Relationship Between Serum IGF-1 and BMI Differs by Age

Genetic variants of LEAP2 are associated with anthropometric traits and circulating insulin-like growth factor-1 concentration: A UK Biobank study

AIM

To test the hypothesis that liver-expressed antimicrobial peptide 2 (LEAP2) genetic variants might influence the susceptibility to human obesity.

METHODS

Using data from the UK Biobank, we identified independent LEAP2 gene single nucleotide polymorphisms (SNPs) and examined their associations with obesity traits and serum insulin-like growth factor-1 (IGF-1) concentration. These associations were evaluated for both individual SNPs and after combining them into a genetic risk score (GRSLEAP2) using linear and logistic regression models. Sex-stratified analyses were also conducted.

RESULTS

Five SNPs showed positive associations with obesity-related traits. rs57880964 was associated with body mass index (BMI) and waist-to-hip ratio adjusted for BMI (WHRadjBMI), in the total population and among women. Four independent SNPs were positively associated with higher serum IGF-1 concentrations in both men and women. GRSLEAP2 was associated with BMI and WHRadjBMI only in women and with serum IGF-1 concentration in both sexes.

CONCLUSIONS

These findings reveal sex-specific associations between key LEAP2 gene variants and several obesity traits, while also indicating a strong independent association of LEAP2 variants with serum IGF-1 concentration.

Exploring Vitamin D Deficiency and IGF Axis Dynamics in Colorectal Adenomas

(1) Colorectal cancer is a major cause of cancer-related death, with colorectal adenomas (CRAs) serving as precursors. Identifying risk factors such as vitamin D deficiency and the insulin-like growth factor (IGF) axis is crucial for prevention. (2) This case-control study included 85 participants (53 CRA patients and 32 controls) who underwent colonoscopy. We measured serum vitamin D3 (cholecalciferol), calcidiol (vitamin D metabolite), calcitriol (active vitamin D metabolite), insulin-like growth factor-1 (IGF-1), and insulin-like growth factor binding protein-3 (IGFBP-3) to explore their associations with CRA risk. (3) Results: We found that lower cholecalciferol levels were a significant risk factor for CRA (OR = 4.63, p = 0.004). Although no significant differences in calcidiol and calcitriol levels were observed between CRA patients and controls, calcidiol deficiency was common in the study population. IGF-1 levels inversely correlated with age, calcitriol, and IGFBP-3 in CRA patients. (4) This study highlights the potential of lower cholecalciferol levels to detect patients at risk of CRA when calcidiol values cannot, suggesting the importance of evaluating different vitamin D metabolites in cancer prevention research. Our findings underscore the need to further investigate the interactions between calcitriol, the active form of vitamin D, and the IGF axis in colorectal cancer development.

Likely causal effects of insulin resistance and IGF-1 bioaction on childhood and adult adiposity: a Mendelian randomization study

BACKGROUND

Circulating insulin and insulin-like growth factor-1 (IGF-1) concentrations are positively correlated with adiposity. However, the causal effects of insulin and IGF-1 on adiposity are unclear.

METHODS

We performed two-sample Mendelian randomization analyses to estimate the likely causal effects of fasting insulin and IGF-1 on relative childhood adiposity and adult body mass index (BMI). To improve accuracy and biological interpretation, we applied Steiger filtering (to avoid reverse causality) and 'biological effect' filtering of fasting insulin and IGF-1 associated variants.

RESULTS

Fasting insulin-increasing alleles (35 variants also associated with higher fasting glucose, indicative of insulin resistance) were associated with lower relative childhood adiposity (P = 3.8 × 10-3) and lower adult BMI (P = 1.4 × 10-5). IGF-1-increasing alleles also associated with taller childhood height (351 variants indicative of greater IGF-1 bioaction) showed no association with relative childhood adiposity (P = 0.077) or adult BMI (P = 0.562). Conversely, IGF-1-increasing alleles also associated with shorter childhood height (306 variants indicative of IGF-1 resistance) were associated with lower relative childhood adiposity (P = 6.7 × 10-3), but effects on adult BMI were inconclusive.

CONCLUSIONS

Genetic causal modelling indicates negative effects of insulin resistance on childhood and adult adiposity, and negative effects of IGF-1 resistance on childhood adiposity. Our findings demonstrate the need to distinguish between bioaction and resistance when modelling variants associated with biomarker concentrations.

Challenges of insulin-like growth factor-1 testing

Insulin-like growth factor 1 (IGF-1), primarily synthesized in the liver, was initially discovered due to its capacity to replicate the metabolic effects of insulin. Subsequently, it emerged as a key regulator of the actions of growth hormone (GH), managing critical processes like cell proliferation, differentiation, and apoptosis. Notably, IGF-1 displays a longer half-life compared to GH, making it less susceptible to factors that may affect GH concentrations. Consequently, the measurement of IGF-1 proves to be more specific and sensitive when diagnosing conditions such as acromegaly or GH deficiency. The recognition of the existence of IGFBPs and their potential to interfere with IGF-1 immunoassays urged the implementation of various techniques to moderate this issue and provide accurate IGF-1 results. Additionally, in response to the limitations associated with IGF-1 immunoassays and the occurrence of discordant IGF-1 results, modern mass spectrometric methods were developed to facilitate the quantification of IGF-1 levels. Taking advantage of their ability to minimize the interference caused by IGF-1 variants, mass spectrometric methods offer the capacity to deliver robust, reliable, and accurate IGF-1 results, relying on the precision of mass measurements. This also enables the potential detection of pathogenic mutations through protein sequence analysis. However, despite the analytical challenges, the discordance in IGF-1 reference intervals can be attributed to a multitude of factors, potentially leading to distinct interpretations of results. The establishment of reference intervals for each assay is a demanding task, and it requires nationwide multicenter collaboration among laboratorians, clinicians, and assay manufacturers to achieve this common goal in a cost-effective and resource-efficient manner. In this comprehensive review, we examine the challenges associated with the standardization of IGF-1 measurement methods, the minimization of pre-analytical factors, and the harmonization of reference intervals. Particular emphasis will be placed on the development of IGF-1 measurement techniques using "top-down" or "bottom-up" mass spectrometric methods.

Identification of potential mediators of the relationship between body mass index and colorectal cancer: a Mendelian randomization analysis

BACKGROUND

Colorectal cancer (CRC) is the third-most-common cancer worldwide and its rates are increasing. Elevated body mass index (BMI) is an established risk factor for CRC, although the molecular mechanisms behind this association remain unclear. Using the Mendelian randomization (MR) framework, we aimed to investigate the mediating effects of putative biomarkers and other CRC risk factors in the association between BMI and CRC.

METHODS

We selected as mediators biomarkers of established cancer-related mechanisms and other CRC risk factors for which a plausible association with obesity exists, such as inflammatory biomarkers, glucose homeostasis traits, lipids, adipokines, insulin-like growth factor 1 (IGF1), sex hormones, 25-hydroxy-vitamin D, smoking, physical activity (PA) and alcohol consumption. We used inverse-variance weighted MR in the main univariable analyses and performed sensitivity analyses (weighted-median, MR-Egger, Contamination Mixture). We used multivariable MR for the mediation analyses.

RESULTS

Genetically predicted BMI was positively associated with CRC risk [odds ratio per SD (5 kg/m2) = 1.17, 95% CI: 1.08-1.24, P-value = 1.4 × 10-5] and robustly associated with nearly all potential mediators. Genetically predicted IGF1, fasting insulin, low-density lipoprotein cholesterol, smoking, PA and alcohol were associated with CRC risk. Evidence for attenuation was found for IGF1 [explained 7% (95% CI: 2-13%) of the association], smoking (31%, 4-57%) and PA (7%, 2-11%). There was little evidence for pleiotropy, although smoking was bidirectionally associated with BMI and instruments were weak for PA.

CONCLUSIONS

The effect of BMI on CRC risk is possibly partly mediated through plasma IGF1, whereas the attenuation of the BMI-CRC association by smoking and PA may reflect confounding and shared underlying mechanisms rather than mediation.

Endothelial deficiency of insulin-like growth factor-1 receptor leads to blood-brain barrier disruption and accelerated endothelial senescence in mice, mimicking aspects of the brain aging phenotype

INTRODUCTION

Age-related blood-brain barrier (BBB) disruption, cerebromicrovascular senescence, and microvascular rarefaction substantially contribute to the pathogenesis of vascular cognitive impairment (VCI) and Alzheimer's disease (AD). Previous studies established a causal link between age-related decline in circulating levels of insulin-like growth factor-1 (IGF-1), cerebromicrovascular dysfunction, and cognitive decline. The aim of our study was to determine the effect of IGF-1 signaling on senescence, BBB permeability, and vascular density in middle-age and old brains.

METHODS

Accelerated endothelial senescence was assessed in senescence reporter mice (VE-Cadherin-CreERT2 /Igf1rfl/fl × p16-3MR) using flow cytometry. To determine the functional consequences of impaired IGF-1 input to cerebromicrovascular endothelial cells, BBB integrity and capillary density were studied in mice with endothelium-specific knockout of IGF1R (VE-Cadherin-CreERT2 /Igf1rfl/fl ) using intravital two-photon microscopy.

RESULTS

In VE-Cadherin-CreERT2 /Igf1rfl/fl mice: (1) there was an increased presence of senescent endothelial cells; (2) cumulative permeability of the microvessels to fluorescent tracers of different molecular weights (0.3-40 kDa) is significantly increased, as compared to that of control mice, whereas decline in cortical capillary density does not reach statistical significance.

CONCLUSIONS

These findings support the notion that IGF-1 signaling plays a crucial role in preserving a youthful cerebromicrovascular endothelial phenotype and maintaining the integrity of the BBB.

General or Central Obesity and Mortality Among US Hispanic and Latino Adults

Importance

The Hispanic and Latino population is the second largest ethnic group in the US, but associations of obesity parameters with mortality in this population remain unclear.

Objective

To investigate the associations of general and central obesity with mortality among US Hispanic and Latino adults.

Design, Setting, and Participants

The Hispanic Community Health Study/Study of Latinos is an ongoing, multicenter, population-based cohort study with a multistage probability sampling method performed in Hispanic and Latino adults aged 18 to 74 years with a baseline between January 1, 2008, and December 31, 2011. Active follow-up for this analyses extended from baseline through February 17, 2022. All analyses accounted for complex survey design (ie, stratification and clustering) and sampling weights to generate estimates representing the noninstitutionalized, 18- to 74-year-old Hispanic or Latino populations from selected communities.

Exposures

Body mass index (BMI; calculated as weight in kilograms divided by height in meters squared), body fat percentage, waist circumference (WC), and waist to hip ratio (WHR).

Main Outcome and Measure

Deaths were ascertained via death certificates, the National Death Index, and active follow-up.

Results

Of 15 773 adults (mean [SE] age, 40.9 [0.3] years; 52.8% female), 686 deaths occurred during a median (IQR) follow-up of 10.0 (9.9-10.2) years. When adjusting for sociodemographic, lifestyle, and family history covariates, hazard ratios (HRs) for mortality were 1.55 (95% CI, 1.08-2.22) for a BMI of 35.0 or greater vs 18.5 to 24.9, 1.22 (95% CI, 0.92-1.64) for the highest vs lowest body fat percentage groups (defined according to sex-, age-, and Hispanic or Latino background-specific BMI distribution), 1.35 (95% CI, 0.98-1.85) for WC greater than 102 cm (men) or 88 cm (women) vs 94 cm (men) or 80 cm (women) or less, and 1.91 (95% CI, 1.28-2.86) for WHR of 0.90 (men) or 0.85 (women) or greater vs less than 0.90 (men) or 0.85 (women). Only WHR was associated with mortality with additional adjustment for major comorbidities (HR, 1.75; 95% CI, 1.17-2.62). The association of WHR with mortality was stronger among women compared with men (P = .03 for interaction), and the association between BMI and mortality was stronger among men (P = .02 for interaction). The positive association between severe obesity (BMI ≥ 35.0) and mortality was observed only among adults with WHR of 0.90 (men) or 0.85 (women) or greater but not among those with WHR below 0.90 (men) or 0.85 (women) (P = .005 for interaction) who had greater hip circumference.

Conclusions and Relevance

In this cohort of US Hispanic and Latino adults, WHR was independently associated with higher all-cause mortality regardless of BMI and prevalent comorbidities. These findings suggest that prioritizing clinical screening and intervention for WHR in this population may be an important public health strategy, with sex-specific strategies potentially being needed.

Abdominal obesity and hydration status as protective factors against mortality in older adults: A prospective study

OBJECTIVES

The aim of this study was to assess the association between different anthropometric and body composition techniques for defining obesity status and to investigate their clinical implications in older hospitalized patients, both during their hospitalization and after discharge.

METHODS

This prospective study included patients ≥60 y of age. They were followed for 18 mo to assess mortality and hospital length of stay. Anthropometric measurements and body composition were evaluated, including body mass index (BMI), waist circumference, waist-to-height ratio, body fat percentage, total body water percentage, and muscle mass. These measurements are associated with prognosis and survival.

RESULTS

A higher BMI, excessive body fat, higher total body water percentage, and abdominal obesity were associated with a lower risk for death (P < 0.05). Higher hydration levels were identified as an independent protective factor against mortality. Obesity, defined by body fat percentage, was associated with a shorter hospital stay (P < 0.05).

CONCLUSION

The present study adds to the growing body of evidence supporting the existence of the obesity paradox in hospitalized older patients. Additionally, our novel finding reveals that higher levels of total body water percentage are associated with decreased odds of mortality. The study emphasizes the importance of considering other anthropometric measurements and body composition in addition to BMI, considering its limitations. These findings have important implications for health care providers when recommending changes in nutritional status for the older adult population.

Circulating IGF-1 and IGFBP-2 may be biomarkers for risk stratification in patients with acute coronary syndrome: A prospective cohort study

BACKGROUND AND AIM

The involvement of insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-2 (IGFBP-2) following acute coronary syndrome (ACS) is rarely studied in clinical practice. Therefore, we sought to evaluate the relationship between IGF-1 and IGFBP-2 concentrations at admission and risk stratification based on the Thrombolysis in Myocardial Infarction (TIMI) risk score in patients with ACS.

METHODS AND RESULTS

In all, 304 patients diagnosed with ACS were included in this study. Plasma IGF-1 and IGFBP-2 were measured using commercially available ELISA kits. The TIMI risk score was calculated and the study population was stratified into high (n = 65), medium (n = 138), and low (n = 101) risk groups. Levels of IGF-1 and IGFBP-2 were analyzed for their predictive ability of risk stratification based on the TIMI risk scores. Correlation analysis showed that IGF-1 levels were negatively correlated with TIMI risk levels (r = -0.144, p = 0.012), while IGFBP-2 levels were significantly and positively correlated with TIMI risk levels (r = 0.309, p < 0.001). In multivariate logistic regression analysis, IGF-1 (odds ratio [OR]: 0.995; 95% confidence interval [CI]: 0.990-1.000; p = 0.043) and IGFBP-2 (OR: 1.002; 95%CI: 1.001-1.003; p < 0.001) were independent predictors of high TIMI risk levels. In receiver operating characteristic curves, the area under the curve values for IGF-1 and IGFBP-2 in the prediction of high TIMI risk levels were 0.605 and 0.723, respectively.

CONCLUSIONS

IGF-1 and IGFBP-2 levels are excellent biomarkers for risk stratification in patients with ACS, which provides further guidance for clinicians to identify patients at high risk and to lower their risk.

Adipose Tissue Hyperplasia and Hypertrophy in Common and Syndromic Obesity-The Case of BBS Obesity

Obesity is a metabolic state generated by the expansion of adipose tissue. Adipose tissue expansion depends on the interplay between hyperplasia and hypertrophy, and is mainly regulated by a complex interaction between genetics and excess energy intake. However, the genetic regulation of adipose tissue expansion is yet to be fully understood. Obesity can be divided into common multifactorial/polygenic obesity and monogenic obesity, non-syndromic and syndromic. Several genes related to obesity were found through studies of monogenic non-syndromic obesity models. However, syndromic obesity, characterized by additional features other than obesity, suggesting a more global role of the mutant genes related to the syndrome and, thus, an additional peripheral influence on the development of obesity, were hardly studied to date in this regard. This review summarizes present knowledge regarding the hyperplasia and hypertrophy of adipocytes in common obesity. Additionally, we highlight the scarce research on syndromic obesity as a model for studying adipocyte hyperplasia and hypertrophy, focusing on Bardet-Biedl syndrome (BBS). BBS obesity involves central and peripheral mechanisms, with molecular and mechanistic alternation in adipocyte hyperplasia and hypertrophy. Thus, we argue that using syndromic obesity models, such as BBS, can further advance our knowledge regarding peripheral adipocyte regulation in obesity.

Association between metabolic syndrome, insulin resistance, and IGF-1 in breast cancer survivors of DIANA-5 study

PURPOSE

Circulating insulin-like growth factor-1 (IGF-1) is positively associated with the risk of BC recurrence, and is more frequently dysregulated in older people, especially in those with metabolic syndrome (MetS) and obesity. This study aimed to analyze the association between IGF-1 levels and indices of MetS and insulin resistance in BC survivors.

METHODS

Baseline data of 563 BC survivors enrolled in the DIet and ANdrogen-5 (DIANA-5; NCT05019989) study were analyzed.

RESULTS

Lower circulating IGF-1 levels in subjects with MetS than in those without MetS were found. After stratification of the patients according to the diagnosis of MetS, we highlighted that the insulin was the main predictor of elevated IGF-1 levels only in subjects without MetS. Moreover, we found an interaction between high-density lipoprotein cholesterol (HDL-C), glycemia, and IGF-1 levels, showing a positive correlation between HDL-C and IGF-1, especially in subjects with higher values of glycemia and without a diagnosis of MetS.

CONCLUSIONS

While IGF-1 levels appear to be much more impaired in subjects diagnosed with MetS, in non-MetS subjects, IGF-1 levels may respond better to metabolic parameters and lifestyle changes. Further studies are needed to analyze the role of physical activity and/or dietary intervention in modulating IGF-1 concentrations in BC survivors.

IMPLICATIONS FOR CANCER SURVIVORS

These results could have important clinical implications for planning customized strategies aimed at modulating IGF-1 levels in BC survivors. In fact, while the IGF-1 system seems to be much more compromised in subjects with a diagnosis of MetS, in noMetS subjects, IGF-1 levels could better respond to lifestyle changes.

Nutrition Strategies Promoting Healthy Aging: From Improvement of Cardiovascular and Brain Health to Prevention of Age-Associated Diseases

BACKGROUND

An increasing number of studies suggest that diet plays an important role in regulating aging processes and modulates the development of the most important age-related diseases.

OBJECTIVE

The aim of this review is to provide an overview of the relationship between nutrition and critical age-associated diseases.

METHODS

A literature review was conducted to survey recent pre-clinical and clinical findings related to the role of nutritional factors in modulation of fundamental cellular and molecular mechanisms of aging and their role in prevention of the genesis of the diseases of aging.

RESULTS

Studies show that the development of cardiovascular and cerebrovascular diseases, neurodegenerative diseases, cognitive impairment and dementia can be slowed down or prevented by certain diets with anti-aging action. The protective effects of diets, at least in part, may be mediated by their beneficial macro- (protein, fat, carbohydrate) and micronutrient (vitamins, minerals) composition.

CONCLUSIONS

Certain diets, such as the Mediterranean diet, may play a significant role in healthy aging by preventing the onset of certain diseases and by improving the aging process itself. This latter can be strengthened by incorporating fasting elements into the diet. As dietary recommendations change with age, this should be taken into consideration as well, when developing a diet tailored to the needs of elderly individuals. Future and ongoing clinical studies on complex anti-aging dietary interventions translating the results of preclinical investigations are expected to lead to novel nutritional guidelines for older adults in the near future.

Age-related decline in circulating IGF-1 associates with impaired neurovascular coupling responses in older adults

Impairment of moment-to-moment adjustment of cerebral blood flow (CBF) to the increased oxygen and energy requirements of active brain regions via neurovascular coupling (NVC) contributes to the genesis of age-related cognitive impairment. Aging is associated with marked deficiency in the vasoprotective hormone insulin-like growth factor-1 (IGF-1). Preclinical studies on animal models of aging suggest that circulating IGF-1 deficiency is causally linked to impairment of NVC responses. The present study was designed to test the hypotheses that decreases in circulating IGF-1 levels in older adults also predict the magnitude of age-related decline of NVC responses. In a single-center cross-sectional study, we enrolled healthy young (n = 31, 11 female, 20 male, mean age: 28.4 + / - 4.2 years) and aged volunteers (n = 32, 18 female, 14 male, mean age: 67.9 + / - 4.1 years). Serum IGF-1 level, basal CBF (phase contrast magnetic resonance imaging (MRI)), and NVC responses during the trail making task (with transcranial Doppler sonography) were assessed. We found that circulating IGF-1 levels were significantly decreased with age and associated with decreased basal CBF. Age-related decline in IGF-1 levels predicted the magnitude of age-related decline in NVC responses. In conclusion, our study provides additional evidence in support of the concept that age-related circulating IGF-1 deficiency contributes to neurovascular aging, impairing CBF and functional hyperemia in older adults.

Insulin-like growth factor-1 levels are associated with high comorbidity of metabolic disorders in obese subjects; a Japanese single-center, retrospective-study

Insulin like growth factor-1 (IGF-1) plays important roles in metabolic functions, especially in adulthood. Additionally, obese subjects are reportedly predisposed to having low absolute IGF-1 levels. However, the prevalence and clinical characteristics of obese subjects with low IGF-1 levels are unknown. We examined 64 obese subjects with a body mass index (BMI) ≥ 35 kg/m², with no history of endocrinological disorders, receiving inpatient care. IGF-1 levels were interpreted based on the IGF-1 standard deviation score (SDS) clinically used and standardized by age and sex (low IGF-1 group; ≤ - 2.0 SDS and standard IGF-1 group; - 2.0 < and <  + 2.0 SDS). Notably, 26.6% of the subjects had low IGF-1. Body fat mass and percentage, but not BMI, were significantly higher in the low than in the standard IGF-1 group. Furthermore, natural log-transformed high-sensitivity C-reactive protein, and the frequencies of dyslipidemia and hyperuricemia were higher in the low IGF-1 group. Moreover, among the subjects without diabetes, fasting glucose levels were significantly higher in the low IGF-1 group. Stepwise variable selection procedure revealed body fat percentage to be a parameter most strongly associated with low IGF-1. Thus, low IGF-1 levels may be an important marker of adiposity-associated metabolic disorders in obese patients.

Effects of high-dose all-trans retinoic acid on longitudinal bone growth of young rats

OBJECTIVE

The signaling axis consisting of GH-IGF1-IGFBP3 is the primary signal taht acts prepubertally to influence height development. Growth plate thinning and even premature closure have been reported in children with tumors treated with retinoid chemotherapy, resulting in long bone dysplasia. Growth failure may occur despite received GH treatment, but the reason is unknown. This study investigate the effect of high-dose all-trans retinoic acid (ATRA) on the development of long bones in growing SD rats.

METHODS

A total of 20 three-week-old male SD rats were randomly divided into a control group and an experimental group (n = 10). Rats were treated by gavage with or without high-dose ATRA for 10 days. The body weights of the rats were recorded daily. At the end of the experiment, we measured the length of nose-tail and tibia, stained the tibia and liver for pathological tissue and RT-PCR reaction, and measured the levels of serum GH, IGF1 and IGFBP3, and so on.

RESULTS

Compared with controls, experimental rats exhibited reduced body weight and shortened nasal-tail and radial tibial length. Cyp26b1 enzyme activity in the liver was elevated, and histopathological staining revealed that the cartilaginous epiphyseal plate was narrowed, the medullary cavity of trabecular bone was sparse, the number of trabecular bones was decreased, trabecular separation was increased, bone marrow mineralization was enhanced, osteoclastic activity was increased, and circulating GH-IGF1-IGFBP3 levels were decreased. However, RT-PCR reaction results of localized proximal tibiae showed upregulation of IGF1 and downregulation of IGFBP3.

CONCLUSIONS

High-dose ATRA intake over a short period of time can reduce GH-IGF1-IGFBP3 levels, affect cartilage and bone homeostasis, and inhibit bone growth in developing animals.

The antagonistic pleiotropy of insulin-like growth factor 1

While insulin-like growth factor-1 (IGF-1) is a well-established modulator of aging and longevity in model organisms, its role in humans has been controversial. In this study, we used the UK Biobank (n = 440,185) to resolve previous ambiguities in the relationship between serum IGF-1 levels and clinical disease. We examined prospective associations of serum IGF-1 with mortality, dementia, vascular disease, diabetes, osteoporosis, and cancer, finding two generalized patterns: First, IGF-1 interacts with age to modify risk in a manner consistent with antagonistic pleiotropy; younger individuals with high IGF-1 are protected from disease, while older individuals with high IGF-1 are at increased risk for incident disease or death. Second, the association between IGF-1 and risk is generally U-shaped, indicating that both high and low levels of IGF-1 may be detrimental. With the exception of a more uniformly positive relationship between IGF-1 and cancer, these effects were remarkably consistent across a wide range of conditions, providing evidence for a unifying pathway that determines risk for most age-associated diseases. These data suggest that IGF-1 signaling could be harmful in older adults, who may actually benefit from the attenuation of biological growth pathways.

Endothelial deficiency of insulin-like growth factor-1 receptor (IGF1R) impairs neurovascular coupling responses in mice, mimicking aspects of the brain aging phenotype

Age-related impairment of neurovascular coupling (NVC; or "functional hyperemia") compromises moment-to-moment adjustment of regional cerebral blood flow to increased neuronal activity and thereby contributes to the pathogenesis of vascular cognitive impairment (VCI). Previous studies established a causal link among age-related decline in circulating levels of insulin-like growth factor-1 (IGF-1), neurovascular dysfunction and cognitive impairment. Endothelium-mediated microvascular dilation plays a central role in NVC responses. To determine the functional consequences of impaired IGF-1 input to cerebromicrovascular endothelial cells, endothelium-mediated NVC responses were studied in a novel mouse model of accelerated neurovascular aging: mice with endothelium-specific knockout of IGF1R (VE-Cadherin-Cre^ERT2/Igf1r^f/f). Increases in cerebral blood flow in the somatosensory whisker barrel cortex (assessed using laser speckle contrast imaging through a cranial window) in response to contralateral whisker stimulation were significantly attenuated in VE-Cadherin-Cre^ERT2/Igf1r^f/f mice as compared to control mice. In VE-Cadherin-Cre^ERT2/Igf1r^f/f mice, the effects of the NO synthase inhibitor L-NAME were significantly decreased, suggesting that endothelium-specific disruption of IGF1R signaling impairs the endothelial NO-dependent component of NVC responses. Collectively, these findings provide additional evidence that IGF-1 is critical for cerebromicrovascular endothelial health and maintenance of normal NVC responses.