The Science
Gsalpha (Gsα) is part of the heterotrimeric G protein complex, a key coupling protein between cell-surface neurotransmitter receptors and intracellular signaling pathways. The alpha subunit of the stimulatory G protein (Gsa) activates the enzyme adenylyl cyclase which also synthesizes the second messenger, cyclic AMP (cAMP). Increased cAMP facilitates intracellular signaling pathways including neuronal activity and neurotransmitter function.
Pax’s founder, Mark M. Rasenick PhD, discovered that much of the Gsα normally moves freely in the membrane to activate adenylyl cyclase to produce cAMP. This supports proper neuronal activity/neurotransmitter function.
In depressed subjects, Gsα sequesters in specialized regions of cell membranes, called lipid rafts, which restrict its signaling capability, weakening Gsα’s activation of adenylyl cyclase through neurotransmitters like serotonin and norepinephrine, and “depressing” neuronal cellular activity. When depression is treated effectively, Gsα moves out of lipid raft regions into the more fluid regions of the cell membrane. This normalizes the adenylyl cyclase/cAMP cascade and neuronal activity. Variations in lipid raft localization of Gsα in platelets correlate with the severity of depressive symptoms as well as the alleviation of those symptoms caused by effective therapy.
Pax’s proprietary product platform, MoodMark®, uses a blood draw and a simple biochemical assay to quantify circulating vs. sequestered levels of Gsα. This provides the first objective, quantitative biochemical “signature” of the existence and severity of depression. By retesting within a few days of starting therapy, MoodMark® might also provide a rapid, objective predictor of the treatment’s ultimate effectiveness in alleviating depression.
Key Journal Articles
Link: Molecular Psychiatry, 2025
Previous studies have shown that the heterotrimeric G protein, Gsalpha (Gsα), is ensconced predominantly in lipid rafts in acutelydepressed subjects with major depressive disorder (MDD) in contrast to healthy controls, and that effective antidepressanttreatment (ADT) facilitates translocation of Gs α from lipid rafts. The measurement of Gsα via prostaglandin E1 stimulation ofadenylyl cyclase (PGE1 stimulation) has been proposed as a peripheral biomarker for assessing clinical status in MDD. We examinedthe Gsα biomarker in a new study. PGE1 stimulation was used to assess the coupling of Gsα with platelet adenylyl cyclase indepressed subjects in active treatment and healthy controls. The Quick Inventory of Depressive Symptomatology (QIDS-C16)measured thresholds of symptom severity at two study visits spaced 2 weeks apart. QIDS-C16scores and PGE1 stimulated responseswere stable between the two study visits. The QIDS-C16was inversely correlated with PGE1 stimulated responses at each visit(rs= −0.33, rs= −0.60, respectively). MDD subjects with mild-moderate depressive symptoms (defined by QIDS-C16≥ 6) hadsignificantly lower PGE1 stimulated responses than asymptomatic MDD subjects (QIDS-C16< 6) or healthy controls (p = 0.001 and0.002 respectively). MDD subjects with moderate depressive symptoms (QIDS-C16≥ 10) had the lowest PGE1 responses of allsubjects (Fisher’s exact = 0.012). These results support our earlier fi ndings that a simple, high-throughput-capable platelet assaymay be a useful biomarker to assess the clinical status of depressed subjects. Larger studies are needed to evaluate the utility of thisbiomarker for diagnosis and treatment response.
In contrast to healthy controls, the heterotrimeric G protein, Gsalpha (Gsα) is ensconced predominantly in lipid rafts in subjects with major depressive disorder (MDD) resulting in impaired stimulation of adenylyl cyclase. In this small proof-of-concept study, we examined the hypothesis that translocation of Gsα from lipid rafts toward a more facile activation of adenylyl cyclase is a biomarker for clinical response to antidepressants. There were 49 subjects with MDD (HamD17 score ≥15) and 59 healthy controls at the screen visit. The AlphaScreen (PerkinElmer) assay measured both basal activity and prostaglandin E1 (PGE1) stimulation of Gsα-adenylyl cyclase to assess the extent of coupling of Gsα with adenylyl cyclase. At screen, platelet samples obtained from MDD subjects revealed significantly lower PGE1 activation of adenylyl cyclase activity than controls (p = 0.02). Subsequently, 19 consenting MDD subjects completed a 6-week open label antidepressant treatment trial. The 11 antidepressant responders (HamD17 improvement ≥50% from screen) revealed significant increase in PGE1-stimulated adenylyl cyclase compared to non-responders (p = 0.05) with an effect size of 0.83 for the PGE1/Gsα lipid-raft biomarker. PGE1 stimulation increased by ≥30% from screen assessment in eight responders (72.7%) and two non-responders (25.0%) [Fisher exact = 0.07] with a positive predictive value for response of 80.0%. In this small, pilot study, increased PGE1 stimulated adenylyl cyclase was associated with antidepressant response in MDD subjects. These data suggest that a simple, high-throughput-capable assay for depression and antidepressant response can be developed.
Future studies are needed to evaluate the utility of this biomarker for the treatment of MDD.
A novel peripheral biomarker for depression and antidepressant response (PDF)
Jiang-Zhou Yu1, Jennifer Wang2, Steven D. Sheridan2, Roy H. Perlis2,3, Mark M. Rasenick 1,4,5,6
Evidence from epidemiological and laboratory studies, as well as randomized placebo-controlled trials, suggests supplementation with n-3 polyunsaturated fatty acids (PUFAs) may be efficacious for treatment of major depressive disorder (MDD). The mechanisms underlying n-3 PUFAs potential therapeutic properties remain unknown. There are suggestions in the literature that glial hypofunction is associated with depressive symptoms and that antidepressants may normalize glial function. In this study, induced pluripotent stem cells (iPSC)-derived neuronal stem cell lines were generated from individuals with MDD. Astrocytes differentiated from patient-derived neuronal stem cells (iNSCs) were verified by GFAP. Cells were treated with eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) or stearic acid (SA). During astrocyte differentiation, we found that n-3 PUFAs increased GFAP expression and GFAP positive cell formation. BDNF and GDNF production were increased in the astrocytes derived from patients subsequent to n-3 PUFA treatment. Stearic Acid (SA) treatment did not have this effect. CREB activity (phosphorylated CREB) was also increased by DHA and EPA but not by SA. Furthermore, when these astrocytes were treated with n-3 PUFAs, the cAMP antagonist, RP-cAMPs did not block n-3 PUFA CREB activation. However, the CREB specific inhibitor (666-15) diminished BDNF and GDNF production induced by n-3 PUFA, suggesting CREB dependence. Together, these results suggested that n-3 PUFAs facilitate astrocyte differentiation, and may mimic effects of some antidepressants by increasing production of neurotrophic factors. The CREB- dependence and cAMP independence of this process suggests a manner in which n-3 PUFA could augment antidepressant effects. These data also suggest a role for astrocytes in both MDD and antidepressant action.
Phatcharee Chukaew1,2, Alex Leow3,4, Witchuda Saengsawang1, Mark M. Rasenick 2,3,5
While several therapeutic strategies exist for depression, most antidepressant drugs require several weeks before reaching full biochemical efficacy and remission is not achieved in many patients. Therefore, biomarkers for depression and drug- response would help tailor treatment strategies. This study made use of banked human lymphoblast cell lines (LCLs) from normal and depressed subjects; the latter divided into remitters and non-remitters. Due to the fact that previous studies have shown effects on growth factors, cytokines, and elements of the cAMP-generating system as potential biomarkers for depression and antidepressant action, these were examined in LCLs. Initial gene and protein expression profiles for signaling cascades related to neuroendocrine and inflammatory functions differ among the three groups. Growth factor genes, including VEGFA and BDNF were significantly down-regulated in cells from depressed subjects. In addition, omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been reported to act as both antidepressants and anti-inflammatories, but the mechanisms for these effects are not established. Here we showed that n-3 PUFAs and escitalopram (selective serotonin reuptake inhibitors, SSRIs) treatment increased adenylyl cyclase (AC) and BDNF gene expression in LCLs. These data are consistent with clinical observations showing that n-3 PUFA and SSRI have antidepressant affects, which may be additive. Contrary to observations made in neuronal and glial cells, n-3 PUFA treatment attenuated cAMP accumulation in LCLs. However, while lymphoblasts show paradoxical responses to neurons and glia, patient-derived lymphoblasts appear to carry potential depression biomarkers making them an important tool for studying precision medicine in depressive patients. Furthermore, these data validate usefulness of n-3 PUFAs in treatment for depression.
Nathan H. Wray and Mark M. Rasenick, Neuropsychopharmacology (2018) 0:1–2
No abstract available
NMDA-receptor independent actions of ketamine: a new chapter in a story that’s not so old (PDF)
Nathan H. Wray et al. Molecular Psychiatry, 2018
Ketamine produces rapid and robust antidepressant effects in depressed patients within hours of administration, often when traditional antidepressant compounds have failed to alleviate symptoms. We hypothesized that ketamine would translocate Gαs from lipid rafts to non-raft microdomains, similarly to other antidepressants but with a distinct, abbreviated treatment duration. C6 glioma cells were treated with 10 μM ketamine for 15 min, which translocated Gαs from lipid raft domains to non-raft domains. Other NMDA antagonist did not translocate Gαs from lipid raft to non-raft domains. The ketamine- induced Gαs plasma membrane redistribution allows increased functional coupling of Gαs and adenylyl cyclase to increase intracellular cyclic adenosine monophosphate (cAMP). Moreover, increased intracellular cAMP increased phosphorylation of cAMP response element-binding protein (CREB), which, in turn, increased BDNF expression. The ketamine-induced increase in intracellular cAMP persisted after knocking out the NMDA receptor indicating an NMDA receptor-independent effect. Furthermore, 10 μM of the ketamine metabolite (2R,6R)-hydroxynorketamine (HNK) also induced Gαs redistribution and increased cAMP. These results reveal a novel antidepressant mechanism mediated by acute ketamine treatment that may contribute to ketamine’s powerful antidepressant effect. They also suggest that the translocation of Gαs from lipid rafts is a reliable hallmark of antidepressant action that might be exploited for diagnosis or drug development
NMDAR-independent, cAMP-dependent antidepressant actions of ketamine (PDF)
J. Biol. Chem. 2016, 291:19725-19733
Depression is a significant public health problem for which currently available medications, if effective, require weeks to months of treatment before patients respond. Previous studies have shown that the G protein responsible for increasing cAMP (Gαs) is increasingly localized to lipid rafts in depressed subjects and that chronic antidepressant treatment translocates Gαs from lipid rafts. Translocation of Gαs, which shows delayed onset after chronic antidepressant treatment of rats or of C6 glioma cells, tracks with the delayed onset of therapeutic action of antidepressants. Because antidepressants appear to specifically modify Gαs localized to lipid rafts, we sought to determine whether structurally diverse antidepressants accumulate in lipid rafts. Sustained treatment of C6 glioma cells, which lack 5-hydroxytryptamine transporters, showed marked concentration of several antidepressants in raft fractions, as revealed by increased absorbance and by mass fingerprint. Closely related molecules without antidepressant activity did not concentrate in raft fractions. Thus, at least two classes of antidepressants accumulate in lipid rafts and effect translocation of Gαs to the non-raft membrane fraction, where it activates the cAMP-signaling cascade. Analysis of the structural determinants of raft localization may both help to explain the hysteresis of antidepressant action and lead to design and development of novel substrates for depression therapeutics.
Davé RH et al. J.Biol.Chem (2011) 286(6):4319–4328
The heterotrimeric, G protein-coupled receptor-associated G protein, Gαs, binds tubulin with nanomolar affinity and disrupts microtubules in cells and in vitro. Here we determine that the activated form of Gαs binds tubulin with a KD of 100 nM, stimulates tubulin GTPase, and promotes microtubule dynamic instability. Moreover, the data reveal that the _3–_5 region of Gαs is a functionally important motif in the Gαs mediated microtubule destabilization. Indeed, peptides corresponding to that region of Gαs mimic Gαs protein in activating tubulin GTPase and increase microtubule dynamic instability.
We have identified specific mutations in peptides or proteins that interfere with this process. The data allow for a model of the Gαs/tubulin interface in which Gαs binds to the microtubule plus-end and activates the intrinsic tubulin GTPase. This model illuminates both the role of tubulin as an “effector” (e.g. adenylyl cyclase) for Gαs and the role of Gαs as a GTPase activator for tubulin. Given the ability of Gαs to translocate intracellularly in response to agonist activation, Gαs may play a role in hormone- or neurotransmitter-induced regulation of cellular morphology.
A Molecular and Structural Mechanism for G Protein-medicated Microtubule Destabilization (PDF)
Cocchi M, et al. Annals of General Psychiatry (2010)
The biomolecular approach to major depression disorder is explained by the different steps that involve cell membrane viscosity, Gsα protein and tubulin. For the first time it is hypothesized that a biomolecular pathway exists, moving from cell membrane viscosity through Gsα protein and Tubulin, which can condition the conscious state and is measurable by electroencephalogram study of the brain’s γ wave synchrony.
Lanqiu Zhang & Mark M. Rasenick, The Journal of Pharmacology & Experimental Therapeutics, Vol. 332, No. 3
Chronic antidepressant treatment has been shown to increase adenylyl cyclase activity, in part, due to translocation of Gsα from lipid rafts to a nonraft fraction of the plasma membrane where they engage in a more facile stimulation of adenylyl cyclase. This effect holds for multiple classes of antidepressants, and for serotonin uptake inhibitors, it occurs in the absence of the serotonin transporter. In the present study, we examined the change in the amount of Gsα in lipid raft and whole cell lysate after exposing C6 cells to escitalopram. The results showed that chronic (but not acute) escitalopram decreased the content of Gsα in lipid rafts, whereas there was no change in overall Gsα content. These effects were drug dose and exposure time-dependent. Although R-citalopram has been reported to antagonize some effects of escitalopram, this compound was without effect on Gsα localization in lipid rafts, and R-citalopram did not inhibit these actions of escitalopram. Escitalopram treatment increased cAMP accumulation, and this seemed due to increased coupling between Gsα and adenyly cyclase. Thus, escitalopram is potent, rapid and efficacious in translocating Gsα from lipid rafts, and this effect seems to occur independently of 5-hydroxytryptamine transporters. Our results suggest that, although antidepressants display distinct affinities for well identified targets (e.g., monoamine transporters), several presynaptic and postsynaptic molecules are probably modified during chronic antidepressant treatment, and these additional targets may be required for clinical efficacy of these drugs.
Chronic Treatment with Escitalopram but Not R-Citalopram (PDF)
Donati RJ, et.al The Journal of Neuroscience, March 19, 2008 28(12):3042–30
Recent in vivo and in vitro studies have demonstrated that Gsα migrates from a Triton X-100 (TX-100)-insoluble membrane domain (lipid raft) to a TX-100-soluble nonraft membrane domain in response to chronic, but not acute, treatment with tricyclic or selective serotonin reuptake inhibitor antidepressants. This migration resulted in a more facile association with adenylyl cyclase. Our hypothesis is that Gsα maybe ensconced, to a greater extent, in lipid rafts during depression, and that one action of chronic antidepressant treatment is to reverse this. In this postmortem study, we examined Gsα membrane localization in the cerebellum and prefrontal cortex of brains from nonpsychiatric control subjects and suicide cases with confirmed unipolar depression. Sequential TX-100 and TX-114 detergent extractions were performed on the brain tissue. In the cerebellum, the ratio of TX-100/TX-114-soluble Gsα is ~2:1 for control versus depressed suicides. Results with prefrontal cortex samples from each group demonstrate a similar trend. These data suggest that depression localizes Gsα to a membrane domain (lipid rafts) where it is less likely to couple to adenylyl cyclase and that antidepressants may upregulate Gsα signaling via disruption of membrane microenvironments. Raft localization of Gsα in human peripheral tissue may thus serve as a biomarker for depression and as a harbinger of antidepressant responsiveness.
Donati RJ, Rasenick MM. Future Neurology (2008) 3(5), 511-514
No abstract available.
Allen JA. Et al. Nature Reviews (2007) 8:128-140
Lipid rafts are specialized structures on the plasma membrane that have an altered lipid composition as well as links to the cytoskeleton. It has been proposed that these structures are membrane domains in which neurotransmitter signalling might occur through a clustering of receptors and components of receptor-activated signalling cascades. The localization of these proteins in lipid rafts, which is affected by the cytoskeleton, also influences the potency and efficacy of neurotransmitter receptors and transporters. The effect of lipid rafts on neurotransmitter signaling has also been implicated in neurological and psychiatric diseases.
Lipid raft microdomains and neurotransmitter signalling (PDF)
Donati RJ, Rasenick MM. Neuropsychopharmacology (2005) 30, 1238–1245
Previous studies demonstrated that Gsa migrates from a Triton X-100 (TTX-100) insoluble membrane domain to a TTX-100 soluble membrane domain in response to chronic treatment with the antidepressants desipramine and fluoxetine. Antidepressant treatment also causes a Gsa redistribution in cells as seen by confocal microscopy. The current studies have focused on examining the possibility that the association between Gsa and the plasma membrane and/or cytoskeleton is altered in response to antidepressant treatment, and that this is relevant to both Gsa redistribution and the increased coupling between Gsa and adenylyl cyclase seen after chronic antidepressant treatment. Chronic treatment of C6 cells with two functionally and structurally distinct antidepressants, desipramine and fluoxetine, decreased the Gsa content of TTX-100 insoluble membrane domains by as much as 60%, while the inactive fluoxetine analog LY368514 had no effect. Disruption of these membrane domains with the cholesterol chelator methyl-b-cyclodextrin altered the localization of many proteins involved in the cAMP signaling cascade, but only Gsa localization was altered by antidepressant treatment. In addition, microtubule disruption with colchicine elicited the movement of Gsa out of detergent-resistant membrane domains in a manner identical to that seen with antidepressant treatment. The data presented here further substantiate the role of Gsa as a major player in antidepressant-induced modification of neuronal signaling and also raise the possibility that an interaction between Gsa and the cytoskeleton is involved in this process.