MiR-375 is Essential for Human Spinal Motor Neuron Development and May Be Involved in Motor Neuron Degeneration

Abstract

The transcription factor REST is a key suppressor of neuronal genes in non-neuronal tissues. REST has been shown to suppress proneuronal microRNAs in neural progenitors indicating that REST-mediated neurogenic suppression may act in part via microRNAs. We used neural differentiation of Rest-null mouse ESC to identify dozens of microRNAs regulated by REST during neural development. One of the identified microRNAs, miR-375, was upregulated during human spinal motor neuron development. We found that miR-375 facilitates spinal motor neurogenesis by targeting the cyclin kinase CCND2 and the transcription factor PAX6. Additionally, miR-375 inhibits the tumor suppressor p53 and protects neurons from apoptosis in response to DNA damage. Interestingly, motor neurons derived from a spinal muscular atrophy patient displayed depressed miR-375 expression and elevated p53 protein levels. Importantly, SMA motor neurons were significantly more susceptible to DNA damage induced apoptosis suggesting that miR-375 may play a protective role in motor neurons. STEM CELLS 2016;34:124-134 SIGNIFICANCE STATEMENTMotor neurons carry information from the brain to the peripheral musculature and loss of motor neurons in neurodegenerative conditions leads to paralysis and ultimately death. Hence, there is great interest in understanding the development of these neurons and how they degenerate in disease. In this study, we have identified a small RNA called miR-375 that is required for motor neuron development and further protects motor neurons from stress. Importantly, we find that diseased motor neurons have reduced amounts of miR-375 suggesting that loss of this RNA may lead to neurodegeneration. Our study opens up a new avenue for therapeutic intervention to rescue degenerating neurons.

MicroRNA exocytosis by large dense-core vesicle fusion

“…miR-375 is the most abundant miRNA in LDCVs (~30% of total miRNA read counts); it is highly expressed in the pancreatic islets34 and motor neurons35, where it regulates neuronal development36. miR-375 is also detected in plasma and serum as a circulating miRNA, and may be a biomarker for diabetes37, hepatocellular carcinoma38, and Alzheimer’s disease39.…”

MotomiRs: miRNAs in Motor Neuron Function and Disease

“…While the activation of Isl1 and Lhx3 transcription factors is required for the expression of motor neuron specific miRNAs, inhibition of RE1-silencing transcription factor (REST) is also required to promote motor neuron identity via activation of miR-375 (Bhinge et al, 2016). REST silencing has been shown to be mediated by miR-124 during development to promote neurogenesis (Visvanathan et al, 2007).…”

“…Once REST is silenced, as demonstrated in REST knock-out mice, there is an increase in the expression of miR-375. MiR-375 directly targets PAX6 and Cyclin D2 ( CCND2 ) transcripts, silencing their expression which in turn promotes motor neuron differentiation (Bhinge et al, 2016). However, PAX6 is also necessary for the production of neural progenitor cells (Bel-Vialar et al, 2007).…”

“…However, PAX6 is also necessary for the production of neural progenitor cells (Bel-Vialar et al, 2007). Thus, miR-124 must silence REST activity in a timely manner to promote the expression of miR-375, which in turn, must also suppress PAX6 activity in a timely manner to allow for the formation of post-mitotic spinal motor neurons (Visvanathan et al, 2007; Bhinge et al, 2016). …”

“…This interaction is considered necessary for motor neuron survival as p53 is a pro-apoptotic gene (Bhinge et al, 2016). DNA damage in developing motor neurons leads to an increased expression of p53, which ultimately results in programmed cell death (Lavin and Gueven, 2006).…”