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

Pablo Granados-Durán,Manuel Cifuentes,Jesús M Grondona,Timothy R Hughes,María Del Mar Fernández-Arjona,Margarita Pérez-Martín,Pedro Fernández-Llebrez,María Dolores López-Ávalos,Krista Johnson,B Paul Morgan

doi:10.3389/fneur.2017.00078

Abstract

Some 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. The 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. The 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. Microbial NA induces a moderate and transient myelin vacuolation that is not caused either by neuroinflammation or complement system activation.

Highlights

Myelin disorders range from spontaneous inherited to acquired due to inflammatory processes, autoimmune disorders, infectious processes, and toxic substances [1]
Myelin vacuolation is the most frequent pathologic feature of myelin sheaths [1,2,3], it should be differentiated from neuronal vacuolation that occurs in some encephalopathies such as bovine spongiform encephalopathy [4]
In brain sections stained with hematoxylin–eosin, vacuolar or spongiform areas were evident in different brain regions 7 days after the ICV injection of NA, occasionally such alterations could be observed as early as 48 h

Summary

Introduction

Myelin disorders range from spontaneous inherited to acquired due to inflammatory processes, autoimmune disorders, infectious processes, and toxic substances [1]. Myelin vacuolation may occur in at least two ways, the most frequent of which is intramyelinic vacuolation This is produced when the myelin lamellae split along the intraperiod line, which in turn reopens the extracellular space initially closed during the formation of myelin [5, 6]. This mechanism can generate vacuoles (filled with unstainable material) at multiple levels within the myelin sheath and has been associated with fluid accumulation in the nervous system parenchyma [6]. Whatever the etiology of vacuole formation, the progression from myelin vacuolation to demyelination may depend on whether the primary defect or target is the myelin sheath or the myelinating cells, and on the time of exposure to the inducing agent [1]

Methods

Results

Conclusion