RNaseT2 knockout rats exhibit hippocampal neuropathology and deficits in memory

Abstract

RNASET2 deficiency in humans is associated with infant cystic leukoencephalopathy, which causes psychomotor impairment, spasticity and epilepsy. A zebrafish mutant model suggests that loss of RNASET2 function leads to neurodegeneration due to the accumulation of non-degraded RNA in the lysosomes. The goal of this study was to characterize the first rodent model of RNASET2 deficiency. The brains of 3- and 12-month-old RNaseT2 knockout rats were studied using multiple magnetic resonance imaging modalities and behavioral tests. While T1- and T2-weighted images of RNaseT2 knockout rats exhibited no evidence of cystic lesions, the prefrontal cortex and hippocampal complex were enlarged in knockout animals. Diffusion-weighted imaging showed altered anisotropy and putative gray matter changes in the hippocampal complex of the RNaseT2 knockout rats. Immunohistochemistry for glial fibrillary acidic protein (GFAP) showed the presence of hippocampal neuroinflammation. Decreased levels of lysosome-associated membrane protein 2 (LAMP2) and elevated acid phosphatase and β-N-acetylglucosaminidase (NAG) activities indicated that the RNASET2 knockout rats likely had altered lysosomal function and potential defects in autophagy. Object recognition tests confirmed that RNaseT2 knockout rats exhibited memory deficits. However, the Barnes maze, and balance beam and rotarod tests indicated there were no differences in spatial memory or motor impairments, respectively. Overall, patients with RNASET2 deficiency exhibited a more severe neurodegeneration phenotype than was observed in the RNaseT2 knockout rats. However, the vulnerability of the knockout rat hippocampus as evidenced by neuroinflammation, altered lysosomal function and cognitive defects indicates that this is still a useful in vivo model to study RNASET2 function.

Failure to clear developmental apoptosis contributes to the pathology of RNASET2-deficient leukoencephalopathy

“…Most importantly, to our knowledge, our zebrafish model is the first man-made animal model of a leukodystrophy that fully recapitulate the patient brain phenotype throughout development and upon adulthood. Murine models of leukodystrophies have failed to reproduce all aspect of the human disease with a recent RNASET2-deficient rat model showed deficiency in object recognition memory but showed no locomotor or spatial memory defects (Sinkevicius et al, 2018). The rnaset2 zebrafish mutants shows hypoactivity in larval stages and tilted swimming in adulthood with an impaired exploratory phenotype.…”

Life without a brain: Neuroradiological and behavioral evidence of neuroplasticity necessary to sustain brain function in the face of severe hydrocephalus

“…The novel object preference task (NOP) was used to assess episodic learning and memory as previously described 11 . The apparatus consisted of a black cube-shaped Plexiglass box (L:60.9 W: 69.2 H:70.5 cm) with no lid, indirectly illuminated with two 40 W incandescent bulbs.…”

“…The Barnes Maze was used to assess spatial learning and memory 11 . The maze consists of a circular platform (121 cm in diameter, elevated 40 cm), with 18 escape holes along the perimeter at 30 cm intervals.…”

Zebrafish disease model of human RNASET2 deficient cystic leukoencephalopathy displays abnormalities in early microglia

“…This hypothesis is supported in a recently established RNASET2 rodent model. RNASET2 deficient rat exhibited altered lysosomal function and autophagy defects and most importantly, neuroinflammation in mutant brains (Sinkevicius et al, 2018).…”

“…However, these disorders do not only show a significant clinical and neuroradiological but also an pathophysiological overlap since both have an impact on nucleotide metabolism and/or sensing, which leads to an abnormal immune response (Crow et al, 2006;Reijns et al, 2012;Rice et al, 2009;Sundal et al, 2015). While a strong neuroinflammatory component is present in AGS patients, as well as in RNASET2 deficient rats (Sinkevicius et al, 2018), such a feature has not been clearly verified yet in patients with RNASET2 deficiency, probably due to the low number of identified patients. The presence of abnormal microglial cells in early mutant larvae in our study provides first experimental evidence that early symptoms in RNASET2 deficient newborns are linked to the innate immune system.…”