White Matter Injury Induced by Perinatal Exposure to Glutaric Acid

Abstract

Glutaric acid (GA) is a neurotoxic metabolite that accumulates in the CNS of patients with glutaric acidemia-I (GA-I), a neurometabolic disease caused by deficient activity of glutaryl-CoA dehydrogenase. Most GA-I patients display characteristic CNS lesions, mainly in the gray and white matter of basal ganglia and cerebral cortex. Neurons and astrocytes are believed to be vulnerable to millimolar concentrations of GA. However, little is known about the effects of GA on oligodendrocytes (OL) and the myelination process in the postnatal brain. Here, we show that a single intracerebroventricular administration of GA to rat neonatal pups induced a selective and long-lasting myelination failure in the striatum but no deleterious effect in the myelination of the corpus callosum. At 45 days post-GA injection, the myelinated area of striatal axonal bundles was decreased by 35 %, and the expression of myelin basic protein and myelin-associated glycoprotein (MAG) reduced by 25 and 60 %, respectively. This was accompanied by long lasting cytopathology features in MAG and CC-1-expressing OLs, which was confirmed by transmission electron microscopy. Remarkably, GA did not induce acute loss of pre-OLs in the striatum as assessed by NG2 or PDGFRα immunohistochemistry, suggesting an indirect and progressive mechanism for OL damage. In accordance, GA-induced white matter injury was restricted to the striatum and associated to GA-induced astrocytosis and neuronal loss. In conclusion, the current evidence indicates a pathogenic mechanism by which GA can permanently affect myelin status.

Increased blood–brain barrier permeability and alterations in perivascular astrocytes and pericytes induced by intracisternal glutaric acid

“…Rat pups were injected at postnatal day 0 with PBS or GA into the cisterna magna to experimentally reproduce a GA-I like encephalopatic crisis as previously reported [23,24,26]. Then, animals were perfused with 1% EB in 4% PFA at 14 or 30 DPI to analyze EB extravasation.…”

“…Then, each animal was injected into the c isterna magna with either GA (1 μmol/g body weight, pH 7.4) [3-5], or an equal volume of vehicle (phosphate buffered saline (PBS), 10 mM, pH 7.4). A maximal volume of 5 μl was injected using a 30G needle attached to a Tygon tube extension to allow correct manipulation and zone identification [23,24,26]. The amount of GA administered ensured immediate high brain concentrations (~100 mM in the cerebrospinal fluid); which is hard to obtain by systemic injection due to limited flux across the BBB [27].…”

“…In a previously-validated model of GA-I consisting of a single intracisternal administration of a pathophysiological dose of GA to newborn rat pups reproducing an acute encephalopathic crisis similar to that described in humans with GA-I, astrocytes presented with oxidative stress, enhanced proliferation rate and S100ß overexpression [23,24]. Remarkably, this early astrocyte reactivity precedes a number of delayed pathological events such as myelination failure and neuron degeneration in the striatum [24,26]. Since astrocytes are also key cellular constituents of the BBB, we have explored whether intracisternal GA could also damage the neurovascular unit.…”

“…In the present study, using our model of GA perinatal administration [23,24,26], we determined whether a single intracisternal dose of GA was sufficient to trigger long term damage on BBB permeability and integrity by analyzing Evans blue (EB) and immunoglobulin G (IgG) extravasation and the protein expression of several components of the neurovascular unit.…”

Glutaric Acid-Mediated Apoptosis in Primary Striatal Neurons

“…Also, the primary neuron model cannot substitute for model of cellular interaction participating in neurotoxicity (e.g., neuron, glial, vascular endothelial cells, etc.) [29]. Some studies suggested astrocyte proliferation protects neurons from the excitotoxic damage induced by 3-OHGA [30].…”