Immune cell–specific SMN expression and sustained immune alterations in treated spinal muscular atrophy
Ines Tapken, Katharina Rahmel-Stein, Christine Ehlers, Federica Cieri, Nora T. Detering, Tobias Schüning, Bogdan Bjelica, Charlotte Mindermann, Svenja Neuhoff, Linda-Isabell Schmitt, Markus Leo, Tim Hagenacker, Sabine Illsinger, Elia Di Schiavi, Theresa Graalmann, Susanne Petri, Ulrich Kalinke, Peter Claus
Ines Tapken, Katharina Rahmel-Stein, Christine Ehlers, Federica Cieri, Nora T. Detering, Tobias Schüning, Bogdan Bjelica, Charlotte Mindermann, Svenja Neuhoff, Linda-Isabell Schmitt, Markus Leo, Tim Hagenacker, Sabine Illsinger, Elia Di Schiavi, Theresa Graalmann, Susanne Petri, Ulrich Kalinke, Peter Claus
View: Text | PDF
Research Article Immunology Muscle biology Neuroscience

Immune cell–specific SMN expression and sustained immune alterations in treated spinal muscular atrophy

Abstract

Mutations in the survival of motor neuron 1 (SMN1) can reduce functional SMN protein levels, which causes spinal muscular atrophy (SMA), a disease affecting the nervous system and peripheral tissues, including the immune system. Yet, SMN expression across immune cell subsets and the effect of SMN-modulating therapies on the immune system remain underexplored. We found that in neonatal mouse spleens, SMN expression was highest in B cells, and was massively reduced in SMA mice. In human PBMCs from adults, DCs and monocytes expressed the highest SMN levels, whereas patients with SMA showed reduced DC frequencies and increased B cell frequencies. Patients receiving systemic versus CNS-restricted therapy showed similar differences in immune cell composition and SMN expression levels. Similarly, an exploratory cohort including untreated patients did not show a substantial treatment-specific effect relative to controls. To assess the effect of differentiation on SMN, we analyzed PMA-treated THP-1 cells and found enhanced aberrant SMN splicing and increased SMN+ Cajal bodies. SMN levels varied across immune cell types, and reduced SMN levels were associated with altered immune cell composition. Immune alterations and decreased SMN levels were observed in both treated and untreated patients with SMA and may have contributed to dysfunctions of the immune system.

Authors

Ines Tapken, Katharina Rahmel-Stein, Christine Ehlers, Federica Cieri, Nora T. Detering, Tobias Schüning, Bogdan Bjelica, Charlotte Mindermann, Svenja Neuhoff, Linda-Isabell Schmitt, Markus Leo, Tim Hagenacker, Sabine Illsinger, Elia Di Schiavi, Theresa Graalmann, Susanne Petri, Ulrich Kalinke, Peter Claus

×

Figure 7

SMNΔ7 mRNA levels decrease and number of SMN+ Cajal bodies increase during PMA-induced THP-1 differentiation.

Options: View larger image (or click on image) Download as PowerPoint
SMNΔ7 mRNA levels decrease and number of SMN+ Cajal bodies increase duri...
(A) Schematic depiction of PMA-induced THP-1 differentiation and subsequent IFN-γ and TNF-α stimulation. As a control, cells were treated with DMSO devoid of PMA. The arrows indicate adherent cells. Images were taken in 20x magnification. (B) Representative (n = 1) agarose gel showing SMN splicing products amplified using primers spanning exons 6–8. (C) Western blot analysis of SMN protein levels in THP-1 cells, PMA-stimulated THP-1 cells, and PMA–IFN-γ/TNF-α–stimulated THP-1 cells, and the motoneuron-like cell line NSC34 with and without starvation for cellular differentiation. Data were normalized to total protein by Ponceau S staining. A representative blot for 3 individual cell cultures and blots is shown. (D) Quantification of SMN protein levels by Western blotting. A multiple-comparison, 2-tailed Student’s t test was performed to determine significance. Data represent the mean ± SD. (E) Representative confocal microscopy images analyzing SMN localization (red) in THP-1 cells (n = 56), PMA-differentiated THP-1 (PMA–THP-1, n = 87), and IFN-γ/TNF-α–stimulated PMA–THP-1 (n = 45). Nuclei were stained with DAPI (blue), and Cajal bodies are labeled as Coilin+ (green). Scale bar: 20 μm. Enlarged cells are highlighted by a white box and show a digitally magnified region of interest. (F) Quantification of SMN+ nuclear bodies per cell. Nuclear bodies were categorized as SMN+ Gems (Coilin–) or SMN– or SMN+ Cajal bodies (Coilin+). *P < 0.0 and ** P < 0.01, by 1-way ANOVA with multiple-comparison correction. Each dot represents a single cell, and data represent the mean ± SD.