Increased plasmin-mediated proteolysis of L1CAM in a mouse model of idiopathic normal pressure hydrocephalus.

Abstract

Idiopathic normal pressure hydrocephalus (iNPH) is a common neurological disorder that is characterized by enlarged cerebral ventricles, gait difficulty, incontinence, and dementia. iNPH usually develops after the sixth decade of life in previously asymptomatic individuals. We recently reported that loss-of-function deletions in <i>CWH43</i> lead to the development of iNPH in a subgroup of patients, but how this occurs is poorly understood. Here, we show that deletions in <i>CWH43</i> decrease expression of the cell adhesion molecule, L1CAM, in the brains of <i>CWH43</i> mutant mice and in human HeLa cells harboring a <i>CWH43</i> deletion. Loss-of-function mutations in L1CAM are a common cause of severe neurodevelopmental defects that include congenital X-linked hydrocephalus. Mechanistically, we find that <i>CWH43</i> deletion leads to decreased N-glycosylation of L1CAM, decreased association of L1CAM with cell membrane lipid microdomains, increased L1CAM cleavage by plasmin, and increased shedding of cleaved L1CAM in the cerebrospinal fluid. <i>CWH43</i> deletion also decreased L1CAM nuclear translocation, suggesting decreased L1CAM intracellular signaling. Importantly, the increase in L1CAM cleavage occurred primarily in the ventricular and subventricular zones where brain <i>CWH43</i> is most highly expressed. Thus, <i>CWH43</i> deletions may contribute to adult-onset iNPH by selectively downregulating L1CAM in the ventricular and subventricular zone.