Disruption of the Axonal Trafficking of Tyrosine Hydroxylase mRNA Impairs Catecholamine Biosynthesis in the Axons of Sympathetic Neurons

Abstract

Tyrosine hydroxylase (TH) is the enzyme that catalyzes the rate-limiting step in the biosynthesis of the catecholamine neurotransmitters. In a previous communication, evidence was provided that TH mRNA is trafficked to the axon, where it is locally translated. In addition, a 50-bp sequence element in the 3′untranslated region (3’UTR) of TH mRNA was identified that directs TH mRNA to distal axons (i.e., zip-code). In the present study, the hypothesis was tested that local translation of TH plays an important role in the biosynthesis of the catecholamine neurotransmitters in the axon and/or presynaptic nerve terminal. Toward this end, a targeted deletion of the axonal transport sequence element was developed, using the lentiviral delivery of the CRISPR/Cas9 system, and two guide RNA (gRNA) sequences flanking the 50-bp cis-acting regulatory element in rat superior cervical ganglion (SCG) neurons. Deletion of the axonal transport element reduced TH mRNA levels in the distal axons and reduced the axonal protein levels of TH and TH activity as measured by phosphorylation of SER40 in SCG neurons. Moreover, deletion of the zip-code diminished the axonal levels of dopamine (DA) and norepinephrine (NE). Conversely, the local translation of exogenous TH mRNA in the distal axon enhanced TH levels and activity, and elevated axonal NE levels. Taken together, these results provide direct evidence to support the hypothesis that TH mRNA trafficking and local synthesis of TH play an important role in the synthesis of catecholamines in the axon and presynaptic terminal.

The Gastric Ganglion of Octopus vulgaris: Preliminary Characterization of Gene- and Putative Neurochemical-Complexity, and the Effect of Aggregata octopiana Digestive Tract Infection on Gene Expression

“…Tyrosine Hydroxylase (TH) positive neurons have been reported to be localized in discrete areas of the cephalopod nervous system including cerebral and gastric ganglia of the developing cuttlefish (Baratte and Bonnaud, 2009 ), and mostly in the posterior buccal lobe of the adult octopus brain (Ponte, 2012 ; see also Ov-Dopamine transporter in Zarrella et al, 2015 ), suggesting the existence of a dopaminergic modulatory system in cephalopods. In the gastric ganglion, TH-IR appears clearly in fibers and we cannot exclude the possibility that this contributes to local synthesis of final products (i.e., dopamine, noradrenaline or octopamine) as recently demonstrated in other organisms (e.g., Gervasi et al, 2016 ; Aschrafi et al, 2017 ).…”

The gastrin-releasing peptide regulates stress-enhanced fear and dopamine signaling

“…Indeed, Th mRNA is transported to axons in sympathetic neurons (Gervasi et al, 2016). Moreover, Th mRNA trafficking and local protein synthesis of the TH play an important role in the synthesis of dopamine in the presynaptic terminal (Aschrafi, Gioio, Dong, & Kaplan, 2017). It is also important to note that the changes in the Th mRNA levels are likely to be acute and result from the fear recall, as the TH protein levels were normal in naïve Grp -/- mice.…”

Energy sensors in drug addiction: A potential therapeutic target

“…DA neurons are characterized by the expression of tyrosine hydroxylase (TH), an enzyme necessary for DA synthesis (as well as GABA and acetylcholine) in the axon 45 . DA neurons can be identified in the VTA and SNc by the occurrence of broad and spontaneous action potentials, the presence of a pacemaker or H‐current generated by the hyperpolarization‐activated cyclic nucleotide‐gated (HCN) channels (a cationic current activated by hyperpolarization of the membrane), in addition to an outward current in response to dopamine as opposed to non‐DA neurons that show narrow action potentials and lack H‐current plus pronounced response to DA 46,47 .…”