Sunday, May 12, 2024
5/12/2024
The mechanisms driving progressive multiple sclerosis (MS) remain enigmatic. Progression of MS correlates with the expression of the cytokine tumor necrosis factor (TNF) in cerebrospinal fluid of patients, suggesting that TNF plays a key role in the disease process. Thus, targeting TNF was suggested as an attractive therapy for MS. Surprisingly, however, TNF-blocking drugs with proven efficacy in other autoimmune diseases triggered onset and exacerbations of MS, which provided evidence that TNF can also contribute to CNS protection and repair. Subsequent work showed that pathogenic TNF effects in EAE are mediated via TNF receptor (TNFR) 1, whereas TNFR2 signaling ameliorates disease and reduces demyelination. TNFR2 is expressed by different cell types in the CNS, including microglia and oligodendrocytes, and its expression by these cells can promote repair and remyelination. Likewise, astrocytes can express TNFR2, but the role of TNFR2 expressed by astrocytes for MS/EAE progression remains unresolved. Astrocytes with pathogenic (A1) or neuroprotective/anti-inflammatory properties (A2) have been described; however, the mechanisms orchestrating detrimental versus beneficial astrocyte functions are still not fully understood. We have obtained exciting preliminary results supporting a central role for astrocyte TNFR2 in curtailing EAE progression by investigating the role of TNFR2 in a “humanized” transgenic mouse model expressing the human MS-associated MHC II allele HLA-DR2b and lacking the expression of TNFR2 molecules, herein called DR2b¿R2 mice. This model provided evidence that the HLA- DR2b molecule favored Th17 development, while impairing Foxp3+ Treg cell formation. Importantly, we observed that DR2b¿R2 mice developed progressive EAE and astrogliosis when CNS resident cells were TNFR2 deficient. Moreover, in DR2b¿R2 animals with EAE, astrocytes showed increased expression of pro-inflammatory cytokines and increased expression of CXCR5. Additionally, CXCL13 was upregulated in the CNS of these mice in line with previous reports that CNS expression of CXCL13 aggravates EAE and promotes chronic white matter lesions that is not dependent on recruitment of CXCR5+ leukocytes from the periphery, and that CXCL13 expressed by damaged neurons can activate astrocytes. Moreover, we observed a striking dichotomy in the expression of TNFR2 between astrocyte populations in DR2b mice with EAE, suggesting that TNFR2 expression may favor astrocyte A2 versus A1 subpopulations. Thus, our proposal will test the central hypothesis that TNFR2 signaling in astrocytes curtails progression of neuroinflammation by restraining pathogenic and promoting protective astrocyte functions. We will test our hypothesis by (1) determining the role of TNFR2 for curtailing pathogenic astrocyte effector functions and preventing EAE progression; and (2) determining the role of TNFR2-regulated CXCL13/CXCR5 signaling for chronic astrocyte activation and function in progressive EAE in DR2b¿R2 mice. We will accomplish the objectives of this proposal by applying innovative new approaches including our progressive EAE model, developing astrocyte-specific TNFR2 and CXCR5 knockout mice, and innovative immunological and molecular biological methods, including single-cell RNA-seq and RNAScope.
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