T-cell receptor Vβ gene usage in CSF lymphocytes in X-linked adrenoleukodystrophy

Immune response of BV-2 microglial cells is impacted by peroxisomal beta-oxidation

Microglia are crucial for brain homeostasis, and dysfunction of these cells is a key driver in most neurodegenerative diseases, including peroxisomal leukodystrophies. In X-linked adrenoleukodystrophy (X-ALD), a neuroinflammatory disorder, very long-chain fatty acid (VLCFA) accumulation due to impaired degradation within peroxisomes results in microglial defects, but the underlying mechanisms remain unclear. Using CRISPR/Cas9 gene editing of key genes in peroxisomal VLCFA breakdown (Abcd1, Abcd2, and Acox1), we recently established easily accessible microglial BV-2 cell models to study the impact of dysfunctional peroxisomal β-oxidation and revealed a disease-associated microglial-like signature in these cell lines. Transcriptomic analysis suggested consequences on the immune response. To clarify how impaired lipid degradation impacts the immune function of microglia, we here used RNA-sequencing and functional assays related to the immune response to compare wild-type and mutant BV-2 cell lines under basal conditions and upon pro-inflammatory lipopolysaccharide (LPS) activation. A majority of genes encoding proinflammatory cytokines, as well as genes involved in phagocytosis, antigen presentation, and co-stimulation of T lymphocytes, were found differentially overexpressed. The transcriptomic alterations were reflected by altered phagocytic capacity, inflammasome activation, increased release of inflammatory cytokines, including TNF, and upregulated response of T lymphocytes primed by mutant BV-2 cells presenting peptides. Together, the present study shows that peroxisomal β-oxidation defects resulting in lipid alterations, including VLCFA accumulation, directly reprogram the main cellular functions of microglia. The elucidation of this link between lipid metabolism and the immune response of microglia will help to better understand the pathogenesis of peroxisomal leukodystrophies.

Pathoetiology of multiple sclerosis: are we barking up the wrong tree?

Despite a century of intensive investigation, the underlying cause of multiple sclerosis has eluded us. It is clear that there exists a prominent progressive degenerative phenotype together with an important autoimmune inflammatory component, and careful histopathological examination always shows, to a greater or lesser degree, concomitant degeneration/demyelination and adaptive T cell-dependent immune responses. Given this picture, it is difficult, if not impossible, to definitively say whether degeneration or autoimmunity is the initiator of the disease. In this review, I put forward the evidence for and against both models and speculate that, in contrast to the accepted view, it is equally likely that multiple sclerosis may be a degenerative disease that secondarily elicits an autoimmune response, and suggest how this might influence therapeutic approaches.

Oligodendroglial impact on axonal function and survival - a hypothesis

PURPOSE OF REVIEW

Although multiple sclerosis is considered the prototype of a primary autoimmune disease in the central nervous system, there is emerging evidence that primary oligodendrocyte dysfunctions can suffice to trigger a secondary immune response in the nervous system. This short review focuses on the possible primary role of oligodendrocytes in axon loss and inflammatory demyelination.

RECENT FINDINGS

The analysis of natural and engineered mouse mutants has provided unexpected insight into oligodendrocyte function beyond that of axonal myelination for rapid impulse propagation. Specifically, mutations in some genes thought to be required for myelin assembly revealed an additional role of oligodendrocytes in supporting long-term axonal function and survival. Other mutations have been reported that cause both central nervous system demyelination and neuroinflammation, with pathological features known from human leukodystrophy patients. In human multiple sclerosis, demyelination leads invariably to axon loss, but the underling pathomechanisms may not be restricted to that of a primary immune-mediated disorder.

SUMMARY

Collectively, experimental and pathological findings point to a primary role of myelinating glia in long-term axonal support and suggest that defects of lipid metabolism in oligodendrocytes contribute to inflammatory myelin diseases.

Immunopathogenesis of adrenoleukodystrophy: current understanding

Adrenoleukodystrophy is a neurometabolic disease with a decreased ability to degrade very long chain fatty acids (VLCFA) and significant phenotypic variation. Unlike most neurometabolic diseases, the success of hematopoietic stem cell transplantation (HSCT) is based on acquiring a new immune system rather than enzyme replacement. VLCFA accumulation appears necessary but not sufficient for pathogenesis. Evidence for the involvement of different components of the immune system in the pathogenesis of the cerebral lesions (cellular, cytokines, humoral, and complement) is reviewed, along with both HSCT and non-HSCT immunologic approaches to treatment and future directions.