Transcranial Magnetic Stimulation in Primary Care: Indications, Risks, and Outcomes

The Psychiatric Consultation Service at Massachusetts General Hospital sees medical and surgical inpatients with comorbid psychiatric symptoms and conditions. During their twice-weekly rounds, Dr Stern and other members of the Consultation Service discuss diagnosis and management of hospitalized patients with complex medical or surgical problems who also demonstrate psychiatric symptoms or conditions. These discussions have given rise to rounds reports that will prove useful for clinicians practicing at the interface of medicine and psychiatry.

Prim Care Companion CNS Disord 2024;26(2):23f03614.

Author affiliations are listed at the end of this article.

Telemedicine-Based Cognitive Examinations During COVID-19 and Beyond: Perspective of the Massachusetts General Hospital Behavioral Neurology & Neuropsychiatry Group

Telehealth and telemedicine have encountered explosive growth since the beginning of the COVID-19 pandemic, resulting in increased access to care for patients located far from medical centers and clinics. Subspecialty clinicians in behavioral neurology & neuropsychiatry (BNNP) have implemented the use of telemedicine platforms to perform cognitive examinations that were previously office based. In this perspective article, BNNP clinicians at Massachusetts General Hospital (MGH) describe their experience performing cognitive examinations via telemedicine. The article reviews the goals, prerequisites, advantages, and potential limitations of performing a video- or telephone-based telemedicine cognitive examination. The article shares the approaches used by MGH BNNP clinicians to examine cognitive and behavioral areas, such as orientation, attention and executive functions, language, verbal learning and memory, visual learning and memory, visuospatial function, praxis, and abstract abilities, as well as to survey for neuropsychiatric symptoms and assess activities of daily living. Limitations of telemedicine-based cognitive examinations include limited access to and familiarity with telecommunication technologies on the patient side, limitations of the technology itself on the clinician side, and the limited psychometric validation of virtual assessments. Therefore, an in-person examination with a BNNP clinician or a formal in-person neuropsychological examination with a neuropsychologist may be recommended. Overall, this article emphasizes the use of standardized cognitive and behavioral assessment instruments that are either in the public domain or, if copyrighted, are nonproprietary and do not require a fee to be used by the practicing BNNP clinician.

Electroconvulsive therapy-induced volumetric brain changes converge on a common causal circuit in depression

Neurostimulation is a mainstream treatment option for major depression. Neuromodulation techniques apply repetitive magnetic or electrical stimulation to some neural target but significantly differ in their invasiveness, spatial selectivity, mechanism of action, and efficacy. Despite these differences, recent analyses of transcranial magnetic stimulation (TMS) and deep brain stimulation (DBS)-treated individuals converged on a common neural network that might have a causal role in treatment response. We set out to investigate if the neuronal underpinnings of electroconvulsive therapy (ECT) are similarly associated with this causal depression network (CDN). Our aim here is to provide a comprehensive analysis in three cohorts of patients segregated by electrode placement (N = 246 with right unilateral, 79 with bitemporal, and 61 with mixed) who underwent ECT. We conducted a data-driven, unsupervised multivariate neuroimaging analysis Principal Component Analysis (PCA) of the cortical and subcortical volume changes and electric field (EF) distribution to explore changes within the CDN associated with antidepressant outcomes. Despite the different treatment modalities (ECT vs TMS and DBS) and methodological approaches (structural vs functional networks), we found a highly similar pattern of change within the CDN in the three cohorts of patients (spatial similarity across 85 regions: r = 0.65, 0.58, 0.40, df = 83). Most importantly, the expression of this pattern correlated with clinical outcomes (t = -2.35, p = 0.019). This evidence further supports that treatment interventions converge on a CDN in depression. Optimizing modulation of this network could serve to improve the outcome of neurostimulation in depression.

The Impact of Sex Hormones on Transcranial Magnetic Stimulation Measures of Cortical Excitability: A Systematic Review and Considerations for Clinical Practice

ABSTRACT

Repetitive transcranial magnetic stimulation (rTMS) has emerged as a promising alternative for the treatment of major depressive disorder (MDD), although its clinical effectiveness varies substantially. The effects of sex hormone fluctuations on cortical excitability have been identified as potential factors that can explain this variability. However, data on how sex hormone changes affect clinical response to rTMS is limited. To address this gap, we reviewed the literature examining the effects of sex hormones and hormonal treatments on transcranial magnetic stimulation (TMS) measures of cortical excitability. Results show that variations of endogenous estrogen, testosterone, and progesterone have modulatory effects on TMS-derived measures of cortical excitability. Specifically, higher levels of estrogen and testosterone were associated with greater cortical excitability, while higher progesterone was associated with lower cortical excitability. This highlights the importance of additional investigation into the effects of hormonal changes on rTMS outcomes and circuit-specific physiological variables. These results call for TMS clinicians to consider performing more frequent motor threshold (MT) assessments in patients receiving high doses of estrogen, testosterone, and progesterone in cases such as in vitro fertilization, hormone replacement therapy, and gender-affirming hormonal treatments. It may also be important to consider physiological hormonal fluctuations and their impact on depressive symptoms and the MT when treating female patients with rTMS.

Electroconvulsive Therapy: Mechanisms of Action, Clinical Considerations, and Future Directions

LEARNING OBJECTIVES

• Outline and discuss the fundamental physiologic, cellular, and molecular mechanisms of ECT to devise strategies to optimize therapeutic outcomes• Summarize the overview of ECT, its efficacy in treating depression, the known effects on cognition, evidence of mechanisms, and future directions.

ABSTRACT

Electroconvulsive therapy (ECT) is the most effective treatment for a variety of psychiatric illnesses, including treatment-resistant depression, bipolar depression, mania, catatonia, and clozapine-resistant schizophrenia. ECT is a medical and psychiatric procedure whereby electrical current is delivered to the brain under general anesthesia to induce a generalized seizure. ECT has evolved a great deal since the 1930s. Though it has been optimized for safety and to reduce adverse effects on cognition, issues persist. There is a need to understand fundamental physiologic, cellular, and molecular mechanisms of ECT to devise strategies to optimize therapeutic outcomes. Clinical trials that set out to adjust parameters, electrode placement, adjunctive medications, and patient selection are critical steps towards the goal of improving outcomes with ECT. This narrative review provides an overview of ECT, its efficacy in treating depression, its known effects on cognition, evidence of its mechanisms, and future directions.

Neurocircuitry Hypothesis and Clinical Experience in Treating Neuropsychiatric Symptoms of Postacute Sequelae of Severe Acute Respiratory Syndrome Coronavirus 2

Persistent symptoms following COVID-19 infection have been termed postacute sequelae of severe acute respiratory syndrome coronavirus 2 infection. Many of these symptoms are neuropsychiatric, such as inattention, impaired memory, and executive dysfunction; these are often colloquially termed "brain fog". These symptoms are common and often persist long after the acute phase. The pattern of these deficits combined with laboratory, neuroimaging, electroencephalographic, and neuropsychological data suggest that these symptoms may be driven by direct and indirect damage to the frontal-subcortical neural networks. Here, we review this evidence, share our clinical experience at an academic medical center, and discuss potential treatment implications. While the exact etiology remains unknown, a neurocircuit-informed understanding of postacute sequelae of severe acute respiratory syndrome coronavirus 2 infection can help guide pharmacology, neuromodulation, and physical and psychological therapeutic approaches.

Post-Acute Sequelae of SARS-CoV-2 Infection: A Descriptive Clinical Study

OBJECTIVE

The investigators aimed to describe the clinical experience of a single center reporting on neuropsychiatric findings among patients experiencing persistent symptoms as part of post-acute sequelae of SARS-CoV-2 (PASC) infection.

METHODS

Data were collected retrospectively (between February 2020 and May 2021) from a cohort (N=100) within a COVID-19 survivors study of patients with persistent symptoms enrolled after a short inpatient stay or who had been outpatients never hospitalized. Patients without confirmatory positive PCR or antibody diagnostic test results were grouped separately as presumptive cases (N=13).

RESULTS

Of the 87 patients with confirmed SARS-CoV-2, 63 (72.4%) were female, and 65 (74.7%) were White. The mean age was 49.2 years (SD=14.9). The most prevalent symptoms after COVID-19 infection were fatigue, "brain fog," headache, anxiety, and sleep issues. Attention and executive function were frequently impaired. The mean Montreal Cognitive Assessment score was 26.0 (SD=2.8). Concentration and attention as well as memory issues were both significantly correlated with the complaint of brain fog.

CONCLUSIONS

These preliminary findings suggest that post-acute sequelae of SARS-CoV-2 vary in frequency and duration with relation to premorbid history and that these conditions affect functional domains and patients' ability to return to work. Longitudinal research with larger cohorts is needed to characterize PASC and to optimize care, especially for vulnerable populations.

Key considerations for the use of ketamine and esketamine for the treatment of depression: focusing on administration, safety, and tolerability

INTRODUCTION

Racemic ketamine, a derivative of phencyclidine, has been used as a dissociative anesthetic since 1970. In 2000, the first randomized controlled trial showed a rapid relief of depressive symptoms. Since then, intravenous ketamine and intranasal S-ketamine have been validated for the treatment of depression and suicidal ideation following dose-response and double-blind placebo-controlled clinical trials. In clinical practice, after dose titration and with repeated treatments, patients may experience approximately 2-3 weeks of symptomatic relief from depression.

AREAS COVERED

Areas covered in this narrative review include mechanism of action, dosing, safety, and tolerability. Some attention is paid to the possibility of R-ketamine as a future antidepressant.

EXPERT OPINION

We recommend further investigation into treatment dosing and frequency strategies as well as approaches that prolong the therapeutic effects. The current fixed dosing of esketamine for obese individuals may be insufficient. Additional investigation into co-administration with somatic and neuromodulation treatments needs investigation. Finally, continuing to monitor research subjects and patients long-term for the emergence of adverse effects on cognition or other organ systems is critical.

Ketamine for treatment of mood disorders and suicidality: A narrative review of recent progress

BACKGROUND

Mood disorders are a leading cause of morbidity. Many patients experience treatment-resistant depression (TRD), and suicide rates are rising. Faster-acting and more effective antidepressant medications are needed. Four decades of research has transformed the use of ketamine from an anesthetic to an outpatient treatment for major depressive disorder (MDD). Ketamine is a N-methyl-d-aspartate (NMDA) receptor antagonist and has been shown to rapidly improve mood symptoms and suicidal ideation by targeting the glutamate system directly.

METHODS

We used the PubMed database to identify relevant articles published until September 1, 2020. We focused on meta-analyses, randomized controlled trials, and original observational studies. We included relevant studies for depression, MDD, TRD, bipolar disorder, anxiety, posttraumatic stress disorder (PTSD), suicide, ketamine, and esketamine.

RESULTS

Both racemic ketamine and esketamine have been shown to rapidly treat depression and suicidality. There is evidence that ketamine can be helpful for anxiety and PTSD; however, more research is needed. Intranasal esketamine has been FDA approved to treat depression.

CONCLUSIONS

This narrative review describes the evolution of ketamine to treat mood disorders and suicidality. We provide the evidence supporting recent developments using esketamine as well as unresolved issues in the field, such as dosing and safety.

Signalosome-Regulated Serum Response Factor Phosphorylation Determining Myocyte Growth in Width Versus Length as a Therapeutic Target for Heart Failure

BACKGROUND

Concentric and eccentric cardiac hypertrophy are associated with pressure and volume overload, respectively, in cardiovascular disease both conferring an increased risk of heart failure. These contrasting forms of hypertrophy are characterized by asymmetrical growth of the cardiac myocyte in mainly width or length, respectively. The molecular mechanisms determining myocyte preferential growth in width versus length remain poorly understood. Identification of the mechanisms governing asymmetrical myocyte growth could provide new therapeutic targets for the prevention or treatment of heart failure.

METHODS

Primary adult rat ventricular myocytes, adeno-associated virus (AAV)-mediated gene delivery in mice, and human tissue samples were used to define a regulatory pathway controlling pathological myocyte hypertrophy. Chromatin immunoprecipitation assays with sequencing and precision nuclear run-on sequencing were used to define a transcriptional mechanism.

RESULTS

We report that asymmetrical cardiac myocyte hypertrophy is modulated by SRF (serum response factor) phosphorylation, constituting an epigenomic switch balancing the growth in width versus length of adult ventricular myocytes in vitro and in vivo. SRF Ser¹⁰³ phosphorylation is bidirectionally regulated by RSK3 (p90 ribosomal S6 kinase type 3) and PP2A (protein phosphatase 2A) at signalosomes organized by the scaffold protein mAKAPβ (muscle A-kinase anchoring protein β), such that increased SRF phosphorylation activates AP-1 (activator protein-1)-dependent enhancers that direct myocyte growth in width. AAV are used to express in vivo mAKAPβ-derived RSK3 and PP2A anchoring disruptor peptides that block the association of the enzymes with the mAKAPβ scaffold. Inhibition of RSK3 signaling prevents concentric cardiac remodeling induced by pressure overload, while inhibition of PP2A signaling prevents eccentric cardiac remodeling induced by myocardial infarction, in each case improving cardiac function. SRF Ser¹⁰³ phosphorylation is significantly decreased in dilated human hearts, supporting the notion that modulation of the mAKAPβ-SRF signalosome could be a new therapeutic approach for human heart failure.

CONCLUSIONS

We have identified a new molecular switch, namely mAKAPβ signalosome-regulated SRF phosphorylation, that controls a transcriptional program responsible for modulating changes in cardiac myocyte morphology that occur secondary to pathological stressors. Complementary AAV-based gene therapies constitute rationally-designed strategies for a new translational modality for heart failure.

Updates on Preclinical and Translational Neuroscience of Mood Disorders: A Brief Historical Focus on Ketamine for the Clinician

BACKGROUND

The development of new-generation antidepressants comes at a time of great clinical need when the global burden of depression, suicide, and other psychiatric conditions continues to increase. Our current treatment armamentarium is limited by the time delay needed for antidepressant effects and the significant number of patients who do not show an adequate response to antidepressants. The past 2 decades of psychiatric research has revealed that ketamine, known to be used only as an anesthetic and drug of abuse and to produce experimental models of psychosis, is effective at subanesthetic doses to ameliorate clinical depression.

METHODS

We performed a systematic search of PubMed/MEDLINE indexed reports to identify clinical and translational research done with ketamine for purposes of treating depression.

RESULTS

We will first present the rationale for investigating ketamine and other N-methyl-D-aspartate receptor antagonists as a novel class of glutamate system targeting antidepressants. We will summarize putative molecular pathways underlying mood disorders and outline a brief history of investigation into ketamine as a treatment for depression. Recent clinical/translational evidence of ketamine's rapid-acting antidepressant mechanism will be critically reviewed in detail.

CONCLUSIONS

At the end of this review, we will opine on the role of ketamine and derivatives in clinical practice.

Non-invasive brain stimulation modalities for the treatment and prevention of opioid use disorder: a systematic review of the literature

The U.S. is currently facing an unprecedented epidemic of opioid-related deaths. Despite the efficacy of the current treatments for opioid use disorder (OUD), including psychosocial interventions and medication-assisted therapy (MAT), many patients remain treatment-resistant and at high risk for overdose. A potential augmentation strategy includes the use of non-invasive brain stimulation (NIBS) techniques, such as transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and auricular vagus nerve stimulation (aVNS). These approaches may have therapeutic benefits by directly or indirectly modulating the neurocircuitry affected in OUD. In this review, we evaluate the available studies on NIBS in the context of OUD withdrawal and detoxification, maintenance, and cravings, while also considering analgesia and safety concerns. In the context of opioid withdrawal and detoxification, a percutaneous form of aVNS has positive results in open-label trials, but has not yet been tested against sham. No randomized studies have reported on the safety and efficacy of NIBS specifically for maintenance treatment in OUD. TMS and tDCS have demonstrated effects on cravings, although published studies were limited by small sample sizes. NIBS may play a role in reducing exposure to opioids and the risk of developing OUD, as demonstrated by studies using tDCS in an experimental pain condition and TMS in a post-operative setting. Overall, while the preliminary evidence and safety for NIBS in the prevention and treatment of OUD appears promising, further research is needed with larger sample sizes, placebo control, and objective biomarkers as outcome measures before strong conclusions can be drawn.

Resilience as a translational endpoint in the treatment of PTSD

Resilience is a neurobiological entity that shapes an individual's response to trauma. Resilience has been implicated as the principal mediator in the development of mental illness following exposure to trauma. Although animal models have traditionally defined resilience as molecular and behavioral changes in stress responsive circuits following trauma, this concept needs to be further clarified for both research and clinical use. Here, we analyze the construct of resilience from a translational perspective and review optimal measurement methods and models. We also seek to distinguish between resilience, stress vulnerability, and posttraumatic growth. We propose that resilience can be quantified as a multifactorial determinant of physiological parameters, epigenetic modulators, and neurobiological candidate markers. This multifactorial definition can determine PTSD risk before and after trauma exposure. From this perspective, we propose the use of an 'R Factor' analogous to Spearman's g factor for intelligence to denote these multifactorial determinants. In addition, we also propose a novel concept called 'resilience reserve', analogous to Stern's cognitive reserve, to summarize the sum total of physiological processes that protect and compensate for the effect of trauma. We propose the development and application of challenge tasks to measure 'resilience reserve' and guide the assessment and monitoring of 'R Factor' as a biomarker for PTSD.

Comparative evaluation of a new magnetic bead-based DNA extraction method from fecal samples for downstream next-generation 16S rRNA gene sequencing

We are colonized by a vast population of genetically diverse microbes, the majority of which are unculturable bacteria that reside within the gastrointestinal tract. As affordable, advanced next-generation sequencing technologies become more widely available, important discoveries about the composition and function of these microbes become increasingly possible. In addition to rapid advancement in sequencing technologies, automated systems have been developed for nucleic acid extraction; however, these methods have yet to be widely used for the isolation of bacterial DNA from fecal samples. Here, we adapted Promega’s Maxwell^® RSC PureFood GMO and Authentication kit for use with fecal samples and compared it to the commonly used Qiagen QIAamp^® PowerFecal^® kit. Results showed that the two approaches yielded similar measures of DNA purity and successful next-generation sequencing amplification and produced comparable composition of microbial communities. However, DNA extraction with the Maxwell^® RSC kit produced higher concentrations with a lower fecal sample input weight and took a fraction of the time compared to the QIAamp^® PowerFecal^® protocol. The results of this study demonstrate that the Promega Maxwell^® RSC system can be used for medium-throughput DNA extraction in a time-efficient manner without compromising the quality of the downstream sequencing.

Muscle A-Kinase Anchoring Protein-α is an Injury-Specific Signaling Scaffold Required for Neurotrophic- and Cyclic Adenosine Monophosphate-Mediated Survival

Neurotrophic factor and cAMP-dependent signaling promote the survival and neurite outgrowth of retinal ganglion cells (RGCs) after injury. However, the mechanisms conferring neuroprotection and neuroregeneration downstream to these signals are unclear. We now reveal that the scaffold protein muscle A-kinase anchoring protein-α (mAKAPα) is required for the survival and axon growth of cultured primary RGCs. Although genetic deletion of mAKAPα early in prenatal RGC development did not affect RGC survival into adulthood, nor promoted the death of RGCs in the uninjured adult retina, loss of mAKAPα in the adult increased RGC death after optic nerve crush. Importantly, mAKAPα was required for the neuroprotective effects of brain-derived neurotrophic factor and cyclic adenosine-monophosphate (cAMP) after injury. These results identify mAKAPα as a scaffold for signaling in the stressed neuron that is required for RGC neuroprotection after optic nerve injury.

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mAKAPα is a stress-specific mediator of RGC survival.

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mAKAP deletion does not affect RGC survival in development or in the uninjured adult retina.

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mAKAP is downregulated after optic nerve injury, and its further deletion exacerbates RGC death.

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mAKAP deletion suppresses the neuroprotective effects of cAMP and BDNF after injury.

After injury or in degenerative diseases, neurons of the central nervous system (CNS) fail to regenerate and often die partly due to a lack of pro-survival, trophic signaling. Better understanding of such signaling is important for the development of therapies that enhance survival and regeneration of neurons after injury. Here we identify a critical regulator of such signaling, mAKAPα, a scaffold protein that coordinates pro-survival signaling to enhance survival and regeneration in CNS neurons after injury. The neuroprotective role of mAKAPα will likely lead to further future insights into the detailed nature of survival signaling in adult neurons.

Abstract 190: Disruption of P90 Ribosomal S6 Kinase Binding 3 to Muscle A-kinase Anchoring Protein In Vivo Via Adeno-associated Virus Expression of a Competing Peptide Attenuates Pressure Overload-induced Cardiac Hypertrophy

RATIONALE: Cardiac myocyte hypertrophy is the main compensatory response to chronic stress in the heart. p90 ribosomal S6 kinase (RSK) family members are effectors for extracellular signal-regulated kinases that induce myocyte growth. RSK3 contains a unique N-terminal domain that mediates RSK3 binding to the muscle A-kinase anchoring protein (mAKAPβ) scaffold. We have previously published that disruption of RSK3-mAKAPβ complexes using a competing peptide inhibited the phenylephrine-induced hypertrophy of neonatal ventricular myocytes in vitro. In vivo, RSK3 gene deletion in mice attenuated the concentric cardiac hypertrophy induced by pressure overload. We hypothesize that RSK3 anchoring to mAKAPβ in myocytes is required for cardiac hypertrophy in vivo.

METHODS AND RESULTS: Adeno-associated viruses (AAV) are gene therapy vectors in development for the treatment of human diseases owing to their nonpathogenic capability for transducing non-dividing cells and their long-term transgene expression. We have used a recombinant AAV2/9 vector to express a mAKAPβ RSK3-binding domain (RBD)-GFP fusion protein under the control of the cardiac myocyte-specific cardiac troponin T promoter. 3 day-old C57BL/6 mice were injected intraperitoneally with either AAV-RBD-GFP or AAV-GFP control virus. At 8 weeks of age mice were subjected to transverse aortic constriction to induce pressure overload (TAC) for two weeks. Cardiac hypertrophy was attenuated in mice injected with the AAV-RBD-GFP virus (biventricular weight indexed to tibial length (mg/mm): 7.7, 8.6, and 9.2 for AAV-RBD, AAV-GFP and non-injected TAC cohorts, respectively; p<0.05 vs. both controls). Echocardiography both corroborated the inhibition of hypertrophy and revealed no deleterious effect on cardiac function attributable to the AAV-RBD-GFP vector.

CONCLUSIONS: Anchored RSK3 regulates pathologic myocyte growth. AAV can successfully deliver a competing peptide inhibiting pathological hypertrophy and should be investigated further as a prevention and/or treatment for heart failure.

The scaffold protein muscle A-kinase anchoring protein β orchestrates cardiac myocyte hypertrophic signaling required for the development of heart failure

BACKGROUND

Cardiac myocyte hypertrophy is regulated by an extensive intracellular signal transduction network. In vitro evidence suggests that the scaffold protein muscle A-kinase anchoring protein β (mAKAPβ) serves as a nodal organizer of hypertrophic signaling. However, the relevance of mAKAPβ signalosomes to pathological remodeling and heart failure in vivo remains unknown.

METHODS AND RESULTS

Using conditional, cardiac myocyte-specific gene deletion, we now demonstrate that mAKAPβ expression in mice is important for the cardiac hypertrophy induced by pressure overload and catecholamine toxicity. mAKAPβ targeting prevented the development of heart failure associated with long-term transverse aortic constriction, conferring a survival benefit. In contrast to 29% of control mice (n=24), only 6% of mAKAPβ knockout mice (n=31) died in the 16 weeks of pressure overload (P=0.02). Accordingly, mAKAPβ knockout inhibited myocardial apoptosis and the development of interstitial fibrosis, left atrial hypertrophy, and pulmonary edema. This improvement in cardiac status correlated with the attenuated activation of signaling pathways coordinated by the mAKAPβ scaffold, including the decreased phosphorylation of protein kinase D1 and histone deacetylase 4 that we reveal to participate in a new mAKAP signaling module. Furthermore, mAKAPβ knockout inhibited pathological gene expression directed by myocyte-enhancer factor-2 and nuclear factor of activated T-cell transcription factors that associate with the scaffold.

CONCLUSIONS

mAKAPβ orchestrates signaling that regulates pathological cardiac remodeling in mice. Targeting of the underlying physical architecture of signaling networks, including mAKAPβ signalosome formation, may constitute an effective therapeutic strategy for the prevention and treatment of pathological remodeling and heart failure.

p90 ribosomal S6 kinase 3 contributes to cardiac insufficiency in α-tropomyosin Glu180Gly transgenic mice

Myocardial interstitial fibrosis is an important contributor to the development of heart failure. Type 3 p90 ribosomal S6 kinase (RSK3) was recently shown to be required for concentric myocyte hypertrophy under in vivo pathological conditions. However, the role of RSK family members in myocardial fibrosis remains uninvestigated. Transgenic expression of α-tropomyosin containing a Glu180Gly mutation (TM180) in mice of a mixed C57BL/6:FVB/N background induces a cardiomyopathy characterized by a small left ventricle, interstitial fibrosis, and diminished systolic and diastolic function. Using this mouse model, we now show that RSK3 is required for the induction of interstitial fibrosis in vivo. TM180 transgenic mice were crossed to RSK3 constitutive knockout (RSK3(-/-)) mice. Although RSK3 knockout did not affect myocyte growth, the decreased cardiac function and mild pulmonary edema associated with the TM180 transgene were attenuated by RSK3 knockout. The improved cardiac function was consistent with reduced interstitial fibrosis in the TM180;RSK3(-/-) mice as shown by histology and gene expression analysis, including the decreased expression of collagens. The specific inhibition of RSK3 should be considered as a potential novel therapeutic strategy for improving cardiac function and the prevention of sudden cardiac death in diseases in which interstitial fibrosis contributes to the development of heart failure.

Anchored p90 ribosomal S6 kinase 3 is required for cardiac myocyte hypertrophy

RATIONALE

Cardiac myocyte hypertrophy is the main compensatory response to chronic stress on the heart. p90 ribosomal S6 kinase (RSK) family members are effectors for extracellular signal-regulated kinases that induce myocyte growth. Although increased RSK activity has been observed in stressed myocytes, the functions of individual RSK family members have remained poorly defined, despite being potential therapeutic targets for cardiac disease.

OBJECTIVE

To demonstrate that type 3 RSK (RSK3) is required for cardiac myocyte hypertrophy.

METHODS AND RESULTS

RSK3 contains a unique N-terminal domain that is not conserved in other RSK family members. We show that this domain mediates the regulated binding of RSK3 to the muscle A-kinase anchoring protein scaffold, defining a novel kinase anchoring event. Disruption of both RSK3 expression using RNA interference and RSK3 anchoring using a competing muscle A-kinase anchoring protein peptide inhibited the hypertrophy of cultured myocytes. In vivo, RSK3 gene deletion in the mouse attenuated the concentric myocyte hypertrophy induced by pressure overload and catecholamine infusion.

CONCLUSIONS

Taken together, these data demonstrate that anchored RSK3 transduces signals that modulate pathologic myocyte growth. Targeting of signaling complexes that contain select kinase isoforms should provide an approach for the specific inhibition of cardiac myocyte hypertrophy and for the development of novel strategies for the prevention and treatment of heart failure.