Protein folding and misfolding inside and outside the cell

The workshop was held at St Catherine's College, Oxford, from March 25-28, 1998, and attracted participants from 32 nations. Protein folding is one of the most important processes in biology since it adds functional flesh to the bare bones of genes, but it has traditionally been studied by people separated both intellectually and physically because they are training in different disciplines. The aim of the meeting was to bring together chemists and structural biologists studying how pure, denatured proteins refold spontaneously in the test tube, with biochemists and cell biologists who are concerned with how proteins fold inside living cells and medical scientists interested in the diseases that result when this process goes wrong. In this report we concentrate on general concepts and themes rather than on detailing every contribution.

Long-term outcomes of therapeutic pelvic lymphadenectomy for stage I endometrial adenocarcinoma

OBJECTIVE

The treatment of patients with stage I endometrial adenocarcinoma is often shorter and less expensive if total abdominal hysterectomy (TAH), bilateral salpingo-oophorectomy (BSO), and therapeutic lymphadenectomy are used rather than TAH, BSO, pelvic lymph node sampling, and pelvic external beam radiation. We studied whether the survival and morbidity of patients treated with therapeutic lymphadenectomy are equal to or better than with these alternative treatments.

METHODS

We reviewed the medical records of patients with stage I endometrial adenocarcinoma who were enrolled in the MetroHealth Medical Center tumor registry between 1970 and 1993 after undergoing full pelvic lymph node dissection, in addition to total abdominal hysterectomy, bilateral salpingo-oophorectomy, and vaginal brachytherapy. The mean number of resected nodes was 33 (median, 31; interquartile range, 19). Patients were followed for 1. 6-20 years (median, 8 years; interquartile range, 5.8 years). Morbidity and survival rates were compared to published series using similar treatment strategies and to those from studies using pelvic external beam radiation and pelvic lymph node sampling rather than lymphadenectomy.

RESULTS

Of 192 patients with pathologic stage I (FIGO 1988) endometrial adenocarcinoma, 178 patients had full pelvic lymph node dissection; 159 patients were evaluable. The 15-year overall survival was 98%; 10- and 15- year disease-free survivals were 96 and 94%, respectively. Overall morbidity was 18% (29/159), and moderate-to-severe morbidity was 13% (21/159). Recurrences were seen in 4.4% (7/159) of patients. Grade and myometrial invasion were not significant predictors of disease-free survival after full pelvic lymph node dissection (grade, P = 0.42; stage, P = 0.67). The results compare favorably with those of similar studies and with studies of pelvic external beam radiation.

CONCLUSIONS

Primary surgical management with total abdominal hysterectomy, bilateral salpingo-oophorectomy, therapeutic pelvic lymphadenectomy, and vaginal brachytherapy is a viable and possibly preferable option for patients with stage I endometrial adenocarcinoma.

Diagnostic validity of the dementia questionnaire for Alzheimer disease

OBJECTIVE

To determine the sensitivity and specificity of postmortem dementia diagnoses based on a retrospective informant interview by comparison with criterion standard neuropathological diagnoses and the results of previous clinical examinations.

SETTING

Three university-based academic research centers.

SUBJECTS

Fifty-four deceased elderly persons with Alzheimer disease, another dementing disorder, a neurologic disease resulting in functional impairment but no dementia, or no neurologic disorder.

METHODS

Blinded nonclinician interviewers administered the Dementia Questionnaire (DQ) by telephone to informants, typically close relatives, who were familiar with the intellectual and functional status of the subjects before death. Two senior clinicians (LJ.T. and C.K.) rated each DQ for the presence or absence of a dementia syndrome during life and for the specific disorders causing the dementia, if present. Raters were blinded to the neuropathological findings and based their assessments only on data provided by responses to the DQ. Comparison was made with diagnoses based on neuropathological assessment. In most cases, the results of antemortem clinical examinations were also available as a check on the clinical diagnosis of the dementia syndrome. Sensitivity and specificity of the DQ diagnoses were computed, and chance-corrected agreement measures were calculated for the 2 independent DQ raters (LJ.T. and C.K.).

RESULTS

Compared with antemortem clinical diagnosis, the average sensitivity of the DQ for the clinical syndrome of dementia was 92.8%, the specificity was 89.5%, and the interrater agreement was 98% (kappa = 0.96). Among 7 subjects with mild dementia (Mini-Mental State Examination score > or = 24 at the last clinical examination), 5 (71%) were correctly identified using the DQ. The DQ correctly indicated the absence of dementia in 8 (80%) of 10 subjects with other neurologic disorders causing functional impairment. Compared with the neuropathological diagnoses, the DQ differentiated Alzheimer disease from other primary causes of dementia with a sensitivity of 89% and a specificity of 72%. The interrater agreement was 93.8% (kappa = 0.85).

CONCLUSIONS

Compared with the results of the antemortem clinical examinations, the DQ was sensitive to the presence of dementia, detected most cases of mild dementia, and discriminated dementia from other neurologic disorders causing functional impairment. Compared with the neuropathological diagnoses, the ability of the DQ to differentiate Alzheimer disease from other dementing disorders indicates that it may be useful as a research tool.

Pulmonary embolus masquerading as pneumonia in a patient with Hodgkin's disease and nephrotic syndrome

Fatal pulmonary embolus is an infrequent cause of death in patients with Hodgkin's disease who respond to initial therapy. This patient had associated minimal change disease and nephrotic syndrome that was responding to therapy, but had this complication. The diagnosis was delayed by the presentation that suggested pneumonia. A high index of suspicion for thrombotic complications and an aggressive diagnostic pursuit thereof are merited in these patients.

Progressive cerebral volume loss in human immunodeficiency virus infection: a longitudinal volumetric magnetic resonance imaging study. HIV Neurobehavioral Research Center Group

OBJECTIVE

To compare rates and anatomical patterns of brain atrophy during 3 stages of human immunodeficiency virus (HIV) disease.

DESIGN

Comparisons of multiple serial brain magnetic resonance images in men without HIV infection and HIV-infected men in Centers for Disease Control and Prevention (CDC, Atlanta, Ga) stages A, B, and C.

SETTING

Longitudinal cohort study of the San Diego HIV Neurobehavioral Research Center, San Diego, Calif.

PARTICIPANTS

Eighty-six HIV-1-positive (HIV-positive) and 23 HIV-negative men who were similar in age and risk group. The number of HIV-positive men in each CDC stage was as follows: A, 33; B, 19; C, 34. All HIV-positive men were free of clinically detectable opportunistic neurologic illness.

MAIN OUTCOME MEASURES

Regional volumes of serial magnetic resonance images converted to standardized slope estimates of change in regional volumes of interest.

RESULTS

Medically asymptomatic men (CDC stage A) and medically symptomatic men (CDC stage C) had more rapid loss of cortical tissues than did HIV-negative men as manifested by higher slopes (Tukey honestly significant difference test, P=.02 and P=.001, respectively) for cortical fluid volume. Accelerated ventricular volume enlargement occurred only in men with CDC stage C disease. Reduction in the volume of white matter was accelerated in participants with CDC stage C disease compared with participants with CDC stage A disease. Of the gray matter regions, only the caudate nucleus sustained accelerated volume loss during CDC stage C disease. Participants whose systemic disease progressed to a higher CDC stage had significantly accelerated ventricular volume increases and caudate atrophy. Rates of cortical and subcortical fluid volume increases and reductions in the volumes of white matter and the caudate nucleus were significantly related to the rate of decline in the CD4+ lymphocyte count.

CONCLUSIONS

In the absence of cerebral opportunistic disease, HIV infection causes progressive atrophy within the gray and white matter in the brain. These changes were most severe in the most advanced stage of disease but were evident even in medically asymptomatic HIV-positive persons. Within the gray matter, the caudate nucleus exhibited progressive volume loss linked to disease stage and the rate of decline of the CD4+ cell count. Structural brain changes can begin in the early stages of HIV infection and accelerate during advanced illness.

Dendritic injury is a pathological substrate for human immunodeficiency virus-related cognitive disorders. HNRC Group. The HIV Neurobehavioral Research Center

To determine the neuropathological substrate of human immunodeficiency virus (HIV)-associated neurocognitive disorders, we examined persons with acquired immunodeficiency syndrome before their death and related their antemortem neuropsychological performance to postmortem indicators of HIV encephalitis, viral burden, and presynaptic and postsynaptic neuronal injury. Of 20 prospectively examined cases, 9 were neurocognitively normal, 5 showed neuropsychological impairment, 5 had minor cognitive/motor disorder, and 1 was demented. Degree of neurocognitive impairment was strongly related to the amount of dendritic simplification based on microtubule-associated protein 2 immunohistochemical staining, somewhat less so to a semiquantitative viral burden score based on numbers of HIV gp41-immunoreactive cells, and much less so to the presence of multinucleated giant cells or microglial nodules. It appears that even milder neurocognitive impairment reflects microneuroanatomical injury to synaptic structures.

Cerebrospinal fluid human immunodeficiency virus type 1 RNA levels are elevated in neurocognitively impaired individuals with acquired immunodeficiency syndrome. HIV Neurobehavioral Research Center Group

To determine whether cerebrospinal fluid (CSF) viral burden measurements can assist in the evaluation of human immunodeficiency virus (HIV)-associated neurocognitive disorders, we quantified HIV type 1 (HIV-1) RNA in CSF. Because previous findings suggested that disease stage, lymphocytic pleocytosis, and HIV-1 RNA levels in plasma may influence CSF viral burden, these variables were examined as potential modifying factors. HIV-1 RNA levels were quantified by using a reverse transcriptase-polymerase chain reaction assay. Performance on a comprehensive neuropsychological (NP) battery was noted in 97 prospectively enrolled, HIV-infected subjects. Among subjects with acquired immunodeficiency syndrome (AIDS) (<200 CD4+ lymphocytes), NP impairment was associated with significantly higher CSF RNA levels (3.1 vs 1.8 log10 copies/ml; p = 0.02); most impaired subjects met criteria for HIV-associated dementia or minor cognitive-motor disorder. In subjects without AIDS, CSF RNA and NP impairment were unrelated. Before AIDS, CSF RNA was strongly correlated to plasma RNA and to pleocytosis, but in AIDS, CSF and plasma RNA were independent. In conclusion, we found elevated CSF HIV-1 RNA levels in NP impaired subjects with AIDS. Before AIDS, systemic viral replication, possibly through CD4+ mononuclear cell trafficking, may govern virus levels in CSF, whereas in AIDS, CD4 cell depletion may unmask a correlation between increased productive central nervous system HIV infection and clinical neurocognitive disorders.

Molecular chaperones: avoiding the crowd

The involvement of two types of molecular chaperone in folding newly synthesized proteins can be rationalized in terms of the crowded nature of the intracellular environment. Recent work sheds light on how these chaperones recognise their substrates and protect them from the problems of macromolecular crowding.

Neurocognitive impairment is an independent risk factor for death in HIV infection. San Diego HIV Neurobehavioral Research Center Group

OBJECTIVE

To determine if mortality is increased in individuals with human immunodeficiency virus type 1 (HIV-1)-associated neurocognitive disorders less severe than frank dementia.

DESIGN

A prospective cohort study; median duration of follow-up was 2.4 years. Kaplan-Meier analysis and Cox proportional hazards models were used to compare survival times according to neurocognitive classification.

SETTING

University-based research unit.

PARTICIPANTS

A volunteer sample of 414 individuals seropositive for HIV-1. Subjects were classified at their baseline evaluation as neuropsychologically (NP) normal or abnormal (impaired in > or = 2 NP test domains). A subgroup of NP abnormal subjects met operational criteria for HIV-associated minor cognitive motor disorder; the remaining subjects were designated NP impaired. Subjects with frank dementia were excluded.

MAIN OUTCOME MEASURE

Mortality.

RESULTS

At the baseline evaluation, 256 (62%) of 414 subjects were designated normal; 109 (26%). NP impaired; and 49 (12%), minor cognitive motor disorder. One hundred six participants (26%) died during follow-up. Compared with the NP normal group, the unadjusted relative risk (RR) of death for all NP abnormal subjects (minor cognitive motor disorder and NP impaired) was significantly increased (RR, 1.7; 95% confidence interval [CI], 1.2-2.6; P < .005). After adjusting for concurrently measured predictors of survival (CD4 lymphocyte counts, Centers for Disease Control and Prevention HIV disease classification, hemoglobin concentration, and serum beta 2-microglobulin) in proportional hazards models, mortality for all NP abnormal subjects remained elevated (RR, 1.8; 95% CI, 1.2-2.8; P < .01). The elevation in mortality risk for subjects with minor cognitive motor disorder was statistically significant (RR, 2.2; 95% CI, 1.2-3.8; P < .01); for NP impaired subjects it was marginally significant (RR, 1.6; 95% CI, 1.0-2.8; P = .06).

CONCLUSIONS

The HIV-infected individuals with NP impairment had a higher risk of dying than those without impairment. This was particularly true for those meeting syndromic diagnostic criteria.

Discovery of molecular chaperones

No Abstract Available

Cerebral amyloid angiopathy in the brains of patients with Alzheimer's disease: the CERAD experience, Part XV

We studied the frequency, severity, and clinical correlations of cerebral amyloid angiopathy (CAA) in 117 CERAD subjects with autopsy-confirmed AD. Eighty-three percent showed at least a mild degree of amyloid angiopathy. Thirty of 117 brains (25.6%) showed moderate to severe CAA affecting the cerebral vessels in one or more cortical regions. These brains also showed a significantly higher frequency of hemorrhages or ischemic lesions than those of subjects with little or no amyloid angiopathy (43.3% versus 23.0%; odds ratio = 2.6, 95% CI = 1.1 to 6.2) High CAA scores also correlated with the presence of cerebral arteriosclerosis and with older age at onset of dementia. Our findings suggest that factors contributing to non-AD-related vascular pathology (e.g., atherosclerosis) may play a role in amyloid deposition in cerebral vessels in AD.

Extrapyramidal motor signs in clinically diagnosed Alzheimer disease

We reviewed clinical case series published over a 10-year period addressing the cross-sectional frequency, incidence, and diagnostic and prognostic significance of extrapyramidal signs (EPS) in Alzheimer disease (AD). The review was prompted by recent reports of Lewy body (LB) pathology in the brains of many AD patients and the association of LB pathology with clinical parkinsonism in AD. In the clinical case series reviewed, we evaluated several possible determinants of prevalent EPS, including neuroleptic use, EPS assessment technique, and dementia severity. Neuroleptics were a well recognized cause of parkinsonism in these reports, though some failed to document the frequency of neuroleptic use. Assessment methods were also important: Studies using structured clinical research scales to rate EPS reported higher frequencies than studies employing routine neurological examination. The relationship between parkinsonism and dementia severity was complex. Some studies found bradykinesia, facial masking, and parkinsonian postural changes even in mildly demented, neuroleptic-naive AD patients. Rigidity, on the other hand, became increasingly common as dementia progressed. AD patients with EPS showed faster cognitive and functional decline and earlier death than those without EPS, even after consideration of differences in initial dementia severity. In the differential diagnosis of dementia with parkinsonism, LB disease in its various forms, including AD with LB, is the principal diagnostic consideration. Future studies of parkinsonism in AD should employ standardized clinical rating scales and should exclude patients on neuroleptics or analyze their results separately. Investigators should report frequencies for individual parkinsonian signs in addition to the overall prevalence of EPS to facilitate meaningful comparisons across studies.

Protein folding in the cell: competing models of chaperonin function

The long-standing view that polypeptide chains newly synthesized inside cells fold spontaneously to their functional conformations in an energy-independent fashion derives from the observation that many pure denatured proteins will refold spontaneously in vitro when the denaturant is removed. This view is being challenged by the alternative proposal that in vivo many chains need to be helped to fold correctly by preexisting proteins acting as molecular chaperones, some of which hydrolyse ATP. The need for molecular chaperones arises because of the high concentrations of transiently interacting protein surfaces inside cells permit the formation of incorrect nonfunctional structures. The best-studied family of molecular chaperones are called the chaperonins, the archetypal examples being the GroEL and GroES proteins of Escherichia coli. The chaperonins increase the yield of correctly refolded polypeptide chains, both by decreasing their propensity to aggregate with one another and by allowing polypeptides kinetically trapped in incorrect conformations to make fresh attempts to refold into the functional conformations. The mechanisms by which the chaperonins achieve these remarkable results are currently under debate. This review surveys competing models for chaperonin action, and emphasizes the importance when evaluating these models of considering the intracellular environment in which the chaperonins have evolved to function.

Revisiting the Anfinsen cage

In the past five years, ideas about protein folding inside cells have changed as a results of experiments with the chaperonin family of molecular chaperones. The folding of at least some proteins is no longer regarded as a spontaneous energy-independent process, but as involving transient interactions with chaperonin ATPases that serve to increase the efficiency of correct folding within the highly crowded intracellular environment. This review discusses in an historical context one model for how the chaperonins function. This model suggests that proteins fold inside cells in the same way as they do in pure dilute solution, but that they do so inside macromolecular Anfinsen cages that serve as sequestration devices to prevent and reverse unproductive interactions.

Site directed chromosomal marking of a fluorescent pseudomonad isolated from the phytosphere of sugar beet; stability and potential for marker gene transfer

A plasmid-free, non-pathogenic, ribosomal RNA group 1 fluorescent pseudomonad, Pseudomonas fluorescens SBW25, was selected from the microflora of sugar beet (Beta vulgaris) and modified to contain constitutively expressed marker genes. By site directed homologous recombination a KX cassette [kanamycin resistance (kanr) and catechol 2,3 dioxygenase (xylE)] and a ZY cassette [lactose utilization (lacZY, beta-galactosidase, lactose permease)] were introduced at least 1 Mbp apart on the 6.6 Mbp bacterial chromosome. Separate sites were selected to provide sensitive detection methods and allow assessments of marker gene stability of the genetically modified micro-organism (GMM), SBW25EeZY6KX, when it colonized the leaves and roots of sugar beet plants following seed inoculation.

The HNRC 500--neuropsychology of HIV infection at different disease stages. HIV Neurobehavioral Research Center

The present study examined neuropsychological (NP) functioning and associated medical, neurological, brain magnetic resonance imaging (MRI), and psychiatric findings in 389 nondemented males infected with Human Immunodeficiency Virus-Type 1 (HIV-1), and in 111 uninfected controls. Using a comprehensive NP test battery, we found increased rates of impairment at each successive stage of HIV infection. HIV-related NP impairment was generally mild, especially in the medically asymptomatic stage of infection, and most often affected attention, speed of information processing, and learning efficiency; this pattern is consistent with earliest involvement of subcortical or frontostriatal brain systems. NP impairment could not be explained on the bases of mood disturbance, recreational drug or alcohol use, or constitutional symptoms; by contrast, impairment in HIV-infected subjects was related to central brain atrophy on MRI, as well as to evidence of cellular immune activation and neurological abnormalities linked to the central nervous system.

Molecular chaperones. Opening and closing the Anfinsen cage

Dynamic interactions between chaperonins allow newly synthesized polypeptides to begin correct folding inside a transiently closed cage. Specialized chaperonins may be used to deal with recalcitrant proteins.