Microbial Neuraminidase Induces a Moderate and Transient Myelin Vacuolation Independent of Complement System Activation

Abstract

AimsSome central nervous system pathogens express neuraminidase (NA) on their surfaces. In the rat brain, a single intracerebroventricular (ICV) injection of NA induces myelin vacuolation in axonal tracts. Here, we explore the nature, the time course, and the role of the complement system in this damage.MethodsThe spatiotemporal analysis of myelin vacuolation was performed by optical and electron microscopy. Myelin basic protein-positive area and oligodendrocyte transcription factor (Olig2)-positive cells were quantified in the damaged bundles. Neuronal death in the affected axonal tracts was assessed by Fluoro-Jade B and anti-caspase-3 staining. To evaluate the role of the complement, membrane attack complex (MAC) deposition on damaged bundles was analyzed using anti-C5b9. Rats ICV injected with the anaphylatoxin C5a were studied for myelin damage. In addition, NA-induced vacuolation was studied in rats with different degrees of complement inhibition: normal rats treated with anti-C5-blocking antibody and C6-deficient rats.ResultsThe stria medullaris, the optic chiasm, and the fimbria were the most consistently damaged axonal tracts. Vacuolation peaked 7 days after NA injection and reverted by day 15. Olig2+ cell number in the damaged tracts was unaltered, and neurodegeneration associated with myelin alterations was not detected. MAC was absent on damaged axonal tracts, as revealed by C5b9 immunostaining. Rats ICV injected with the anaphylatoxin C5a displayed no myelin injury. When the complement system was experimentally or constitutively inhibited, NA-induced myelin vacuolation was similar to that observed in normal rats.ConclusionMicrobial NA induces a moderate and transient myelin vacuolation that is not caused either by neuroinflammation or complement system activation.

Long‐term priming of hypothalamic microglia is associated with energy balance disturbances under diet‐induced obesity

“…Microglial cells morphology was analyzed using FIJI free software (http://fiji.sc/Fiji). A comprehensive explanation of the procedure is available elsewhere (Fernández-Arjona et al, 2017). Briefly, the TIFF image was subjected to RGB channel separation, and the blue channel was chosen for the analysis (as the brown color from oxidized diaminobenzidine is enhanced in this channel).…”

“…Various aspects of NA-induced inflammation have been described during the previous years (Fernandez-Arjona et al, 2019a;Fernandez-Arjona et al, 2021;Granados-Durán et al, 2015;Granados-Durán et al, 2016;Granados-Durán et al, 2017). For instance, NA is able to activate microglial cells acting primarily through the pattern receptor toll-like receptor 4 (TLR4) (Fernandez-Arjona et al, 2019a).…”

“…We established that a single dose of 500 mU of NA administered ICV in rats or mice provoked conventional symptoms of neuroinflammation such as peripheral cells infiltration, activation of resident microglia and astrocytes, increased levels of mediators such as cytokines, complement system activation (Fernandez‐Arjona et al, 2017; Fernandez‐Arjona et al, 2019a, 2019b; Granados‐Durán et al, 2015; Granados‐Durán et al, 2016), and blood brain barrier permeability (unpublished data). Other symptoms included myelin vacuolation (Granados‐Durán et al, 2017) and ependymal cell damage (Fernandez‐Arjona et al, 2021; Granados‐Durán et al, 2016). After 2–3 weeks, most signs of inflammation have disappeared, and animals seem completely recovered (Granados‐Durán et al, 2015, and unpublished results), thus supporting the acute nature of the inflammatory process.…”

Microglial activation by microbial neuraminidase through TLR2 and TLR4 receptors

“…Also, NA itself can induce the activation of the complement system, which is present in the cerebrospinal fluid [31]. Other damages provoked by NA in the CNS include myelin vacuolation, ependymal denudation, ventriculomegaly, and eventually hydrocephalus [27, 28, 32]. The wide range of effects of NA within the CNS makes it worth to explore its mechanism of action.…”

Increasing brain N‐acetylneuraminic acid alleviates hydrocephalus‐induced neurological deficits

“…In humans, biallelic mutations in the NANS gene, 73 which impairs endogenous Neu5Ac synthesis, have been linked to prenatal hydrocephalus and demyelination. 60 , 74 Experimental studies have shown that low‐dose neuraminidase‐induced astrogliosis and demyelination, 75 , 76 while high‐dose neuraminidase‐induced hydrocephalus in rats. 21 However, there is currently no commercialized pharmacological intervention available to reduce brain Neu5Ac in animal models.…”