Heparanase 2, mutated in urofacial syndrome, mediates peripheral neural development in Xenopus

Abstract

Urofacial syndrome (UFS; previously Ochoa syndrome) is an autosomal recessive disease characterized by incomplete bladder emptying during micturition. This is associated with a dyssynergia in which the urethral walls contract at the same time as the detrusor smooth muscle in the body of the bladder. UFS is also characterized by an abnormal facial expression upon smiling, and bilateral weakness in the distribution of the facial nerve has been reported. Biallelic mutations in HPSE2 occur in UFS. This gene encodes heparanase 2, a protein which inhibits the activity of heparanase. Here, we demonstrate, for the first time, an in vivo developmental role for heparanase 2. We identified the Xenopus orthologue of heparanase 2 and showed that the protein is localized to the embryonic ventrolateral neural tube where motor neurons arise. Morpholino-induced loss of heparanase 2 caused embryonic skeletal muscle paralysis, and morphant motor neurons had aberrant morphology including less linear paths and less compactly-bundled axons than normal. Biochemical analyses demonstrated that loss of heparanase 2 led to upregulation of fibroblast growth factor 2/phosphorylated extracellular signal-related kinase signalling and to alterations in levels of transcripts encoding neural- and muscle-associated molecules. Thus, a key role of heparanase 2 is to buffer growth factor signalling in motor neuron development. These results shed light on the pathogenic mechanisms underpinning the clinical features of UFS and support the contention that congenital peripheral neuropathy is a key feature of this disorder.

Urinary Tract Effects of HPSE2 Mutations

“…[4][5][6][7] HPSE2 encodes heparanase 2, 8 which inhibits endo-b-Dglucuronidase activity of heparanase 1, 9 itself implicated in releasing growth factors from heparan sulfate proteoglycans. [10][11][12] Since the first descriptions of HPSE2 mutations in UFS in 2010, 4,5 only two further such families have been reported. 6,7 We here describe seven new UFS kindreds with HPSE2 mutations, representing the largest series to date of genetically defined, overtly unrelated families.…”

“…4 The in-frame deletion of asparagine 254 in Family 6 targets an amino acid conserved between human, mouse, and frog heparanase 2. 12 It is predicted to be nitrogen-linked glycosylated 13 (Figure 1A) and may direct endoplasmic reticulum processing of heparanase 2. 13 Mahmood et al 7 reported a homozygous HPSE2 mutation changing asparagine 543 to isoleucine.…”

“…13 Mahmood et al 7 reported a homozygous HPSE2 mutation changing asparagine 543 to isoleucine. The asparagine, located in the carboxy-terminus, is also highly conserved between vertebrate orthologs, 12 but it is not predicted to be glycosylated. Its role needs further study.…”

“…27 In turn, this supports the conclusion that the HPSE2 gene product is necessary for peripheral neural control of bladder function. Heparanase 2 deficiency during Xenopus embryogenesis increases phospho-ERK (pERK), 12 so we immunoprobed mouse pelvic ganglia for pERK (Supplemental Figure 4). Although a subset of neural cell bodies immunostained for pERK, the patterns were similar in mutants and wild-type littermates.…”

Chronic Kidney Disease in a Boy with Enuresis: The Diagnosis Behind the Smile

“…Some others proposed that two separate lesions affecting facial nerve nucleus and sacral cord motor nuclei innervating the external sphincter were responsible (6). The most recent studies in animal models indicate a peripheral autonomic neuropathy for BD in UFS (7,8).…”