Rainbo Hultman

Site-specific analysis of protein S-acylation by resin-assisted capture

Protein S-acylation is a major posttranslational modification whereby a cysteine thiol is converted to a thioester. A prototype is S-palmitoylation (fatty acylation), in which a protein undergoes acylation with a hydrophobic 16 carbon lipid chain. Although this modification is a well-recognized determinant of protein function and localization, current techniques to study cellular S-acylation are cumbersome and/or technically demanding. We recently described a simple and robust methodology to rapidly identify S-nitrosylation sites in proteins via resin-assisted capture (RAC) and provided an initial description of the applicability of the technique to S-acylated proteins (acyl-RAC). Here we expand on the acyl-RAC assay, coupled with mass spectrometry-based proteomics, to characterize both previously reported and novel sites of endogenous S-acylation. Acyl-RAC should therefore find general applicability in studies of both global and individual protein S-acylation in mammalian cells.

Cortical control of affective networks.

Transcranial magnetic stimulation and deep brain stimulation have emerged as therapeutic modalities for treatment refractory depression; however, little remains known regarding the circuitry that mediates the therapeutic effect of these approaches. Here we show that direct optogenetic stimulation of prefrontal cortex (PFC) descending projection neurons in mice engineered to express Chr2 in layer V pyramidal neurons (Thy1–Chr2 mice) models an antidepressant-like effect in mice subjected to a forced-swim test. Furthermore, we show that this PFC stimulation induces a long-lasting suppression of anxiety-like behavior (but not conditioned social avoidance) in socially stressed Thy1–Chr2 mice: an effect that is observed >10 d after the last stimulation. Finally, we use optogenetic stimulation and multicircuit recording techniques concurrently in Thy1–Chr2 mice to demonstrate that activation of cortical projection neurons entrains neural oscillatory activity and drives synchrony across limbic brain areas that regulate affect. Importantly, these neural oscillatory changes directly correlate with the temporally precise activation and suppression of limbic unit activity. Together, our findings show that the direct activation of cortical projection systems is sufficient to modulate activity across networks underlying affective regulation. They also suggest that optogenetic stimulation of cortical projection systems may serve as a viable therapeutic strategy for treating affective disorders.

Prefrontal cortex reactivity underlies trait vulnerability to chronic social defeat stress

Psychological stress contributes to the onset and exacerbation of nearly all neuropsychiatric disorders. Individual differences in stress-regulatory circuits can therefore dramatically affect vulnerability to these illnesses. Here we identify neural circuit mechanisms underlying individual differences in vulnerability to stress using a murine model of chronic social defeat stress. In chronically stressed mice, we find that the degree of prefrontal cortex (PFC) control of amygdala activity predicts stress-susceptibility in individual mice. Critically, we also find that individual differences in PFC activation (i.e. reactivity) during exposure to an aggressor mouse predict the emergence stress-induced behavioral deficits in stress naïve mice. Finally, we show that naturally occurring differences in PFC reactivity directly correspond to the intrinsic firing rate of PFC neurons. This demonstrates that naturally occurring differences in PFC function underlie individual differences in vulnerability to stress, raising the hypothesis that PFC modulation may prevent stress-induced psychiatric disorders.

Gαz regulates BDNF-induction of axon growth in cortical neurons

The disruption of neurotransmitter and neurotrophic factor signaling in the central nervous system (CNS) is implicated as the root cause of neuropsychiatric disorders, including schizophrenia, epilepsy, chronic pain, and depression. Therefore, identifying the underlying molecular mechanisms by which neurotransmitter and neurotrophic factor signaling regulates neuronal survival or growth may facilitate identification of more effective therapies for these disorders. Previously, our lab found that the heterotrimeric G protein, Gz, mediates crosstalk between G protein-coupled receptors and neurotrophin signaling in the neural cell line PC12. These data, combined with Gαz expression profiles--predominantly in neuronal cells with higher expression levels corresponding to developmental times of target tissue innervation--suggested that Gαz may play an important role in neurotrophin signaling and neuronal development. Here, we provide evidence in cortical neurons, both manipulated ex vivo and those cultured from Gz knockout mice, that Gαz is localized to axonal growth cones and plays a significant role in the development of axons of cortical neurons in the CNS. Our findings indicate that Gαz inhibits BDNF-stimulated axon growth in cortical neurons, establishing an endogenous role for Gαz in regulating neurotrophin signaling in the CNS.

Signaling Through Gz

Publisher Summary Several studies have been carried out to pinpoint specific brain regions and developmental stages where Gz is transcribed or expressed. The limited tissue distribution of Gαz, its unusual biochemical properties, the identification of Gαz-specific effectors, and the inability of other Gαi subfamily members to substitute for Gαz in vivo support unique physiologic roles for Gz. The rate of GDP dissociation from Gαz is extremely slow as compared to that of most other G-protein α subunits, and almost completely suppressed at Mg 2+ concentrations greater than 100 μM. Most receptors that couple to Gi proteins can also activate Gz if the G protein or receptors are overexpressed in cells. Although the precise roles of Gz in cellular signaling are still being established, accumulating evidence points to the involvement of this unique Gi subfamily member in several facets of cell biology. First, the temporal and spatial expression patterns of Gαz suggest a possible role in neuron growth and/or differentiation. Gz also appears to regulate platelet function through adrenergic receptor signaling. In addition, Gz participates in the physiologic regulation of insulin secretion from the pancreatic β cells. Finally, Gz may be involved in processes impacting on mood or behavior. These distinct roles further define Gz as unique among the Gi subfamily of heterotrimeric G proteins.

Brain-wide Electrical Spatiotemporal Dynamics Encode Depression Vulnerability

Brain-wide fluctuations in local field potential oscillations reflect emergent network-level signals that mediate behavior. Cracking the code whereby these oscillations coordinate in time and space (spatiotemporal dynamics) to represent complex behaviors would provide fundamental insights into how the brain signals emotional pathology. Using machine learning, we discover a spatiotemporal dynamic network that predicts the emergence of major depressive disorder (MDD)-related behavioral dysfunction in mice subjected to chronic social defeat stress. Activity patterns in this network originate in prefrontal cortex and ventral striatum, relay through amygdala and ventral tegmental area, and converge in ventral hippocampus. This network is increased by acute threat, and it is also enhanced in three independent models of MDD vulnerability. Finally, we demonstrate that this vulnerability network is biologically distinct from the networks that encode dysfunction after stress. Thus, these findings reveal a convergent mechanism through which MDD vulnerability is mediated in the brain.

A convergent depression vulnerability pathway encoded by emergent spatiotemporal dynamics

Fluctuations in brain local field potential (LFP) oscillations reflect emergent network-level signals that mediate behavior. Cracking the code whereby these LFP oscillations coordinate in time and space (spatiotemporal dynamics) to represent complex behaviors would provide fundamental insights into how the brain signals emotional processes at the network level. Here we use machine learning to integrate LFP activity acquired concurrently from seven cortical and subcortical brain regions into an analytical model that predicts the emergence of depression-related behavioral dysfunction across individual mice subjected to chronic social defeat stress. We uncover a spatiotemporal dynamic network in which activity originates in prefrontal cortex (PFC) and nucleus accumbens (NAc, ventral striatum), relays through amygdala and ventral tegmental area (VTA), and converges in ventral hippocampus (VHip). The activity of this network correlates with acute threat responses and brain-wide cellular firing, and it is enhanced in three independent molecular-, physiological-, and behavioral-based models of depression vulnerability. Finally, we use two antidepressant manipulations to demonstrate that this vulnerability network is biologically distinct from the networks that signal behavioral dysfunction after stress. Thus, corticostriatal to VHip-directed spatiotemporal dynamics organized at the network level are a novel convergent depression vulnerability pathway.

Tuning the Brain-Gut Axis in Health and Disease

Recent breakthroughs in gut microbiome-derived technologies and therapies, coupled with the lack of invasiveness associated with them, provide attractive routes of biomarker and therapeutic development. Alongside such breakthroughs, an ever-growing body of literature indicates a strong connection between brain activity and microbial populations in the gut. The paucity of effective psychiatric therapies makes the gut microbiota/brain connection a particularly enticing field. This article reviews some of the mechanisms of connection between the gut and the brain, their potential relationship to psychiatric disorders, and the therapeutic potential that arises from them.

Chapter 202 – Signaling Through Gz

Publisher Summary Several studies have been carried out to pinpoint specific brain regions and developmental stages where Gz is transcribed or expressed. The limited tissue distribution of Gαz, its unusual biochemical properties, the identification of Gαz-specific effectors, and the inability of other Gαi subfamily members to substitute for Gαz in vivo support unique physiologic roles for Gz. The rate of GDP dissociation from Gαz is extremely slow as compared to that of most other G-protein α subunits, and almost completely suppressed at Mg 2+ concentrations greater than 100 μM. Most receptors that couple to Gi proteins can also activate Gz if the G protein or receptors are overexpressed in cells. Although the precise roles of Gz in cellular signaling are still being established, accumulating evidence points to the involvement of this unique Gi subfamily member in several facets of cell biology. First, the temporal and spatial expression patterns of Gαz suggest a possible role in neuron growth and/or differentiation. Gz also appears to regulate platelet function through adrenergic receptor signaling. In addition, Gz participates in the physiologic regulation of insulin secretion from the pancreatic β cells. Finally, Gz may be involved in processes impacting on mood or behavior. These distinct roles further define Gz as unique among the Gi subfamily of heterotrimeric G proteins.

Signaling Through G z

Publisher Summary Several studies have been carried out to pinpoint specific brain regions and developmental stages where Gz is transcribed or expressed. The limited tissue distribution of Gαz, its unusual biochemical properties, the identification of Gαz-specific effectors, and the inability of other Gαi subfamily members to substitute for Gαz in vivo support unique physiologic roles for Gz. The rate of GDP dissociation from Gαz is extremely slow as compared to that of most other G-protein α subunits, and almost completely suppressed at Mg 2+ concentrations greater than 100 μM. Most receptors that couple to Gi proteins can also activate Gz if the G protein or receptors are overexpressed in cells. Although the precise roles of Gz in cellular signaling are still being established, accumulating evidence points to the involvement of this unique Gi subfamily member in several facets of cell biology. First, the temporal and spatial expression patterns of Gαz suggest a possible role in neuron growth and/or differentiation. Gz also appears to regulate platelet function through adrenergic receptor signaling. In addition, Gz participates in the physiologic regulation of insulin secretion from the pancreatic β cells. Finally, Gz may be involved in processes impacting on mood or behavior. These distinct roles further define Gz as unique among the Gi subfamily of heterotrimeric G proteins.