Aberrant regulation of the GSK ‐3β/ NRF 2 axis unveils a novel therapy for adrenoleukodystrophy

Abstract

The nuclear factor erythroid 2‐like 2 (NRF2) is the master regulator of endogenous antioxidant responses. Oxidative damage is a shared and early‐appearing feature in X‐linked adrenoleukodystrophy (X‐ALD) patients and the mouse model (Abcd1 null mouse). This rare neurometabolic disease is caused by the loss of function of the peroxisomal transporter ABCD1, leading to an accumulation of very long‐chain fatty acids and the induction of reactive oxygen species of mitochondrial origin. Here, we identify an impaired NRF2 response caused by aberrant activity of GSK‐3β. We find that GSK‐3β inhibitors can significantly reactivate the blunted NRF2 response in patients’ fibroblasts. In the mouse models (Abcd1 − and Abcd1 −/Abcd2 −/− mice), oral administration of dimethyl fumarate (DMF/BG12/Tecfidera), an NRF2 activator in use for multiple sclerosis, normalized (i) mitochondrial depletion, (ii) bioenergetic failure, (iii) oxidative damage, and (iv) inflammation, highlighting an intricate cross‐talk governing energetic and redox homeostasis in X‐ALD. Importantly, DMF halted axonal degeneration and locomotor disability suggesting that therapies activating NRF2 hold therapeutic potential for X‐ALD and other axonopathies with impaired GSK‐3β/NRF2 axis.

GSK3β is a key regulator of the ROS-dependent necrotic death induced by the quinone DMNQ

“…The described pathway is pathological relevant and it is implicated in other models of cell death elicited by oxidative stress. Examples are the ischemia and reperfusion injury in the brain 57 , in hepatocytes 58,59 , during diabetic nephropathies 60 , in a model for Alzheimer disease 61 and in other models of neurological diseases 62,63 .…”

High‐dose biotin restores redox balance, energy and lipid homeostasis, and axonal health in a model of adrenoleukodystrophy

“…SeeBlue Plus2 Pre-Stained (Invitrogen, Thermo Fisher Scientific Inc.) was used as a ladder. Immunoblotting was carried out with the avidin-biotin peroxidase method, as reported earlier (59).…”

“…We then evaluated the correlation between the observed improvements in locomotor dysfunction and arrested axonal degeneration. Abcd1 − /Abcd2 −/− mice presented an overt neuropathological phenotype characterized by the following: (i) microgliosis ( Figure 3D,E, Supporting Figure S2A) and astrocytosis ( Figure 3G-H, Supporting Figure S2B), as detected by Iba1 and GFAP staining, respectively; (ii) axonal damage suggested by the accumulation of synaptophysin ( Figure 3J,K, Supporting Figure S2C) and amyloid precursor protein (APP) in axonal swellings ( Figure 3M,N, Supporting Figure S2C); (iii) scattered myelin debris around the axonal ovoids, probably secondary to axonal degeneration, as detected by Sudan black ( Figure 3P,Q); (iv) reduced SMI-32 staining in motor neurons, an indicator of disturbed neurofilament status ( Figure 3S,T); (v); a diminished amount of cytochrome c ( Figure 3V,W), which is a marker of mitochondrial depletion; and (vi) increased staining for malondialdehyde (MDA), a marker of lipoxidation ( Figure 3Y,Z) (16,32,33,39,48,49,57,59). We found that treatment with high-dose biotin in Abcd1 − /Abcd2 −/− mice efficaciously suppressed microgliosis ( Figure 3D-F, Supporting Figure S2A) and astrocytosis ( Figure 3G-I, Supporting Figure S2B).…”

“…Double mutant Abcd1 − /Abcd2 −/− mice develop more substantial accumulation of VLCFAs and more severe, earlier onset axonopathy starting at 12 months of age, which makes this model better suited for therapeutic assays (57). Indeed, this mouse model was instrumental in pinpointing early oxidative damage, mitochondrial depletion and bioenergetic failure as early, intertwined culprits of axonal degeneration (23,39,40) and in identifying therapeutic targets along the way (32,33,48,49,59). This knowledge aligns X-ALD physiopathogenesis with that of the most prevalent neurodegenerative disorders, including MS (22).…”

“…Here, we used X-ALD patient's primary fibroblasts and two mouse models of X-ALD (Abcd1 − and Abcd1 − /Abcd2 −/− mice) to investigate the preclinical efficacy and mode of action of high-dose biotin on the established biochemical hallmarks of redox dyshomeostasis and energetic failure, as well as axonal damage and locomotor function (41,49,59). Moreover, we uncovered novel alterations that results from the loss of the Abcd1 transporter, specifically profound dysregulation of the lipogenesis and fatty acid degradation pathways governed by mTOR/SREBP-1c in the spinal cord concomitant with global increases in triglycerides and lipid droplets.…”