Mechanisms of metabolic stress induced cell death of human oligodendrocytes: relevance for progressive multiple sclerosis

Abstract

Oligodendrocyte (OL) injury and loss are central features of evolving lesions in multiple sclerosis. Potential causative mechanisms of OL loss include metabolic stress within the lesion microenvironment. Here we use the injury response of primary human OLs (hOLs) to metabolic stress (reduced glucose/nutrients) in vitro to help define the basis for the in situ features of OLs in cases of MS. Under metabolic stress in vitro, we detected reduction in ATP levels per cell that precede changes in survival. Autophagy was initially activated, although ATP levels were not altered by inhibitors (chloroquine) or activators (Torin-1). Prolonged stress resulted in autophagy failure, documented by non-fusion of autophagosomes and lysosomes. Consistent with our in vitro results, we detected higher expression of LC3, a marker of autophagosomes in OLs, in MS lesions compared to controls. Both in vitro and in situ, we observe a reduction in nuclear size of remaining OLs. Prolonged stress resulted in increased ROS and cleavage of spectrin, a target of Ca2+-dependent proteases. Cell death was however not prevented by inhibitors of ferroptosis or MPT-driven necrosis, the regulated cell death (RCD) pathways most likely to be activated by metabolic stress. hOLs have decreased expression of VDAC1, VDAC2, and of genes regulating iron accumulation and cyclophilin. RNA sequencing analyses did not identify activation of these RCD pathways in vitro or in MS cases. We conclude that this distinct response of hOLs, including resistance to RCD, reflects the combined impact of autophagy failure, increased ROS, and calcium influx, resulting in metabolic collapse and degeneration of cellular structural integrity. Defining the basis of OL injury and death provides guidance for development of neuro-protective strategies.

Age-dependent effects of metformin on human oligodendrocyte lineage cell ensheathment capacity

“…; the latter stress conditions were used as ‘positive’ controls, as we have previously reported. 29 , 30 As shown in Panels E–H, the metformin-induced increase in pAMPK expression was considerably less pronounced compared to LG and NG conditions (range 1.2–1.6-fold of control versus 3.3–5.7-fold of control) in both adult and paediatric A+ and A− cells.…”

“…The LG and NG conditions result in a rapid reduction of ATP levels and AMPK activation. 30 Neumann et al . 19 , 40 attributed the effect of starvation and metformin on promoting myelination in aged animals to signalling via the AMPK pathway.…”

Targeted RNAseq Revealed the Gene Expression Signature of Ferroptosis-Related Processes Associated with Disease Severity in Patients with Multiple Sclerosis

“…Several studies have investigated ferroptosis mechanisms in oligodendrocytes, as their loss is one of the hallmarks of progressive MS. Oligodendrocyte loss and demyelination were associated with ferroptosis [ 8 ]. Yet, in a state of metabolic stress, ferrostatin-1, a ferroptosis inhibitor, did not prevent oligodendrocyte death [ 41 ]. However, resistance of oligodendrocytes to oxidative stress, in comparison to HeLa cells, was characterized by the upregulation of CDKN1A , a gene responsible for reduction in sensitivity to ferroptosis, and SAT1 , a key metabolic regulator in the catabolism of polyamines previously related to ferroptosis [ 42 ].…”