Characterization of tyramine β-hydroxylase, an enzyme upregulated by stress in Periplaneta americana

Abstract

Octopamine (OA) is an important neuroactive substance that modulates several physiological functions and behaviors of various invertebrate species. This biogenic monoamine, structurally related to noradrenaline, acts as a neurotransmitter, a neuromodulator, or a neurohormone in insects. The tyramine b-hydroxylase (TBH) catalyzes the last step in OA biosynthesis and thus plays a key role in the regulation of synthesis and secretion of OA in neurons. The aim of this study was to characterize TBH in the cockroach Periplaneta americana and to get a better understanding of its regulation under stress conditions in this insect. First of all, five full-length cDNAs encoding TBH isoforms were cloned from the nerve cord of the physiological model P. americana. PaTBH transcripts were found mainly expressed in nervous tissues and in octopaminergic dorsal unpaired median neurons. In addition, a new ELISA assay was developed so as to allow determination of both OA level and TBH activity in stressed cockroaches. Mechanical stressful stimulation led to a significant increase in TBH activity after 1 and 24 h, with a higher induction after 1 h than after 24 h. Thus, TBH could be considered as a promising biomarker of stress in insects rather than OA.

A population of descending tyraminergic/octopaminergic projection neurons of the insect deutocerebrum

“…This is supported by results from locusts where octopamine is involved in a coordinated response to stress and where synthesis of octopamine in these deutocerebral neurons (OA3/TA-cluster) was only observed after the animals had been stressed (Ferch, 2018;Kononenko et al, 2009). Corresponding to the results in locusts it was shown for cockroaches that the enzyme necessary for synthesizing octopamine from tyramine, tßh, is upregulated by stressful stimuli (Châtel et al, 2013). As the "unstressed" control cockroaches and control stick insects in this study exhibited both tyramine-and octopamine-ir this would suggest that both cockroaches and stick insects used in this study experienced stress already under control conditions.…”

“…Cockroaches in this study were not deliberately stressed but cooled before dissection. However, consistent with the idea of octopamine being synthesized after stressing stimuli is the finding in cockroaches that the tßh‐enzyme (tyramine‐ß‐hydroxylase), which is necessary for octopamine synthesis, is upregulated by stress (Châtel et al, ; see Section 5).…”

Deciphering the Function of Octopaminergic Signaling on Wing Polyphenism of the Pea Aphid Acyrthosiphon pisum

“…The TβH assay was based on the hydroxylation of tyramine (Lehman et al, 2000a,b; Châtel et al, 2013; Figure 2C). All steps were performed in the dark or under dim light.…”

Trace Amines and Their Receptors

“…Although an AADC-like, DOPA decarboxylase enzyme may also be present, this does not appear to act on L-tyrosine (Han et al, 2010). In addition to being active in its own right, TYR can be further acted upon by tyramine-b-hydroxylase enzymes to generate OCT (Monastirioti et al, 1996;Alkema et al, 2005;Nishimura et al, 2008;Châtel et al, 2013). Again, multiple isozymic forms are present in some species (Châtel et al, 2013).…”

“…In addition to being active in its own right, TYR can be further acted upon by tyramine-b-hydroxylase enzymes to generate OCT (Monastirioti et al, 1996;Alkema et al, 2005;Nishimura et al, 2008;Châtel et al, 2013). Again, multiple isozymic forms are present in some species (Châtel et al, 2013). Formation of TYR from dopamine via a dopamine dehydroxylase pathway is also possible in some species (Walker and Kerkut, 1978;Roeder, 2005).…”