0.053-0.225) with 19.7 % mediation proportion. CONCLUSIONS: This food supplement containing phosphatidylserine could improve different cognitive functions of MCI patients, especially short-term memory, and increase serum n-3 PUFAs and neurotransmitters levels. Serum ALA level might play a mediation role.

Can calmodulin bind to lipids of the cytosolic leaflet of plasma membranes?

Calmodulin (CaM) is a ubiquitous calcium-sensitive messenger in eukaryotic cells. It was previously shown that CaM possesses an affinity for diverse lipid moieties, including those found on CaM-binding proteins. These facts, together with our observation that CaM accumulates in membrane-rich protrusions of HeLa cells upon increased cytosolic calcium, motivated us to perform a systematic search for unmediated CaM interactions with model lipid membranes mimicking the cytosolic leaflet of plasma membranes. A range of experimental techniques and molecular dynamics simulations prove unambiguously that CaM interacts with lipid bilayers in the presence of calcium ions. The lipids phosphatidylserine (PS) and phosphatidylethanolamine (PE) hold the key to CaM-membrane interactions. Calcium induces an essential conformational rearrangement of CaM, but calcium binding to the headgroup of PS also neutralizes the membrane negative surface charge. More intriguingly, PE plays a dual role-it not only forms hydrogen bonds with CaM, but also destabilizes the lipid bilayer increasing the exposure of hydrophobic acyl chains to the interacting proteins. Our findings suggest that upon increased intracellular calcium concentration, CaM and the cytosolic leaflet of cellular membranes can be functionally connected.

The Role of TIM-1 and CD300a in Zika Virus Infection Investigated with Cell-Based Electrical Impedance.

Orthoflaviviruses cause a major threat to global public health, and no antiviral treatment is available yet. Zika virus (ZIKV) entry, together with many other viruses, is known to be enhanced by phosphatidylserine (PS) receptors such as T-cell immunoglobulin mucin domain protein 1 (TIM-1). In this study, we demonstrate for the first time, using cell-based electrical impedance (CEI) biosensing, that ZIKV entry is also enhanced by expression of CD300a, another PS receptor. Furthermore, inhibiting CD300a in immature monocyte-derived dendritic cells partially but significantly inhibits ZIKV replication. As we have previously demonstrated that CEI is a useful tool to study Orthoflavivirus infection in real time, we now use this technology to determine how these PS receptors influence the kinetics of in vitro ZIKV infection. Results show that ZIKV entry is highly sensitive to minor changes in TIM-1 expression, both after overexpression of TIM-1 in infection-resistant HEK293T cells, as well as after partial knockout of TIM-1 in susceptible A549 cells. These results are confirmed by quantification of viral copy number and viral infectivity, demonstrating that CEI is highly suited to study and compare virus-host interactions. Overall, the results presented here demonstrate the potential of targeting this universal viral entry pathway.

New Therapeutic Strategies in Retinal Vascular Diseases: A Lipid Target, Phosphatidylserine, and Annexin A5-A Future Theranostic Pairing in Ophthalmology.

Despite progress in the management of patients with retinal vascular and degenerative diseases, there is still an unmet clinical need for safe and effective therapeutic options with novel mechanisms of action. Recent mechanistic insights into the pathogenesis of retinal diseases with a prominent vascular component, such as retinal vein occlusion (RVO), diabetic retinopathy (DR) and wet age-related macular degeneration (AMD), may open up new treatment paradigms that reach beyond the inhibition of vascular endothelial growth factor (VEGF). Phosphatidylserine (PS) is a novel lipid target that is linked to the pathophysiology of several human diseases, including retinal diseases. PS acts upstream of VEGF and complement signaling pathways. Annexin A5 is a protein that targets PS and inhibits PS signaling. This review explores the current understanding of the potential roles of PS as a target and Annexin A5 as a therapeutic. The clinical development status of Annexin A5 as a therapeutic and the potential utility of PS-Annexin A5 as a theranostic pairing in retinal vascular conditions in particular is described.

DHA-enriched phosphatidylserine ameliorates cyclophosphamide-induced liver injury via regulating the gut-liver axis.

OBJECTIVE: This study explores the therapeutic effects and mechanisms of DHA-enriched phosphatidylserine (DHA-PS) on liver injury induced by cyclophosphamide (CTX) in mice, focusing on the gut-liver axis. METHODS: A mouse model was established by administering CTX (80 mg/kg) intraperitoneally for 5 days. DHA-PS (50 or 100 mg/kg) was administered for the next 7 days to assess its reparative impact on liver damage. RESULTS: The findings revealed significant improvements in liver biochemical indices, inflammatory markers, and oxidative stress levels in the mice treated with DHA-PS. Through non-targeted metabolomics analysis, DHA-PS mitigated CTX-induced metabolic disruptions by modulating lipid, amino acid, and pyrimidine metabolism. Immunofluorescence analysis further confirmed that DHA-PS reduced the expression of liver-associated inflammatory proteins by inhibiting the TLR4/NF-κB pathway. Additionally, DHA-PS restored the intestinal barrier, evidenced by adjustments in the levels of intestinal lipopolysaccharide (LPS), secretory immunoglobulin A (sIgA), and tight junction proteins (Claudin-1, Occludin, and ZO-1). It also improved gut microbiota balance by enhancing microbial diversity, increasing beneficial bacteria, and altering community structures. CONCLUSION: These results suggest that DHA-PS could be a potential therapeutic agent or functional food for CTX-induced liver injury through its regulation of the gut-liver axis.

Acquisition of anti-phosphatidylserine IgM and IgG antibodies by infants and their mothers over time in Uganda.

Background: Production of anti-phosphatidylserine (anti-PS) antibodies has been associated with malaria and can aggravate pathology. How these autoantibodies develop during early childhood in a malaria context is not known. We examined levels of anti-PS IgG and IgM antibodies in a longitudinal cohort of mother-baby pairs during birth, in the infants at 2.5, 6 months, and in mothers and their babies at 9 months postpartum. Results: There was no difference between levels of anti-PS IgG in cord blood and the mothers' peripheral blood at birth. However, anti-PS IgM levels were significantly higher in the mothers compared to the infants' cord blood, and IgM levels were steadily increasing during the first 9 months of the infants' life. In infants that had the highest anti-PS IgM levels at birth, there was a decline until 6 months with a rise at 9 months. Infants that possessed high anti-PS IgG at birth also exhibited a progressive decline in levels. When anti-PS were correlated to different fractions of B-cells, there were several correlations with P. falciparum specific atypical B cells both at birth and at 2.5 months for the infants, especially for anti-PS IgM. Anti-PS also correlated strongly to C1q-fixing antibodies at birth. Conclusion: These results show that anti-PS IgG acquired by mothers could be transferred transplacentally and that IgM antibodies targeting PS are acquired during the first year of life. These results have increased the knowledge about autoimmune responses associated with infections in early life and is critical for a comprehensive understanding of malaria vaccine functionality in endemic areas.

Red Blood Cell Membrane Spontaneously Coated Nanoprodrug Based on Phosphatidylserine for Antiatherosclerosis Applications.

Atherosclerosis (AS) is characterized by the accumulation of lipids within the walls of coronary arteries, leading to arterial narrowing and hardening. It serves as the primary etiology and pathological basis for cardiovascular diseases affecting the heart and brain. However, conventional pharmacotherapy is constrained by inadequate drug delivery and pronounced toxic side effects. Moreover, the inefficacy of nanomedicine delivery systems in controlling disease progression may be attributed to nonspecific clearance by the mononuclear phagocyte system. Thus, a biomimetic platform spontaneously enveloped by red blood cell membrane is exploited for anti-atherosclerosis applications, offering favorable biocompatibility. The CLIKKPF polypeptide is introduced to develop red blood cell membrane spontaneously encapsulated nanotherapeutics only through simple coincubation. Given the functional modifications, RBC@P-LVTNPs is beneficial to facilitate the target drug delivery to the atherosclerotic lesion, responding precisely to the pathological ROS accumulation, thereby accelerating the on-demand drug release. Both in vivo and in vitro results also confirm the significant therapeutic efficacy and favorable biocompatibility of the biomimetic nanomedicine delivery system, thus providing a promising candidate for nanotherapeutics against AS.

Collagen patches releasing phosphatidylserine liposomes guide M1-to-M2 macrophage polarization and accelerate simultaneous bone and muscle healing.

Bilateral communication between bones and muscles is essential for healing composite bone-muscle injuries from orthopedic surgeries and trauma. However, these injuries are often characterized by exaggerated inflammation, which can disrupt bone-muscle crosstalk, thereby seriously delaying the healing of either tissue. Existing approaches are largely effective at healing single tissues. However, simultaneous healing of multiple tissues remains challenging, with little research conducted to date. Here we introduce collagen patches that overcome this overlooked issue by harnessing the plasticity of macrophage phenotypes. Phosphatidylserine liposomes (PSLs) capable of shifting the macrophage phenotype from inflammatory M1 into anti-inflammatory/prohealing M2 were coated on collagen patches via a layer-by-layer method. Original collagen patches failed to improve tissue healing under inflammatory conditions coordinated by M1 macrophages. In contrast, PSL-coated collagen patches succeeded in accelerating bone and muscle healing by inducing a microenvironment dominated by M2 macrophages. In cell experiments, differentiation of preosteoblasts and myoblasts was completely inhibited by secretions of M1 macrophages but unaffected by those of M2 macrophages. RNA-seq analysis revealed that type I interferon and interleukin-6 signaling pathways were commonly upregulated in preosteoblasts and myoblasts upon stimulation with M1 macrophage secretions, thereby compromising their differentiation. This study demonstrates the benefit of PSL-mediated M1-to-M2 macrophage polarization for simultaneous bone and muscle healing, offering a potential strategy toward simultaneous regeneration of multiple tissues. STATEMENT OF SIGNIFICANCE: Existing approaches for tissue regeneration, which primarily utilize growth factors, have been largely effective at healing single tissues. However, simultaneous healing of multiple tissues remains challenging and has been little studied. Here we demonstrate that collagen patches releasing phosphatidylserine liposomes (PSLs) promote M1-to-M2 macrophage polarization and are effective for simultaneous healing of bone and muscle. Transcriptome analysis using next-generation sequencing reveals that differentiation of preosteoblasts and myoblasts is inhibited by the secretions of M1 macrophages but promoted by those of M2 macrophages, highlighting the importance of timely regulation of M1-to-M2 polarization in tissue regeneration. These findings provide new insight to tissue healing of multiple tissues.

Development of betabodies: The next generation of phosphatidylserine targeting agents.

Externalized phosphatidylserine (PS) is a phospholipid and a selective marker of the tumor microenvironment (TME). It is exposed on the outer leaflet of the plasma membrane of tumor-associated endothelial cells, apoptotic tumor cells, and some viable tumor cells, where it functions in part to suppress immune responses by binding to PS receptors expressed on tumor-infiltrating myeloid cells. PS has been targeted with antibodies, such as bavituximab, that bind the phospholipid via a cofactor, ß2-glycoprotein 1 (ß2GP1); these antibodies showed excellent specificity for tumor vasculature and induce an immune stimulatory environment. We have advanced this concept by developing the next generation of PS targeting agent, a fusion protein (betabody) constructed by linking PS-binding domain V of ß2GP1 to the Fc of an IgG2a. Betabodies bind to externalized PS with high affinity (∼1 nM), without the requirement of a co-factor and localize robustly to the TME. We demonstrate that betabodies are a direct PS-targeting agent that has the potential to be used as anti-tumor therapy, drug delivery vehicles, and tools for imaging the TME.

Molecular insights into human phosphatidylserine synthase 1 reveal its inhibition promotes LDL uptake.

In mammalian cells, two phosphatidylserine (PS) synthases drive PS synthesis. Gain-of-function mutations in the Ptdss1 gene lead to heightened PS production, causing Lenz-Majewski syndrome (LMS). Recently, pharmacological inhibition of PSS1 has been shown to suppress tumorigenesis. Here, we report the cryo-EM structures of wild-type human PSS1 (PSS1WT), the LMS-causing Pro269Ser mutant (PSS1P269S), and PSS1WT in complex with its inhibitor DS55980254. PSS1 contains 10 transmembrane helices (TMs), with TMs 4-8 forming a catalytic core in the luminal leaflet. These structures revealed a working mechanism of PSS1 akin to the postulated mechanisms of the membrane-bound O-acyltransferase family. Additionally, we showed that both PS and DS55980254 can allosterically inhibit PSS1 and that inhibition by DS55980254 activates the SREBP pathways, thus enhancing the expression of LDL receptors and increasing cellular LDL uptake. This work uncovers a mechanism of mammalian PS synthesis and suggests that selective PSS1 inhibitors have the potential to lower blood cholesterol levels.