Current concepts on the pathophysiology of idiopathic chronic adult hydrocephalus: Are we facing another neurodegenerative disease?

Kidins220 deficiency causes ventriculomegaly via SNX27-retromer-dependent AQP4 degradation

Several psychiatric, neurologic and neurodegenerative disorders present increased brain ventricles volume, being hydrocephalus the disease with the major manifestation of ventriculomegaly caused by the accumulation of high amounts of cerebrospinal fluid (CSF). The molecules and pathomechanisms underlying cerebral ventricular enlargement are widely unknown. Kinase D interacting substrate of 220 kDa (KIDINS220) gene has been recently associated with schizophrenia and with a novel syndrome characterized by spastic paraplegia, intellectual disability, nystagmus and obesity (SINO syndrome), diseases frequently occurring with ventriculomegaly. Here we show that Kidins220, a transmembrane protein effector of various key neuronal signalling pathways, is a critical regulator of CSF homeostasis. We observe that both KIDINS220 and the water channel aquaporin-4 (AQP4) are markedly downregulated at the ventricular ependymal lining of idiopathic normal pressure hydrocephalus (iNPH) patients. We also find that Kidins220 deficient mice develop ventriculomegaly accompanied by water dyshomeostasis and loss of AQP4 in the brain ventricular ependymal layer and astrocytes. Kidins220 is a known cargo of the SNX27-retromer, a complex that redirects endocytosed plasma membrane proteins (cargos) back to the cell surface, thus avoiding their targeting to lysosomes for degradation. Mechanistically, we show that AQP4 is a novel cargo of the SNX27-retromer and that Kidins220 deficiency promotes a striking and unexpected downregulation of the SNX27-retromer that results in AQP4 lysosomal degradation. Accordingly, SNX27 silencing decreases AQP4 levels in wild-type astrocytes whereas SNX27 overexpression restores AQP4 content in Kidins220 deficient astrocytes. Together our data suggest that the KIDINS220-SNX27-retromer-AQP4 pathway is involved in human ventriculomegaly and open novel therapeutic perspectives.

[Idiopathic normal pressure hydrocephalus: High incidence in people over 80 years of age]

INTRODUCTION

Idiopathic normal pressure hydrocephalus is usually observed in adults over 60 years of age. The highest incidence of cases is between 70 and 80 years-old, and it could be under-diagnosed in over 80 year-olds.

OBJECTIVE

A description is presented on the overall incidence and age group incidence, the delay in the diagnosis, and main outcomes.

PATIENTS AND METHODS

A descriptive study was performed on patients with idiopathic normal pressure hydrocephalus, in the population of Osona County during the years 2010-2015.

RESULTS

The annual incidence rate was 4.43 per 100,000 inhabitants. The incidence increased with age; from 8.09 per 100,000 in the 60 to 69 years age group, to 23.61 per 100,000 in the 70-79 years age group of, and to 37.02 per 100,000 in the 80-89 years age. The delay in the diagnosis was 15.01 ± 10.35 months. All the patients improved after surgery, but only 73.3% of the patients maintained the improvement after one year.

CONCLUSIONS

Idiopathic normal pressure hydrocephalus is an age related disease and probably underdiagnosed in the elderly. An early diagnosis and a clinical suspicion are essential in patients over 80 years old.