Biology subjects

Kunjamma, R. B.

Publications and source records attributed to Kunjamma, R. B..

4 recordsLinked to original sources

bioRxiv2023

eIF2B Activator Rescues Neonatal Lethality of an eIF2Bα Sugar Phosphate Binding Mutation Associated with Vanishing White Matter Disease

eIF2B is a decameric guanine nucleotide exchange factor (GEF) that is essential for protein synthesis and a key effector of the integrated stress response (ISR). Hypomorphic mutations in any of the eIF2B subunits are associated with Vanishing White Matter Disease (VWM), a leukodystrophy characterized by ISR activation and white matter loss. Here, we showed that the VWM-associated N208Y eIF2B mutation, which abolishes sugar phosphate binding, led to a drastic reduction in its level in cells and concomitant ISR activation. We found that N208Y homozygous mice are small and die shortly after birth. Remarkably, continuous availability of 2BAct, a small molecule eIF2B activator, in food rescued the lethality and significantly extended their lifespan. 2BAct-maintained N208Y homozygous mice, however, developed motor deficits and loss of myelin with age. As is the case for milder VWM models, ISR induction was restricted to the central nervous system in treated animals. Upon 2BAct withdrawal, adult mutant mice deteriorated quickly, the ISR was induced in all peripheral tissues tested and resulted in high levels of circulating FGF21 and GDF15. This model provides a novel platform to study the impact of ISR activation across tissues with temporal control.

neuroscience↗

bioRxiv2023

Insights into the mechanism of oligodendrocyte protection and remyelination enhancement by the integrated stress response

CNS inflammation triggers activation of the integrated stress response (ISR). We previously reported that prolonging the ISR protects remyelinating oligodendrocytes and promotes remyelination in the presence of inflammation (Chen et al., eLife, 2021). However, the exact mechanisms through which this occurs remain unknown. Here, we investigated whether the ISR modulator Sephin1 in combination with the oligodendrocyte differentiation enhancing reagent bazedoxifene (BZA) is able to accelerate remyelination under inflammation, and the underlying mechanisms mediating this pathway. We find that the combined treatment of Sephin1 and BZA is sufficient to accelerate early-stage remyelination in mice with ectopic IFN-{gamma} expression in the CNS. IFN-{gamma}, which is a critical inflammatory cytokine in multiple sclerosis (MS), inhibits oligodendrocyte precursor cell (OPC) differentiation in culture and triggers a mild ISR. Mechanistically, we further show that BZA promotes OPC differentiation in the presence of IFN-{gamma}, while Sephin1 enhances the IFN-{gamma}-induced ISR by reducing protein synthesis and increasing RNA stress granule formation in differentiating oligodendrocytes. Finally, the ISR suppressor 2BAct is able to partially lessen the beneficial effect of Sephin1 on disease progression, in an MS mouse model of experimental autoimmune encephalitis (EAE). Overall, our findings uncover distinct mechanisms of action of BZA and Sephin1 on oligodendrocyte lineage cells under inflammatory stress, suggesting that a combination therapy may effectively promote restoring neuronal function in MS patients.

neuroscience↗

bioRxiv2020

Prolonging the integrated stress response enhances CNS remyelination in an inflammatory environment

The inflammatory environment of demyelinated lesions in multiple sclerosis (MS) patients contributes to remyelination failure. Inflammation activates a cytoprotective pathway, the integrated stress response (ISR), but it remains unclear whether enhancing the ISR can improve remyelination in an inflammatory environment. To examine this possibility, the remyelination stage of experimental autoimmune encephalomyelitis (EAE), as well as a mouse model that incorporates cuprizone-induced demyelination along with CNS delivery of the proinflammatory cytokine IFN-{gamma} were used here. We demonstrate that either genetic or pharmacological ISR enhancement significantly increased the number of remyelinating oligodendrocytes and remyelinated axons in the inflammatory lesions. Moreover, the combined treatment of Sephin1 with the oligodendrocyte differentiation enhancing reagent bazedoxifene increased myelin thickness of remyelinated axons to pre-lesion levels. Taken together, our findings indicate that prolonging the ISR protects remyelinating oligodendrocytes and promotes remyelination in the presence of inflammation, suggesting that ISR enhancement may provide reparative benefit to MS patients.

neuroscience↗

bioRxiv2019

Targeted complement inhibition at synapses prevents microglial synaptic engulfment and synapse loss in demyelinating disease

Multiple sclerosis (MS) is a demyelinating, autoimmune disease of the central nervous system. While work has focused on axon loss in MS, far less is known about synaptic changes. Here, in striking similarity to other neurodegenerative diseases, we identify in postmortem human MS tissue and in nonhuman primate and mouse MS models profound synapse loss and microglial synaptic engulfment. These events can occur independently of local demyelination, neuronal degeneration, and peripheral immune cell infiltration, but coincide with gliosis and increased localization of complement component C3, but not C1q, at synapses. Finally, we use AAV9 to overexpress the complement inhibitor Crry at activated C3-bound synapses in mice and demonstrate robust protection of synapses and visual function. These results mechanistically dissect synapse loss as an early pathology in MS. We further provide a novel gene therapy approach to prevent synapse loss by microglia, which may be broadly applicable to other neurodegenerative diseases.

neuroscience↗