Peripheral myelin protein 22 is regulated post‐transcriptionally by miRNA‐29a

Abstract

Peripheral myelin protein 22 (PMP22) is a dose-sensitive, disease-associated protein primarily expressed in myelinating Schwann cells. Either reduction or overproduction of PMP22 can result in hereditary neuropathy, suggesting a requirement for correct protein expression for peripheral nerve biology. PMP22 is post-transcriptionally regulated and the 3′untranslated region (3′UTR) of the gene exerts a negative effect on translation. MicroRNAs (miRNAs) are small regulatory molecules that function at a post-transcriptional level by targeting the 3′UTR in a reverse complementary manner. We used cultured Schwann cells to demonstrate that alterations in the miRNA biogenesis pathway affect PMP22 levels, and endogenous PMP22 is subjected to miRNA regulation. GW-body formation, the proposed cytoplasmic site for miRNA-mediated repression, and Dicer expression, an RNase III family ribonuclease involved in miRNA biogenesis, are co-regulated with the differentiation state of Schwann cells. Furthermore, the levels of Dicer inversely correlate with PMP22, while the inhibition of Dicer leads to elevated PMP22. Microarray analysis of actively-proliferating and differentiated Schwann cells, in conjunction with bioinformatics programs, identified several candidate PMP22-targeting miRNAs. Here we demonstrate that miR-29a binds and inhibits PMP22 reporter expression through a specific miRNA seed binding region. Over-expression of miR-29a enhances the association of PMP22 RNA with Argonaute 2, a protein involved in miRNA function, and reduces the steady-state levels of PMP22. In contrast, inhibition of endogenous miR-29a relieves the miRNA-mediated repression of PMP22. Correlation analyses of miR-29 and PMP22 in sciatic nerves reveal an inverse relationship, both developmentally and in post-crush injury. These results identify PMP22 as a target of miRNAs and suggest that myelin gene expression by Schwann cells is regulated by miRNAs.

Interleukin-6 upregulates the expression of PMP22 in cultured rat Schwann cells via a JAK2-dependent pathway

“…Earlier studies have revealed that PMP22 expression is regulated transcriptionally by cyclic AMP [25] and post-transcriptionally by microRNA-29a [27]. The relationship between these regulatory processes and the present results is currently unclear.…”

Brain-specific knockdown of miR-29 results in neuronal cell death and ataxia in mice

“…Apart from having roles in neuronal cell differentiation, miR-29a also is seen to be down-regulated in Schwann cells which are in proliferative and differentiating stages, in vitro in culture and in vivo during development, and after sciatic nerve injury (Verrier et al 2009). …”

Copy number variation upstream of PMP22 in Charcot–Marie–Tooth disease

“…It harbors no associated mutations in its coding exons, alternative first exons 1A or 1B or adjacent sequences nor in a recently described microRNA binding site in its non-coding 3¢ tail. 28 A search for mutations in TEKT3 that is located within the duplication also did not yield any abnormalities suggesting that this 186-kb duplication is in fact responsible for the disease. TEKT3 is primarily expressed in the male germ lineage in which it is believed to be involved in spermatozoa transport 29 with a much lower expression in brain.…”

“…We also excluded mutations in a recently described region in the PMP22 3¢UTR targeted by miR-29a that was shown to regulate expression of PMP22. 28 The TEKT3 gene that is located within the duplication was additionally examined for mutations but again, only polymorphisms were encountered (Figure 1).…”