Unlocking Remyelination: New Hope for Treating Progressive Multiple Sclerosis Through Wnt Signaling
A growing body of research suggests that targeting the Wnt/β-catenin signaling pathway could hold the key to reversing nerve damage and halting the progression of multiple sclerosis, offering a potential breakthrough for patients who don’t respond to current treatments.
Multiple Sclerosis (MS) affects approximately 2.8 million people worldwide, with an average onset at age 32, and stands as a leading cause of non-traumatic neurological disability in young adults. The disease disproportionately impacts women, with diagnoses occurring in roughly twice as many women (63%) as men (31%) globally. Clinically, MS presents with a diverse range of neurological deficits, including optic neuritis, sensory disturbances, and motor weakness, often following a relapsing-remitting or progressive course. While current disease-modifying therapies (DMTs) effectively manage inflammation and reduce relapse rates, they often fail to address the underlying nerve damage and progressive disability experienced by many patients.
This therapeutic gap has spurred a shift in focus towards remyelination – the process of rebuilding the protective myelin sheath around nerve fibers. Successful remyelination restores nerve signal transmission and protects against further degeneration. “Pathological studies of MS lesions demonstrate that remyelination can occur, particularly in early or active lesions,” highlighting the body’s inherent capacity for repair. However, in chronic lesions, this process stalls, not due to a lack of precursor cells, but rather due to inhibitory signals within the surrounding environment.
Recent research has pinpointed the Wnt/β-catenin signaling pathway as a critical regulator of remyelination. This highly conserved intracellular signaling cascade plays a crucial role in cell fate and proliferation, particularly within the oligodendroglial lineage – the cells responsible for producing myelin. Studies by Fancy and colleagues revealed that the transcription factor Tcf7l2, a key component of the Wnt pathway, is re-expressed in demyelinated lesions during remyelination. This reactivation coincides with active β-catenin signaling, and genetic activation of the pathway delays the differentiation of oligodendrocyte precursor cells (OPCs) into mature, myelin-producing cells, identifying differentiation as a key bottleneck in the process. These findings were further corroborated in human MS tissue, where Tcf7l2-positive oligodendrocytes were found in active lesions but absent in chronic ones, linking Wnt pathway activation to remyelination failure in vivo.
Further investigation has focused on intracellular regulators of the Wnt/β-catenin pathway, such as Axin2, a protein that promotes β-catenin degradation. Research indicates that in demyelinated lesions, Axin2 transcripts persist in OPCs that fail to differentiate, while the activity of tankyrase, an enzyme that regulates Axin2 stability, limits its accumulation, perpetuating Wnt signaling. Pharmacological inhibition of tankyrases, using compounds like XAV939, has shown promise in preclinical studies, stabilizing Axin2, enhancing β-catenin degradation, and improving remyelination in mice. However, this effect was not observed in Axin2-null mice, underscoring the importance of Axin2 in this process.
The Wnt pathway’s influence extends beyond OPCs, demonstrating a complex interplay with other cell types. Notably, studies have shown that inhibiting Wnt signaling in endothelial cells (ECs) – cells lining blood vessels – actually worsened clinical outcomes in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Researchers found that Wnt/β-catenin signaling in ECs partially protected the blood-brain barrier (BBB), limiting immune cell infiltration. Inhibiting this signaling removed this protective mechanism, leading to increased disease severity. Interestingly, the drug teriflunomide, used to treat MS, was found to promote BBB integrity by upregulating claudin-1, a tight junction protein, through activation of Wnt-2b signaling.
The extracellular environment surrounding demyelinated lesions also plays a role in modulating Wnt signaling. Extracellular sulfatases (Sulf1 and Sulf2) have been identified as regulators of inhibitory signaling, impairing OPC recruitment and differentiation by potentiating both Wnt and bone morphogenic protein (BMP) signaling. Ablation of these sulfatases enhanced remyelination, even with ongoing Wnt activation. However, combining sulfatase inhibition with a Wnt antagonist did not yield additive benefits, suggesting that Wnt and BMP pathways converge on a shared downstream mechanism.
Recent research has even revisited the role of Tcf7l2, revealing a surprising complexity. Contrary to previous assumptions, studies now suggest that Tcf7l2 actually promotes oligodendrocyte differentiation by suppressing BMP4 signaling, an inhibitor of myelination. Deletion of Tcf7l2 upregulated BMP4 signaling, while overexpression reduced BMP4 protein levels. Simultaneous deletion of Tcf7l2 and BMP4 rescued myelin gene expression defects, further illustrating the intricate interplay between these pathways.
The pursuit of novel interventions to address the progressive nature of MS represents a significant step forward. The Wnt/β-catenin signaling pathway offers a promising avenue for therapeutic development, but a nuanced approach is crucial. “Interventions in the Wnt/β-catenin signaling pathway requires a nuanced approach that is aware of different Wnt components, cell-specificity, and its effects on other pathways,” emphasizing the need for targeted therapies that consider the complex interactions within the MS microenvironment.
[Figure 1: In the absence of Wnt ligands (Wnt-OFF), cytoplasmic β-catenin is phosphorylated by a destruction complex composed of glycogen synthase kinase-3β (GSK3β), casein kinase 1 (CK1a), axis inhibition protein (AXIN), and adenomatous polyposis coli (APC), leading to its ubiquitination and proteasomal degradation resulting in transcriptional repression of Wnt target genes.13 During the Wnt-ON state, Wnt binds to Frizzled (Fz) receptor and lipoprotein-related protein 5/6 (LRP5/6), Dishevelled (Dsh) is activated and leads to the disassembly of the destruction complex and stabilizes and increases cytoplasmic β-catenin.13 The increased β-catenin then translocates intracellularly to the nucleus and binds to T cell factor/lymphoid enhancer-binding factor (TCF/LEF) and controls expression of target genes. 13]
