Currently, available drugs for multiple sclerosis (MS) are predominantly immune-modulatory. They are effective in reducing relapses, but not in slowing down or stopping progressive disease course. Therefore, there is a need to develop treatment strategies that will provide neuroprotection and halt disability progression. Pregnancy is neuroprotective in patients with MS. A pregnancy hormone and a moderate estrogen receptor beta (ERβ)-ligand, estriol, has been reported to have beneficial effects on reducing relapses and improving cognition when treated in MS patients. Although, the mechanisms of ERβ-ligand mediated treatment effects on neuroprotection remains poorly understood. Here I hypothesized that ERβ signaling on CD11c+ immune cells and Olig1+ oligodendrocytes plays an essential role in providing neuroprotection and enhancing remyelination. To test the hypothesis, I created conditional knockout mice (CKO) with ERβ deleted from each cell type using the Cre-LoxP recombinase system and investigated neuroprotective effects of ERβ-ligand treatment in experimental autoimmune encephalomyelitis (EAE) and cuprizone diet-induced demyelinating disease models. Also, I used RiboTag mice to determine oligodendrocyte specific gene expression to understand the molecular mechanisms of remyelination. Subsequently, I studied the mechanisms of ERβ-ligand treatment effects in oligodendrocytes during remyelination.

The results revealed that ERβ-ligand treatment reduced pro-inflammatory responses through ERβ on CD11c+ myeloid DC/MΦ and increased oligodendrocyte maturation through ERβ on Olig1+ oligodendrocytes during EAE. The use of CKO mice proved that both were necessary as one without the other was not sufficient. Mechanistic insights on remyelination using the RiboTag mice revealed that oligodendrocytes upregulate de novo cholesterol biosynthesis during remyelination after chronic demyelination. Furthermore, when compared to vehicle treated naturally remyelinating mice, ERβ-ligand treated mice showed enhanced remyelination by increasing oligodendrocyte maturation, increasing cholesterol synthesis pathway genes, increasing oligodendrocyte progenitor cells (OPCs), and increasing Sox2 expression in OPCs during remyelination. I extended our investigation of ERβ-ligand treatment in the cuprizone model to the EAE model, to discover that ERβ-ligand treated mice showed neuroprotection by increasing oligodendrocyte maturation, and increasing cholesterol synthesis pathway genes, but not by increasing OPC Sox2 expression. This comprehensive approach using two different demyelinating disease models of MS and two transgenic mouse models provided critical insights regarding treatment effects of ERβ-ligand on neuroprotection and remyelination in vivo.