Primary angle closure glaucoma (PACG) susceptibility gene PLEKHA7 encodes a novel Rac1/Cdc42 GAP that modulates cell migration and blood-aqueous barrier function

Abstract

PLEKHA7, a gene recently associated with primary angle closure glaucoma (PACG), encodes an apical junctional protein expressed in components of the blood aqueous barrier (BAB). We found that PLEKHA7 is down-regulated in lens epithelial cells and in iris tissue of PACG patients. PLEKHA7 expression also correlated with the C risk allele of the sentinel SNP rs11024102 with the risk allele carrier groups having significantly reduced PLEKHA7 levels compared to non-risk allele carriers. Silencing of PLEKHA7 in human immortalized non-pigmented ciliary epithelium (h-iNPCE) and primary trabecular meshwork cells, which are intimately linked to BAB and aqueous humor outflow respectively, affected actin cytoskeleton organization. PLEKHA7 specifically interacts with GTP-bound Rac1 and Cdc42, but not RhoA, and the activation status of the two small GTPases is linked to PLEKHA7 expression levels. PLEKHA7 stimulates Rac1 and Cdc42 GTP hydrolysis, without affecting nucleotide exchange, identifying PLEKHA7 as a novel Rac1/Cdc42 GAP. Consistent with the regulatory role of Rac1 and Cdc42 in maintaining the tight junction permeability, silencing of PLEKHA7 compromises the paracellular barrier between h-iNPCE cells. Thus, downregulation of PLEKHA7 in PACG may affect BAB integrity and aqueous humor outflow via its Rac1/Cdc42 GAP activity, thereby contributing to disease etiology.

Cooperative binding of the tandem WW domains of PLEKHA7 to PDZD11 promotes conformation-dependent interaction with tetraspanin 33

“…The precise molecular mechanisms through which PLEKHA7 is implicated in disease (5, 6), morphogenesis (8, 23), and diverse cellular functions ( 9 – 11 ) are poorly understood. Here we address the structure-function relationships of the N-terminal tandem WW domains of PLEKHA7, a critically important region for the ability of PLEKHA7 to scaffold and cluster transmembrane proteins ( 13 , 15 ).…”

“…In a zebrafish model, the PLEKHA7 homolog Hadp1 is required for cardiac morphogenesis and contractility ( 8 ). PLEKHA7 has also been involved in the control of microRNA processing ( 9 , 10 ) and Rho GTPase activity ( 11 ). In cultured cells and mice, PLEKHA7 is required to make cells more susceptible to the cytotoxic effects of Staphylococcus aureus α-toxin, through a mechanism that involves junctional clustering of ADAM10, mediated by tetraspanin 33 (Tspan33) ( 12 , 13 ).…”

COL11A1 Polymorphisms Are Associated with Primary Angle-Closure Glaucoma Severity

“…Pathogenic mutations in this gene can result in type II Stickler syndrome and Marshall syndrome [6, 7], while rs1676486 on COL11A1 is associated with lumbar disc herniation susceptibility [8]. Pleckstrin homology domain-containing family A member 7 (PLEKHA7) is an adherens junction protein [9] required for organizing the epithelial architecture and contributes to tissue homeostasis. Since it is likely involved in regulating fluid flow across the inner wall of the Schlemm's canal [10], it was proposed that mutations in this gene could affect fluid dynamics in the pathophysiology of angle-closure glaucoma [11].…”

Mutations in SPATA13/ASEF2 cause primary angle closure glaucoma

“…PLEKHA7 encodes an apical junctional protein that is expressed in the non-pigmented ciliary epithelium, a key component of the blood aqueous barrier (BAB). Lee et al found that PLEKHA7 is down regulated in the iris of PACG patients that carry the C risk allele at SNP 11024102 [13]. Silencing of PLEKHA7 in non-pigmented ciliary epithelium (NPCE) affected actin cytoskeleton organization in vitro.…”

“…Variants in PLEKHA7, an adherens junction protein, increase the risk of sudden, symptomatic pressure rises in PACG [10]. This protein is expressed in iris, ciliary body, and choroid [12] and has GTPaseactivating protein (GAP) activity [13]. SNPs in other candidate genes, including HGF (hepatocyte growth factor) [14], HSP70 (heat-shock protein 70) [15], MFRP (membrane type frizzled related protein) [16], eNOS (endothelial nitric oxide synthase) [15] and MMP9 (matrix metalloproteinase-9) [17] also have significant association with PACG.…”