Abstract
Lesch-Nyhan Disease (LND) is the result of mutations in the X-linked gene encoding the purine metabolic enzyme, hypoxanthine guanine phosphoribosyl transferase (HPRT). LND gives rise to severe neurological anomalies including mental retardation, dystonia, chorea, pyramidal signs and a compulsive and aggressive behavior to self injure. The neurological phenotype in LND has been shown to reflect aberrant dopaminergic signaling in the basal ganglia, however there are little data correlating the defect in purine metabolism to the neural-related abnormalities. In the present studies, we find that HPRT-deficient neuronal cell lines have reduced CREB (cAMP response element-binding protein) expression and intracellular cyclic AMP (cAMP), which correlates with attenuated CREB-dependent transcriptional activity and a reduced phosphorylation of protein kinase A (PKA) substrates such as synapsin (p-syn I). Of interest, we found increased expression of phosphodiesterase 10A (PDE10A) in HPRT-deficient cell lines and that the PDE10 inhibitor papaverine and PDE10A siRNA restored cAMP/PKA signaling. Furthermore, reconstitution of HPRT expression in mutant cells partly increased cAMP signaling synapsin phosphorylation. In conclusion, our data show that HPRT-deficiency alters cAMP/PKA signaling pathway, which is in part due to the increased of PDE10A expression and activity. These findings suggest a mechanistic insight into the possible causes of LND and highlight PDE10A as a possible therapeutic target for this intractable neurological disease.
Highlights
Mutations in the gene encoding the purine biosynthetic enzyme Hypoxanthine phosphoribosyltransferase (HPRT) (IMP: pyrophosphate Phosphoribosyltransferase; EC 2.4.2.8) leads to both metabolic and neurological defects that can lead to Lesch-Nyhan Disease (LND)
Among the GO terms, the ‘‘purine nucleotide metabolic process’’ term contains the list of genes involved in the cyclic AMP (cAMP)/protein kinase A (PKA) pathway, such as the transcription factor cAMP response element binding protein (CREB) that had previously been identified as a potential target of miR-181a [7]
We found that CREB-dependent promoter activity as measured by the level of green fluorescence intensity was reduced by 50% in HPRTknockdown HEK293 cells upon forskolin treatment (Fig. 1G & 1H)
Summary
Mutations in the gene encoding the purine biosynthetic enzyme Hypoxanthine phosphoribosyltransferase (HPRT) (IMP: pyrophosphate Phosphoribosyltransferase; EC 2.4.2.8) leads to both metabolic and neurological defects that can lead to Lesch-Nyhan Disease (LND). HPRT-deficiency has been shown to alter the expression of a number of transcription factors and key signaling components that are necessary for neuronal development, these data still do not fully elucidate the relationship between the defect in the purine metabolism and the neural phenotype associated with LND [3,4,5,6]. Our data show that HPRT-deficiency leads to a reduced expression of CREB, blunted cAMP production and reduced phosphorylation of PKA substrates, including phosphosynapsin, in HPRT-deficient MN9D neuronal cell lines. Our data provide a mechanism by which blunted cAMP/PKA signaling and phosphorylation of PKA substrates, such as synapsin, may contribute to the neurological phenotype associated with HPRT-deficiency and highlights PDE10 as a potential target for LND
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