Chaperonin-assisted protein folding: a chronologue.

This chronologue seeks to document the discovery and development of an understanding of oligomeric ring protein assemblies known as chaperonins that assist protein folding in the cell. It provides detail regarding genetic, physiologic, biochemical, and biophysical studies of these ATP-utilizing machines from both in vivo and in vitro observations. The chronologue is organized into various topics of physiology and mechanism, for each of which a chronologic order is generally followed. The text is liberally illustrated to provide firsthand inspection of the key pieces of experimental data that propelled this field. Because of the length and depth of this piece, the use of the outline as a guide for selected reading is encouraged, but it should also be of help in pursuing the text in direct order.

Hsp110 mitigates α-synuclein pathology in vivo.

Parkinson's disease is characterized by the aggregation of the presynaptic protein α-synuclein and its deposition into pathologic Lewy bodies. While extensive research has been carried out on mediators of α-synuclein aggregation, molecular facilitators of α-synuclein disaggregation are still generally unknown. We investigated the role of molecular chaperones in both preventing and disaggregating α-synuclein oligomers and fibrils, with a focus on the mammalian disaggregase complex. Here, we show that overexpression of the chaperone Hsp110 is sufficient to reduce α-synuclein aggregation in a mammalian cell culture model. Additionally, we demonstrate that Hsp110 effectively mitigates α-synuclein pathology in vivo through the characterization of transgenic Hsp110 and double-transgenic α-synuclein/Hsp110 mouse models. Unbiased analysis of the synaptic proteome of these mice revealed that overexpression of Hsp110 can override the protein changes driven by the α-synuclein transgene. Furthermore, overexpression of Hsp110 is sufficient to prevent endogenous α-synuclein templating and spread following injection of aggregated α-synuclein seeds into brain, supporting a role for Hsp110 in the prevention and/or disaggregation of α-synuclein pathology.

Transfer of pathogenic and nonpathogenic cytosolic proteins between spinal cord motor neurons in vivo in chimeric mice.

Recent studies have reported spread of pathogenic proteins in the mammalian nervous system, but whether nonpathogenic ones spread is unknown. We initially investigated whether spread of a mutant amyotrophic lateral sclerosis-associated cytosolic superoxide dismutase 1 (SOD1) protein between motor neurons could be detected in intact chimeric mice. Eight-cell embryos from G85R SOD1YFP and G85R SOD1CFP mice were aggregated, and spinal cords of adult chimeric progeny were examined for motor neurons with cytosolic double fluorescence. By 3 mo of age, we observed extensive double fluorescence, including in amyotrophic lateral sclerosis-affected cranial nerve motor nuclei but not in the relatively spared extraocular nuclei. Chimeras of nonpathogenic wtSOD1YFP and G85R SOD1CFP also exhibited double fluorescence. In a third chimera, mitochondrial mCherry did not transfer to G85R SOD1YFP motor neurons, suggesting that neither RNA nor organelles transfer, but mito-mCherry neurons received G85R SOD1YFP. In a chimera of ChAT promoter-EGFP and mito-mCherry, EGFP efficiently transferred to mito-mCherry+ cells. Thus, nonpathogenic cytosolic proteins appear capable of transfer. During study of both the SOD1FP and EGFP chimeras, we observed fluorescence also in small cells neighboring the motor neurons, identified as mature gray matter oligodendrocytes. Double fluorescence in the G85R SOD1FP chimera and observation of the temporal development of fluorescence first in motor neurons and then in these oligodendrocytes suggest that they may be mediators of transfer of cytosolic proteins between motor neurons.

Extended survival of misfolded G85R SOD1-linked ALS mice by transgenic expression of chaperone Hsp110.

Recent studies have indicated that mammalian cells contain a cytosolic protein disaggregation machinery comprised of Hsc70, DnaJ homologs, and Hsp110 proteins, the last of which acts to accelerate a rate-limiting step of nucleotide exchange of Hsc70. We tested the ability of transgenic overexpression of a Thy1 promoter-driven human Hsp110 protein, HspA4L (Apg1), in neuronal cells of a transgenic G85R SOD1YFP ALS mouse strain to improve survival. Notably, G85R is a mutant version of Cu/Zn superoxide dismutase 1 (SOD1) that is unable to reach native form and that is prone to aggregation, with prominent YFP-fluorescent aggregates observed in the motor neurons of the transgenic mice as early as 1 mo of age. The several-fold overexpression of Hsp110 in motor neurons of these mice was associated with an increased median survival from ∼5.5 to 7.5 mo and increased maximum survival from 6.5 to 12 mo. Improvement of survival was also observed for a G93A mutant SOD1 ALS strain. We conclude that neurodegeneration associated with cytosolic misfolding and aggregation can be ameliorated by overexpression of Hsp110, likely enhancing the function of a cytosolic disaggregation machinery.

Absence of lipofuscin in motor neurons of SOD1-linked ALS mice.

Lipofuscin, or aging pigment, is accreted as red autofluorescence in the lysosomes of motor neuron cell bodies in the ventral horn of WT mice by 3 mo of age. Strikingly, in two presymptomatic ALS mouse strains transgenic for mutant human Cu/Zn superoxide dismutase (SOD1), G85R SOD1YFP and G93A SOD1, little or no lipofuscin was detected in motor neuron cell bodies. Two markers of autophagy, sequestosome 1 (SQSTM1/p62) and microtubule-associated protein 1 light chain 3 (LC3), were examined in the motor neuron cell bodies of G85R SOD1YFP mice and found to be reduced relative to WT SOD1YFP transgenic mice. To elucidate whether the autophagy/lysosome pathway was either impaired or hyperactive in motor neurons, chloroquine was administered to 3-mo-old G85R SOD1YFP mice to block lysosomal hydrolysis. After 2 wk, lipofuscin was now observed in motor neurons, and SQSTM1 and LC3 levels approached those of WT SOD1YFP mice, suggesting that the autophagy/lysosome pathway is hyperactive in motor neurons of SOD1-linked ALS mice. This seems to be mediated at least in part through the mammalian target of rapamycin complex 1 (MTORC1) pathway, because levels of Ser757-phosphorylated Unc-51-like kinase 1 (ULK1), an MTORC1 target, were greatly reduced in the G85R SOD1YFP motor neurons, correspondent to an activated state of ULK1 that initiates autophagy.

Molecular chaperone Hsp110 rescues a vesicle transport defect produced by an ALS-associated mutant SOD1 protein in squid axoplasm.

Mutant human Cu/Zn superoxide dismutase 1 (SOD1) is associated with motor neuron toxicity and death in an inherited form of amyotrophic lateral sclerosis (ALS; Lou Gehrig disease). One aspect of toxicity in motor neurons involves diminished fast axonal transport, observed both in transgenic mice and, more recently, in axoplasm isolated from squid giant axons. The latter effect appears to be directly mediated by misfolded SOD1, whose addition activates phosphorylation of p38 MAPK and phosphorylation of kinesin. Here, we observe that several different oligomeric states of a fusion protein, comprising ALS-associated human G85R SOD1 joined with yellow fluorescent protein (G85R SOD1YFP), which produces ALS in transgenic mice, inhibited anterograde transport when added to squid axoplasm. Inhibition was blocked both by an apoptosis signal-regulating kinase 1 (ASK1; MAPKKK) inhibitor and by a p38 inhibitor, indicating the transport defect is mediated through the MAPK cascade. In further incubations, we observed that addition of the mammalian molecular chaperone Hsc70, abundantly associated with G85R SOD1YFP in spinal cord of transgenic mice, exerted partial correction of the transport defect, associated with diminished phosphorylation of p38. Most striking, the addition of the molecular chaperone Hsp110, in a concentration substoichiometric to the mutant SOD1 protein, completely rescued both the transport defect and the phosphorylation of p38. Hsp110 has been demonstrated to act as a nucleotide exchange factor for Hsc70 and, more recently, to be able to cooperate with it to mediate protein disaggregation. We speculate that it can cooperate with endogenous squid Hsp(c)70 to mediate binding and/or disaggregation of mutant SOD1 protein, abrogating toxicity.

GroEL/GroES cycling: ATP binds to an open ring before substrate protein favoring protein binding and production of the native state.

The GroEL/GroES reaction cycle involves steps of ATP and polypeptide binding to an open GroEL ring before the GroES encapsulation step that triggers productive folding in a sequestered chamber. The physiological order of addition of ATP and nonnative polypeptide, typically to the open trans ring of an asymmetrical GroEL/GroES/ADP complex, has been unknown, although there have been assumptions that polypeptide binds first, allowing subsequent ATP-mediated movement of the GroEL apical domains to exert an action of forceful unfolding on the nonnative polypeptide. Here, using fluorescence measurements, we show that the physiological order of addition is the opposite, involving rapid binding of ATP, accompanied by nearly as rapid apical domain movements, followed by slower binding of nonnative polypeptide. In order-of-addition experiments, approximately twice as much Rubisco activity was recovered when nonnative substrate protein was added after ATP compared with it being added before ATP, associated with twice as much Rubisco protein recovered with the chaperonin. Furthermore, the rate of Rubisco binding to an ATP-exposed ring was twice that observed in the absence of nucleotide. Finally, when both ATP and Rubisco were added simultaneously to a GroEL ring, simulating the physiological situation, the rate of Rubisco binding corresponded to that observed when ATP had been added first. We conclude that the physiological order, ATP binding before polypeptide, enables more efficient capture of nonnative substrate proteins, and thus allows greater recovery of the native state for any given round of the chaperonin cycle.

Chaperonin-mediated protein folding: using a central cavity to kinetically assist polypeptide chain folding.

The chaperonin ring assembly GroEL provides kinetic assistance to protein folding in the cell by binding non-native protein in the hydrophobic central cavity of an open ring and subsequently, upon binding ATP and the co-chaperonin GroES to the same ring, releasing polypeptide into a now hydrophilic encapsulated cavity where productive folding occurs in isolation. The fate of polypeptide during binding, encapsulation, and folding in the chamber has been the subject of recent experimental studies and is reviewed and considered here. We conclude that GroEL, in general, behaves passively with respect to its substrate proteins during these steps. While binding appears to be able to rescue non-native polypeptides from kinetic traps, such rescue is most likely exerted at the level of maximizing hydrophobic contact, effecting alteration of the topology of weakly structured states. Encapsulation does not appear to involve 'forced unfolding', and if anything, polypeptide topology is compacted during this step. Finally, chamber-mediated folding appears to resemble folding in solution, except that major kinetic complications of multimolecular association are prevented.

Requirement for binding multiple ATPs to convert a GroEL ring to the folding-active state.

Production of the folding-active state of a GroEL ring involves initial cooperative binding of ATP, recruiting GroES, followed by large rigid body movements that are associated with ejection of bound substrate protein into the encapsulated hydrophilic chamber where folding commences. Here, we have addressed how many of the 7 subunits of a GroEL ring are required to bind ATP to drive these events, by using mixed rings with different numbers of wild-type and variant subunits, the latter bearing a substitution in the nucleotide pocket that allows specific block of ATP binding and turnover by a pyrazolol pyrimidine inhibitor. We observed that at least 2 wild-type subunits were required to bind GroES. By contrast, the triggering of polypeptide release and folding required a minimum of 4 wild-type subunits, with the greatest extent of refolding observed when all 7 subunits were wild type. This is consistent with the requirement for a "power stroke" of forceful apical movement to eject polypeptide into the chamber.

Folding trajectories of human dihydrofolate reductase inside the GroEL GroES chaperonin cavity and free in solution.

The chaperonin GroEL binds non-native polypeptides in an open ring via hydrophobic contacts and then, after ATP and GroES binding to the same ring as polypeptide, mediates productive folding in the now hydrophilic, encapsulated cis chamber. The nature of the folding reaction in the cis cavity remains poorly understood. In particular, it is unclear whether polypeptides take the same route to the native state in this cavity as they do when folding spontaneously free in solution. Here, we have addressed this question by using NMR measurements of the time course of acquisition of amide proton exchange protection of human dihydrofolate reductase (DHFR) during folding in the presence of methotrexate and ATP either free in solution or inside the stable cavity formed between a single ring variant of GroEL, SR1, and GroES. Recovery of DHFR refolded by the SR1/GroES-mediated reaction is 2-fold higher than in the spontaneous reaction. Nevertheless, DHFR folding was found to proceed by the same trajectories inside the cis folding chamber and free in solution. These observations are consistent with the description of the chaperonin chamber as an "Anfinsen cage" where polypeptide folding is determined solely by the amino acid sequence, as it is in solution. However, if misfolding occurs in the confinement of the chaperonin cavity, the polypeptide chain cannot undergo aggregation but rather finds its way back to a productive pathway in a manner that cannot be accomplished in solution, resulting in the observed high overall recovery.

Suicide rate in schizophrenia in the Northern Finland 1966 Birth Cohort.

BACKGROUND: Suicide rate among schizophrenia patients may vary for several reasons, one of the most important being the time point of the suicide during the illness process. However, prospective studies on suicide risk in population-based cohort of individuals with new-onset schizophrenia have been lacking. METHOD: The data were collected for 10,934 individuals alive in Finland at the age of 16 from the genetically homogenous, population-based Northern Finland 1966 Birth Cohort ascertained already during mid-pregnancy. The Finnish Hospital Discharge Register was used until the end of 1997 (age 31) to identify cases with mental disorder. Case records were scrutinized and diagnoses were re-checked for DSM-III-R criteria. One hundred subjects met the DSM-III-R criteria for schizophrenia. Deaths by the end of year 2005 (age 39) were ascertained from death certificates. RESULTS: Suicides (n = 7) accounted for 50% of all the deaths at age from 16 to 39. Seven (7.0%) subjects with schizophrenia had committed suicide; suicide rate being 2.9% (1/35) for women and 9.2% (6/65) for men. Furthermore, 71% of suicides in schizophrenia occurred during the first 3 years after onset of illness. CONCLUSION: The suicide rate for patients with new-onset schizophrenia followed until the age of 39 was high and accounted for half of the deaths. Great majority of the suicides took place during the first years of the illness.

Functional co-primary measures for clinical trials in schizophrenia: results from the MATRICS Psychometric and Standardization Study.

OBJECTIVE: During the consensus meetings of the National Institute of Mental Health Measurement and Treatment Research to Improve Cognition in Schizophrenia (NIMH-MATRICS) Initiative, the U.S. Food and Drug Administration took the position that a drug for this purpose should show changes on 1) an accepted consensus cognitive performance measure and 2) an additional measure (i.e., a co-primary) that is considered functionally meaningful. The goal of the current study was to describe steps to evaluate four potential co-primary measures for psychometric properties and validity. METHOD: As part of the five-site MATRICS Psychometric and Standardization Study (PASS), two measures of functional capacity and two interview-based measures of cognition were evaluated in 176 patients with schizophrenia (167 of these patients were retested 4 weeks later). RESULTS: Data are presented for each co-primary measure for test-retest reliability, utility as a repeated measure, relationship to cognitive performance, relationship to functioning, tolerability/practicality, and number of missing data. CONCLUSIONS: Psychometric properties of all of the measures were considered acceptable, and the measures were generally comparable across the various criteria, except that the functional capacity measures had stronger relationships to cognitive performance and fewer missing data. The development and evaluation of potential co-primary measures is still at an early stage, and it was decided not to endorse a single measure for clinical trials at this point. The current findings offer the initial steps to identify functionally meaningful co-primary measures in this area and will help to guide further evaluation of such measures.

The MATRICS Consensus Cognitive Battery, part 2: co-norming and standardization.

OBJECTIVE: The consensus cognitive battery developed by the National Institute of Mental Health's (NIMH's) Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative includes 10 independently developed tests that are recommended as the standard battery for clinical trials of cognition-enhancing interventions for schizophrenia. To facilitate interpretation of results from the MATRICS Consensus Cognitive Battery using a common scaling across tests, normative data were obtained from a single representative U.S. community sample with the battery administered as a unit. METHOD: The MATRICS Consensus Cognitive Battery was administered to 300 individuals from the general community at five sites in differing geographic regions. For each site, recruitment was stratified by age, gender, and education. A scientific survey sampling method was used to help avoid sampling bias. The battery was administered in a standard order to each participant in a single session lasting approximately 60 minutes. Descriptive data were generated, and age, gender, and education effects on performance were examined. RESULTS: Prominent age and education effects were observed across tests. The results for gender differed by measure, suggesting the need for age and gender corrections in clinical trials. The MATRICS Consensus Cognitive Battery components were co-normed, with allowance for demographic corrections. CONCLUSIONS: Co-norming a battery such as the MATRICS Consensus Cognitive Battery, comprising tests from independent test developers each with their own set of norms, facilitates valid interpretation of test scores and communication of findings across studies. These normative data will aid in estimating the magnitude of change during clinical trials of cognition-enhancing agents and make it possible to derive more directly interpretable composite scores.

The MATRICS Consensus Cognitive Battery, part 1: test selection, reliability, and validity.

OBJECTIVE: The lack of an accepted standard for measuring cognitive change in schizophrenia has been a major obstacle to regulatory approval of cognition-enhancing treatments. A primary mandate of the National Institute of Mental Health's Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative was to develop a consensus cognitive battery for clinical trials of cognition-enhancing treatments for schizophrenia through a broadly based scientific evaluation of measures. METHOD: The MATRICS Neurocognition Committee evaluated more than 90 tests in seven cognitive domains to identify the 36 most promising measures. A separate expert panel evaluated the degree to which each test met specific selection criteria. Twenty tests were selected as a beta battery. The beta battery was administered to 176 individuals with schizophrenia and readministered to 167 of them 4 weeks later so that the 20 tests could be compared directly. RESULTS: The expert panel ratings are presented for the initially selected 36 tests. For the beta battery tests, data on test-retest reliability, practice effects, relationships to functional status, practicality, and tolerability are presented. Based on these data, 10 tests were selected to represent seven cognitive domains in the MATRICS Consensus Cognitive Battery. CONCLUSIONS: The structured consensus method was a feasible and fair mechanism for choosing candidate tests, and direct comparison of beta battery tests in a common sample allowed selection of a final consensus battery. The MATRICS Consensus Cognitive Battery is expected to be the standard tool for assessing cognitive change in clinical trials of cognition-enhancing drugs for schizophrenia. It may also aid evaluation of cognitive remediation strategies.

How should DSM-V criteria for schizophrenia include cognitive impairment?

Neurocognitive impairment is considered a core component of schizophrenia and is increasingly under investigation as a potential treatment target. On average, cognitive impairment is severe to moderately severe compared with healthy controls, and almost all patients with schizophrenia demonstrate cognitive decrements compared with their expected level if they had not developed the illness. Compared with patients with affective disorders, cognitive impairment in schizophrenia appears earlier, is more severe, and tends to be more independent of clinical symptoms. While the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, description of schizophrenia includes several references to cognitive impairment, neither the diagnostic criteria nor the subtypology of schizophrenia include a requirement of cognitive impairment. We forward for consideration a proposal that the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, criteria include a specific criterion of "a level of cognitive functioning suggesting a consistent severe impairment and/or a significant decline from premorbid levels considering the patient's educational, familial, and socioeconomic background." The inclusion of this criterion may increase the "point of rarity" with affective psychoses and may increase clinicians' awareness of cognitive impairment, potentially leading to more accurate prognosis and better treatment outcomes. Future research will need to address the validity of these possibilities. The reliable determination of cognitive impairment as part of a standard diagnostic evaluation may present challenges to diagnosticians with limited resources or insufficient expertise. Various cognitive assessment methods for clinicians, including brief assessments and interview-based assessments, are discussed. Given the current emphasis on the development of cognitive treatments, the evaluation of cognition in schizophrenia is an essential component of mental health education.

Assessment of community functioning in people with schizophrenia and other severe mental illnesses: a white paper based on an NIMH-sponsored workshop.

People with schizophrenia frequently have significant problems in community functioning. Progress in developing effective interventions to ameliorate these problems has been slowed by the absence of reliable and valid measures that are suitable for use in clinical trials. The National Institute of Mental Health convened a workgroup in September 2005 to examine this issue and make recommendations to the field that would foster research in this area. This article reports on issues raised at the meeting. Many instruments have been developed to assess community functioning, but overall insufficient attention has been paid to psychometric issues and many instruments are not suitable for use in clinical trials. Consumer self-report, informant report, ratings by clinicians and trained raters, and behavioral assessment all can provide useful and valid information in some circumstances and may be practical for use in clinical trials. However, insufficient attention has been paid to when and how different forms of assessment and sources of information are useful or how to understand inconsistencies. A major limiting factor in development of reliable and valid instruments is failure to develop a suitable model of functioning and its primary mediators and moderators. Several examples that can guide thinking are presented. Finally, the field is limited by the absence of an objective gold standard of community functioning. Hence, outcomes must be evaluated in part by "clinical significance." This criterion is problematic because different observers and constituencies often have different opinions about what types of change are clinically important and how much change is significant.

Mood disorders: cardiovascular and diabetes comorbidity.

PURPOSE OF REVIEW: Depression is often associated with medical comorbidity. New research quantifies patterns of mood disorder in illnesses such as cardiovascular disease and diabetes, evaluates the prognostic significance of mood symptoms, and seeks to identify common mechanisms for both mood and medical disease. This review provides recent findings on comorbidity, summarizes mechanistic hypotheses, and outlines developments in treatment and services. RECENT FINDINGS: Depression occurs in up to one-quarter of patients with cardiovascular disease and diabetes. Depressed patients with heart disease have poorer medical outcomes including increased risk of reinfarction and all-cause mortality. Patients with diabetes and depression have poorer glycemic control, more diabetes symptoms, and greater all-cause mortality. Depression is associated with both biological (hypothalamic-pituitary-adrenal axis dysregulation) and psychosocial processes (adherence, poorer diet, and exercise) that may mediate adverse medical outcomes. Antidepressant treatments are effective in treating depression in medically ill patients, but their impact on medical outcomes remains to be quantified. SUMMARY: Depression, cardiovascular disease, and diabetes are among the most common chronic illnesses affecting an aging population. Depression is treatable in patients with medical illnesses, and collaborative care models can yield better detection and depression treatment in primary care settings in which most patients with depression are seen.

No evidence for a forced-unfolding mechanism during ATP/GroES binding to substrate-bound GroEL: no observable protection of metastable Rubisco intermediate or GroEL-bound Rubisco from tritium exchange.

In tritium-hydrogen exchange experiments, the large GroEL substrate Rubisco was unfolded and exchanged in urea/acid/tritiated water, then diluted into either protic buffer or protic buffer containing GroEL. The respective Rubisco metastable folding intermediate or Rubisco-GroEL binary complex was then separated from residual tritium after varying times of exchange by centrifugation through P-10 or G-25 resin. No significant tritium was recovered in either case, in contrast to an earlier report. Thus, although the earlier-proposed forced unfolding mechanism for the action of GroEL on a bound polypeptide, occurring during ATP/GroES binding, remains an attractive hypothesis, the data here do not provide any indication that it is involved in the folding of Rubisco.

Recovery from schizophrenic psychoses within the northern Finland 1966 Birth Cohort.

BACKGROUND: Because of widely disparate findings from follow-up studies, the likelihood of recovery from schizophrenia remains controversial. We report the extent of recovery from schizophrenia in a population-based cohort. METHOD: Subjects with psychotic disorders were recruited from the Northern Finland 1966 Birth Cohort. Of the 91 subjects who agreed to participate, 59 were diagnosed with schizophrenia and 12 were diagnosed with schizophrenia spectrum disorders (schizophreniform psychosis, schizoaffective or delusional disorder) by DSM-III-R criteria. Diagnoses were established by interviewing the subjects, checking the Finnish Hospital Discharge Register, and reviewing their medical records. To assess recovery, we used the Clinical Global Impressions; the Positive and Negative Syndrome Scale; the Social and Occupational Functioning Assessment Scale; and information about psychiatric hospitalizations, use of antipsychotic medication, and occupational status. RESULTS: Only 1 subject (1.7%) with DSM-III-R schizophrenia and 3 subjects (25%) with schizophrenia spectrum disorders fully recovered; 1 schizophrenia subject (1.7%) and 2 schizophrenia spectrum subjects (16.7%) experienced partial recovery. CONCLUSION: The data indicate that, at least until age 35, complete recovery from schizophrenia is rare, and the prognosis for the disorder is far more serious than suggested by some follow-up studies.

A summary of the FDA-NIMH-MATRICS workshop on clinical trial design for neurocognitive drugs for schizophrenia.

OBJECTIVE: On April 23, 2004, a joint meeting of the FDA, NIMH, MATRICS investigators, and experts from academia and the pharmaceutical industry was convened to develop guidelines for the design of clinical trials of cognitive-enhancing drugs for neurocognitive impairments in patients with schizophrenia. METHOD: Experts were asked to address specific questions relating to clinical trial design of adjunctive/co-treatment and broad spectrum agents. At the workshop, experts reviewed relevant evidence before offering the discussion panel proposed guidelines for a given subset of questions. The discussion panel, which consisted of presenters and representatives from FDA, NIMH, academia, and industry, deliberated to reach consensus on suggested guidelines. When evidence was insufficient, suggested guidelines represent the opinion of a cross-section of the presenters and discussion panel. RESULTS: Guidelines were developed for inclusion criteria, the use of co-primary outcome measures, and statistical approaches for study design. Consensus was achieved regarding diagnostic and concomitant medication inclusion criteria and on the use of cognitive screening measures. A key guideline was to limit the trial to patients in the residual phase of their illness, who have a predefined level of positive, negative, and affective symptoms. The most difficult issues were the feasibility of including a co-primary measure of functional improvement and the choice of comparator agent for a trial of a broad spectrum agent (with antipsychotic and cognitive-enhancing effects). CONCLUSIONS: The suggested guidelines represent reasonable starting points for trial design of cognitive-enhancing drugs, with the understanding that new data, subsequent findings, or other methodological considerations may lead to future modifications.