A NPAS4-NuA4 complex couples synaptic activity to DNA repair.

Neuronal activity is crucial for adaptive circuit remodelling but poses an inherent risk to the stability of the genome across the long lifespan of postmitotic neurons1-5. Whether neurons have acquired specialized genome protection mechanisms that enable them to withstand decades of potentially damaging stimuli during periods of heightened activity is unknown. Here we identify an activity-dependent DNA repair mechanism in which a new form of the NuA4-TIP60 chromatin modifier assembles in activated neurons around the inducible, neuronal-specific transcription factor NPAS4. We purify this complex from the brain and demonstrate its functions in eliciting activity-dependent changes to neuronal transcriptomes and circuitry. By characterizing the landscape of activity-induced DNA double-strand breaks in the brain, we show that NPAS4-NuA4 binds to recurrently damaged regulatory elements and recruits additional DNA repair machinery to stimulate their repair. Gene regulatory elements bound by NPAS4-NuA4 are partially protected against age-dependent accumulation of somatic mutations. Impaired NPAS4-NuA4 signalling leads to a cascade of cellular defects, including dysregulated activity-dependent transcriptional responses, loss of control over neuronal inhibition and genome instability, which all culminate to reduce organismal lifespan. In addition, mutations in several components of the NuA4 complex are reported to lead to neurodevelopmental and autism spectrum disorders. Together, these findings identify a neuronal-specific complex that couples neuronal activity directly to genome preservation, the disruption of which may contribute to developmental disorders, neurodegeneration and ageing.

Circadian hepatocyte clocks keep synchrony in the absence of a master pacemaker in the suprachiasmatic nucleus or other extrahepatic clocks.

It has been assumed that the suprachiasmatic nucleus (SCN) synchronizes peripheral circadian oscillators. However, this has never been convincingly shown, since biochemical time series experiments are not feasible in behaviorally arrhythmic animals. By using long-term bioluminescence recording in freely moving mice, we show that the SCN is indeed required for maintaining synchrony between organs. Surprisingly, however, circadian oscillations persist in the livers of mice devoid of an SCN or oscillators in cells other than hepatocytes. Hence, similar to SCN neurons, hepatocytes can maintain phase coherence in the absence of Zeitgeber signals produced by other organs or environmental cycles.

Macromolecular Assemblies of the Mammalian Circadian Clock.

The mammalian circadian clock is built on a feedback loop in which PER and CRY proteins repress their own transcription. We found that in mouse liver nuclei all three PERs, both CRYs, and Casein Kinase-1δ (CK1δ) are present together in an ∼1.9-MDa repressor assembly that quantitatively incorporates its CLOCK-BMAL1 transcription factor target. Prior to incorporation, CLOCK-BMAL1 exists in an ∼750-kDa complex. Single-particle electron microscopy (EM) revealed nuclear PER complexes purified from mouse liver to be quasi-spherical ∼40-nm structures. In the cytoplasm, PERs, CRYs, and CK1δ were distributed into several complexes of ∼0.9-1.1 MDa that appear to constitute an assembly pathway regulated by GAPVD1, a cytoplasmic trafficking factor. Single-particle EM of two purified cytoplasmic PER complexes revealed ∼20-nm and ∼25-nm structures, respectively, characterized by flexibly tethered globular domains. Our results define the macromolecular assemblies comprising the circadian feedback loop and provide an initial structural view of endogenous eukaryotic clock machinery.

Specificity in circadian clock feedback from targeted reconstitution of the NuRD corepressor.

Mammalian circadian rhythms are generated by a negative feedback loop in which PERIOD (PER) proteins accumulate, form a large nuclear complex (PER complex), and bind the transcription factor CLOCK-BMAL1, repressing their own expression. We found that mouse PER complexes include the Mi-2/nucleosome remodelling and deacetylase (NuRD) transcriptional corepressor. Unexpectedly, two NuRD subunits, CHD4 and MTA2, constitutively associate with CLOCK-BMAL1, with CHD4 functioning to promote CLOCK-BMAL1 transcriptional activity. At the onset of negative feedback, the PER complex delivers the remaining complementary NuRD subunits to DNA-bound CLOCK-BMAL1, thereby reconstituting a NuRD corepressor that is important for circadian transcriptional feedback and clock function. The PER complex thus acquires full repressor activity only upon successful targeting of CLOCK-BMAL1. Our results show how specificity is generated in the clock despite its dependence on generic transcriptional regulators and reveal the existence of active communication between the positive and negative limbs of the circadian feedback loop.

Individually experienced heat stress among elderly residents of an urban slum and rural village in India.

The elderly are one of the most vulnerable groups to heat-related illnesses and mortality. In tropical countries like India, where heat waves have increased in frequency and severity, few studies have focused on the level of stress experienced by the elderly. The study presented here included 130 elderly residents of Kolkata slums and 180 elderly residents of rural villages about 75 km south of Kolkata. It used miniature monitoring devices to continuously measure temperature, humidity, and heat index experienced during everyday activities over 24-h study periods, during hot summer months. In the Kolkata slum, construction materials and the urban heat island effect combined to create hotter indoor than outdoor conditions throughout the day, and particularly at night. As a result, elderly slum residents were 4.3 times more likely to experience dangerous heat index levels (≥ 45°C) compared to rural village elderly. In both locations, the median 24-h heat indexes of active elderly were up to 2°C higher than inactive/sedentary elderly (F = 25.479, p < 0.001). Among Kolkata slums residents, there were no significant gender differences in heat exposure during the day or night, but in the rural village, elderly women were 4 times more likely to experience dangerous heat index levels during the hottest times of the day compared to elderly men. Given the decline in thermoregulatory capacity associated with aging and the increasing severity of extreme summer heat in India, these results forecast a growing public health challenge that will require both scientific and government attention.

Using multiple correspondence analysis to identify behaviour patterns associated with overweight and obesity in Vanuatu adults.

OBJECTIVE: The present study evaluates the use of multiple correspondence analysis (MCA), a type of exploratory factor analysis designed to reduce the dimensionality of large categorical data sets, in identifying behaviours associated with measures of overweight/obesity in Vanuatu, a rapidly modernizing Pacific Island country. DESIGN: Starting with seventy-three true/false questions regarding a variety of behaviours, MCA identified twelve most significantly associated with modernization status and transformed the aggregate binary responses of participants to these twelve questions into a linear scale. Using this scale, individuals were separated into three modernization groups (tertiles) among which measures of body fat were compared and OR for overweight/obesity were computed. SETTING: Vanuatu.ParticipantsNi-Vanuatu adults (n 810) aged 20-85 years. RESULTS: Among individuals in the tertile characterized by positive responses to most of or all the twelve modernization questions, weight and measures of body fat and the likelihood that measures of body fat were above the US 75th percentile were significantly greater compared with individuals in the tertiles characterized by mostly or partly negative responses. CONCLUSIONS: The study indicates that MCA can be used to identify individuals or groups at risk for overweight/obesity, based on answers to simply-put questions. MCA therefore may be useful in areas where obtaining detailed information about modernization status is constrained by time, money or manpower.

Coming to grips with economic development: Variation in adult hand grip strength during health transition in Vanuatu.

OBJECTIVES: To determine whether (1) maximal handgrip strength (HGS) is associated with inter-island level of economic development in Vanuatu, (2) how associations between island of residence and HGS are mediated by age, sex, body size/composition, and individual sociodeomographic variation, and (3) whether HGS is predictive of hypertension. MATERIAL AND METHODS: HGS was collected from 833 adult (aged 18 and older) men and women on five islands representing a continuum of economic development in Vanuatu. HGS was measured using a handheld dynamometer. Participants were administered in an extensive sociobehavioral questionnaire and were also assessed for height, weight, percent body fat, forearm skinfold thickness, forearm circumference, and blood pressure. RESULTS: HGS was significantly greater in men than in women regardless of island of residence. HGS was also significantly positively associated with inter-island level of economic development. Grip strength-to-weight ratio was not different across islands except in older individuals, where age-related decline occurred primarily on islands with greater economic development. HGS significantly declined with age in both men and women. CONCLUSION: HGS is positively associated with modernization in Vanuatu, but the relationship between HGS and modernization is largely due to an association of both variables with increased body size on more modernized islands. Further research on the role of individual variation in diet and physical activity are necessary to clarify the relationship between HGS and modernization.

Ownership of consumer electronics is associated with measures of adiposity during health transition in Vanuatu.

OBJECTIVE: The Republic of Vanuatu, like many developing nations, is undergoing a rapid health transition. Our previous study identified several behavioral risk factors for the rising prevalence of obesity. Unexpectedly, daily time spent using television and radio was revealed as a protective factor for obesity in 2007. In this study, we sought to explore associations between ownership of consumer electronics (CE) and measures of adiposity in Vanuatu in 2011. METHODS: We surveyed 873 adults from five islands varying in level of economic development. Height, weight, and waist circumferences; triceps, subscapular, and suprailiac skinfolds; and percent body fat by bioelectrical impedance were measured. Ownership of eight types of CE, diet through 24-h dietary recall and leisure-time activity patterns were assessed using a questionnaire. RESULTS: Participants from more developed islands owned more types of CE, and revealed higher measures of adiposity on average as well as higher prevalence of obesity/central obesity. When controlling for demographic factors, and dietary and activity patterns, increased measures of adiposity and risk for obesity/central obesity were associated with ownership of cellphones, music players, televisions, video players, microwaves, and/or refrigerators. Positive correlations between CE ownership and measures of adiposity were mainly observed among men on the two most developed islands. CONCLUSIONS: The results of this study indicate a possible role of CE use in the rising prevalence of obesity and the shift to a sedentary lifestyle in Vanuatu and many other modernizing regions, where prevention efforts including education on healthy use of CE are imperative.

Secular change in adult stature associated with modernization in Vanuatu.

OBJECTIVE: To determine whether: (1) there is a secular increase in adult stature in Vanuatu, and (2) whether adult stature is positively associated with modernization in Vanuatu. METHODS: This study reports on stature measurements collected on 650 adult (age > 17 years) men and women from four islands of varying economic development in Vanuatu. Measurements were collected as part of the Vanuatu Health Transitions Research Project in 2007 and 2011. RESULTS: Stature increased significantly in adults born between the 1940s and 1960s in Vanuatu, before leveling off in those born between the 1970s and 1990s. Adults are significantly taller on Efate, the most modernized island in the study sample, than on the less economically developed islands. CONCLUSIONS: Modernization is likely associated with improvements in child growth in Vanuatu, as assessed by gains in adult stature.

Larger FVC and FEV1 among Tibetans compared to Han born and raised at high altitude.

OBJECTIVES: This study compares forced vital capacity (FVC) and Forced Expiratory Volume at 1 Second (FEV1 ) of Tibetans with those of Han who were born and raised at high altitude. MATERIALS AND METHODS: FVC and FEV1 tests were conducted among 1,063 children and adolescents between the ages of 6 and 20 years, and 184 adults between the ages of 21 and 39 years who had lived their entire lives at 3200 m, 3800 m and 4300 m in Qinghai Provence, Peoples Republic of China. RESULTS: Even though FVC and FEV1 values of Han born and raised at high altitude are generally lower than those of Tibetans through age 15 in girls and age 16 in boys, differences are largely explained by variation in stature (height-squared) and chest circumference. Among older adolescents and adults, the FVC and FEV1 values of Tibetans are significantly larger than those of Han born and raised at high altitude; and are much larger than would be predicted, based on stature and chest circumference. DISCUSSION: These results indicate that the large FVC and FEV1 values of Tibetan adults develop primarily from an accelerated pattern of lung growth that begins during mid-to-late adolescence and possibly extends into young adulthood. This developmental pattern is not only distinct from that of Han born and raised at high altitude, but also from those of Andean Quechua and Aymara. The pace of lung function growth may therefore represent another feature distinguishing the Tibetan from the Andean pattern of adaptation to high altitude hypoxia. Because of this, a search for features in the Tibetan genome related to this lung function growth phenotype might be productive and important.

A positive feedback loop links circadian clock factor CLOCK-BMAL1 to the basic transcriptional machinery.

Circadian clocks in mammals are built on a negative feedback loop in which the heterodimeric transcription factor circadian locomotor output cycles kaput (CLOCK)-brain, muscle Arnt-like 1 (BMAL1) drives the expression of its own inhibitors, the PERIOD and CRYPTOCHROME proteins. Reactivation of CLOCK-BMAL1 occurs at a specific time several hours after PERIOD and CRYPTOCHROME protein turnover, but the mechanism underlying this process is unknown. We found that mouse BMAL1 complexes include TRAP150 (thyroid hormone receptor-associated protein-150; also known as THRAP3). TRAP150 is a selective coactivator for CLOCK-BMAL1, which oscillates under CLOCK-BMAL1 transcriptional control. TRAP150 promotes CLOCK-BMAL1 binding to target genes and links CLOCK-BMAL1 to the transcriptional machinery at target-gene promoters. Depletion of TRAP150 caused low-amplitude, long-period rhythms, identifying it as a positive clock element. The activity of TRAP150 defines a positive feedback loop within the clock and provides a potential mechanism for timing the reactivation of circadian transcription.

Impact of modernization on adult body composition on five islands of varying economic development in Vanuatu.

OBJECTIVE: The Republic of Vanuatu, similar to other South Pacific island nations, is undergoing a rapid health transition as a consequence of modernization. The pace of modernization is uneven across Vanuatu's 63 inhabited islands, resulting in differential impacts on overall body composition and prevalence of obesity among islands, and between men and women. In this study, we investigated (1) how modernization impacts body composition between adult male and female Melanesians living on four islands of varying economic development in Vanuatu, and (2) how body composition differs between adult Melanesians and Polynesians living on rural islands in Vanuatu. METHODS: Anthropometric measurements were taken on adult male and female Melanesians aged 18 years and older (n = 839) on the islands of Ambae (rural), Aneityum (rural with tourism), Nguna (rural with urban access), and Efate (urban) in Vanuatu, in addition to Polynesian adults on Futuna (rural). RESULTS: Mean measurements of body mass and fatness, and prevalence of obesity, were greatest on the most modernized islands in our sample, particularly among women. Additionally, differences between men and women became more pronounced on islands that were more modernized. Rural Polynesians on Futuna exhibited greater body mass, adiposity, and prevalence of obesity than rural Melanesians on Ambae. CONCLUSIONS: We conclude that Vanuatu is undergoing an uneven and rapid health transition resulting in increased prevalence of obesity, and that women are at greatest risk for developing obesity-related chronic diseases in urbanized areas in Vanuatu.

CIPC is a mammalian circadian clock protein without invertebrate homologues.

At the core of the mammalian circadian clock is a feedback loop in which the heterodimeric transcription factor CLOCK-Brain, Muscle Arnt-like-1 (BMAL1) drives expression of its negative regulators, periods (PERs) and cryptochromes (CRYs). Here, we provide evidence that CLOCK-Interacting Protein, Circadian (CIPC) is an additional negative-feedback regulator of the circadian clock. CIPC exhibits circadian regulation in multiple tissues, and it is a potent and specific inhibitor of CLOCK-BMAL1 activity that functions independently of CRYs. CIPC-CLOCK protein complexes are present in vivo, and depletion of endogenous CIPC shortens the circadian period length. CIPC is unrelated to known proteins and has no recognizable homologues outside vertebrates. Our results suggest that negative feedback in the mammalian circadian clock is divided into distinct pathways, and that the addition of new genes has contributed to the complexity of vertebrate clocks.

Adult lipids associated with early life growth in traditional Melanesian societies undergoing rapid modernization: a longitudinal study of the mid-20th century.

Both poor fetal development and accelerated post-natal growth have been linked to adult dyslipidemias in many studies conducted in developed societies. It is not known, however, whether these relationships only characterize populations with typical Western diets or if they also may develop in groups at the early stages of a dietary transition. Our longitudinal study of traditional rural populations in the Southwest Pacific during a period of extremely rapid modernization in diet and life-styles shows a nascent association between child growth retardation, subsequent growth acceleration, and adult lipid values in spite of a continuing prevalence of very low lipid levels. However, our results do not entirely conform to results from populations with "modern" diets. Outcome (i.e., young adult) cholesterol and triglyceride levels are more consistently related to initial measures of body fat and growth in body fat measures than with stature, while outcome apo A-1 is more consistently related to initial stature or stature growth than to measures of body fat. We suggest this may reflect a pattern characteristic of the initial stages of "modernization" associated with dietary change, with stronger and more pervasive relationships emerging only later as populations complete the dietary transition.

Coping with extreme heat: current exposure and implications for the future.

A preview of how effective behavioral, biological and technological responses might be in the future, when outdoor conditions will be at least 2°C hotter than current levels, is available today from studies of individuals already living in extreme heat. In areas where high temperatures are common-particularly those in the hot and humid tropics-several studies report that indoor temperatures in low-income housing can be significantly hotter than those outdoors. A case study indicates that daily indoor heat indexes in almost all the 123 slum dwellings monitored in Kolkata during the summer were above 41°C (106°F) for at least an hour. Economic constraints make it unlikely that technological fixes, such as air conditioners, will remedy conditions like these-now or in the future. People without access to air conditioning will have to rely on behavioral adjustments and/or biological/physiological acclimatization. One important unknown is whether individuals who have lived their entire lives in hot environments without air conditioning possess natural levels of acclimatization greater than those indicated by controlled laboratory studies. Answering questions about the future will require more studies of heat conditions experienced by individuals, more information on indoor versus outdoor heat conditions, and a greater understanding of the behavioral and biological adjustments made by people living today in extremely hot conditions.

Responses of Han migrants compared to Tibetans at high altitude.

While many studies have compared Tibetans and low-altitude born Han living at high altitude, few have carefully controlled the chronological age at which lowlanders migrated, the length of time they had lived at high altitude, their nutrition, and their socio-economic status. This has produced an array of results that frequently do not support the hypothesis that Tibetans and Han show fundamental differences in their response to hypoxia. Unlike the situation in the Andes, only one study has tested the developmental adaptation hypothesis on the Qinghai-Tibetan plateau. This study shows that Tibetans and Han of the same age, who were born and raised in the same towns at the same altitudes, show considerable overlap in the individual distribution of [Hb], SaO2 and lung volumes. These results indicate that second-generation Han make substantial developmental adjustments to hypoxia that are not reflected in studies of first-generation migrants. Thus, there is a great need for further developmental studies to determine whether and/or how Han and Tibetan responses to hypoxia diverge, as well as for studies exploring whether Han and Tibetans who show similar responses also share genetic adaptations.

Modernization and the onset of overweight and obesity in Bougainville and Solomon Islands children: cross-sectional and longitudinal comparisons between 1966 and 1986.

This set of cross-sectional and longitudinal data from children and young adults in certain Bougainville and Solomon Islands populations undergoing rapid modernization during the period 1966-1986 reveals very different responses to essentially the same stimuli-the introduction and widespread availability of western dietary items and reductions in habitual activity. Our analyses of over 2,000 children and young adults first measured in 1966-1972, with follow-up surveys in 1968-1970 and 1985-1986, show changes in overweight/obesity in these communities have their onset around puberty, and are not related to differences in childhood growth stunting. The prevalence of overweight and obesity increased substantially during the period of this study among young adults, particularly women, and in groups with more Polynesian affinities, where the frequency of overweight (BMI ≥ 25) tripled over this 20-year interval. However, the BMI of the more Papuan groups on Bougainville remained remarkably stable, even though they were close to the epicenter of modernization during this period, the Bougainville Copper Mine.

Daily rhythms of food-anticipatory behavioral activity do not require the known circadian clock.

When food availability is restricted to a particular time each day, mammals exhibit food-anticipatory activity (FAA), a daily increase in locomotor activity preceding the presentation of food. Considerable historical evidence suggests that FAA is driven by a food-entrainable circadian clock distinct from the master clock of the suprachiasmatic nucleus. Multiple food-entrainable circadian clocks have been discovered in the brain and periphery, raising strong expectations that one or more underlie FAA. We report here that mutant mice lacking known circadian clock function in all tissues exhibit normal FAA both in a light-dark cycle and in constant darkness, regardless of whether the mutation disables the positive or negative limb of the clock feedback mechanism. FAA is thus independent of the known circadian clock. Our results indicate either that FAA is not the output of an oscillator or that it is the output of a circadian oscillator different from known circadian clocks.

Measures of autozygosity in decline: globalization, urbanization, and its implications for medical genetics.

This research investigates the influence of demographic factors on human genetic sub-structure. In our discovery cohort, we show significant demographic trends for decreasing autozygosity associated with population variation in chronological age. Autozygosity, the genomic signature of consanguinity, is identifiable on a genome-wide level as extended tracts of homozygosity. We identified an average of 28.6 tracts of extended homozygosity greater than 1 Mb in length in a representative population of 809 unrelated North Americans of European descent ranging in chronological age from 19-99 years old. These homozygous tracts made up a population average of 42 Mb of the genome corresponding to 1.6% of the entire genome, with each homozygous tract an average of 1.5 Mb in length. Runs of homozygosity are steadily decreasing in size and frequency as time progresses (linear regression, p<0.05). We also calculated inbreeding coefficients and showed a significant trend for population-wide increasing heterozygosity outside of linkage disequilibrium. We successfully replicated these associations in a demographically similar cohort comprised of a subgroup of 477 Baltimore Longitudinal Study of Aging participants. We also constructed statistical models showing predicted declining rates of autozygosity spanning the 20th century. These predictive models suggest a 14.0% decrease in the frequency of these runs of homozygosity and a 24.3% decrease in the percent of the genome in runs of homozygosity, as well as a 30.5% decrease in excess homozygosity based on the linkage pruned inbreeding coefficients. The trend for decreasing autozygosity due to panmixia and larger effective population sizes will likely affect the frequency of rare recessive genetic diseases in the future. Autozygosity has declined, and it seems it will continue doing so.

Heat Exposure, Heat-Related Symptoms and Coping Strategies among Elderly Residents of Urban Slums and Rural Vilages in West Bengal, India.

The impact of heat stress among the elderly in India-particularly the elderly poor-has received little or no attention. Consequently, their susceptibility to heat-related illnesses is virtually unknown, as are the strategies they use to avoid, or deal with, the heat. This study examined perceptions of comfort, heat-related symptoms, and coping behaviors of 130 elderly residents of Kolkata slums and 180 elderly residents of rural villages south of Kolkata during a 90-day period when the average 24-h heat indexes were between 38.6 °C and 41.8 °C. Elderly participants in this study reported being comfortable under relatively warm conditions-probably explained by acclimatization to the high level of experienced heat stress. The prevalence of most heat-related symptoms was significantly greater among elderly women, who also were more likely to report multiple symptoms and more severe symptoms. Elderly women in the rural villages were exposed to significantly hotter conditions during the day than elderly men, making it likely that gender differences in symptom frequency, number and severity were related to gender differences in heat stress. Elderly men and elderly village residents made use of a greater array of heat-coping behaviors and exhibited fewer heat-related symptoms than elderly women and elderly slum residents. Overall, heat measurements and heat-related symptoms were less likely to be significant predictors of most coping strategies than personal characteristics, building structures and location. This suggests that heat-coping behaviors during hot weather were the result of complex, culturally influenced decisions based on many different considerations besides just heat stress.