Vulnerability to relapse during periods of attempted abstinence from cocaine use is hypothesized to result from the rewiring of brain reward circuitries, particularly ventral tegmental area (VTA) dopamine neurons. How cocaine exposures act on midbrain dopamine neurons to precipitate addiction-relevant changes in gene expression is unclear. We found that histone H3 glutamine 5 dopaminylation (H3Q5dop) plays a critical role in cocaine-induced transcriptional plasticity in the midbrain. Rats undergoing withdrawal from cocaine showed an accumulation of H3Q5dop in the VTA. By reducing H3Q5dop in the VTA during withdrawal, we reversed cocaine-mediated gene expression changes, attenuated dopamine release in the nucleus accumbens, and reduced cocaine-seeking behavior. These findings establish a neurotransmission-independent role for nuclear dopamine in relapse-related transcriptional plasticity in the VTA.

Histone H3 monoaminylations at glutamine(Q) 5 represent an important family of epigenetic markers in neurons that play critical roles in the mediation of permissive gene expression. We previously demonstrated that H3Q5 serotonylation(ser) and dopaminylation(dop) are catalyzed by the Transglutaminase 2 (TGM2) enzyme. Here, we found that TGM2 additionally functions as an “eraser” and “re-writer” of H3 monoaminylations, and identified a new class of this modification, H3Q5 histaminylation(his), which displayed dynamic diurnal expression in brain and contributed to neural rhythmicity. We found that H3Q5his, versus H3Q5ser, inhibited binding of the MLL1 complex to the H3 N-terminus and attenuated its methyltransferase activity on H3 lysine(K) 4. We determined that H3Q5 monoaminylation dynamics are dictated by local monoamine concentrations, which are sensed by TGM2. This noncanonical mechanism indicated that histone monoaminylations can be established and removed by a single enzyme based upon its sensing of cellular microenvironments.One sentence summaryA single enzyme, TGM2, bidirectionally controls H3 monoaminylation dynamics, which, in turn, facilitate neural rhythmicity.

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