ASIC1a-associated mechanical hypersensitivity in the GlaKO Fabry disease mouse model.

Pain in Fabry disease (FD) is generally accepted to result from neuronal damage in the peripheral nervous system as a consequence of excess lipid storage caused by alpha-galactosidase A (α-Gal A) deficiency. Signatures of pain arising from nerve injuries are generally associated with changes of number, location and phenotypes of immune cells within dorsal root ganglia (DRG). However, the neuroimmune processes in the DRG linked to accumulating glycosphingolipids in Fabry disease are insufficiently understood.Therefore, using indirect immune fluorescence microscopy, transmigration assays and FACS together with transcriptomic signatures associated with immune processes, we assessed age-dependent neuroimmune alterations in DRG obtained from mice with a global depletion of α-Gal A as a valid mouse model for FD. Macrophage numbers in the DRG of FD mice were unaltered, and BV-2 cells as a model for monocytic cells did not show augmented migratory reactions to glycosphingolipids exposure suggesting that these do not act as chemoattractants in FD. However, we found pronounced alterations of lysosomal signatures in sensory neurons and of macrophage morphology and phenotypes in FD DRG. Macrophages exhibited reduced morphological complexity indicated by a smaller number of ramifications and more rounded shape, which were age dependent and indicative of premature monocytic aging together with upregulated expression of markers CD68 and CD163.In our FD mouse model, the observed phenotypic changes in myeloid cell populations of the DRG suggest enhanced phagocytic and unaltered proliferative capacity of macrophages as compared to wildtype control mice. We suggest that macrophages may participate in FD pathogenesis and targeting macrophages at an early stage of FD may offer new treatment options other than enzyme replacement therapy.

Noninvasive and objective biomarkers for disease-associated pathology are critical for clinical trials. For Fabry disease, one important pathological change due to the deficiency of the lysosomal enzyme α-galactosidase A (α-GAL) caused is accumulation of globotriaosylceramide (Gb3) in dorsal root ganglion (DRG) neurons, which manifests as the overall DRG hypertrophy. Magnetic resonance imaging (MRI) has been successfully used to noninvasively measure DRG enlargement in Fabry patients, and DRG volumetric MRI can be a potential noninvasive biomarker for Gb3 accumulations in DRG neurons in clinical trials. To evaluate disease progression and treatment response in preclinical proof-of-concept studies, we developed an in vivo MRI method to measure DRG size in the G3Stg/GLA knockout mouse model of Fabry disease. Compared to the wild type mice, the DRG enlargement in the Fabry mice was observed as early as 8 weeks of age, and a single administration of the human α-GAL-encoding adeno-associated virus (AAVGLA) normalized the enlarged DRG to the age-matched wild type mice. The DRG normalization was observed within 4 weeks of gene therapy (12 weeks of age) and was sustained up to 24 weeks of age. Furthermore, behavioral testing and histological/immunohistochemistry analyses of the DRG tissues corroborated the MRI findings. Volumetric DRG MRI has the sensitivity to measure Gb3 pathology-induced DRG volume changes and treatment response in live mice and can be a translational imaging biomarker in clinical trials for Fabry disease.

The human lysosomal enzymes alpha-galactosidase (alpha-GAL, EC 3.2.1.22) and alpha-N-acetylgalactosaminidase (alpha-NAGAL, EC 3.2.1.49) share 46% amino acid sequence identity and have similar folds. The active sites of the two enzymes share 11 of 13 amino acids, differing only where they interact with the 2-position of the substrates. Using a rational protein engineering approach, we interconverted the enzymatic specificity of alpha- GAL and alpha-NAGAL. The engineered alpha-GAL (which we call alpha-GAL(SA)) retains the antigenicity of alpha-GAL but has acquired the enzymatic specificity of alpha-NAGAL. Conversely, the engineered alpha-NAGAL (which we call alpha-NAGAL(EL)) retains the antigenicity of alpha-NAGAL but has acquired the enzymatic specificity of the alpha-GAL enzyme. Comparison of the crystal structures of the designed enzyme alpha-GAL(SA) to the wild-type enzymes shows that active sites of alpha-GAL(SA) and alpha-NAGAL superimpose well, indicating success of the rational design. The designed enzymes might be useful as non-immunogenic alternatives in enzyme replacement therapy for treatment of lysosomal storage disorders such as Fabry disease.

Background: Hindpaw injection of formalin in rodents is used to assess acute persistent pain. The response to formalin is biphasic. The initial response (first minutes) is thought to be linked to inflammatory, peripheral mechanisms, while the latter (around 30 min after the injection), is linked to central mechanisms. This model is useful to analyze the effect of drugs at one or both phases, and the involvement of ion channels in the response. Acid-sensing ion channels (ASICs) regulate synaptic activities and play important roles in pain conditions. Recently, psalmotoxin-1 (Pctx-1), a toxin that inhibits ASIC1a-constituted channels, and antisense ASIC1a-RNA, intrathecal administered in mice were shown to affect both phases of the test. Methods: The mouse formalin test was performed on C57/BL6 7- to 9-week-old mice. Behavioral tests were conducted and tissue was extracted to detect proteins (ASIC1 and pERK) and ASIC1-mRNA and mir485-5p levels. Results: The injection of formalin was accompanied by an increase in ASIC1 levels. This was detected at the contralateral anterior cingulate cortex (ACC) compared to the ipsilateral side, and both sides of the ACC of vehicle-injected animals. At the spinal cord and dorsal root ganglia, ASIC1 levels followed a gradient stronger at lumbar (L) 3 and decreased towards L5. Gender differences were detected at the ACC; with female mice showing higher ASIC1a levels at the ACC. No significant changes in ASIC1-mRNA levels were detected. Evidence suggests ASIC1 upregulation depends on regulatory microRNAs. Conclusion: This work highlights the important role of ASIC1 in pain and the potential role of pharmacological therapies aimed at this channel.

Fabry disease (FD) is a rare life-threatening disorder caused by deficiency of the alpha-galactosidase A (GLA) enzyme with a characteristic pain phenotype. Impaired GLA production or function leads to the accumulation of the cell membrane compound globotriaosylceramide (Gb3) in the neurons of the dorsal root ganglia (DRG) of FD patients. Applying immunohistochemistry (IHC) and quantitative real-time polymerase chain reaction (qRT PCR) analysis on DRG tissue of the GLA knockout (KO) mouse model of FD, we address the question of how Gb3 accumulation may contribute to FD pain and focus on the immune system and pain-associated ion channel gene expression. We show a higher Gb3 load in the DRG of young (<6 months) (p < 0.01) and old (≥12 months) (p < 0.001) GLA KO mice compared to old wildtype (WT) littermates, and an overall suppressed immune response in the DRG of old GLA KO mice, represented by a reduced number of CD206+ macrophages (p < 0.01) and lower gene expression levels of the inflammation-associated targets interleukin(IL)1b (p < 0.05), IL10 (p < 0.001), glial fibrillary acidic protein (GFAP) (p < 0.05), and leucine rich alpha-2-glycoprotein 1 (LRG1) (p < 0.01) in the DRG of old GLA KO mice compared to old WT. Dysregulation of immune-related genes may be linked to lower gene expression levels of the pain-associated ion channels calcium-activated potassium channel 3.1 (KCa3.1) and transient receptor potential ankyrin 1 channel (TRPA1). Ion channel expression might further be disturbed by impaired sphingolipid recruitment mediated via the lipid raft marker flotillin-1 (FLOT1). This impairment is represented by an increased number of FLOT1+ DRG neurons with a membranous expression pattern in old GLA KO mice compared to young GLA KO, young WT, and old WT mice (p < 0.001 each). Further, we provide evidence for aberrant behavior of GLA KO mice, which might be linked to dysregulated ion channel gene expression levels and disturbed FLOT1 distribution patterns. Behavioral testing revealed mechanical hypersensitivity in young (p < 0.01) and old (p < 0.001) GLA KO mice compared to WT, heat hypersensitivity in young GLA KO mice (p < 0.001) compared to WT, age-dependent heat hyposensitivity in old GLA KO mice (p < 0.001) compared to young GLA KO mice, and cold hyposensitivity in young (p < 0.001) and old (p < 0.001) GLA KO mice compared to WT, which well reflects the clinical phenotype observed in FD patients.

The exact subunit combinations of functional native acid-sensing ion channels (ASICs) have not been established yet, but both homomeric and heteromeric channels are likely to exist. To determine the ability of different subunits to assemble into heteromeric channels, a number of ASIC1a-, ASIC1b-, ASIC2a-, ASIC2b-, and ASIC3-containing homo- and heteromeric channels were studied by whole-cell patch clamp recordings with respect to pH sensitivity, desensitization kinetics, and level of sustained current normalized to peak current. Analyzing and comparing data for these three features demonstrated unique heteromeric channels in a number of co-expression experiments. Formation of heteromeric ASIC1a+2a and ASIC1b+2a channels was foremost supported by the desensitization characteristics that were independent of proton concentration, a feature none of the respective homomeric channels has. Several lines of evidence supported formation of ASIC1a+3, ASIC1b+3, and ASIC2a+3 heteromeric channels. The most compelling was the desensitization characteristics, which, besides being proton-independent, were faster than those of any of the respective homomeric channels. ASIC2b, which homomerically expressed is not activated by protons per se, did not appear to form unique heteromeric combinations with other subunits and in fact appeared to suppress the function of ASIC1b. Co-expression of three subunits such as ASIC1a+2a+3 and ASIC1b+2a+3 resulted in data that could best be explained by coexistence of multiple channel populations within the same cell. This observation seems to be in good agreement with the fact that ASIC-expressing sensory neurons display a variety of acid-evoked currents.

Immunohistochemical analysis of acid-sensing ion channel 2 expression in rat dorsal root ganglion and effects of axotomy

Anti-CD25 Targeted Killing of Bicistronically Transduced Cells: A Novel Safety Mechanism Against Retroviral Genotoxicity

Acid-sensing ion channels (ASICs) are emerging as fundamental players in the regulation of neural plasticity and in pathological conditions. Here we showed that lead (Pb2+), a well known neurotoxic metal ion, reversibly and concentration-dependently inhibited ASIC currents in the acutely dissociated spinal dorsal horn and hippocampal CA1 neurons of rats. In vitro expression of ASIC subunits in combination demonstrated that both ASIC1 and -3 subunits were sensitive to Pb2+. Mechanistically, Pb2+ reduced the pH sensitivity of ASICs independent of membrane voltage change. Moreover, Pb2+ inhibited the ASIC-mediated membrane depolarization and the elevation of intracellular Ca2+ concentration. In addition, we compared the effect of Pb2+ with that of Ca2+ or amiloride to explore the possible interactions of Pb2+ and Ca2+ in regulating ASICs, and we found that Pb2+ inhibited ASIC currents independent of the amiloride/Ca2+ blockade. Because ASIC1b and -3 subunits are mainly expressed in peripheral neurons, our data identified ASIC1a-containing Ca2+-permeable ASIC as a novel central target of Pb2+ action, which may contribute to Pb2+ neurotoxicity.

Mas1-related G-protein-coupled receptors (Mrgprs), comprising more than 50 distinct members, are specifically expressed in primary sensory neurons. Reflecting the diversity and specificity of stimuli they detect, Mrgprs are involved in pain, touch, and itch-related behaviors. Sensory-neuron-specific acid-sensing ion channel 3 (ASIC3) is essential for touch and inflammatory pain, but mice lacking ASIC3 have complex behavioral alterations in various modalities of pain and touch. To understand whether Mrgprs are involved in complex behavioral alterations found in ASIC3-deficient mice, we examined Mrgpr gene expression in ASIC3(-/-) mice. Only MrgprB4 expression has shown significant change. MrgprB4 expression was increased in ASIC3(-/-) dorsal root ganglia (DRG) but decreased in ASIC3(-/-) trigeminal ganglia. The distinct alterations in DRG and trigeminal ganglia imply that MrgprB4 could have multiple functions. Given that MrgprB4 is expressed in neurons that may detect gentle touch and that ASIC3(-/-) mice have altered sensitivity of mechanoreceptors for light touch, the expression change of MrgprB4 is more likely related to the altered touch behaviors of ASIC3(-/-) mice.

Effect of a Temperature Increase in the Non-Noxious Range on Proton-Evoked ASIC and TRPV1 Activity

Vibrational spectroscopy can detect characteristic biomolecular signatures and thus has the potential to support diagnostics. Fabry disease (FD) is a lipid disorder disease that leads to accumulations of globotriaosylceramide in different organs, including the heart, which is particularly critical for the patient’s prognosis. Effective treatment options are available if initiated at early disease stages, but many patients are late- or under-diagnosed. Since Coherent anti-Stokes Raman (CARS) imaging has a high sensitivity for lipid/protein shifts, we applied CARS as a diagnostic tool to assess cardiac FD manifestation in an FD mouse model. CARS measurements combined with multivariate data analysis, including image preprocessing followed by image clustering and data-driven modeling, allowed for differentiation between FD and control groups. Indeed, CARS identified shifts of lipid/protein content between the two groups in cardiac tissue visually and by subsequent automated bioinformatic discrimination with a mean sensitivity of 90–96%. Of note, this genotype differentiation was successful at a very early time point during disease development when only kidneys are visibly affected by globotriaosylceramide depositions. Altogether, the sensitivity of CARS combined with multivariate analysis allows reliable diagnostic support of early FD organ manifestation and may thus improve diagnosis, prognosis, and possibly therapeutic monitoring of FD.

Background:Fibromyalgia (FM) is a syndrome involving chronic pain, fatigue, sleep difficulties, morning stiffness and muscle cramping lasting longer than 3 months. The epidemiological prevalence is approximately 3–5% in women and increases with age. Antagonism of acid-sensing ion channel 3 (ASIC3) reportedly attenuates acid saline-induced FM pain in mice.Aims:Whether pre-treatment with electroacupuncture (EA) or APETx2 can attenuate mechanical hyperalgesia in this murine model remains unknown.Methods:Accordingly, we examined the analgesic effect of EA in a murine model of FM pain induced by dual injections of acid saline and investigated whether EA or APETx2 can attenuate FM pain via the ASIC3 channel.Results:EA significantly reduced mechanical hyperalgesia in this model. ASIC3 antagonism, induced by injecting APETx2, also significantly reduced mechanical hyperalgesia. The expression of ASIC3 in the dorsal root ganglia, spinal cord and thalamus was increased after FM model induction. Over-expression of these nociceptive channels was attenuated by pre-treatment with EA or an ASIC3 antagonist.Conclusion:Our data reveal that both EA and ASIC3 blockade significantly reduce FM pain in mice via the ASIC3, Nav1.7 and Nav1.8 signalling pathways. Moreover, our findings support the potential clinical use of EA for the treatment of FM pain.

BACKGROUNDThe exercise pressor reflex (EPR), mediated by mechano‐ and metabosensitive skeletal muscle afferent feedback, is exaggerated in spontaneously hypertensive rats. This cardiovascular reflex dysfunction could be the result of disease‐related abnormalities in the expression and/or sensitivity of molecular receptors located on the terminal end of these muscle afferents, altered central integration of muscle afferent feedback, and/or altered end‐organ responsiveness to a given sympathetic activity.PURPOSETo examine dorsal root ganglion (DRG) gene and protein expression of molecular receptors recognized to be significant determinants of the EPR in control (CTRL) and spontaneous hypertensive rats (SHR).METHODSTwelve lumbar DRGs (6 left, 6 right) were harvested from each of the ten CTRL (mean arterial blood pressure (MAP): 99 ± 2 mmHg) and the ten SHR (MAP: 146 ± 3 mmHg) male rats. DRGs from the right side were quickly frozen for later extraction and RNA sequencing. All mRNA values were normalized to transcripts per million (TPM). DRGs from the left were quickly frozen and later assessed for protein expression by Western Blot. All protein was normalized to GAPDH. Analyses were focused on the transient receptor potential cation channel 1 (TRPV1), acid‐sensing ion channel 3 (ASIC3), purinergic receptor 2X3 (P2X3), and prostaglandin E2 receptor 4 (EP4).RESULTSmRNA content was similar between SHR and CTRL animals (TRPV1: 113 ± 9 TPM vs 110 ± 13 TPM; ASIC3: 39 ± 9 vs 44 ± 7; P2X3: 246 ± 16 vs 246 ± 26; EP4: 10 ± 1 vs 9 ± 1, respectively; all P &gt; 0.18). In contrast, SHR animals demonstrated a greater protein expression for all receptors measured compared to CTRL animals (TRPV1: 1.47 ± 0.20% vs 0.86 ± 0.06%; ASIC3: 1.36 ± 0.09 vs 0.77 ± 0.07; P2X3: 1.49 ± 0.11 vs 1.18 ± 0.11; EP4: 1.36 ± 0.21 vs 1.11 ± 0.13; all P &lt; 0.01).CONCLUSIONIn the face of an equivalent mRNA content in the SHR and CRTL DRG, the substantially greater receptor protein content in the SHR supports the potential for a dysregulated expression of muscle receptor protein in the hypertensive rats. Furthermore, these findings suggest an abnormally increased content of EPR‐related molecular receptors as a potential mechanism contributing to the exaggerated EPR which characterizes these animals.Support or Funding InformationHL‐116579This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Simple SummaryAlthough mRNA injection-based protein supplementation has emerged as a feasible strategy for treating Fabry disease, whether the administration of lipid nanoparticle-encapsulated mRNA results in the alteration of the metabolome in the in vivo system remains largely unknown. In the present study, an mRNA encoding α-Gal A was developed and exhibited efficient therapeutic effects. Moreover, metabolomics analysis revealed significant alterations in metabolites related to arachidonic acid metabolism, amino acid metabolism, and glycolysis/gluconeogenesis pathways.mRNA injection-based protein supplementation has emerged as a feasible treatment for Fabry disease. However, whether the introduction of LNP-encapsulated mRNA results in the alteration of metabolomics in an in vivo system remains largely unknown. In the present study, α-galactosidase A (α-Gal A) mRNA was generated and injected into the Fabry disease mouse model. The α-Gal A protein was successfully expressed. The level of globotriaosylsphingosine (Lyso-Gb3), a biomarker for Fabry disease, as well as pro-inflammatory cytokines such as nuclear factor kappa-B (NF-κB), interleukin 6 (IL-6), and tumor necrosis factor-α (TNF-α), were greatly decreased compared to the untreated control, indicating the therapeutic outcome of the mRNA drug. Metabolomics analysis found that the level of 20 metabolites was significantly altered in the plasma of mRNA-injected mice. These compounds are primarily enriched in the arachidonic acid metabolism, alanine, aspartate and glutamate metabolism, and glycolysis/gluconeogenesis pathways. Arachidonic acid and 5-hydroxyeicosatetraenoic acid (5-HETE), both of which are important components in the eicosanoid pathway and related to inflammation response, were significantly increased in the injected mice, possibly due to the presence of lipid nanoparticles. Moreover, mRNA can effectively alter the level of metabolites in the amino acid and energy metabolic pathways that are commonly found to be suppressed in Fabry disease. Taken together, the present study demonstrated that in addition to supplementing the deficient α-Gal A protein, the mRNA-based therapeutic agent can also affect levels of metabolites that may help in the recovery of metabolic homeostasis in the full body system.