Spring viremia of carp virus, abbreviated SVCV, belongs to the family Rhabdoviridae, a group of enveloped, negative-sense RNA viruses that includes well-known terrestrial pathogens such as rabies virus and vesicular stomatitis virus. In aquaculture, rhabdoviruses are notorious for their high infectivity at water temperatures below 20 degrees Celsius, a property that has caused significant economic losses across fish farming operations worldwide. SVCV, which infects carp and related cyprinid species, causes hemorrhages, edema, and high mortality, and outbreaks typically occur in temperate seasons when water temperatures are low. Despite decades of research, the molecular mechanisms underlying this temperature-dependent infectivity and pathogenicity had not been clearly defined, leaving a substantial gap in the understanding of how aquatic viruses adapt to their thermal environment.

To address this question, the research team used SVCV as a model system and examined how cold conditions alter the biochemistry of the host cell in ways that favor viral replication. Their central discovery concerns palmitoylation, the reversible attachment of palmitic acid, a saturated fatty acid containing sixteen carbon atoms, to specific cysteine residues on proteins. Palmitoylation is catalyzed by a family of enzymes known as DHHC-domain-containing acyltransferases, and it serves as a common mechanism for regulating protein stability, membrane association, and intracellular trafficking. The authors found that when zebrafish, the experimental host, are kept at low temperatures, the levels of palmitic acid within their cells rise markedly, creating an abundant substrate pool for this lipid modification machinery.

The critical target of this cold-induced lipid surge is the SVCV glycoprotein, known simply as the G protein, which decorates the viral envelope and mediates both attachment to host cells and the assembly of new virions. The study demonstrates that elevated palmitic acid availability at low temperatures promotes palmitoylation of the G protein, and that this modification has two important consequences. First, palmitoylation enhances the stability of the G protein, protecting it from degradation and allowing more of it to accumulate within infected cells. Second, the modification promotes the localization of the G protein to the cell membrane, the site where enveloped viruses assemble and exit the host cell. Together, these effects facilitate viral budding, the process by which newly formed virions acquire their lipid envelope and are released to infect neighboring cells.

Beyond identifying the modification itself, the researchers pinpointed the enzyme responsible for carrying it out. Through their experiments, they identified ZDHHC15a, a member of the DHHC acyltransferase family, as the specific acyltransferase that mediates palmitoylation of the SVCV G protein. Importantly, the expression of ZDHHC15a is upregulated at low temperatures, meaning that cold conditions act twice in favor of the virus: they increase the supply of palmitic acid substrate and simultaneously boost the levels of the enzyme that attaches it to the viral glycoprotein. This dual effect provides a mechanistic explanation for why SVCV and related rhabdoviruses replicate so efficiently in cold water, converting a broad environmental variable into a precise molecular event at the viral envelope assembly step.

The mechanistic insight also suggested a potential therapeutic strategy. Because palmitoylation of the G protein depends on specific sequence features at the palmitoylation site, the authors designed a competitive peptide targeting this site, reasoning that it could occupy the enzymatic machinery and prevent the authentic modification of the viral glycoprotein. Their experiments showed that this peptide exhibited potent antiviral activity, blocking the palmitoylation-dependent enhancement of viral replication. This proof of concept is significant for aquaculture, where antiviral options are limited and disease control relies heavily on vaccination, biosecurity, and temperature management. A peptide-based intervention that exploits the temperature-dependent palmitoylation pathway could offer a targeted means of suppressing SVCV outbreaks during cold seasons when the virus is most dangerous.

A particularly striking aspect of the study is its suggestion that the mechanism is not unique to SVCV. The researchers observed a similar palmitoylation-dependent process in other aquatic rhabdoviruses that are also susceptible to low temperatures, indicating that this lipid-mediated adaptation may be a shared strategy among cold-adapted fish viruses. If this holds true more broadly, it would imply that the temperature sensitivity of aquatic rhabdoviruses reflects a convergent biochemical adaptation centered on the manipulation of host fatty acid metabolism and acyltransferase activity. Such a shared vulnerability would be attractive from an applied perspective, since a single intervention targeting the palmitoylation pathway could potentially protect farmed fish against multiple rhabdovirus species simultaneously.

The broader significance of the work extends beyond fish health. Temperature is a fundamental determinant of viral fitness for many pathogens, and the mechanisms by which viruses sense and exploit thermal cues are incompletely understood across virology. By showing that a host lipid modification pathway responds to cold and directly enhances the stability and membrane localization of a viral glycoprotein, the study provides a concrete example of how environmental temperature can be translated into molecular changes that favor viral propagation. The authors note that their findings hold broader significance for understanding the temperature-adaptive evolution of other aquatic viruses, suggesting that lipid metabolism may represent a general axis of host-virus interaction shaped by thermal ecology.

From an ecological and economic standpoint, the results arrive at a time when aquaculture is expanding rapidly to meet global protein demand, and cold-water fish species such as carp constitute a major share of production in many regions. Seasonal temperature drops, which are unavoidable in open pond systems, have historically correlated with waves of rhabdovirus outbreaks, and climate variability may further complicate these patterns by altering the timing and severity of cold periods. A mechanistic understanding of why cold favors these viruses gives fish health managers a rational basis for interventions, whether through breeding for resistant stocks, modulating lipid metabolism through feed additives, or deploying antiviral peptides during high-risk seasons. The identification of ZDHHC15a as a host factor also raises the possibility of genetic or pharmacological approaches that dampen the cold-induced upregulation of this enzyme without harming the fish.

Looking forward, the study opens several avenues for further investigation. It will be important to determine how low temperatures signal the increase in palmitic acid levels and the upregulation of ZDHHC15a in fish cells, and whether related lipid modifications influence the glycoproteins of other temperature-sensitive viruses in aquatic and terrestrial hosts. The competitive peptide strategy will also need to be validated in practical aquaculture settings, where delivery, stability, and cost are critical considerations. Nevertheless, the core finding stands as a clear demonstration that a seemingly simple environmental variable, the temperature of the water, is translated through host lipid biochemistry into a direct enhancement of viral replication. By tracing that chain from cold water to fatty acid accumulation to glycoprotein palmitoylation to efficient viral budding, the researchers have transformed a long-standing observation in fish virology into a defined molecular pathway, and in doing so have provided both a conceptual framework and a concrete therapeutic target for combating one of aquaculture’s most persistent viral threats.

Subject of Research: Temperature-dependent palmitoylation of the spring viremia of carp virus glycoprotein and its role in cold-enhanced rhabdovirus replication in fish

Article Title: Palmitoylation of glycoproteins under low temperature enhances SVCV replication

Article References: Li, C., Zhang, Y., Zhang, Y., Gao, Y., Lu, Y., Cao, S., Ye, J., & Liu, X. (2026). Palmitoylation of glycoproteins under low temperature enhances SVCV replication. PLOS Pathogens, 22(9), e1014654. https://doi.org/10.1371/journal.ppat.1014654

Image Credits: AI Generated

DOI: 10.1371/journal.ppat.1014654

Keywords: SVCV, rhabdovirus, palmitoylation, glycoprotein, ZDHHC15a, palmitic acid, fish virology, aquaculture, low temperature, viral budding, antiviral peptide, zebrafish

The research team prepared pork leg meat by removing connective tissue and grinding lean and fat portions together at a ratio of 8.5 to 1.5. Into this base emulsion they mixed a seasoned formulation containing sugar, fish sauce, glycerol, spices, salt, and water, then varied the gelatin concentration from 0 to 2.5 percent by weight. Each formulation was printed into a rectangular slab mimicking pork jerky using a food-grade extrusion printer operating at 25 degrees Celsius with a 1.55-millimeter nozzle, 100 percent infill, and a printing speed of 30 millimeters per second. The printed products were then hot-air dried, baked, and analyzed for everything from gel strength to moisture distribution.

Rheological measurements revealed why gelatin matters so much. In dynamic frequency sweeps, the storage modulus G-prime exceeded the loss modulus G-double-prime in every formulation, meaning the material behaved predominantly as a solid-like viscoelastic gel. That solid-like character is exactly what a printed layer needs: it allows the extruded strand to support the weight of subsequent layers without collapsing. Gel strength rose significantly with gelatin content, climbing from 119.62 grams in the untreated paste to 154.48 grams at the highest dosage, a change the authors attribute to hydrogen bonds forming between gelatin molecules and the myofibrillar proteins that make up 50 to 55 percent of pork’s total protein.

But more gelatin is not always better. When the concentration reached 2 percent, the researchers observed clogging and adhesion at the nozzle, likely because undissolved gelatin particles or overly viscous aggregates disrupted the uniformity of the paste and jammed the extrusion process. The sweet spot turned out to be 1 percent gelatin, which produced the best layer adhesion, the highest printing fidelity, and no structural collapse. Confocal laser scanning microscopy confirmed the story visually: without gelatin the protein network was loose and porous with large voids, while moderate gelatin addition produced a densely cross-linked, compact matrix. At 2.5 percent, however, the network showed signs of stacking and compression, as excess macromolecular gelatin crowded the native pork proteins.

Water is the hidden variable in printed meat. Using low-field nuclear magnetic resonance, the team identified three water populations in the gels — bound water, immobilized water, and free water — corresponding to relaxation peaks at roughly 0.01 to 10, 10 to 100, and 100 to 1000 milliseconds. At the optimal 1 percent gelatin level, all three relaxation times reached their shortest values, indicating the tightest integration of water into the protein network, while the free-water fraction peaked at 1.09 percent, providing just enough lubrication for smooth extrusion. Water-holding capacity climbed in a dose-dependent manner, reaching 80 percent at 1 percent gelatin, and the baking loss rate fell to its minimum of 48.63 percent at the same concentration — a meaningful economic gain, since every percentage point of moisture lost during cooking is weight and value lost from the product.

Fourier-transform infrared spectroscopy added a conformational dimension to the findings. The alpha-helix content of the proteins, which was only 17 percent in the unmodified paste, rose to 23 percent as gelatin increased to 1.5 percent, while the proportion of disordered random coils initially declined. Because alpha-helical content reflects hydrophobic groups and sulfhydryl groups being folded back into the protein interior, this shift signals a more ordered, elastic gel. The authors note that gel performance peaks at a certain degree of helical unfolding or re-formation, and their data pinpoint 1 percent gelatin as the concentration that achieves that balance.

The most novel part of the study, however, descends to the molecular scale. Because myofibrillar proteins contain fluorescent tryptophan and tyrosine residues, the team could use fluorescence spectroscopy as a molecular spy. When oleic acid or palmitic acid — the two predominant fatty acids in pork — were added to purified myofibrillar protein, the intrinsic fluorescence dimmed progressively, with quenching efficiencies of 51.70 percent for oleic acid and 50.74 percent for palmitic acid in the binary systems. Stern-Volmer analysis showed that the quenching constants decreased as temperature rose from 328.15 to 338.15 kelvin, the signature of static quenching: the fatty acids form stable, non-fluorescent ground-state complexes with the protein rather than merely colliding with it.

Gelatin rewired these interactions in revealing ways. In the ternary systems containing gelatin, quenching efficiencies dropped to 33.81 percent for the oleic acid combination and 41.5 percent for palmitic acid, showing that gelatin partially shields the protein’s fluorescent residues from fatty acid binding. Binding constants and the number of binding sites both increased in the presence of gelatin, with the effect stronger for palmitic acid than for oleic acid. Thermodynamic analysis of enthalpy and entropy changes showed that oleic acid alone binds myofibrillar protein through hydrophobic interactions, an endothermic process that strengthens with heat. Add gelatin, however, and the dominant forces shift to van der Waals interactions and hydrogen bonds — the same forces that govern palmitic acid binding with or without gelatin. Synchronous fluorescence spectra reinforced the picture, showing blue shifts of up to 4 nanometers that indicate the amino acid microenvironments became less polar and more hydrophobic, with gelatin exerting a stronger influence on tyrosine than on tryptophan.

What makes this study compelling is the way it connects the molecular ledger to the printed object on the plate. Gelatin’s thermally reversible triple-helix gelation and strong shear-thinning behavior give the paste the flow profile needed for smooth extrusion and the rapid re-gelling needed for self-supporting layers, while its protein nature lets it weave directly into the myofibrillar network in a way that polysaccharide hydrocolloids such as carrageenan and gellan gum cannot. By modulating how fatty acids bind to the protein matrix — softening quenching, increasing binding capacity, and steering oleic acid toward hydrogen-bonded association — gelatin stabilizes the entire lipid-protein-water architecture that determines whether a printed pork product holds its shape, retains its moisture, and survives the oven. For a field racing toward personalized nutrition, cultured-meat scaffolds, and printed meals for dysphagia patients, the message is that printability is not just a rheology problem; it is a molecular recognition problem, and the right hydrocolloid can solve both at once.

Subject of Research: Gelatin modulation of 3D printing properties and fatty acid–myofibrillar protein interactions in pork mince

Article Title: Study on the modulation of the properties of 3D printing pork mince and interaction mechanisms with myofibrillar proteins and fatty acids by gelatin

Article References: Wu, L., Wang, A., & Cui, Q. (2026). Study on the modulation of the properties of 3D printing pork mince and interaction mechanisms with myofibrillar proteins and fatty acids by gelatin. Food Chemistry: X, Article 104543. https://doi.org/10.1016/j.fochx.2026.104543

Image Credits: AI Generated

DOI: Not provided

Keywords: 3D food printing, gelatin, pork mince, myofibrillar proteins, oleic acid, palmitic acid, fluorescence spectroscopy, rheology, water-holding capacity, protein conformation, food hydrocolloids, static quenching

MASH develops when excessive lipid accumulation in the liver triggers chronic inflammation, hepatocellular injury, and ultimately fibrosis, the scarring process that replaces functional tissue with rigid extracellular matrix. In Japan alone, several million individuals are estimated to be affected, and disease progression is tightly linked to obesity, diabetes, and dyslipidemia. When adipose tissue becomes inflamed, it floods the circulation with free fatty acids and pro-inflammatory cytokines, amplifying the hepatic inflammatory milieu. Yet while the broad role of lipid overload in liver disease is well established, the mechanisms by which individual fatty acid species contribute to fibrogenesis have remained frustratingly opaque.

Central to the new work is the concept of macrophage polarization, the remarkable plasticity of innate immune cells that allows them to shift between functionally distinct states. Resting M0 macrophages can polarize toward pro-inflammatory M1 phenotypes, driven by stimuli such as lipopolysaccharide and interferon-gamma and characterized by production of tumor necrosis factor-alpha and inducible nitric oxide synthase, or toward anti-inflammatory M2 phenotypes induced by interleukin-4 and interleukin-13, marked by expression of peroxisome proliferator-activated receptor gamma and other mediators of tissue repair and fibrosis. Because dysregulated macrophage polarization is a key determinant of chronic inflammatory diseases including MASH, the research team led by investigators at Osaka Metropolitan University set out to determine whether specific fatty acids could bias this process in cultured cells.

Using bone marrow-derived macrophages isolated from male Wistar rats, the researchers exposed cells to albumin-conjugated palmitic acid, oleic acid, or palmitoleic acid at non-cytotoxic concentrations of 0.1 and 0.2 millimolar while simultaneously polarizing them toward M1 or M2 states. The results were strikingly fatty acid-specific. Palmitic acid, the saturated species that accounts for roughly 31 percent of plasma free fatty acids, significantly increased Tnf mRNA and boosted both iNOS and TNF-alpha protein expression in M1 macrophages, effectively reinforcing their inflammatory profile. It also consistently suppressed PPARgamma, a master transcriptional regulator of alternative activation, in M2 macrophages. Because PPARgamma negatively constrains NF-kappaB-mediated inflammatory signaling, its suppression may tilt macrophages toward a more pro-inflammatory identity.

The unsaturated fatty acids told a different story. Oleic acid, which makes up approximately 27 percent of plasma free fatty acids, increased Nos2 and Tnf mRNA in resting and M2 macrophages, but these transcriptional changes never materialized into detectable protein, and their magnitude was trivial compared with genuine M1 induction. Nevertheless, oleic acid proved far from benign: it significantly enhanced reactive oxygen species production in M1 macrophages and reduced several M2-associated markers, including PPARgamma and Ym1. This context dependence is notable given previous reports of oleic acid’s anti-inflammatory effects mediated through the free fatty acid receptor FFAR4 and adiponectin-driven AMPK activation. Palmitoleic acid, the monounsaturated omega-7 species, displayed its own signature: it dampened iNOS protein expression and significantly suppressed ROS production in M1 macrophages, consistent with prior evidence that it can antagonize palmitate-induced inflammation through AMPK and TLR4-related mechanisms, yet it too reduced selected M2 markers.

Oxidative stress emerged as a central theme. Using the chemiluminescent probe L-012, the team measured superoxide generation in polarized macrophages and found that ROS production was markedly higher in M1 cells than in M0 or M2 counterparts, confirming that the inflammatory program is intrinsically linked to redox activity. Critically, fatty acid treatment had minimal effects on ROS in resting and M2 macrophages, but palmitic acid and oleic acid each significantly increased superoxide production in M1 macrophages, while palmitoleic acid significantly decreased it. Since the majority of detected ROS was superoxide, likely originating from mitochondria and NADPH oxidase complexes, the data suggest that palmitate-induced oxidative stress in inflammatory macrophages may involve NOX-dependent mechanisms, a hypothesis the authors note requires direct testing of TLR4 and NF-kappaB pathways in future work.

The researchers then turned to the other half of the fibrotic dialogue: hepatic stellate cells, which reside quiescently in the space of Disse storing vitamin A-laden lipid droplets until chronic injury drives them to activate, express alpha-smooth muscle actin, and deposit type I collagen. In a first series of experiments, direct treatment of primary rat stellate cells with any of the three fatty acids failed to alter alpha-SMA, cytoglobin, TGF-beta, or Col1a1 expression at either the mRNA or protein level, indicating that none of the tested lipids directly activates stellate cells under these conditions. This negative result is itself meaningful, redirecting attention from direct lipotoxicity toward immune-mediated indirect pathways.

When stellate cells were instead cultured in conditioned media harvested from fatty acid-treated polarized macrophages, the picture shifted. The dominant determinant of stellate cell marker expression was the macrophages’ polarization status rather than the fatty acid they had received. Conditioned media from M1 macrophages reduced both alpha-SMA and cytoglobin expression in stellate cells compared with media from resting M0 cells, and fatty acid-specific effects were modest and marker-dependent. Cytoglobin deserves particular attention: this antioxidant protein protects stellate cells by scavenging reactive oxygen species and maintaining redox homeostasis, and its reduction, as documented in previous studies of NASH, can weaken antioxidant defenses and heighten susceptibility to oxidative DNA damage. The authors therefore interpret their data as evidence that fatty acid-dependent macrophage reprogramming can secondarily modify stellate cell redox-related responses, without claiming that fatty acids directly drive stellate cell activation.

The study is not without limitations, which the authors candidly enumerate. TLR4-dependent signaling was not directly assessed, ROS measurements relied primarily on L-012 chemiluminescence rather than complementary probes, the entire system was in vitro and awaits validation in animal models of MASH, stellate cell activation was evaluated by marker expression rather than functional assays of proliferation, migration, and contractility, and some experiments employed relatively small numbers of biological replicates. The fatty acid concentrations chosen, 0.2 millimolar, were selected after preliminary cytotoxicity testing and sit below concentrations commonly used in the field, though local concentrations within the hepatic microenvironment may differ from systemic levels.

Even with these caveats, the work delivers a provocative message: lipid composition, not merely lipid quantity, is a meaningful determinant of immune-stromal interactions in the liver. By showing that a saturated fatty acid pushes macrophages toward inflammatory, ROS-generating phenotypes while a monounsaturated omega-7 species dampens them, and that these shifts ripple outward to alter antioxidant signaling in the cells that build scar tissue, the study sketches a plausible mechanism linking dietary fat quality to fibrogenic progression in metabolic liver disease. If confirmed in vivo, the findings could open new avenues for intervening in MASH not simply by reducing fat intake, but by reshaping the fatty acid milieu that instructs the immune system how to respond to it.

Subject of Research: Fatty acid species-dependent regulation of macrophage polarization, oxidative stress, and macrophage-hepatic stellate cell crosstalk in liver fibrosis.

Article Title: Fatty acid species differentially regulate macrophage polarization and oxidative stress with secondary effects on macrophage–HSC crosstalk

Article References: Nakanishi, K., Shinkawa, H., Takemura, S., Nakagawa, K., Minamiyama, Y., & Ishizawa, T. (2026). Fatty acid species differentially regulate macrophage polarization and oxidative stress with secondary effects on macrophage– HSC crosstalk. Physiological Reports, 14(17), Article e71082. https://doi.org/10.14814/phy2.71082

Image Credits: AI Generated

DOI: 10.14814/phy2.71082

Keywords: macrophage polarization, fatty acids, palmitic acid, oleic acid, palmitoleic acid, hepatic stellate cells, liver fibrosis, MASH, oxidative stress, PPARgamma, cytoglobin, TLR4