Pathogenic SCN2A variants cause early-stage dysfunction in patient-derived neurons

Pathogenic heterozygous variants in SCN2A, which encodes the neuronal sodium channel NaV1.2, cause different types of epilepsy or intellectual disability (ID)/autism without seizures. Previous studies using mouse models or heterologous systems suggest that NaV1.2 channel gain-of-function typically causes epilepsy, whereas loss-of-function leads to ID/autism. How altered channel biophysics translate into patient neurons remains unknown. Here, we investigated iPSC-derived early-stage cortical neurons from ID patients harboring diverse pathogenic SCN2A variants [p.(Leu611Valfs*35); p.(Arg937Cys); p.(Trp1716*)] and compared them with neurons from an epileptic encephalopathy (EE) patient [p.(Glu1803Gly)] and controls. ID neurons consistently expressed lower NaV1.2 protein levels. In neurons with the frameshift variant, NaV1.2 mRNA and protein levels were reduced by ~ 50%, suggesting nonsense-mediated decay and haploinsufficiency. In other ID neurons, only protein levels were reduced implying NaV1.2 instability. Electrophysiological analysis revealed decreased sodium current density and impaired action potential (AP) firing in ID neurons, consistent with reduced NaV1.2 levels. In contrast, epilepsy neurons displayed no change in NaV1.2 levels or sodium current density, but impaired sodium channel inactivation. Single-cell transcriptomics identified dysregulation of distinct molecular pathways including inhibition of oxidative phosphorylation in neurons with SCN2A haploinsufficiency and activation of calcium signaling and neurotransmission in epilepsy neurons. Together, our patient iPSC-derived neurons reveal characteristic sodium channel dysfunction consistent with biophysical changes previously observed in heterologous systems. Additionally, our model links the channel dysfunction in ID to reduced NaV1.2 levels and uncovers impaired AP firing in early-stage neurons. The altered molecular pathways may reflect a homeostatic response to NaV1.2 dysfunction and can guide further investigations.

OP0095 SINGLE-CELL RNA SEQUENCING REVEALS POTENT ANTI-INFLAMMATORY AND ANTIFIBROTIC ACTIVITIES OF DIMETHYL-ALPHA-KETOGLUTARATE ON EXPLANTED SKIN FROM PATIENTS WITH SYSTEMIC SCLEROSIS

Background

Activated fibroblasts are the main drivers of skin fibrosis in SSc. We have recently identified dimethyl alpha-ketoglutarate (dm-aKG) as a potential repressor of myofibroblast differentiation and profibrotic activity in cultured skin fibroblasts.

Objectives

To further analyse the clinical translation of our findings by investigating the antifibrotic capacity of dm-aKG on explanted skin biopsies from SSc patients.

Methods

We cultured forearm punch skin biopsies from SSc patients (n=10) for 24h ex vivo in the presence/absence of 6 mM dm-aKG. Thereafter, skin biopsies (n=4) were dissociated into single cells using a combined mechanical-enzymatic dissociation protocol, followed by single cell (sc)RNA-seq library preparation (10x Genomics) and sequencing (Illumina, NovaSeq6000, 50,000 reads/cell). We mapped the scRNA-seq reads to the reference genome GRCh38.p13 and analysed the data with R/Bioconductor tools. We deconvoluted cell types in bulk skin transcriptomes from SSc cohorts (GSE: 45485, 59785, 9285, 32413) using human skin scRNA-seq data1. The secretion of IL-6, procollagen-1, PRO-C1 (N-terminal type I collagen pro-peptide), C1M (MMP-degradation fragment of type I collagen), and fibronectin (FBN-C) from cultured skin (n=10) was measured in supernatants by ELISA. We analysed gene and protein expression in TGFβ-activated healthy and SSc dermal fibroblasts (DF, n=10) treated or not with dm-aKG using qPCR, Western blot and ELISA. Contractile properties of DF were assessed by gel contraction assay. Traction forces generated by DF were determined by reference-free traction force microscopy.

Results

Dissociated cultured SSc skin exhibited comparable cell yield and viability in the presence (20,203; 89%) and absence (25,280; 93%) of dm-aKG, respectively. scRNA-seq skin analysis included 20,869 high quality single cell profiles segregating into 10 distinct skin cell populations (Figure 1A). This analysis demonstrated decreased proportion of fibroblasts and increased proportion of keratinocytes in dm-aKG treated skin (p<0.05; Figure 1B). Among skin cell types, skin fibroblasts exhibited the largest amount of differentially expressed genes upon dm-aKG treatment (44%, n=779, x-fold>0.5, FDR<0.05), suggesting that these cells are key targets of dm-aKG therapy in SSc skin. We identified inflammatory/cytokine signalling (hub genes IL6, STAT1) and extracellular matrix (ECM) organization (hub genes MMP1, ITGB3) as top downregulated biological processes in fibroblasts in dm-aKG treated SSc skin (Figure 1C), coinciding with a decreased abundance of proinflammatory skin fibroblast subpopulation. Specifically, these cells were identified as the main source of IL6 (Figure 1D) and were enriched in SSc skin as revealed by deconvolution analysis of skin transcriptomes. Furthermore, dm-aKG reduced the secretion of IL-6, procollagen-1 and C1M, but not pro-C1 and FBN-C, from cultured skin explants. In cultured DF, dm-aKG blocked the inflammatory (IL-6, pSTAT3), profibrotic (aSMA, Fibronectin, Procollagen-1, Pro-C1) and contractile activities, and significantly diminished traction forces exerted by DF on the matrix substrate.

Figure 1.

scRNA-seq – comparison of untreated and dm-aKG treated paired skin biopsies. (A) UMAP plot with annotated skin cells, (B) differential abundance of main skin cell types, (C) volcano plot of DE genes with top downregulated gene ontology (GO) pathways in dm-aKG treated skin fibroblasts, (D) IL6 expression in untreated (blue) and treated (pink) skin fibroblasts.

Conclusion

Dm-aKG broadly interferes with inflammatory and ECM organizational activities of skin fibroblasts in culture and in explanted skin from SSc patients. These results confirm that dm-aKG might represent a potential new therapeutic approach for efficient targeting of skin inflammation and fibrosis in SSc.

References

[1]He H et al. J Allergy Clin Immunol 2020

Acknowledgements

This work was supported by a research grant from FOREUM Foundation for Research in Rheumatology and University Medical Centre Ljubljana.

Disclosure of Interests

Blaž Burja: None declared, Dominique Paul: None declared, Reto Gerber: None declared, Sam G. Edalat: None declared, Muriel Elhai Speakers bureau: BMS, Elena Pachera: None declared, Rahel S. Zingg: None declared, Francesca Michela Pramotton: None declared, Sofie Falkenløve Madsen: None declared, Kristina Buerki: None declared, Giampietro Costanza: None declared, Michael Whitfield: None declared, Anne-Christine Bay-Jensen: None declared, Snežna Sodin-Šemrl: None declared, Matija Tomsic: None declared, Gabriela Kania: None declared, Hubert Rehrauer: None declared, Oliver Distler Speakers bureau: Bayer, Boehringer Ingelheim, Janssen, Medscape, Consultant of: Abbvie, Acceleron, Alcimed, Amgen, AnaMar, Arxx, AstraZeneca, Baecon, Blade, Bayer, Boehringer Ingelheim, Corbus, CSL Behring, 4P Science, Galapagos, Glenmark, Horizon, Inventiva, Kymera, Lupin, Miltenyi Biotec, Mitsubishi Tanabe, MSD, Novartis, Prometheus, Roivant, Sanofi and Topadur, Grant/research support from: Kymera, Mitsubishi Tanabe, Boehringer Ingelheim, Ziga Rotar: None declared, Mark Robinson: None declared, Katja Lakota: None declared, Mojca Frank Bertoncelj: None declared.

Insight into the beneficial immunomodulatory mechanism of the sevoflurane metabolite hexafluoro-2-propanol in a rat model of endotoxaemia

Volatile anaesthetics such as sevoflurane attenuate inflammatory processes, thereby impacting patient outcome significantly. Their inhalative administration is, however, strictly limited to controlled environments such as operating theatres, and thus an intravenously injectable immunomodulatory drug would offer distinct advantages. As protective effects of volatile anaesthetics have been associated with the presence of trifluorinated carbon groups in their basic structure, in this study we investigated the water-soluble sevoflurane metabolite hexafluoro-2-propanol (HFIP) as a potential immunomodulatory drug in a rat model of endotoxic shock. Male Wistar rats were subjected to intravenous lipopolysaccharide (LPS) and thereafter were treated with HFIP. Plasma and tissue inflammatory mediators, neutrophil invasion, tissue damage and haemodynamic stability were the dedicated end-points. In an endotoxin-induced endothelial cell injury model, underlying mechanisms were elucidated using gene expression and gene reporter analyses. HFIP reduced the systemic inflammatory response significantly and decreased endotoxin-induced tissue damage. Additionally, the LPS-provoked drop in blood pressure of animals was resolved by HFIP treatment. Pathway analysis revealed that the observed attenuation of the inflammatory process was associated with reduced nuclear factor kappa B (NF-κΒ) activation and suppression of its dependent transcripts. Taken together, intravenous administration of HFIP exerts promising immunomodulatory effects in endotoxaemic rats. The possibility of intravenous administration would overcome limitations of volatile anaesthetics, and thus HFIP might therefore represent an interesting future drug candidate for states of severe inflammation.

Experimental heart transplantation: effect of cyclosporine on expression and activity of metzincins

Metzincins, such as matrix metalloproteases (MMP), and extracellular matrix (ECM) proteins are differentially regulated in inflammation. We hypothesised that metzincins are also dysregulated in experimental acute cardiac allograft rejection. We investigated the Dark Agouti-to-Lewis (DA-to-Lew) rat model of acute cardiac allograft rejection. Cyclosporine (CsA) (7.5 mg/kg/d) was given from transplantation to sacrifice (day +5). At that time, mRNA levels were analysed by Affymetrix genechip and quantitative reverse transcription polymerase chain reaction (qRTPCR). MMP protein and activities were analysed by immunohistology, fluorometry, zymography and Western blots. In untreated rejected DA allografts, mRNA levels of MMP-2/-7/-9/-/12-/14, a disintegrin and metalloprotease (ADAM)-17, tissue inhibitor of metalloprotease (TIMP)-1/-3 were increased, whereas MMP-11/-16/-24 and TIMP-2/-4 were lowered compared to native DA hearts. With respect to these untreated allografts, CsA lowered mRNA levels of MMP-7, TIMP-1/-3 (TIMP-2/-4 remained relatively low) and ADAM17, but augmented mRNA levels of MMP-11/-16/-23 and of many ECM genes. Immunohistology showed increased staining of MMP-2 in acute rejection (AR). Overall MMP activity was augmented in both transplanted groups, but CsA reduced MMP-9 activity and MMP-14 production. Taken together, MMP and TIMP were upregulated during acute AR. CsA ameliorated histology of rejection but showed potential pro-fibrotic effects. Thus, MMP and TIMP may play a role in acute cardiac allograft rejection, and beneficial modification of the MMP-ECM balance requires interventions beyond CsA.