Norepinephrine Deficiency Is Caused by Combined Abnormal mRNA Processing and Defective Protein Trafficking of Dopamine β-Hydroxylase

Abstract

Human norepinephrine (NE) deficiency (or dopamine ␤-hydroxylase (DBH) deficiency) is a rare congenital disorder of primary autonomic failure, in which neurotransmitters NE and epinephrine are undetectable. Although potential pathogenic mutations, such as a common splice donor site mutation (IVS1؉2T3 C) and various missense mutations, in NE deficiency patients were identified, molecular mechanisms underlying this disease remain unknown. Here, we show that the IVS1؉2T3 C mutation results in a non-detectable level of DBH protein production and that all three missense mutations tested lead to the DBH protein being trapped in the endoplasmic reticulum (ER). Supporting the view that mutant DBH induces an ER stress response, exogenous expression of mutant DBH dramatically induced expression of BiP, a master ER chaperone. Furthermore, we found that a pharmacological chaperone, glycerol, significantly rescued defective trafficking of mutant DBH proteins. Taken together, we propose that NE deficiency is caused by the combined abnormal processing of DBH mRNA and defective protein trafficking and that this disease could be treated by a pharmacological chaperone(s). Norepinephrine (NE)3 is a key neurotransmitter that is synthesized in both the CNS and the peripheral nervous system and regulates many essential functions, including attention, memory, emotion, and autonomic and cardiovascular function. Like dopamine (DA) and epinephrine, NE is a catecholamine neurotransmitter and is synthesized by oxidative hydroxylation of DA catalyzed by dopamine ␤-hydroxylase (DBH). DBH is a hallmark protein of noradrenergic cells and is specifically expressed in noradrenergic neurons and chromaffin cells of the adrenal medulla. Among catecholamine-synthesizing enzymes, DBH is unique in that it is localized within large dense core vesicles (LDCV), where it exists in both soluble and membranebound forms (1). During neurotransmission, the soluble form of DBH is released into the synaptic cleft together with NE by exocytosis (2). As a result of such synaptic release, both NE and DBH are readily detectable in plasma and cerebrospinal fluid (3).NE deficiency (or DBH deficiency) is a rare congenital disorder, first described in 1986 (4, 5). Given the fundamental role of NE in CNS and peripheral nervous system functions, the report of adult patients with undetectable NE is both surprising and interesting. The report of frequent miscarriages and spontaneous abortions in mothers of known NE deficiency cases (5, 6) suggests the interesting possibility that there could be many more undiagnosed fetal and neonatal deaths resulting from NE deficiency and that those adult patients are lucky survivors. In line with this, a DBH knock-out mouse study showed less than 5% live births (7), where mortality appeared to be due to cardiovascular failure caused by NE deficiency in utero, which is reminiscent of tyrosine hydroxylase null mice (8). Pathophysiologically, NE deficiency is a severe autonomic disorder exhibiting sympathetic noradrenergic failure and adreno...

L‐Threo‐Dihydroxyphenylserine corrects neurochemical abnormalities in a menkes disease mouse model

“…Taken together with anecdotal successes of L‐DOPS in medical management of Menkes disease survivors and individuals with DBH deficiency, our preclinical results suggest that L‐DOPS may have wider clinical application. Alternative treatments such as pharmacological chaperones, recently proposed for subjects with NE deficiency due to misfolded mutant DBH proteins, are not relevant for situations in which defective copper transport represents the underlying molecular basis. Although L‐DOPS alone does not correct the fundamental defect in copper transport responsible for neurodegeneration in Menkes disease, it may ameliorate noradrenergic hypofunction and be useful, in combination with other treatment.…”

“…However, Menkes disease survivors as well as patients with its milder allelic variant, occipital horn syndrome, often exhibit persistent signs of DBH deficiency, including low norepinephrine (NE) levels, orthostatic hypotension, hypothermia, and chronic diarrhea . These findings are similar to the autonomic problems encountered in patients with NE deficiency caused by mutations in the DBH gene, an autosomal recessive trait …”

Dopamine beta‐hydroxylase and its genetic variants in human health and disease

“…Recent reevaluation of patients with DβH deficiency identifies several non‐synonymous coding region polymorphisms within DβH that result in nearly undetectable DβH protein expression (Kim et al ; Kim et al ). A novel splice junction polymorphism (rs74853476 (IVS1 + 2T→C)) that produces a mutation that causes early termination of translation was identified in several DβH deficiency patients (Kim et al ). Also, many DβH deficiency patients share additional coding region polymorphisms; namely, Ala348Glu, Asp100Glu, and Asp331Asn.…”

“…In the case of the splice junction polymorphism rs74853476, recent modeling work suggests that this polymorphism reduces DβH protein secretion by up to 95%. The current belief is that another genetic DβH polymorphism is required to cause complete DβH deficiency (Kim et al ; Deinum et al ; Kim et al ). In this endeavor, a potential non‐synonymous coding region polymorphism, rs863225246, that introduces a new cysteine residue Tyr565Cys, is believed to contribute to DβH deficiency (Kim et al ).…”

“…Our study of rs6271 in IBD strongly supports effects of the rs6271 SNP that produce lower circulating levels of the protein and increased homospecific activity (Gonzalez‐Lopez et al ). The four DβH gene missense mutations associated with DβH deficiency, rs267606760 (Val101Met), rs77576840 (Asp114Glu), rs75215331 (Ala362Glu), and rs267606761 (Asp345Asn), are believed to also disrupt stability/misfolding of the protein (Kim et al ).…”