Omega-3 Fatty Acids Modulate TRPV4 Function through Plasma Membrane Remodeling

The chondrocyte "mechanome": Activation of the mechanosensitive ion channels TRPV4 and PIEZO1 drives unique transcriptional signatures

The mechanosensitive ion channels Transient Receptor Potential Vanilloid 4 (TRPV4) and PIEZO1 transduce physiologic and supraphysiologic magnitudes of mechanical signals in the chondrocyte, respectively. TRPV4 activation promotes chondrogenesis, while PIEZO1 activation by supraphysiologic deformations drives cell death. The mechanisms by which activation of these channels discretely drives changes in gene expression to alter cell behavior remain to be determined. To date, no studies have contrasted the transcriptomic response to activation of these channels nor has any published data attempted to correlate these transcriptomes to alterations in cellular function. This study used RNA sequencing to comprehensively investigate the transcriptomes associated with activation of TRPV4 or PIEZO1, revealing that TRPV4 and PIEZO drive distinct transcriptomes and also exhibit unique co-regulated clusters of genes. Notably, activation of PIEZO1 through supraphysiologic deformation induced a transient inflammatory profile that overlapped with the interleukin (IL)-1-responsive transcriptome and contained genes associated with cartilage degradation and osteoarthritis progression. However, both TRPV4 and PIEZO1 were also shown to elicit anabolic effects. PIEZO1 expression promoted a pro-chondrogenic transcriptome under unloaded conditions, and daily treatment with PIEZO1 agonist Yoda1 significantly increased sulfated glycosaminoglycan deposition in vitro. These findings emphasize the presence of a broad "mechanome" with distinct effects of TRPV4 and PIEZO1 activation in chondrocytes, suggesting complex roles for PIEZO1 in both the physiologic and pathologic responses of chondrocytes. The identification of transcriptomic profiles unique to or shared by PIEZO1 and TRPV4 (distinct from IL-1-induced inflammation) could inform future therapeutic designs targeting these channels for the management and treatment of osteoarthritis.

The sphingosine 1-phosphate analogue, FTY720, modulates the lipidomic signature of the mouse hippocampus

The small-molecule drug, FTY720 (fingolimod), is a synthetic sphingosine 1-phosphate (S1P) analogue currently used to treat relapsing-remitting multiple sclerosis in both adults and children. FTY720 can cross the blood-brain barrier (BBB) and, over time, accumulate in lipid-rich areas of the central nervous system (CNS) by incorporating into phospholipid membranes. FTY720 has been shown to enhance cell membrane fluidity, which can modulate the functions of glial cells and neuronal populations involved in regulating behaviour. Moreover, direct modulation of S1P receptor-mediated lipid signalling by FTY720 can impact homeostatic CNS physiology, including neurotransmitter release probability, the biophysical properties of synaptic membranes, ion channel and transmembrane receptor kinetics, and synaptic plasticity mechanisms. The aim of this study was to investigate how chronic FTY720 treatment alters the lipid composition of CNS tissue in adolescent mice at a key stage of brain maturation. We focused on the hippocampus, a brain region known to be important for learning, memory, and the processing of sensory and emotional stimuli. Using mass spectrometry-based lipidomics, we discovered that FTY720 increases the fatty acid chain length of hydroxy-phosphatidylcholine (PCOH) lipids in the mouse hippocampus. It also decreases PCOH monounsaturated fatty acids (MUFAs) and increases PCOH polyunsaturated fatty acids (PUFAs). A total of 99 lipid species were up-regulated in the mouse hippocampus following 3 weeks of oral FTY720 exposure, whereas only 3 lipid species were down-regulated. FTY720 also modulated anxiety-like behaviours in young mice but did not affect spatial learning or memory formation. Our study presents a comprehensive overview of the lipid classes and lipid species that are altered in the hippocampus following chronic FTY720 exposure and provides novel insight into cellular and molecular mechanisms that may underlie the therapeutic or adverse effects of FTY720 in the central nervous system.

Integrative chemical and multiomics analyses of tetracycline removal mechanisms in Pseudomonas sp. DX-21

Tetracycline (TC), widely found in various environments, poses significant risks to ecosystems and human health. While efficient biodegradation removes TC, the mechanisms underlying this process have not been elucidated. This study investigated the molecular mechanisms underlying TC biosorption and transfer within the extracellular polymeric substances (EPS) of strain DX-21 and its biodegradation process using fourier transform infrared spectroscopy, molecular docking, and multiomics. Under TC stress, DX-21 increased TC biosorption by secreting more extracellular polysaccharides and proteins, particularly the latter, mitigating toxicity. Moreover, specialized transporter proteins with increased binding capacity facilitated TC movement from the EPS to the cell membrane and within the cell. Transcriptomic and untargeted metabolomic analyses revealed that the presence of TC led to the differential expression of 306 genes and significant alterations in 37 metabolites. Notably, genes related to key enzymes, such as electron transport, peroxidase, and oxidoreductase, exhibited significant differential expression. DX-21 combated and degraded TC by regulating metabolism, altering cell membrane permeability, enhancing oxidative defense, and enhancing energy availability. Furthermore, integrative omics analyses indicated that DX-21 degrades TC via various enzymes, reallocating resources from other biosynthetic pathways. These results advance the understanding of the metabolic responses and regulatory mechanisms of DX-21 in response to TC.

Targeting TRPV4 Channels for Cancer Pain Relief

Despite the unique and complex nature of cancer pain, the activation of different ion channels can be related to the initiation and maintenance of pain. The transient receptor potential vanilloid 4 (TRPV4) is a cation channel broadly expressed in sensory afferent neurons. This channel is activated by multiple stimuli to mediate pain perception associated with inflammatory and neuropathic pain. Here, we focused on summarizing the role of TRPV4 in cancer etiology and cancer-induced pain mechanisms. Many studies revealed that the administration of a TRPV4 antagonist and TRPV4 knockdown diminishes nociception in chemotherapy-induced peripheral neuropathy (CIPN). Although the evidence on TRPV4 channels' involvement in cancer pain is scarce, the expression of these receptors was reportedly enhanced in cancer-induced bone pain (CIBP), perineural, and orofacial cancer models following the inoculation of tumor cells to the bone marrow cavity, sciatic nerve, and tongue, respectively. Effective pain management is a continuous problem for patients diagnosed with cancer, and current guidelines fail to address a mechanism-based treatment. Therefore, examining new molecules with potential antinociceptive properties targeting TRPV4 modulation would be interesting. Identifying such agents could lead to the development of treatment strategies with improved pain-relieving effects and fewer adverse effects than the currently available analgesics.

Liver X receptor agonist upregulates LPCAT3 in human aortic endothelial cells

Objective

Endothelial cells (ECs) play an important role in tissue homeostasis. Recently, EC lipid metabolism has emerged as a regulator of EC function. The liver X receptors (LXRs) are involved in the transcriptional regulation of genes involved in lipid metabolism and have been identified as a potential target in cardiovascular disease. We aimed to decipher the role of LXRs in the regulation of lipid metabolism in human aortic endothelial cells.

Approach and Results

Lipid composition analysis of endothelial cells treated with the LXR agonist T0901317 revealed that LXR activation increased the proportion of polyunsaturated fatty acids (PUFAs) and decreased the proportion of saturated fatty acids. The LXR agonist decreased the uptake of fatty acids (FAs) by ECs. This effect was abolished by LXRα silencing. LXR activation increased the activity and the expression of lysophosphatidylcholine acyltransferase, LPCAT3, which is involved in the turnover of FAs at the sn-2 position of phospholipids. Transcriptomic analysis also revealed that LXRs increased the expression of key genes involved in the synthesis of PUFAs, including FA desaturase one and 2, FA elongase 5 and fatty acid synthase. Subsequently, the LXR agonist increased PUFA synthesis and enhanced arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid content in the EC phospholipids. Modification of the FA composition of ECs by LXRs led to a decrease of arachidonate and linoleate derived prostaglandins synthesis and release. No change on markers of inflammation induced by plasma from sickle cell patient were observed in presence of LXR agonist.

Conclusion

These results identify LXR as a key regulator of lipid metabolism in human aortic endothelial cells and a direct effect of LXR agonist on lysophosphatidylacyl transferase (LPCAT3).

TRPV4-dependent Ca2+ influx determines cholesterol dynamics at the plasma membrane

The activities of the transient receptor potential vanilloid 4 (TRPV4), a Ca2+-permeable nonselective cation channel, are controlled by its surrounding membrane lipids (e.g., cholesterol, phosphoinositides). The transmembrane region of TRPV4 contains a cholesterol recognition amino acid consensus (CRAC) motif and its inverted (CARC) motif located in the plasmalemmal cytosolic leaflet. TRPV4 localizes in caveolae, a bulb-shaped cholesterol-rich domain at the plasma membrane. Here, we visualized the spatiotemporal interactions between TRPV4 and cholesterol at the plasma membrane in living cells by dual-color single-molecule imaging using total internal reflection fluorescence microscopy. To this aim, we labeled cholesterol at the cytosolic leaflets of the plasma membrane using a cholesterol biosensor, D4H. Our single-molecule tracking analysis showed that the TRPV4 molecules colocalize with D4H-accessible cholesterol molecules mainly in the low fluidity membrane domains in which both molecules are highly clustered. Colocalization of TRPV4 and D4H-accessible cholesterol was observed both inside and outside of caveolae. Agonist-evoked TRPV4 activation remarkably decreased colocalization probability and association rate between TRPV4 and D4H-accessible cholesterol molecules. Interestingly, upon TRPV4 activation, the particle density of D4H-accessible cholesterol molecules was decreased and the D4H-accessible cholesterol molecules in the fast-diffusing state were increased at the plasma membrane. The introduction of skeletal dysplasia-associated R616Q mutation into the CRAC/CARC motif of TRPV4, which reduced the interaction with cholesterol clusters, could not alter the D4H-accessible cholesterol dynamics. Mechanistically, TRPV4-mediated Ca2+ influx and the C-terminal calmodulin-binding site of TRPV4 are essential for modulating the plasmalemmal D4H-accessible cholesterol dynamics. We propose that TRPV4 remodels its surrounding plasmalemmal environment by manipulating cholesterol dynamics through Ca2+ influx.

5,6-diHETE lactone (EPA-L) mediates hypertensive microvascular dilation by activating the endothelial GPR-PLC-IP3 signaling pathway

Endothelial microvascular dysfunction affects multi-organ pathologic processes that contribute to increased vascular tone and is at the base of impaired metabolic and cardiovascular diseases. The vascular dilation impaired by nitric oxide (NO) deficiency in such dysfunctional endothelium is often balanced by endothelial-derived hyperpolarizing factors (EDHFs), which play a critical role in managing vascular tone. Our latest research has uncovered a new group of lactone oxylipins produced in the polyunsaturated fatty acids (PUFAs) CYP450 epoxygenase pathway, significantly affecting vascular dilation. The lactone oxylipin, derived from arachidonic acid (5,6-diHET lactone, AA-L), has been previously shown to facilitate vasodilation dependent on the endothelium in isolated human microvessels. The administration of the lactone oxylipin derived from eicosapentaenoic acid (5,6-diHETE lactone, EPA-L) to hypertensive rats demonstrated a significant decrease in blood pressure and improvement in the relaxation of microvessels. However, the molecular signaling processes that underlie these observations were not fully understood. The current study delineates the molecular pathways through which EPA-L promotes endothelium-dependent vascular dilation. In microvessels from hypertensive individuals, it was found that EPA-L mediates endothelium-dependent vasodilation while the signaling pathway was not dependent on NO. In vitro studies on human endothelial cells showed that the hyperpolarization mediated by EPA-L relies on G-protein-coupled receptor (GPR)-phospholipase C (PLC)-IP3 signaling that further activates calcium-dependent potassium flux. The pathway was confirmed using a range of inhibitors and cells overexpressing GPR40, where a specific antagonist reduced the calcium levels and outward currents induced by EPA-L. The downstream AKT and endothelial NO synthase (eNOS) phosphorylations were non-significant. These findings show that the GPR-PLC-IP3 pathway is a key mediator in the EPA-L-triggered vasodilation of arterioles. Therefore, EPA-L is identified as a significant lactone-based PUFA metabolite that contributes to endothelial and vascular health.

FA2H controls cool temperature sensing through modifying membrane sphingolipids in Drosophila

Animals have evolved the ability to detect ambient temperatures, allowing them to search for optimal living environments. In search of the molecules responsible for cold-sensing, we examined a Gal4 insertion line in the larvae of Drosophila melanogaster from previous screening work, which has a specific expression pattern in the cooling cells (CCs). We identified that the targeted gene, fa2h, which encodes a fatty acid 2-hydroxylase, plays an important role in cool temperature sensing. We found that fa2h mutants exhibit defects in cool avoidance behavior and that this phenotype could be rescued by genetically re-introducing the wild-type version of FA2H in CCs but not the enzymatically disabled point mutation version. Calcium imaging data showed that CCs require fa2h to respond to cool temperature. Lipidomic analysis revealed that the 2-hydroxy sphingolipids content in the cell membranes diminished in fa2h mutants, resulting in increased fluidity of CC neuron membranes. Furthermore, in mammalian systems, we showed that FA2H strongly regulates the function of the TRPV4 channel in response to its agonist treatment and warming. Taken together, our study has uncovered a novel role of FA2H in temperature sensing and has provided new insights into the link between membrane lipid composition and the function of temperature-sensing ion channels.

Do patients benefit from omega-3 fatty acids?

Omega-3 fatty acids (O3FAs) possess beneficial properties for cardiovascular (CV) health and elevated O3FA levels are associated with lower incident risk for CV disease (CVD.) Yet, treatment of at-risk patients with various O3FA formulations has produced disparate results in large, well-controlled and well-conducted clinical trials. Prescription formulations and fish oil supplements containing low-dose mixtures of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have routinely failed to prevent CV events in primary and secondary prevention settings when added to contemporary care, as shown most recently in the STRENGTH and OMEMI trials. However, as observed in JELIS, REDUCE-IT, and RESPECT-EPA, EPA-only formulations significantly reduce CVD events in high-risk patients. The CV mechanism of action of EPA, while certainly multifaceted, does not depend solely on reductions of circulating lipids, including triglycerides (TG) and LDL, and event reduction appears related to achieved EPA levels suggesting that the particular chemical and biological properties of EPA, as compared to DHA and other O3FAs, may contribute to its distinct clinical efficacy. In vitro and in vivo studies have shown different effects of EPA compared with DHA alone or EPA/DHA combination treatments, on atherosclerotic plaque morphology, LDL and membrane oxidation, cholesterol distribution, membrane lipid dynamics, glucose homeostasis, endothelial function, and downstream lipid metabolite function. These findings indicate that prescription-grade, EPA-only formulations provide greater benefit than other O3FAs formulations tested. This review summarizes the clinical findings associated with various O3FA formulations, their efficacy in treating CV disease, and their underlying mechanisms of action.

Omega-3 PUFA and the fitness and cognition of the nematode Caenorhabditis elegans under different environmental conditions

Many invertebrate species possess the metabolic ability to synthesize long-chain ω3 polyunsaturated fatty acids (PUFA) de novo. Due to their diverse effects on membrane architecture, neuroplasticity, growth and reproduction, PUFA have a high potential to positively influence the fitness of an organism. But how and when do these supposed advantages actually come into play? Other species, that are often closely related, pass natural selection without this special metabolic ability. The ω3-PUFA rich model organism Caenorhabditis elegans (Nematoda) and its mutant fat-1(wa9), lacking these PUFA, are a suitable test system. We analyzed potential impairments in reproduction and growth in a soil assay. Further, chemotaxis after aversive olfactory, associative learning and integration of a second sensory signal were assessed on agar plates. Moreover, we analyzed the phospholipid pattern of both C. elegans strains and further free-living nematodes species at different temperatures. While the phenotypic effects were rather small under standard conditions, lowering the temperature to 15 or even 10 °C or reducing the soil moisture, led to significant limitations, with the investigated parameters for neuroplasticity being most impaired. The ω3-PUFA free C. elegans mutant strain fat-1 did not adapt the fatty acid composition of its phospholipids to a decreasing temperature, while ω3-PUFA containing nematodes proportionally increased this PUFA group. In contrats, other ω3-PUFA free nematode species produced significantly more ω6-PUFA. Thus, the ability to synthesize long-chain ω3-PUFA de novo likely is fundamental for an increase in neuroplasticity and an efficient way for regulating membrane fluidity to maintain their functionality.

Role of TRPV4 on vascular tone regulation in pathophysiological states

Vascular tone regulation is a key event in controlling blood flow in the body. Endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) help regulate the vascular tone. Abnormal vascular responsiveness to various stimuli, including constrictors and dilators, has been observed in pathophysiological states although EC and VSMC coordinate to maintain the exquisite balance between contraction and relaxation in vasculatures. Thus, investigating the mechanisms underlying vascular tone abnormality is very important in maintaining vascular health and treating vasculopathy. Increased intracellular free Ca2+ concentration ([Ca2+]i) is one of the major triggers initiating each EC and VSMC response. Transient receptor potential vanilloid family member 4 (TRPV4) is a Ca2+-permeable non-selective ion channel, which is activated by several stimuli, and is presented in both ECs and VSMCs. Therefore, TRPV4 plays an important role in vascular responses. Emerging evidence indicates the role of TRPV4 on the functions of ECs and VSMCs in various pathophysiological states, including hypertension, diabetes, and obesity. This review focused on the link between TRPV4 and the functions of ECs/VSMCs, particularly its role in vascular tone and responsiveness to vasoactive substances.

Maresin-1 prevents blood-spinal cord barrier disruption associated with TRPV4 elevation in the experimental model of spinal cord injury

Recently, we reported the TRPV4 ion channel activation and its association with secondary damage after spinal cord injury (SCI). TRPV4 activation is linked with blood-spinal cord barrier (BSCB) disruption, endothelial damage, and inflammation after SCI. Specialized pro-resolving mediators (SPM) are endogenous lipid mediators released for inflammation resolution. Studies suggest that SPM could act as an endogenous antagonist of ion channels directly or indirectly at the plasma membrane. Herein, we studied the effect of maresin-1, a docosahexaenoic acid (DHA)-derived SPM, in SCI-induced TRPV4 expression and subsequent associated damage. First, employing a particular agonist (4αPDD) in endothelial and neuronal cell lines, we examined the potential of maresin-1 to block TRPV4 activation. Then we quantify the DHA levels in plasma and epicenter of the spinal cord in sham and at 1, 3, 7, 14, 21, and 28-days post-injury (DPI) using LC-MS. Then, we exogenously administered maresin-1 using two dosing regimens i.e., single-dose (1 μg) and multiple-dose (1 μg/day for seven days), to confirm its role in the TRPV4 inhibition and its linked damage. After SCI, DHA levels decrease in the spinal cord epicenter area as well as in the plasma. Treatment with maresin-1 attenuates TRPV4 expression, inflammatory cytokines, and chemokines and impedes neutrophil infiltration. Furthermore, treatment with maresin-1 prevents BSCB disruption, alleviates glial scar formation, and improves functional recovery. Thus, our results suggest that maresin-1 could modulate TRPV4 expression and could be a safe and promising approach to target inflammation and BSCB damage after SCI.

The Role of Lipids in the Regulation of Immune Responses

Lipid metabolism plays a major role in the regulation of the immune system. Exogenous (dietary and microbial-derived) and endogenous (non-microbial-derived) lipids play a direct role in regulating immune cell activation, differentiation and expansion, and inflammatory phenotypes. Understanding the complexities of lipid-immune interactions may have important implications for human health, as certain lipids or immune pathways may be beneficial in circumstances of acute infection yet detrimental in chronic inflammatory diseases. Further, there are key differences in the lipid effects between specific immune cell types and location (e.g., gut mucosal vs. systemic immune cells), suggesting that the immunomodulatory properties of lipids may be tissue-compartment-specific, although the direct effect of dietary lipids on the mucosal immune system warrants further investigation. Importantly, there is recent evidence to suggest that lipid-immune interactions are dependent on sex, metabolic status, and the gut microbiome in preclinical models. While the lipid-immune relationship has not been adequately established in/translated to humans, research is warranted to evaluate the differences in lipid-immune interactions across individuals and whether the optimization of lipid-immune interactions requires precision nutrition approaches to mitigate or manage disease. In this review, we discuss the mechanisms by which lipids regulate immune responses and the influence of dietary lipids on these processes, highlighting compelling areas for future research.

Impact of membrane lipid polyunsaturation on dopamine D2 receptor ligand binding and signaling

Increasing evidence supports a relationship between lipid metabolism and mental health. In particular, the biostatus of polyunsaturated fatty acids (PUFAs) correlates with some symptoms of psychiatric disorders, as well as the efficacy of pharmacological treatments. Recent findings highlight a direct association between brain PUFA levels and dopamine transmission, a major neuromodulatory system implicated in the etiology of psychiatric symptoms. However, the mechanisms underlying this relationship are still unknown. Here we demonstrate that membrane enrichment in the n-3 PUFA docosahexaenoic acid (DHA), potentiates ligand binding to the dopamine D2 receptor (D2R), suggesting that DHA acts as an allosteric modulator of this receptor. Molecular dynamics simulations confirm that DHA has a high preference for interaction with the D2R and show that membrane unsaturation selectively enhances the conformational dynamics of the receptor around its second intracellular loop. We find that membrane unsaturation spares G protein activity but potentiates the recruitment of β-arrestin in cells. Furthermore, in vivo n-3 PUFA deficiency blunts the behavioral effects of two D2R ligands, quinpirole and aripiprazole. These results highlight the importance of membrane unsaturation for D2R activity and provide a putative mechanism for the ability of PUFAs to enhance antipsychotic efficacy.

Vascular Smooth Muscle TRPV4 (Transient Receptor Potential Vanilloid Family Member 4) Channels Regulate Vasoconstriction and Blood Pressure in Obesity

BACKGROUND

Vascular endothelium and smooth muscle work together to keep the balance of vasomotor tone and jointly maintain vascular homeostasis. Ca²⁺-permeable ion channel TRPV4 (transient receptor potential vanilloid family member 4) in endothelial cells regulates endothelium-dependent vasodilation and contraction in various states. However, how vascular smooth muscle cell TRPV4 (TRPV4_SMC) contributes to vascular function and blood pressure regulation in physiological and pathologically obese condition has not been fully studied.

METHODS

We generated smooth muscle TRPV4-deficient mice and developed diet-induced obese mice model and analyzed the role of TRPV4_SMC in intracellular Ca²⁺ ([Ca²⁺]_i) regulation and vasoconstriction. Vasomotor changes of mouse mesenteric artery were measured by wire, and pressure myography. [Ca²⁺]_i were measured by fluo-4 staining. Blood pressure was recorded by telemetric device.

RESULTS

Vascular TRPV4_SMC played different roles in regulating vasomotor tone than endothelial TRPV4 due to their different features of [Ca²⁺]_i regulation. Loss of TRPV4_SMC attenuated U46619- and phenylephrine-induced contraction, suggesting its involvement in regulating vascular contractility. Mesenteric arteries from obese mice showed SMC hyperplasia, suggesting an increased level of TRPV4_SMC. Loss of TRPV4_SMC did not influence the development of obesity but protected mice from obesity-induced vasoconstriction and hypertension. In arteries deficient in SMC TRPV4, SMCs F-actin polymerization and RhoA dephosphorylation were attenuated under contractile stimuli. Moreover, SMC-dependent vasoconstriction was inhibited in human resistance arteries with TRPV4 inhibitor application.

CONCLUSIONS

Our data identify TRPV4_SMC as a regulator of vascular contraction in both physiological states and pathologically obese mice. TRPV4_SMC contributes to the ontogeny of vasoconstriction and hypertension induced by TRPV4_SMC over-expression in obese mice mesenteric artery.

Linoleic acid improves PIEZO2 dysfunction in a mouse model of Angelman Syndrome

Angelman syndrome (AS) is a neurogenetic disorder characterized by intellectual disability and atypical behaviors. AS results from loss of expression of the E3 ubiquitin-protein ligase UBE3A from the maternal allele in neurons. Individuals with AS display impaired coordination, poor balance, and gait ataxia. PIEZO2 is a mechanosensitive ion channel essential for coordination and balance. Here, we report that PIEZO2 activity is reduced in Ube3a deficient male and female mouse sensory neurons, a human Merkel cell carcinoma cell line and female human iPSC-derived sensory neurons with UBE3A knock-down, and de-identified stem cell-derived neurons from individuals with AS. We find that loss of UBE3A decreases actin filaments and reduces PIEZO2 expression and function. A linoleic acid (LA)-enriched diet increases PIEZO2 activity, mechano-excitability, and improves gait in male AS mice. Finally, LA supplementation increases PIEZO2 function in stem cell-derived neurons from individuals with AS. We propose a mechanism whereby loss of UBE3A expression reduces PIEZO2 function and identified a fatty acid that enhances channel activity and ameliorates AS-associated mechano-sensory deficits.

Human skeletal dysplasia causing L596P-mutant alters the conserved amino acid pattern at the lipid-water-Interface of TRPV4

TRPV4 is a polymodal and non-selective cation channel that is activated by multiple physical and chemical stimuli. >50 naturally occurring point-mutation of TRPV4 have been identified in human, most of which induce different diseases commonly termed as channelopathies. While, these mutations are either "gain-of-function" or "loss-of-function" in nature, the exact molecular and cellular mechanisms behind such diverse channelopathies are largely unknown. In this work, we analyze the evolutionary conservation of individual amino acids present in the lipid-water-interface (LWI) regions and the relationship of TRPV4 with membrane cholesterol. Our data suggests that the positive-negative charges and hydrophobic-hydrophilic amino acids form "specific patterns" in the LWI region which remain conserved throughout the vertebrate evolution and thus suggesting for the specific microenvironment where TRPV4 remain functional. Notably, Spondylometaphyseal Dysplasia, Kozlowski (SMDK) disease causing L596P mutation disrupts this pattern significantly at the LWI region. L596P mutant also sequesters Caveolin-1 differently, especially in partial cholesterol-depleted (~40 % reduction) conditions. L596P shows altered localization in membrane and enhanced Ca²⁺-influx properties in cell as well as in filopodia-like structures. We propose that conserved pattern of amino acids is an important parameter for proper localization and functions of TRPV4 in physiological conditions. These findings also offer a new paradigm to analyze the channelopathies caused by mutations in LWI regions of other channels as well.

The role of endothelial TRP channels in age-related vascular cognitive impairment and dementia

Transient receptor potential (TRP) proteins are part of a superfamily of polymodal cation channels that can be activated by mechanical, physical, and chemical stimuli. In the vascular endothelium, TRP channels regulate two fundamental parameters: the membrane potential and the intracellular Ca²⁺ concentration [(Ca²⁺)_i]. TRP channels are widely expressed in the cerebrovascular endothelium, and are emerging as important mediators of several brain microvascular functions (e.g., neurovascular coupling, endothelial function, and blood-brain barrier permeability), which become impaired with aging. Aging is the most significant risk factor for vascular cognitive impairment (VCI), and the number of individuals affected by VCI is expected to exponentially increase in the coming decades. Yet, there are currently no preventative or therapeutic treatments available against the development and progression of VCI. In this review, we discuss the involvement of endothelial TRP channels in diverse physiological processes in the brain as well as in the pathogenesis of age-related VCI to explore future potential neuroprotective strategies.

Regulation of ThermoTRP Channels by PIP2 and Cholesterol

Transient receptor potential (TRP) ion channels are proteins that are expressed by diverse tissues and that play pivotal functions in physiology. These channels are polymodal and are activated by several stimuli. Among TRPs, some members of this family of channels respond to changes in ambient temperature and are known as thermoTRPs. These proteins respond to heat or cold in the noxious range and some of them to temperatures considered innocuous, as well as to mechanical, osmotic, and/or chemical stimuli. In addition to this already complex ability to respond to different signals, the activity of these ion channels can be fine-tuned by lipids. Two lipids well known to modulate ion channel activity are phosphatidylinositol 4,5-bisphosphate (PIP2) and cholesterol. These lipids can either influence the function of these proteins through direct interaction by binding to a site in the structure of the ion channel or through indirect mechanisms, which can include modifying membrane properties, such as curvature and rigidity, by regulating their expression or by modulating the actions of other molecules or signaling pathways that affect the physiology of ion channels. Here, we summarize the key aspects of the regulation of thermoTRP channels by PIP2 and cholesterol.

Genetic- and diet-induced ω-3 fatty acid enrichment enhances TRPV4-mediated vasodilation in mice

TRPV4 channel activation in endothelial cells leads to vasodilation, while impairment of TRPV4 activity is implicated in vascular dysfunction. Strategies that increase TRPV4 activity could enhance vasodilation and ameliorate vascular disorders. Here, we show that supplementation with eicosapentaenoic acid (EPA), an ω-3 polyunsaturated fatty acid known to have beneficial cardiovascular effects, increases TRPV4 activity in human endothelial cells of various vascular beds. Mice carrying the C. elegans FAT-1 enzyme, which converts ω-6 to ω-3 polyunsaturated fatty acids, display higher EPA content and increased TRPV4-mediated vasodilation in mesenteric arteries. Likewise, mice fed an EPA-enriched diet exhibit enhanced and prolonged TRPV4-dependent vasodilation in an endothelial cell-specific manner. We also show that EPA supplementation reduces TRPV4 desensitization, which contributes to the prolonged vasodilation. Neutralization of positive charges in the TRPV4 N terminus impairs the effect of EPA on channel desensitization. These findings highlight the beneficial effects of manipulating fatty acid content to enhance TRPV4-mediated vasodilation.

Quantitative determination of sn-positional phospholipid isomers in MSn using silver cationization

Glycerophospholipids are one of the fundamental building blocks for life. The acyl chain connectivity to the glycerol backbone constitutes different sn-positional isomers, which have great diversity and importance for biological function. However, to fully realize their impact on function, analytical techniques that can identify and quantify sn-positional isomers in chemically complex biological samples are needed. Here, we utilize silver ion cationization in combination with tandem mass spectrometry (MSⁿ) to identify sn-positional isomers of phosphatidylcholine (PC) species. In particular, a labile carbocation is generated through a neutral loss (NL) of AgH, the dissociation of which provides diagnostic product ions that correspond to acyl chains at the sn-1 or sn-2 position. The method is comparable to currently available methods, has a sensitivity in the nM–µM range, and is compatible with quantitative imaging using mass spectrometry in MS⁴. The results reveal a large difference in isomer concentrations and the ion images show that the sn-positional isomers PC 18:1_18:0 are homogeneously distributed, whereas PC 18:1_16:0 and PC 20:1_16:0 show distinct localizations to sub-hippocampal structures.

Omega-3 fatty acid epoxides produced by PAF-AH2 in mast cells regulate pulmonary vascular remodeling

Pulmonary hypertension is a fatal rare disease that causes right heart failure by elevated pulmonary arterial resistance. There is an unmet medical need for the development of therapeutics focusing on the pulmonary vascular remodeling. Bioactive lipids produced by perivascular inflammatory cells might modulate the vascular remodeling. Here, we show that ω-3 fatty acid-derived epoxides (ω-3 epoxides) released from mast cells by PAF-AH2, an oxidized phospholipid-selective phospholipase A2, negatively regulate pulmonary hypertension. Genetic deletion of Pafah2 in mice accelerate vascular remodeling, resulting in exacerbation of hypoxic pulmonary hypertension. Treatment with ω-3 epoxides suppresses the lung fibroblast activation by inhibiting TGF-β signaling. In vivo ω-3 epoxides supplementation attenuates the progression of pulmonary hypertension in several animal models. Furthermore, whole-exome sequencing for patients with pulmonary arterial hypertension identifies two candidate pathogenic variants of Pafah2. Our findings support that the PAF-AH2-ω-3 epoxide production axis could be a promising therapeutic target for pulmonary hypertension.

Pulmonary hypertension is a fatal disease that causes right heart failure due to pulmonary artery stenosis. Here, the authors find that ω-3 epoxides produced by the phospholipase PAF-AH2 in mast cells regulate pulmonary vascular remodeling.

Direct Regulation of Hyperpolarization-Activated Cyclic-Nucleotide Gated (HCN1) Channels by Cannabinoids

Cannabinoids are a broad class of molecules that act primarily on neurons, affecting pain sensation, appetite, mood, learning, and memory. In addition to interacting with specific cannabinoid receptors (CBRs), cannabinoids can directly modulate the function of various ion channels. Here, we examine whether cannabidiol (CBD) and Δ9-tetrahydrocannabinol (THC), the most prevalent phytocannabinoids in Cannabis sativa, can regulate the function of hyperpolarization-activated cyclic-nucleotide-gated (HCN1) channels independently of CBRs. HCN1 channels were expressed in Xenopus oocytes since they do not express CBRs, and the effects of cannabinoid treatment on HCN1 currents were examined by a two-electrode voltage clamp. We observe opposing effects of CBD and THC on HCN1 current, with CBD acting to stimulate HCN1 function, while THC inhibited current. These effects persist in HCN1 channels lacking the cyclic-nucleotide binding domain (HCN1ΔCNBD). However, changes to membrane fluidity, examined by treating cells with TX-100, inhibited HCN1 current had more pronounced effects on the voltage-dependence and kinetics of activation than THC, suggesting this is not the primary mechanism of HCN1 regulation by cannabinoids. Our findings may contribute to the overall understanding of how cannabinoids may act as promising therapeutic molecules for the treatment of several neurological disorders in which HCN function is disturbed.

Omega-3 Polyunsaturated Fatty Acids-Vascular and Cardiac Effects on the Cellular and Molecular Level (Narrative Review)

In the prevention and treatment of cardiovascular disease, in addition to the already proven effective treatment of dyslipidemia, hypertension and diabetes mellitus, omega-3 polyunsaturated fatty acids (n-3 PUFAs) are considered as substances with additive effects on cardiovascular health. N-3 PUFAs combine their indirect effects on metabolic, inflammatory and thrombogenic parameters with direct effects on the cellular level. Eicosapentaenoic acid (EPA) seems to be more efficient than docosahexaenoic acid (DHA) in the favorable mitigation of atherothrombosis due to its specific molecular properties. The inferred mechanism is a more favorable effect on the cell membrane. In addition, the anti-fibrotic effects of n-3 PUFA were described, with potential impacts on heart failure with a preserved ejection fraction. Furthermore, n-3 PUFA can modify ion channels, with a favorable impact on arrhythmias. However, despite recent evidence in the prevention of cardiovascular disease by a relatively high dose of icosapent ethyl (EPA derivative), there is still a paucity of data describing the exact mechanisms of n-3 PUFAs, including the role of their particular metabolites. The purpose of this review is to discuss the effects of n-3 PUFAs at several levels of the cardiovascular system, including controversies.

C. elegans PEZO-1 is a mechanosensitive ion channel involved in food sensation

PIEZO channels are force sensors essential for physiological processes, including baroreception and proprioception. The Caenorhabditis elegans genome encodes an orthologue gene of the Piezo family, pezo-1, which is expressed in several tissues, including the pharynx. This myogenic pump is an essential component of the C. elegans alimentary canal, whose contraction and relaxation are modulated by mechanical stimulation elicited by food content. Whether pezo-1 encodes a mechanosensitive ion channel and contributes to pharyngeal function remains unknown. Here, we leverage genome editing, genetics, microfluidics, and electropharyngeogram recording to establish that pezo-1 is expressed in the pharynx, including in a proprioceptive-like neuron, and regulates pharyngeal function. Knockout (KO) and gain-of-function (GOF) mutants reveal that pezo-1 is involved in fine-tuning pharyngeal pumping frequency, as well as sensing osmolarity and food mechanical properties. Using pressure-clamp experiments in primary C. elegans embryo cultures, we determine that pezo-1 KO cells do not display mechanosensitive currents, whereas cells expressing wild-type or GOF PEZO-1 exhibit mechanosensitivity. Moreover, infecting the Spodoptera frugiperda cell line with a baculovirus containing the G-isoform of pezo-1 (among the longest isoforms) demonstrates that pezo-1 encodes a mechanosensitive channel. Our findings reveal that pezo-1 is a mechanosensitive ion channel that regulates food sensation in worms.

Regulation and functions of membrane lipids: Insights from Caenorhabditis elegans

The Caenorhabditis elegans plasma membrane is composed of glycerophospholipids and sphingolipids with a small cholesterol. The C. elegans obtain the majority of the membrane lipids by modifying fatty acids present in the bacterial diet. The metabolic pathways of membrane lipid biosynthesis are well conserved across the animal kingdom. In C. elegans CDP-DAG and Kennedy pathway produce glycerophospholipids. Meanwhile, the sphingolipids are synthesized through a different pathway. They have evolved remarkably diverse mechanisms to maintain membrane lipid homeostasis. For instance, the lipid bilayer stress operates to accomplish homeostasis during any perturbance in the lipid composition. Meanwhile, the PAQR-2/IGLR-2 complex works with FLD-1 to balance unsaturated to saturated fatty acids to maintain membrane fluidity. The loss of membrane lipid homeostasis is observed in many human genetic and metabolic disorders. Since C. elegans conserved such genes and pathways, it can be used as a model organism.

What is the ability of inflamed endothelium to uptake exogenous saturated fatty acids? A proof-of-concept study using spontaneous Raman, SRS and CARS microscopy

Endothelial cells (EC) in vivo buffer and regulate the transfer of plasma fatty acid (FA) to the underlying tissues. We hypothesize that inflammation could alter the functionality of the EC, i.e., their capacity and uptake of different FA. The aim of this work is to verify the functionality of inflamed cells by analyzing their ability to uptake and accumulate exogenous saturated FA. Control and inflammatory human microvascular endothelial cells stimulated in vitro with two deuterium-labeled saturated FA (D-FA), i.e., palmitic (D₃₁-PA) and myristic (D₂₇-MA) acids. Cells were measured both by spontaneous and stimulated Raman imaging to extract detailed information about uptaken FA, whereas coherent anti-Stokes Raman scattering and fluorescence imaging showed the global content of FA in cells. Additionally, we employed atomic force microscopy to obtain a morphological image of the cells. The results indicate that the uptake of D-FA in inflamed cells is dependent on their concentration and type. Cells accumulated D-FA when treated with a low concentration, and the effect was more pronounced for D₂₇-MA, in normal cells, but even more so, in inflamed cells. In the case of D₃₁-PA, a slightly increased uptake was observed for inflamed cells when administered at higher concentration. The results provide a better understanding of the EC inflammation and indicate the impact of the pathological state of the EC on their capacity to buffer fat. All the microscopic methods used showed complementarity in the analysis of FA uptake by EC, but each method recognized this process from a different perspective.

DHA-phospholipids control membrane fusion and transcellular tunnel dynamics

Metabolic studies and animal knockout models point to the critical role of polyunsaturated docosahexaenoic acid (22:6, DHA)-containing phospholipids (PLs) in physiology. Here, we investigated the impact of DHA-PLs on the dynamics of transendothelial cell macroapertures (TEMs) triggered by RhoA inhibition-associated cell spreading. Lipidomic analyses show that human umbilical vein endothelial cells (HUVECs) subjected to DHA-diet undergo a 6-fold enrichment in DHA-PLs at plasma membrane (PM) at the expense of monounsaturated OA-PLs. Consequently, DHA-PLs enrichment at the PM induces a reduction of cell thickness and shifts cellular membranes towards a permissive mode of membrane fusion for transcellular tunnel initiation. We provide evidence that a global homeostatic control of membrane tension and cell cortex rigidity minimizes overall changes of TEM area through a decrease of TEM size and lifetime. Conversely, low DHA-PL levels at the PM leads to the opening of unstable and wider TEMs. Together, this provides evidence that variations of DHA-PLs levels in membranes affect cell biomechanical properties.

Anti-Inflammatory Function of Fatty Acids and Involvement of Their Metabolites in the Resolution of Inflammation in Chronic Obstructive Pulmonary Disease

Lipid metabolism plays an important role in many lung functions. Disorders of lipid metabolism are part of the pathogenesis of chronic obstructive pulmonary disease (COPD). Lipids are involved in numerous cross-linkages with inflammation. Recent studies strongly support the involvement of fatty acids as participants in inflammation. They are involved in the initiation and resolution of inflammation, including acting as a substrate for the formation of lipid mediators of inflammation resolution. Specialized pro-inflammatory mediators (SPMs) belonging to the classes of lipoxins, resolvins, maresins, and protectins, which are formed enzymatically from unsaturated fatty acids, are now described. Disorders of their production and function are part of the pathogenesis of COPD. SPMs are currently the subject of active research in order to find new drugs. Short-chain fatty acids are another important participant in metabolic and immune processes, and their role in the pathogenesis of COPD is of great clinical interest.

Omega-3 fatty acids improve flow-induced vasodilation by enhancing TRPV4 in arteries from diet-induced obese mice

AIMS

Previous studies have shown the intake of omega-3 polyunsaturated fatty acids is associated with low rates of obesity and ischaemic pathologies. Omega-3 also have anti-inflammatory and plaque-stabilization effects and regulate vasodilation and constriction. However, there are few studies of the role of omega-3 in flow-induced vasodilation involving Ca2+-permeable ion channel TRPV4 in high-fat diet-induced obese (DIO) mouse. Here, we determined whether omega-3 protect against vascular dysfunction induced by a high-fat diet by enhancing TRPV4 activity and subsequently improving flow-mediated vasodilation.

METHODS AND RESULTS

Flow-mediated vasodilation in second-order mesenteric arteries from mice was measured using a pressure myograph. The intracellular Ca2+ concentration in response to flow and GSK1016790A (a TRPV4 agonist) was measured by Fluo-4 fluorescence. Whole-cell current was measured by patch clamp. Cell membrane tether force was measured by atomic force microscopy. Impairment of flow-mediated vasodilation in arteries and Ca2+ influx in endothelial cells from DIO mice was restored by omega-3 treatment. The improved flow-induced vasodilation was inhibited by the TRPV4 antagonist HC067047 and in TRPV4-/- mice. Omega-3 treatment enhanced endothelial TRPV4 activity and altered cell membrane mechanic property, as indicated by enhanced GSK1016790A-induced Ca2+ influx and whole-cell current and altered membrane mean tether force in endothelial cells from DIO mice.

CONCLUSION

Omega-3 improve vascular function by improving flow-induced vasodilation via enhancing TRPV4 activity in the endothelium of obese mice which may be related to improved cell membrane physical property. Activation of TRPV4 in endothelium plays an important role in the protective mechanisms of omega-3 against vascular dysfunction in obesity by improving flow-mediated vasodilation.

The Transient Receptor Potential Vanilloid 4 Channel and Cardiovascular Disease Risk Factors

Vascular endothelial cells regulate arterial tone through the release of nitric oxide and other diffusible factors such as prostacyclin and endothelium derived hyperpolarizing factors. Alongside these diffusible factors, contact-mediated electrical propagation from endothelial cells to smooth muscle cells via myoendothelial gap junctions, termed endothelium-dependent hyperpolarization (EDH), plays a critical role in endothelium-dependent vasodilation in certain vascular beds. A rise in intracellular Ca²⁺ concentration in endothelial cells is a prerequisite for both the production of diffusible factors and the generation of EDH, and Ca²⁺ influx through the endothelial transient receptor potential vanilloid 4 (TRPV4) ion channel, a nonselective cation channel of the TRP family, plays a critical role in this process in various vascular beds. Emerging evidence suggests that the dysregulation of endothelial TRPV4 channels underpins endothelial dysfunction associated with cardiovascular disease (CVD) risk factors, including hypertension, obesity, diabetes, and aging. Because endothelial dysfunction is a precursor to CVD, a better understanding of the mechanisms underlying impaired TRPV4 channels could lead to novel therapeutic strategies for CVD prevention. In this mini review, we present the current knowledge of the pathophysiological changes in endothelial TRPV4 channels associated with CVD risk factors, and then explore the underlying mechanisms involved.

Characterization of the Structural Diversity and Structure-Specific Behavior of Oxidized Phospholipids by LC-MS/MS

Polyunsaturated fatty acids (PUFAs), esterified to phospholipids, are susceptible to oxidation. They form oxidized phospholipids (OxPLs) by oxygenases or reactive oxygen species (ROS), or both. These OxPLs are associated with various diseases, such as atherosclerosis, pulmonary injuries, neurodegenerative diseases, cancer, and diabetes. Since many types of OxPLs seem to be generated in vivo, precise determination of their structural diversity is required to understand their potential structure-specific functions. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a powerful method to quantitatively measure the structural diversity of OxPLs present in biological samples. This review outlines recent advances in analytical methods for OxPLs and their physiological relevance in health and diseases.

Chia oil prevents chemical and immune-mediated inflammatory responses in mice: Evidence for the underlying mechanisms

Chia (Salvia hispanica L.) is an herbaceous plant used as omega-3 polyunsaturated fatty acid (ω-3 PUFA) source that presents a range of beneficial effects on human health. Herein, it was used a chia oil containing over than 62% of α-linolenic acid (ALA), a compound widely related to anti-inflammatory actions. Chia oil effect was tested using paw edema and mechanical hyperalgesia induced by carrageenan, and ear edema induced by croton oil, histamine, and capsaicin. Croton oil was used in both preventive and therapeutic treatment schedules of chia oil while histamine and capsaicin were used only in preventive treatment schedule. Chia oil mechanism of action was investigated using nociception and paw edema response induced by intraplantar injection of acidified saline (ASIC activator), PGE₂ (prostaglandin pathway), cinnamaldehyde (TRPA1 activator), bradykinin (BK pathway), menthol (TRPM8 activator), and capsaicin (TRPV1 activator). Further, RT-PCR for inflammatory mediators (TRPA1, NF-κB, PPAR-γ, COX-2, IL-6, TNF, FPR2, FAAH, MAGL, and IL-12A) induced by carrageenan, NLRP3 inflammasome activation, and the cell viability were then accessed. Later, chia oil actions were evaluated in the experimental autoimmune encephalomyelitis (EAE), a multiple sclerosis (MS) model. Chia oil showed anti-edematogenic and anti-hyperalgesic effects when administered 1 h before pro-inflammatory stimulus - particularly carrageenan and croton oil. Moreover, chia oil upregulated the mRNA levels of COX-2 and formyl peptide receptor 2 (FPR2) while reduced IL-6 expression in the spinal cord of mice submitted to i.pl. injection of carrageenan. Interestingly, chia oil mediates antinociceptive effects in mice decreasing the nociceptive response induced by acidified saline, PGE₂, and cinnamaldehyde, but not by bradykinin, menthol, and capsaicin. On the EAE model, chia oil preventively administered attenuated EAE-induced motor deficits and mechanical hyperalgesia in mice, suggesting a valuable effect of chia oil supplementation in regulating inflammatory responses and some immune functions during immune-mediated inflammatory disorders (IMID). Nonetheless, additional reports will need to assess the effect of chia oil in well-controlled clinical trials performed in MS patients.

Hydrodynamics of immiscible binary fluids with viscosity contrast: a multiparticle collision dynamics approach

We present a multiparticle collision dynamics (MPC) implementation of layered immiscible fluids A and B of different shear viscosities separated by planar interfaces. The simulated flow profile for imposed steady shear motion and the time-dependent shear stress functions are in excellent agreement with our continuum hydrodynamics results for the composite fluid. The wave-vector dependent transverse velocity auto-correlation functions (TVAF) in the bulk-fluid regions of the layers decay exponentially, and agree with those of single-phase isotropic MPC fluids. In addition, we determine the hydrodynamic mobilities of an embedded colloidal sphere moving steadily parallel or transverse to a fluid-fluid interface, as functions of the distance from the interface. The obtained mobilities are in good agreement with hydrodynamic force multipoles calculations, for a no-slip sphere moving under creeping flow conditions near a clean, ideally flat interface. The proposed MPC fluid-layer model can be straightforwardly implemented, and it is computationally very efficient. Yet, owing to the spatial discretization inherent to the MPC method, the model can not reproduce all hydrodynamic features of an ideally flat interface between immiscible fluids.

Fasting increases 18:2-containing phosphatidylcholines to complement the decrease in 22:6-containing phosphatidylcholines in mouse skeletal muscle

Fasting stimulates catabolic reactions in skeletal muscle to survive nutrient deprivation. Cellular phospholipids have large structural diversity due to various polar-heads and acyl-chains that affect many cellular functions. Skeletal muscle phospholipid profiles have been suggested to be associated with muscle adaptations to nutritional and environmental status. However, the effect of fasting on skeletal muscle phospholipid profiles remains unknown. Here, we analyzed phospholipids using liquid chromatography mass spectrometry. We determined that fasting resulted in a decrease in 22:6-containing phosphatidylcholines (PCs) (22:6-PCs) and an increase in 18:2-containing PCs (18:2-PCs). The fasting-induced increase in 18:2-PCs was sufficient to complement 22:6-PCs loss, resulting in the maintenance of the total amount of polyunsaturated fatty acid (PUFA)-containing PCs. Similar phospholipid alterations occurred in insulin-deficient mice, which indicate that these observed phospholipid perturbations were characteristic of catabolic skeletal muscle. In lysophosphatidic acid acyltransferase 3-knockout muscles that mostly lack 22:6-PCs, other PUFA-containing PCs, mainly 18:2-PCs, accumulated. This suggests a compensatory mechanism for skeletal muscles to maintain PUFA-containing PCs.

A Genetic Titration of Membrane Composition in C. elegans Reveals its Importance for Multiple Cellular and Physiological Traits

Communicating editor: B. Grant

The composition and biophysical properties of cellular membranes must be tightly regulated to maintain the proper functions of myriad processes within cells. To better understand the importance of membrane homeostasis, we assembled a panel of five Caenorhabditis elegans strains that show a wide span of membrane composition and properties, ranging from excessively rich in saturated fatty acids (SFAs) and rigid to excessively rich in polyunsaturated fatty acids (PUFAs) and fluid. The genotypes of the five strain are, from most rigid to most fluid: paqr-1(tm3262); paqr-2(tm3410), paqr-2(tm3410), N2 (wild-type), mdt-15(et14); nhr-49(et8), and mdt-15(et14); nhr-49(et8); acs-13(et54). We confirmed the excess SFA/rigidity-to-excess PUFA/fluidity gradient using the methods of fluorescence recovery after photobleaching (FRAP) and lipidomics analysis. The five strains were then studied for a variety of cellular and physiological traits and found to exhibit defects in: permeability, lipid peroxidation, growth at different temperatures, tolerance to SFA-rich diets, lifespan, brood size, vitellogenin trafficking, oogenesis, and autophagy during starvation. The excessively rigid strains often exhibited defects in opposite directions compared to the excessively fluid strains. We conclude that deviation from wild-type membrane homeostasis is pleiotropically deleterious for numerous cellular/physiological traits. The strains introduced here should prove useful to further study the cellular and physiological consequences of impaired membrane homeostasis.

From stretch to deflection: the importance of context in the activation of mammalian, mechanically activated ion channels

The ability of cells to convert mechanical perturbations into biochemical information is an essential aspect of mammalian physiology. The molecules that mediate such mechanotransduction include mechanically activated ion channels, which directly convert mechanical inputs into electrochemical signals. The unifying feature of these channels is that their open probability increases with the application of a mechanical input. However, the structure, activation profile and sensitivity of distinct mechanically activated ion channels vary from channel to channel. In this review, we discuss how ionic currents can be mechanically evoked and monitored in vitro, and describe the distinct activation profiles displayed by a range of mammalian channels. In addition, we discuss the various mechanisms by which the best-characterized mammalian, mechanically activated ion channel, PIEZO1, can be modulated. The diversity of activation and modulation of these mammalian ion channels suggest that these molecules may facilitate a finely controlled and diverse ability to sense mechanical inputs in mammalian cells.

Paradigm shift: the primary function of the "Adiponectin Receptors" is to regulate cell membrane composition

The ADIPOR1 and ADIPOR2 proteins (ADIPORs) are generally considered as adiponectin receptors with anti-diabetic properties. However, studies on the yeast and C. elegans homologs of the mammalian ADIPORs, and of the ADIPORs themselves in various mammalian cell models, support an updated/different view. Based on findings in these experimental models, the ADIPORs are now emerging as evolutionarily conserved regulators of membrane homeostasis that do not require adiponectin to act as membrane fluidity sensors and regulate phospholipid composition. More specifically, membrane rigidification activates ADIPOR signaling to promote fatty acid desaturation and incorporation of polyunsaturated fatty acids into membrane phospholipids until fluidity is restored. The present review summarizes the evidence supporting this new view of the ADIPORs, and briefly examines physiological consequences.

EPA and DHA differentially modulate membrane elasticity in the presence of cholesterol

Polyunsaturated fatty acids (PUFAs) modify the activity of a wide range of membrane proteins and are increasingly hypothesized to modulate protein activity by indirectly altering membrane physical properties. Among the various physical properties affected by PUFAs, the membrane area expansion modulus (K_a), which measures membrane strain in response to applied force, is expected to be a significant controller of channel activity. Yet, the impact of PUFAs on membrane K_a has not been measured previously. Through a series of micropipette aspiration studies, we measured the apparent K_a (K_app) of phospholipid model membranes containing nonesterified fatty acids. First, we measured membrane K_app as a function of the location of the unsaturated bonds and degree of unsaturation in the incorporated fatty acids and found that K_app generally decreases in the presence of fatty acids with three or more unsaturated bonds. Next, we assessed how select ω-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), affect the K_app of membranes containing cholesterol. In vesicles prepared with high amounts of cholesterol, which should increase the propensity of the membrane to phase segregate, we found that inclusion of DHA decreases the K_app in comparison to EPA. We also measured how these ω-3 PUFAs affect membrane fluidity and bending rigidity to determine how membrane K_app changes in relation to these other physical properties. Our study shows that PUFAs generally decrease the K_app of membranes and that EPA and DHA have differential effects on K_app when membranes contain higher levels of cholesterol. Our results suggest membrane phase behavior and the distribution of membrane-elasticizing amphiphiles impact the ability of a membrane to stretch.

An ω-3, but Not an ω-6 Polyunsaturated Fatty Acid Decreases Membrane Dipole Potential and Stimulates Endo-Lysosomal Escape of Penetratin

Although the largely positive intramembrane dipole potential (DP) may substantially influence the function of transmembrane proteins, its investigation is deeply hampered by the lack of measurement techniques suitable for high-throughput examination of living cells. Here, we describe a novel emission ratiometric flow cytometry method based on F66, a 3-hydroxiflavon derivative, and demonstrate that 6-ketocholestanol, cholesterol and 7-dehydrocholesterol, saturated stearic acid (SA) and ω-6 γ-linolenic acid (GLA) increase, while ω-3 α-linolenic acid (ALA) decreases the DP. These changes do not correlate with alterations in cell viability or membrane fluidity. Pretreatment with ALA counteracts, while SA or GLA enhances cholesterol-induced DP elevations. Furthermore, ALA (but not SA or GLA) increases endo-lysosomal escape of penetratin, a cell-penetrating peptide. In summary, we have developed a novel method to measure DP in large quantities of individual living cells and propose ALA as a physiological DP lowering agent facilitating cytoplasmic entry of penetratin.

Omega-3 Polyunsaturated Fatty Acids: Versatile Roles in Blood Pressure Regulation

Significance: Hypertension is characterized as the imbalance of vasoconstriction and vasodilatation. Hypertension is influenced by genetic variation and environmental risk factors, such as unhealthy diet. Clinical trial results suggest that increasing intake of foods rich in n-3 polyunsaturated fatty acids (PUFAs) is beneficial for hypertension. Recent Advances: We summarized recent clinical trials regarding supplementation with n-3 PUFAs to reduce blood pressure (BP) in untreated hypertensive and normotensive subjects and systematically discussed the antihypertension mechanisms of n-3 PUFAs/n-3 oxylipins, including reducing oxidative stress, altering functions of membrane-related proteins, and competing with n-6 PUFAs/n-6 oxylipins in regulating vasodilator release. Critical Issues: Previous studies considered n-3 PUFAs as single molecules with beneficial roles in hypertension. Recently, researchers have paid more attention to the metabolism of n-3 PUFAs and explored molecular mechanisms of n-3 PUFAs and oxylipins derived from n-3 PUFAs in hypertension interventions. Future Directions: Based on the metabolism of n-3 PUFAs/n-3 oxylipins and mechanisms in BP control, we suggested that supplementation of n-3 PUFAs combined with agents targeting PUFA metabolism or the related signal pathways may amplify their effects to treat hypertension and other cardiovascular diseases. Antioxid. Redox Signal. 34, 800-810.

TRPing to the Point of Clarity: Understanding the Function of the Complex TRPV4 Ion Channel

The transient receptor potential vanilloid 4 channel (TRPV4) belongs to the mammalian TRP superfamily of cation channels. TRPV4 is ubiquitously expressed, activated by a disparate array of stimuli, interacts with a multitude of proteins, and is modulated by a range of post-translational modifications, the majority of which we are only just beginning to understand. Not surprisingly, a great number of physiological roles have emerged for TRPV4, as have various disease states that are attributable to the absence, or abnormal functioning, of this ion channel. This review will highlight structural features of TRPV4, endogenous and exogenous activators of the channel, and discuss the reported roles of TRPV4 in health and disease.

Omega-3 polyunsaturated fatty acids and hypertension: a review of vasodilatory mechanisms of docosahexaenoic acid and eicosapentaenoic acid

Hypertension is often characterised by impaired vasodilation involving dysfunction of multiple vasodilatory mechanisms. ω-3 polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) can reduce blood pressure and vasodilation. In the endothelium, DHA and EPA improve function including increased NO bioavailability. However, animal studies show that DHA- and EPA-mediated vasodilation persists after endothelial removal, indicating a role for vascular smooth muscle cells (VSMCs). The vasodilatory effects of ω-3 PUFAs on VSMCs are mediated via opening of large conductance calcium-activated potassium channels (BK_Ca ), ATP-sensitive potassium channels (K_ATP ) and possibly members of the K_v 7 family of voltage-activated potassium channels, resulting in hyperpolarisation and relaxation. ω-3 PUFA actions on BK_Ca and voltage-gated ion channels involve electrostatic interactions that are dependent on the polyunsaturated acyl tail, cis-geometry of these double bonds and negative charge of the carboxyl headgroup. This suggests structural manipulation of ω-3 PUFA could generate novel, targeted, therapeutic leads.

TRPV4 integrates matrix mechanosensing with Ca2+ signaling to regulate extracellular matrix remodeling

In healthy connective tissues, mechanosensors trigger the generation of Ca²⁺ signals, which enable cells to maintain the structure of the fibrillar collagen matrix through actomyosin contractile forces. Transient receptor potential vanilloid type 4 (TRPV4) is a mechanosensitive Ca²⁺ -permeable channel that, when expressed in cell-matrix adhesions of the plasma membrane, regulates extracellular matrix (ECM) remodeling. In high prevalence disorders such as fibrosis and tumor metastasis, dysregulated matrix remodeling is associated with disruptions of Ca²⁺ homeostasis and TRPV4 function. Here, we consider that ECM polymers transmit cell-activating mechanical signals to TRPV4 in cell adhesions. When activated, TRPV4 regulates fibrillar collagen remodeling, thereby altering the mechanical properties of the ECM. In this review, we integrate functionally connected processes of matrix remodeling to highlight how TRPV4 in cell adhesions and matrix mechanics are reciprocally regulated through Ca²⁺ signaling.

Deficiency of Inositol Monophosphatase Activity Decreases Phosphoinositide Lipids and Enhances TRPV1 Function In Vivo

Membrane remodeling by inflammatory mediators influences the function of sensory ion channels. The capsaicin- and heat-activated transient receptor potential vanilloid 1 (TRPV1) channel contributes to neurogenic inflammation and pain hypersensitivity, in part because of its potentiation downstream of phospholipase C-coupled receptors that regulate phosphoinositide lipid content. Here, we determined the effect of phosphoinositide lipids on TRPV1 function by combining genetic dissection, diet supplementation, and behavioral, biochemical, and functional analyses in Caenorhabditis elegans As capsaicin elicits heat and pain sensations in mammals, transgenic TRPV1 worms exhibit an aversive response to capsaicin. TRPV1 worms with low levels of phosphoinositide lipids display an enhanced response to capsaicin, whereas phosphoinositide lipid supplementation reduces TRPV1-mediated responses. A worm carrying a TRPV1 construct lacking the distal C-terminal domain features an enhanced response to capsaicin, independent of the phosphoinositide lipid content. Our results demonstrate that TRPV1 activity is enhanced when the phosphoinositide lipid content is reduced, and the C-terminal domain is key to determining agonist response in vivo.

Cytochrome P450 Metabolism of Polyunsaturated Fatty Acids and Neurodegeneration

Due to the aging population in the world, neurodegenerative diseases have become a serious public health issue that greatly impacts patients' quality of life and adds a huge economic burden. Even after decades of research, there is no effective curative treatment for neurodegenerative diseases. Polyunsaturated fatty acids (PUFAs) have become an emerging dietary medical intervention for health maintenance and treatment of diseases, including neurodegenerative diseases. Recent research demonstrated that the oxidized metabolites, particularly the cytochrome P450 (CYP) metabolites, of PUFAs are beneficial to several neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease; however, their mechanism(s) remains unclear. The endogenous levels of CYP metabolites are greatly affected by our diet, endogenous synthesis, and the downstream metabolism. While the activity of omega-3 (ω-3) CYP PUFA metabolites and omega-6 (ω-6) CYP PUFA metabolites largely overlap, the ω-3 CYP PUFA metabolites are more active in general. In this review, we will briefly summarize recent findings regarding the biosynthesis and metabolism of CYP PUFA metabolites. We will also discuss the potential mechanism(s) of CYP PUFA metabolites in neurodegeneration, which will ultimately improve our understanding of how PUFAs affect neurodegeneration and may identify potential drug targets for neurodegenerative diseases.

Ca2+-mediated enhancement of anesthetic diffusion across phospholipid multilamellar systems

Although sharing common properties with other divalent cations, calcium ions induce fine-tuned electrostatic effects essential in many biological processes. Not only related with protein structure or ion channels, calcium is also determinant for other biomolecules such as lipids or even drugs. Cellular membranes are the first interaction barriers for drugs. Depending on their hydrophilic, hydrophobic or amphipathic properties, they have to overcome such barriers to permeate and diffuse through inner lipid bilayers, cells or even tissues. In this context, the role of calcium in the permeation of cationic amphiphilic drugs (CADs) through lipid membranes is not well understood. We combine differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) to investigate the effect of Ca²⁺ on the interlamellar diffusion kinetics of the local anesthetic tetracaine (TTC) in multilamellar artificial membrane systems. Our DSC results show the interesting phenomenon that TTC diffusion can be modified in two different ways in the presence of Ca²⁺. Furthermore, TTC diffusion exhibits a thermal-dependent membrane interaction in the presence of Ca²⁺. The FTIR results suggest the presence of ion-dipole interactions between Ca²⁺ and the carbonyl group of TTC, leading us to hypothesize that Ca²⁺ destabilizes the hydration shell of TTC, which in turn diffuses deeper into the multilamellar lipid structures. Our results demonstrate the relevance of the Ca²⁺ ion in the drug permeation and diffusion through lipid bilayers.

Neuronal lipolysis participates in PUFA-mediated neural function and neurodegeneration

Lipid droplets (LDs) are dynamic cytoplasmic organelles present in most eukaryotic cells. The appearance of LDs in neurons is not usually observed under physiological conditions, but is associated with neural diseases. It remains unclear how LD dynamics is regulated in neurons and how the appearance of LDs affects neuronal functions. We discovered that mutations of two key lipolysis genes atgl-1 and lid-1 lead to LD appearance in neurons of Caenorhabditis elegans. This neuronal lipid accumulation protects neurons from hyperactivation-triggered neurodegeneration, with a mild decrease in touch sensation. We also discovered that reduced biosynthesis of polyunsaturated fatty acids (PUFAs) causes similar effects and synergizes with decreased lipolysis. Furthermore, we demonstrated that these changes in lipolysis and PUFA biosynthesis increase PUFA partitioning toward triacylglycerol, and reduced incorporation of PUFAs into phospholipids increases neuronal protection. Together, these results suggest the crucial role of neuronal lipolysis in cell-autonomous regulation of neural functions and neurodegeneration.

Piezo1 Forms Specific, Functionally Important Interactions with Phosphoinositides and Cholesterol

Touch, hearing, and blood pressure regulation require mechanically gated ion channels that convert mechanical stimuli into electrical currents. One such channel is Piezo1, which plays a key role in the transduction of mechanical stimuli in humans and is implicated in diseases, such as xerocytosis and lymphatic dysplasia. There is building evidence that suggests Piezo1 can be regulated by the membrane environment, with the activity of the channel determined by the local concentration of lipids, such as cholesterol and phosphoinositides. To better understand the interaction of Piezo1 with its environment, we conduct simulations of the protein in a complex mammalian bilayer containing more than 60 different lipid types together with electrophysiology and mutagenesis experiments. We find that the protein alters its local membrane composition, enriching specific lipids and forming essential binding sites for phosphoinositides and cholesterol that are functionally relevant and often related to Piezo1-mediated pathologies. We also identify a number of key structural connections between the propeller and pore domains located close to lipid-binding sites.