Induction of Survival of Motor Neuron (SMN) Protein Deficiency in Spinal Astrocytes by Small Interfering RNA as an In Vitro Model of Spinal Muscular Atrophy

Ginsenoside Rg1 regulates astrocytes to promote angiogenesis in spinal cord injury via the JAK2/STAT3 signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Ginseng (Panax ginseng C. A. Mey) is a common traditional Chinese medicine used for anti-inflammation, anti-apoptosis, anti-oxidative stress, and neuroprotection. Ginsenosides Rg1, the main active components isolated from ginseng, may be a feasible therapy for spinal cord injury (SCI).

AIMS OF THE STUDY

SCI causes endothelial cell death and blood vessel rupture, ultimately resulting in long-term neurological impairment. As a result, encouraging spinal angiogenesis may be a feasible therapy for SCI. This investigation aimed to validate the capacity of ginsenoside Rg1 in stimulating angiogenesis within the spinal cord.

MATERIALS AND METHODS

Rats with SCI were injected intraperitoneally with ginsenoside Rg1. The effectiveness of ginsenoside Rg1 was assessed using the motor function score and the motor-evoked potential (MEP). Immunofluorescence techniques were applied to identify the spinal cord's angiogenesis. Angiogenic factors were examined through Western Blot (WB) and Immunohistochemistry. Oxygen-glucose deprivation (OGD) was employed to establish the hypoxia-ischemia model in vitro, and astrocytes (As) were given ginsenoside Rg1 and co-cultured with spinal cord microvascular endothelial cells (SCMECs). Immunofluorescence, wound healing test, and tube formation assay were used to identify the co-cultured SCMECs' activity. Finally, network pharmacology analysis and siRNA transfection were applied to verify the mechanism of ginsenoside Rg1 promoting angiogenesis.

RESULTS

The rats with SCI treated with ginsenoside Rg1 indicated more significant functional recovery, more pronounced angiogenesis, and higher levels of angiogenic factor expression. In vitro, the co-culture system with ginsenoside Rg1 intervention improved SCMECs' capacity for proliferating, migrating, and forming tubes, possibly by promoting the expression of vascular endothelial growth factor (VEGF) in As via the janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway.

CONCLUSION

Ginsenoside Rg1 can regulate As to promote angiogenesis, which may help to understand the mechanism of promoting SCI recovery.

Alteration of LARGE1 abundance in patients and a mouse model of 5q-associated spinal muscular atrophy

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by recessive pathogenic variants affecting the survival of motor neuron (SMN1) gene (localized on 5q). In consequence, cells lack expression of the corresponding protein. This pathophysiological condition is clinically associated with motor neuron (MN) degeneration leading to severe muscular atrophy. Additionally, vulnerability of other cellular populations and tissues including skeletal muscle has been demonstrated. Although the therapeutic options for SMA have considerably changed, treatment responses may differ thus underlining the persistent need for validated biomarkers. To address this need and to identify novel marker proteins for SMA, we performed unbiased proteomic profiling on cerebrospinal fluid derived (CSF) from genetically proven SMA type 1-3 cases and afterwards performed ELISA studies on CSF and serum samples to validate the potential of a novel biomarker candidates in both body fluids. To further decipher the pathophysiological impact of this biomarker, immunofluorescence studies were carried out on spinal cord and skeletal muscle derived from a 5q-SMA mouse model. Proteomics revealed increase of LARGE1 in CSF derived from adult patients showing a clinical response upon treatment with nusinersen. Moreover, LARGE1 levels were validated in CSF samples of further SMA patients (type 1-3) by ELISA. These studies also unveiled a distinguishment between groups in improvement of motor skills: adult patients do present with lowered level per se at baseline visit while no elevation upon treatment in the pediatric cohort can be observed. ELISA-based studies of serum samples showed no changes in the pediatric cohort but unraveled elevated level in adult patients responding to future intervention with nusinersen, while non-responders did not show a significant increase. Additional immunofluorescence studies of LARGE1 in MN and skeletal muscle of a SMA type 3 mouse model revealed an increase of LARGE1 during disease progression. Our combined data unraveled LARGE1 as a protein dysregulated in serum and CSF of SMA-patients (and in MN and skeletal muscle of SMA mice) holding the potential to serve as a disease marker for SMA and enabling to differentiate between patients responding and non-responding to therapy with nusinersen.

Spinal astrocyte dysfunction drives motor neuron loss in late-onset spinal muscular atrophy

Spinal muscular atrophy (SMA) is a progressive neuromuscular disorder caused by a loss of the survival of motor neuron 1 (SMN1) gene, resulting in a loss of spinal motor neurons (MNs), leading to muscle weakness and wasting. The pathogenesis of MN loss in SMA and the selective vulnerability in different cellular populations are not fully understood. To investigate the role of spinal astrocytes in the pathogenesis of late-onset SMA, we used a mouse model in addition to in vitro approaches. Immunostaining, Western blot analysis, small interfering ribonucleic acid (siRNA) transfections, functional assays, enzyme-linked immunosorbent assay (ELISA), behavioral tests, and electrophysiological measurements were performed. Early activation of spinal astrocytes and a reduction of the excitatory amino acid transporter 1 (EAAT1) on postnatal day (P) 20 preceded the loss of spinal MNs in SMA mice occurring on P42. EAAT1 reduction resulted in elevated glutamate levels in the spinal cord of SMA mice at P20 and P42. SMA-like astrocytes generated by siRNA and an ex vivo model of glutamate excitotoxicity involving organotypic spinal cord slice cultures revealed the critical role of glutamate homeostasis in the degeneration of MNs. The pre-emptive administration of arundic acid (AA), as an inhibitor of astrocyte activation, to SMA mice prior to the loss of motor neurons (P28) resulted in elevated EAAT1 protein levels compared to vehicle-treated SMA mice and prevented the increase of glutamate in the spinal cord and the loss of spinal MNs. Furthermore, AA preserved motor functions during behavioral experiments, the electrophysiological properties, and muscle alteration of SMA mice. In a translational approach, we transfected healthy human fibroblasts with SMN1 siRNA, resulting in reduced EAAT1 expression and reduced uptake but increased glutamate release. These findings were verified by detecting elevated glutamate levels and reduced levels of EAAT1 in cerebrospinal fluid of untreated SMA type 2 and 3 patients. In addition, glutamate was elevated in serum samples, while EAAT1 was not detectable. Our data give evidence for the crucial role of spinal astrocytes in the pathogenesis of late-onset SMA, a potential driving force for MN loss by glutamate excitotoxicity caused by EAAT1 reduction as an early pathophysiological event. Furthermore, our study introduces EAAT1 as a potential therapeutic target for additional SMN-independent therapy strategies to complement SMN-enhancing drugs.

Glial fibrillary acidic protein in cerebrospinal fluid of patients with spinal muscular atrophy

Objective

Activated astroglia is involved in the pathophysiology of neurodegenerative diseases and has also been described in animal models of spinal muscular atrophy (SMA). Given the urgent need of biomarkers for treatment monitoring of new RNA‐modifying and gene replacement therapies in SMA, we examined glial fibrillary acidic protein concentrations in cerebrospinal fluid (cGFAP) as a marker of astrogliosis in SMA.

Methods

58 adult patients and 21 children with genetically confirmed 5q‐associated SMA from four German motor neuron disease specialist care centers and 30 age‐ and sex‐matched controls were prospectively included in this study. cGFAP was measured and correlated to motor performance and disease severity. Additionally, we compared cGFAP with neurofilament light chain concentrations in cerebrospinal fluid (cNfL).

Results

cGFAP concentrations did not differ from controls but showed higher levels in more severely affected patients after adjustment for patients' age. Normalized cNfL values were associated with disease severity. Within 14 months of nusinersen treatment, cGFAP concentrations did not change, while cNfL decreased significantly.

Interpretation

cGFAP is not an outstanding biomarker in SMA, but might support the hypothesis that glial activation is involved in SMA pathology. Unlike previously suggested, cNfL may be a promising biomarker also in adult patients with SMA, which should be subject to further investigations.