Sanguinarine modulates microglial function via PPARγ activation and protects against CNS demyelination.

Microglia aggregate in regions of active inflammation and demyelination in the CNS of multiple sclerosis (MS) patients and are considered pivotal in the disease process. Targeting microglia is a promising therapeutic approach for myelin repair. Previously, we identified two candidates for microglial modulation and remyelination using a Connectivity Map (CMAP)-based screening strategy. Interestingly, with results that overlapped, sanguinarine (SAN) emerged as a potential drug candidate to modulate microglial polarization and promote remyelination. In the current study, we demonstrate the efficacy of SAN in mitigating the MS-like experimental autoimmune encephalomyelitis (EAE) in a dose-dependent manner. Meanwhile, prophylactic administration of a medium dose (2.5 mg/kg) significantly reduces disease incidence and ameliorates clinical signs in EAE mice. At the cellular level, SAN reduces the accumulation of microglia in the spinal cord. Morphological analyses and immunophenotyping reveal a less activated state of microglia following SAN administration, supported by decreased inflammatory cytokine production in the spinal cord. Mechanistically, SAN skews primary microglia towards an immunoregulatory state and mitigates proinflammatory response through PPARγ activation. This creates a favorable milieu for the differentiation of oligodendrocyte progenitor cells (OPCs) when OPCs are incubated with conditioned medium from SAN-treated microglia. We further extend our investigation into the cuprizone-induced demyelinating model, confirming that SAN treatment upregulates oligodendrocyte lineage genes and increases myelin content, further suggesting its pro-myelination effect. In conclusion, our data propose SAN as a promising candidate adding to the preclinical therapeutic arsenal for regulating microglial function and promoting myelin repair in CNS demyelinating diseases such as MS.

Activation of TRPV1 receptor facilitates myelin repair following demyelination via the regulation of microglial function.

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel that is activated by capsaicin (CAP), the main component of chili pepper. Despite studies in several neurological diseases, the role of TRPV1 in demyelinating diseases remains unknown. Herein, we reported that TRPV1 expression was increased within the corpus callosum during demyelination in a cuprizone (CPZ)-induced demyelination mouse model. TRPV1 deficiency exacerbated motor coordinative dysfunction and demyelination in CPZ-treated mice, whereas the TRPV1 agonist CAP improved the behavioral performance and facilitated remyelination. TRPV1 was predominantly expressed in Iba1+ microglia/macrophages in human brain sections of multiple sclerosis patients and mouse corpus callosum under demyelinating conditions. TRPV1 deficiency decreased microglial recruitment to the corpus callosum, with an associated increase in the accumulation of myelin debris. Conversely, the activation of TRPV1 by CAP enhanced the recruitment of microglia to the corpus callosum and potentiated myelin debris clearance. Using real-time live imaging we confirmed an increased phagocytic function of microglia following CAP treatment. In addition, the expression of the scavenger receptor CD36 was increased, and that of the glycolysis regulators Hif1a and Hk2 was decreased. We conclude that TRPV1 is an important regulator of microglial function in the context of demyelination and may serve as a promising therapeutic target for demyelinating diseases such as multiple sclerosis.