IGF-I and the aging mammalian brain. Exp Gerontol. 2011;46:96-99. [PMID: 20863877 DOI: 10.1016/j.exger.2010.08.022]

The Aggravating Role of Failing Neuropeptide Networks in the Development of Sporadic Alzheimer's Disease

Alzheimer's disease imposes an increasing burden on aging Western societies. The disorder most frequently appears in its sporadic form, which can be caused by environmental and polygenic factors or monogenic conditions of incomplete penetrance. According to the authors, in the majority of cases, Alzheimer's disease represents an aggravated form of the natural aging of the central nervous system. It can be characterized by the decreased elimination of amyloid β1-42 and the concomitant accumulation of degradation-resistant amyloid plaques. In the present paper, the dysfunction of neuropeptide regulators, which contributes to the pathophysiologic acceleration of senile dementia, is reviewed. However, in the present review, exclusively those neuropeptides or neuropeptide families are scrutinized, and the authors' investigations into their physiologic and pathophysiologic activities have made significant contributions to the literature. Therefore, the pathophysiologic role of orexins, neuromedins, RFamides, corticotrope-releasing hormone family, growth hormone-releasing hormone, gonadotropin-releasing hormone, ghrelin, apelin, and natriuretic peptides are discussed in detail. Finally, the therapeutic potential of neuropeptide antagonists and agonists in the inhibition of disease progression is discussed here.

Gene deletion of Pregnancy-associated Plasma Protein-A (PAPP-A) improves pathology and cognition in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is a progressive neurodegenerative disease of age with no effective preventative or treatment approaches. Deeper understanding of the mechanisms underlying the accumulation of toxic β-amyloid oligopeptides and the formation of amyloid plaque in AD has the potential to identify new therapeutic targets. Prior research links the insulin-like growth factor (IGF) system to pathologic mechanisms underlying AD. Suppression of local IGF-I receptor (IGFIR) signaling in AD mice has been shown to reduce plaque formation in the brain and delay neurodegeneration and behavioral changes. However, direct inhibitors of IGFIR signaling are not a viable treatment option for AD due to the essentiality of the IGFIR in physiological growth and metabolism. We have previously demonstrated a more selective means to reduce local IGFIR signaling through inhibition of PAPP-A, a novel zinc metalloprotease that regulates local IGF-I bioavailability through cleavage of inhibitory IGF binding proteins. Here we tested if deletion of PAPP-A in a mouse model of AD provides protection against pathology and behavioral changes. We show that compared to AD mice, AD/PAPP-A KO mice had significantly less plaque burden, reduced astrocytic activation, decreased IGF-IR activity, and improved cognition. Human senile AD plaques showed specific immunostaining for PAPP-A. Thus, inhibition of PAPP-A expression or activity may represent a novel treatment strategy for AD.

Emerging role of Metformin in Alzheimer's disease: A translational view

Alzheimer's disease (AD) constitutes a major public-health issue of our time. Regrettably, despite our considerable understanding of the pathophysiological aspects of this disease, current interventions lead to poor outcomes. Furthermore, experimentally promising compounds have continuously failed when translated to clinical trials. Along with increased population ageing, Type 2 Diabetes Mellitus (T2DM) has become an extremely common condition, mainly due to unbalanced dietary habits. Substantial epidemiological evidence correlates T2DM with cognitive impairment as well. Considering that brain insulin resistance, mitochondrial dysfunction, oxidative stress, and amyloidogenesis are common phenomena, further approaching the common features among these pathological conditions. Metformin constitutes the first-choice drug to preclude insulin resistance in T2DM clinical management. Experimental evidence suggests that its functions might include neuroprotective effects, in addition to its hypoglycemic activity. This review aims to summarize and discuss current knowledge of experimental data on metformin on this path towards translational medicine. Finally, we discuss the controversial data of responses to metformin in vitro, and in vivo, animal models and human studies.

Investigating Modifiable Risk Factors Across Dementia Subtypes: Insights from the UK Biobank

This study investigates the relationship between modifiable risk factors and dementia subtypes using data from 460,799 participants in the UK Biobank. Utilizing univariate Cox proportional hazards regression models, we examined the associations between 83 modifiable risk factors and the risks of all-cause dementia (ACD), Alzheimer's disease (AD), and vascular dementia (VD). Composite scores for different domains were generated by aggregating risk factors associated with ACD, AD, and VD, respectively, and their joint associations were assessed in multivariable Cox models. Additionally, population attributable fractions (PAF) were utilized to estimate the potential impact of eliminating adverse characteristics of the risk domains. Our findings revealed that an unfavorable medical history significantly increased the risk of ACD, AD, and VD (hazard ratios (HR) = 1.88, 95% confidence interval (95% CI): 1.74-2.03, p < 0.001; HR = 1.80, 95% CI: 1.54-2.10, p < 0.001; HR = 2.39, 95% CI: 2.10-2.71, p < 0.001, respectively). Blood markers (PAF = 12.1%; 17.4%) emerged as the most important risk domain for preventing ACD and VD, while psychiatric factors (PAF = 18.3%) were the most important for preventing AD. This study underscores the potential for preventing dementia and its subtypes through targeted interventions for modifiable risk factors. The distinct insights provided by HR and PAF emphasize the importance of considering both the strength of the associations and the population-level impact of dementia prevention strategies. Our research provides valuable guidance for developing effective public health interventions aimed at reducing the burden of dementia, representing a significant advancement in the field.

Molecular mechanisms linking type 2 diabetes mellitus and late-onset Alzheimer's disease: A systematic review and qualitative meta-analysis

Research evidence indicating common metabolic mechanisms through which type 2 diabetes mellitus (T2DM) increases risk of late-onset Alzheimer's dementia (LOAD) has accumulated over recent decades. The aim of this systematic review is to provide a comprehensive review of common mechanisms, which have hitherto been discussed in separate perspectives, and to assemble and evaluate candidate loci and epigenetic modifications contributing to polygenic risk linkages between T2DM and LOAD. For the systematic review on pathophysiological mechanisms, both human and animal studies up to December 2023 are included. For the qualitative meta-analysis of genomic bases, human association studies were examined; for epigenetic mechanisms, data from human studies and animal models were accepted. Papers describing pathophysiological studies were identified in databases, and further literature gathered from cited work. For genomic and epigenomic studies, literature mining was conducted by formalised search codes using Boolean operators in search engines, and augmented by GeneRif citations in Entrez Gene, and other sources (WikiGenes, etc.). For the systematic review of pathophysiological mechanisms, 923 publications were evaluated, and 138 gene loci extracted for testing candidate risk linkages. 3 57 publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight insulin signalling, inflammation and inflammasome pathways, proteolysis, gluconeogenesis and glycolysis, glycosylation, lipoprotein metabolism and oxidation, cell cycle regulation or survival, autophagic-lysosomal pathways, and energy. Documented findings suggest interplay between brain insulin resistance, neuroinflammation, insult compensatory mechanisms, and peripheral metabolic dysregulation in T2DM and LOAD linkage. The results allow for more streamlined longitudinal studies of T2DM-LOAD risk linkages.

IGF1R deficiency in vascular smooth muscle cells impairs myogenic autoregulation and cognition in mice

Introduction

Cerebrovascular pathologies contribute to cognitive decline during aging, leading to vascular cognitive impairment and dementia (VCID). Levels of circulating insulin-like growth factor 1 (IGF-1), a vasoprotective hormone, decrease during aging. Decreased circulating IGF-1 in animal models leads to the development of VCID-like symptoms, but the cellular mechanisms underlying IGF-1-deficiency associated pathologies in the aged cerebrovasculature remain poorly understood. Here, we test the hypothesis that vascular smooth muscle cells (VSMCs) play an integral part in mediating the vasoprotective effects of IGF-1.

Methods

We used a hypertension-based model of cerebrovascular dysfunction in mice with VSMC-specific IGF-1 receptor (Igf1r) deficiency and evaluated the development of cerebrovascular pathologies and cognitive dysfunction.

Results

VSMC-specific Igf1r deficiency led to impaired cerebral myogenic autoregulation, independent of blood pressure changes, which was also associated with impaired spatial learning and memory function as measured by radial arm water maze and impaired motor learning measured by rotarod. In contrast, VSMC-specific IGF-1 receptor knockdown did not lead to cerebral microvascular rarefaction.

Discussion

These studies suggest that VSMCs are key targets for IGF-1 in the context of cerebrovascular health, playing a role in vessel stability alongside other cells in the neurovascular unit, and that VSMC dysfunction in aging likely contributes to VCID.

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.

Analysis of the relationship between mild cognitive impairment and serum klotho protein and insulin-like growth factor-1 in the elderly

BACKGROUND

Mild cognitive impairment (MCI) is a mild memory or cognitive impairment.

OBJECTIVE

To explore the relationship between serum klotho (K1) protein and insulin-like growth factor-1 and mild cognitive impairment in the elderly in order to provide accurate and appropriate indicators for clinical diagnosis and treatment of MCI.

METHODS

This randomized stratified study adopted a multistage cluster sampling method. 161 elderly patients with mild cognitive impairment were included as the MCI group, and 161 healthy people matched with the MCI group in gender, age and education were selected as the control group.

RESULTS

The levels of serum K1 protein and insulin-like growth factor-1 in the MCI group were lower than those in the control group (P< 0.05). Both IGF-1 and K1 had predictive value for MCI (P< 0.05). The area under the curve (AUC) of IGF-1 for predicting MCI was 0.859 (95% CI: 0.790∼0.929), and the AUC of K1 for predicting MCI was 0.793 (95% CI: 0.694∼0.892). The value of joint prediction of the two indicators was the highest, with an AUC of 0.939 (95% CI: 0.896-0.993).

CONCLUSION

High serum K1 and insulin-like growth factor-1 are the protective factors of cognitive impairment in MCI patients. Both IGF-1 and serum K1 proteins have predictive value for MCI, and the combination of the two indicators has the highest predictive value.

Metformin: A Review of Potential Mechanism and Therapeutic Utility Beyond Diabetes

Metformin has been designated as one of the most crucial first-line therapeutic agents in the management of type 2 diabetes mellitus. Primarily being an antihyperglycemic agent, metformin also has a plethora of pleiotropic effects on various systems and processes. It acts majorly by activating AMPK (Adenosine Monophosphate-Activated Protein Kinase) in the cells and reducing glucose output from the liver. It also decreases advanced glycation end products and reactive oxygen species production in the endothelium apart from regulating the glucose and lipid metabolism in the cardiomyocytes, hence minimizing the cardiovascular risks. Its anticancer, antiproliferative and apoptosis-inducing effects on malignant cells might prove instrumental in the malignancy of organs like the breast, kidney, brain, ovary, lung, and endometrium. Preclinical studies have also shown some evidence of metformin's neuroprotective role in Parkinson's disease, Alzheimer's disease, multiple sclerosis and Huntington's disease. Metformin exerts its pleiotropic effects through varied pathways of intracellular signalling and exact mechanism in the majority of them remains yet to be clearly defined. This article has extensively reviewed the therapeutic benefits of metformin and the details of its mechanism for a molecule of boon in various conditions like diabetes, prediabetes, obesity, polycystic ovarian disease, metabolic derangement in HIV, various cancers and aging.

Cognitive Deficits in Aging Related to Changes in Basal Forebrain Neuronal Activity

Aging is a physiological process accompanied by a decline in cognitive performance. The cholinergic neurons of the basal forebrain provide projections to the cortex that are directly engaged in many cognitive processes in mammals. In addition, basal forebrain neurons contribute to the generation of different rhythms in the EEG along the sleep/wakefulness cycle. The aim of this review is to provide an overview of recent advances grouped around the changes in basal forebrain activity during healthy aging. Elucidating the underlying mechanisms of brain function and their decline is especially relevant in today's society as an increasingly aged population faces higher risks of developing neurodegenerative diseases such as Alzheimer's disease. The profound age-related cognitive deficits and neurodegenerative diseases associated with basal forebrain dysfunction highlight the importance of investigating the aging of this brain region.

Cell non-autonomous regulation of cerebrovascular aging processes by the somatotropic axis

Age-related cerebrovascular pathologies, ranging from cerebromicrovascular functional and structural alterations to large vessel atherosclerosis, promote the genesis of vascular cognitive impairment and dementia (VCID) and exacerbate Alzheimer's disease. Recent advances in geroscience, including results from studies on heterochronic parabiosis models, reinforce the hypothesis that cell non-autonomous mechanisms play a key role in regulating cerebrovascular aging processes. Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) exert multifaceted vasoprotective effects and production of both hormones is significantly reduced in aging. This brief overview focuses on the role of age-related GH/IGF-1 deficiency in the development of cerebrovascular pathologies and VCID. It explores the mechanistic links among alterations in the somatotropic axis, specific macrovascular and microvascular pathologies (including capillary rarefaction, microhemorrhages, impaired endothelial regulation of cerebral blood flow, disruption of the blood brain barrier, decreased neurovascular coupling, and atherogenesis) and cognitive impairment. Improved understanding of cell non-autonomous mechanisms of vascular aging is crucial to identify targets for intervention to promote cerebrovascular and brain health in older adults.

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.

Metabolic actions of the growth hormone-insulin growth factor-1 axis and its interaction with the central nervous system

The growth hormone/insulin growth factor-1 axis is a key endocrine system that exerts profound effects on metabolism by its actions on different peripheral tissues but also in the brain. Growth hormone together with insulin growth factor-1 perform metabolic adjustments, including regulation of food intake, energy expenditure, and glycemia. The dysregulation of this hepatic axis leads to different metabolic disorders including obesity, type 2 diabetes or liver disease. In this review, we discuss how the growth hormone/insulin growth factor-1 axis regulates metabolism and its interactions with the central nervous system. Finally, we state our vision for possible therapeutic uses of compounds based in the components of this hepatic axis.

Long-term stability and age-dependence of six regulatory serum proteins

Aim: The development of biomarker-based diagnostic procedures often relies on samples stored for several years. We aimed to investigate the influence of storage time and patient age on six neuroregulatory and immunoregulatory serum biomarkers. Materials & methods: We quantified six biomarkers in serum from 151 individuals using ELISA. Serum was stored at -80°C for up to 9.5 years. Results: When associating storage time with biomarker values, BDNF, VEGF-A and TGF-β1 showed a significant increase over time; IGF-1, MCP-1 and IL-18 did not. Associating participant age with biomarkers, only IL-18 in Alzheimer's disease patients showed a significant increase. Conclusion: Storage time can influence results of biomarkers in human serum. This needs to be considered when assessing samples stored for several years.

Response Facilitation Induced by Insulin-Like Growth Factor-I in the Primary Somatosensory Cortex of Mice Was Reduced in Aging

Aging is accompanied by a decline in cognition that can be due to a lower IGF-I level. We studied response facilitation induced in primary somatosensory (S1) cortical neurons by repetitive stimulation of whiskers in young and old mice. Layer 2/3 and 5/6 neurons were extracellularly recorded in young (≤ 6 months of age) and old (≥ 20 month of age) anesthetized mice. IGF-I injection in S1 cortex (10 nM; 0.2 μL) increased whisker responses in young and old animals. A stimulation train at 8 Hz induced a long-lasting response facilitation in only layer 2/3 neurons of young animals. However, all cortical neurons from young and old animals showed long-lasting response facilitation when IGF-I was applied in the S1 cortex. The reduction in response facilitation in old animals can be due to a reduction in the IGF-I receptors as was indicated by the immunohistochemistry study. Furthermore, a reduction in the performance of a whisker discrimination task was observed in old animals. In conclusion, our findings indicate that there is a reduction in the synaptic plasticity of S1 neurons during aging that can be recovered by IGF-I. Therefore, it opens the possibility of use IGF-I as a therapeutic tool to ameliorate the effects of heathy aging.

Recent Neurotherapeutic Strategies to Promote Healthy Brain Aging: Are we there yet?

Owing to the global exponential increase in population ageing, there is an urgent unmet need to develop reliable strategies to slow down and delay the ageing process. Age-related neurodegenerative diseases are among the main causes of morbidity and mortality in our contemporary society and represent a major socio-economic burden. There are several controversial factors that are thought to play a causal role in brain ageing which are continuously being examined in experimental models. Among them are oxidative stress and brain inflammation which are empirical to brain ageing. Although some candidate drugs have been developed which reduce the ageing phenotype, their clinical translation is limited. There are several strategies currently in development to improve brain ageing. These include strategies such as caloric restriction, ketogenic diet, promotion of cellular nicotinamide adenine dinucleotide (NAD+) levels, removal of senescent cells, 'young blood' transfusions, enhancement of adult neurogenesis, stem cell therapy, vascular risk reduction, and non-pharmacological lifestyle strategies. Several studies have shown that these strategies can not only improve brain ageing by attenuating age-related neurodegenerative disease mechanisms, but also maintain cognitive function in a variety of pre-clinical experimental murine models. However, clinical evidence is limited and many of these strategies are awaiting findings from large-scale clinical trials which are nascent in the current literature. Further studies are needed to determine their long-term efficacy and lack of adverse effects in various tissues and organs to gain a greater understanding of their potential beneficial effects on brain ageing and health span in humans.

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-CreERT2/Igf1rf/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-CreERT2/Igf1rf/f mice as compared to control mice. In VE-Cadherin-CreERT2/Igf1rf/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.

Reduced Insulin-Like Growth Factor-I Effects in the Basal Forebrain of Aging Mouse

It is known that aging is frequently accompanied by a decline in cognition. Furthermore, aging is associated with lower serum IGF-I levels that may contribute to this deterioration. We studied the effect of IGF-I in neurons of the horizontal diagonal band of Broca (HDB) of young (≤6 months old) and old (≥20-month-old) mice to determine if changes in the response of these neurons to IGF-I occur along with aging. Local injection of IGF-I in the HDB nucleus increased their neuronal activity and induced fast oscillatory activity in the electrocorticogram (ECoG). Furthermore, IGF-I facilitated tactile responses in the primary somatosensory cortex elicited by air-puffs delivered in the whiskers. These excitatory effects decreased in old mice. Immunohistochemistry showed that cholinergic HDB neurons express IGF-I receptors and that IGF-I injection increased the expression of c-fos in young, but not in old animals. IGF-I increased the activity of optogenetically-identified cholinergic neurons in young animals, suggesting that most of the IGF-I-induced excitatory effects were mediated by activation of these neurons. Effects of aging were partially ameliorated by chronic IGF-I treatment in old mice. The present findings suggest that reduced IGF-I activity in old animals participates in age-associated changes in cortical activity.

Insulin-like growth factor 1 gene transfer for sporadic Alzheimer's disease: New evidence for trophic factor mediated hippocampal neuronal and synaptic recovery-based behavior improvement

Sporadic Alzheimer's disease (sAD) is the most prevalent neurodegenerative disorder with no cure. Patients typically suffer from cognitive impairment imprinted by irreversible neocortex and hippocampal degeneration with overt synaptic and neuron dysfunction. Insulin-like growth factor 1 (IGF1) has proven to be a potent neuroprotective molecule in animal models of age-related neurodegeneration. In this regard, adenoviral gene transfer aiming at IGF1 brain overexpression has been hitherto an underexplored approach for the sAD treatment. We postulated enhanced IGF1 signaling in the brain as a restorative means in the diseased brain to revert cognitive deficit and restore hippocampal function. We implemented recombinant adenovirus mediated intracerebroventricular IGF1 gene transfer on the streptozotocin (STZ) induced sAD rat model, using 3-month-old male Sprague Dawley rats. This approach enhanced IGF1 signaling in the hippocampus and dampened sAD phosphorylated Tau. We found a remarkable short-term improvement in species-typical behavior, recognition memory, spatial memory, and depressive-like behavior. Histological analysis revealed a significant recovery of immature hippocampal neurons. We additionally recorded an increase in hippocampal microglial cells, which we suggest to exert anti-inflammatory effects. Finally, we found decreased levels of pre- and postsynaptic proteins in the hippocampus of STZ animals. Interestingly, IGF1 gene transfer increased the levels of PSD95 and GAD65/67 synaptic markers, indicating that the treatment enhanced the synaptic plasticity. We conclude that exogenous activation of IGF1 signaling pathway, 1 week after intracerebroventricular STZ administration, protects hippocampal immature neurons, dampens phosphorylated Tau levels, improves synaptic function and therefore performs therapeutically on the sAD STZ model. Hence, this study provides strong evidence for the use of this trophic factor to treat AD and age-related neurodegeneration.

Investigating the Relationship Between IGF-I, IGF-II, and IGFBP-3 Concentrations and Later-Life Cognition and Brain Volume

BACKGROUND

The insulin/insulin-like signaling (IIS) pathways, including insulin-like growth factors (IGFs), vary with age. However, their association with late-life cognition and neuroimaging parameters is not well characterized.

METHODS

Using data from the British 1946 birth cohort, we investigated associations of IGF-I, IGF-II and IGF binding protein 3 (IGFBP-3; measured at 53 and 60-64 years of age) with cognitive performance [word-learning test (WLT) and visual letter search (VLS) at 60-64 years and 69 years of age] and cognitive state [Addenbrooke's Cognitive Exam III (ACE-III) at 69-71 years of age], and in a proportion, quantified neuroimaging measures [whole brain volume (WBV), white matter hyperintensity volume (WMHV), hippocampal volume (HV)]. Regression models included adjustments for demographic, lifestyle, and health factors.

RESULTS

Higher IGF-I and IGF-II at 53 years of age was associated with higher ACE-III scores [ß 0.07 95% confidence interval (CI) (0.02, 0.12); scoreACE-III 89.48 (88.86, 90.1), respectively). IGF-II at 53 years of age was additionally associated with higher WLT scores [scoreWLT 20 (19.35, 20.65)]. IGFBP-3 at 60 to 64 years of age was associated with favorable VLS score at 60 to 64 and 69 years of age [ß 0.07 (0.01, 0.12); ß 0.07 (0.02, 0.12), respectively], higher memory and cognitive state at 69 years of age [ß 0.07 (0.01, 0.12); ß 0.07 (0.01, 0.13), respectively], and reduced WMHV [ß -0.1 (-0.21, -0.00)]. IGF-I/IGFBP-3 at 60 to 64 years of was associated with lower VLS scores at 69 years of age [ß -0.08 (-0.15, -0.02)].

CONCLUSIONS

Increased measure in IIS parameters (IGF-I, IGF-II, and IGFBP-3) relate to better cognitive state in later life. There were apparent associations with specific cognitive domains (IGF-II relating to memory; IGFBP-3 relating to memory, processing speed, and WMHV; and IGF-I/IGFBP-3 molar ratio related to slower processing speed). IGFs and IGFBP-3 are associated with favorable cognitive function outcomes.

Positive Association Between Serum Insulin-Like Growth Factor-1 and Cognition in Patients with Cerebral Small Vessel Disease

Cognitive impairment is one of the main complications of cerebral small vessel disease (CSVD). Serum insulin-like growth factor-1 (IGF-1) might serve as a marker for the risk of cognitive decline in patients with CSVD. We investigated the association of IGF-1 with the development of cognitive impairment in patients with CSVD. We included 216 patients with CVSD (mean age, 67.57 ± 8.53 years; 31.9% female). We compared 117 (54.2%) patients who developed cognitive impairment with 99 (45.8%) patients without cognitive impairment. Patients who developed cognitive impairment had significantly lower levels of IGF-I (p < 0 .001), suggesting that altered IGF-1 signaling may be a risk factor for cognitive decline in patients with CSVD.

IGF1R signaling regulates astrocyte-mediated neurovascular coupling in mice: implications for brain aging

Aging is associated with a significant deficiency in circulating insulin-like growth factor-1 (IGF-1), which has an important role in the pathogenesis of age-related vascular cognitive impairment (VCI). Impairment of moment-to-moment adjustment of regional cerebral blood flow via neurovascular coupling (NVC) importantly contributes to VCI. Previous studies established a causal link between circulating IGF-1 deficiency and neurovascular dysfunction. Release of vasodilator mediators from activated astrocytes plays a key role in NVC. To determine the impact of impaired IGF-1 signaling on astrocytic function, astrocyte-mediated NVC responses were studied in a novel mouse model of astrocyte-specific knockout of IGF1R (GFAP-CreERT2/Igf1rf/f) and accelerated neurovascular aging. We found that mice with disrupted astrocytic IGF1R signaling exhibit impaired NVC responses, decreased stimulated release of the vasodilator gliotransmitter epoxy-eicosatrienoic acids (EETs), and upregulation of soluble epoxy hydrolase (sEH), which metabolizes and inactivates EETs. Collectively, our findings provide additional evidence that IGF-1 promotes astrocyte health and maintains normal NVC, protecting cognitive health.

Intracisternal IGF-1 gene therapy abrogates kainic acid-induced excitotoxic damage of the rat spinal cord

Development of alternative therapies for treating functional deficits after different neurological damages is a challenge in neuroscience. Insulin-like growth factor-1 (IGF-1) is a potent neurotrophic factor exerting neuroprotective actions in brain and spinal cord. It is used to prevent or treat injuries of the central nervous system using different administration routes in different animal models. In this study, we evaluated whether intracisternal (IC) route for IGF-1 gene therapy may abrogate or at least reduce the structural and behavioral damages induced by the intraparenchymal injection of kainic acid (KA) into the rat spinal cord. Experimental (Rad-IGF-1) and control (Rad-DsRed-KA) rats were evaluated using a battery of motor and sensory tests before the injection of the recombinant adenovector (day -3), before KA injection (day 0) and at every post-injection (pi) time point (days 1, 2, 3 and 7 pi). Histopathological changes and neuronal and glial counting were assessed. Pretreatment using IC delivery of RAd-IGF-1 improved animal's general condition and motor and sensory functions as compared to Rad-DsRed-KA-injected rats. Besides, IC Rad-IGF-1 therapy abrogated later spinal cord damage and reduced the glial response induced by KA as observed in Rad-DsRed-KA rats. We conclude that the IC route for delivering RAd-IGF-1 prevents KA-induced excitotoxicity in the spinal cord.

Value of a Panel of 6 Serum Biomarkers to Differentiate Between Healthy Controls and Mild Cognitive Impairment Due to Alzheimer Disease

BACKGROUND

There is considerable evidence suggesting that inflammatory responses may be involved in the neurodegenerative cascade of Alzheimer disease (AD). Blood-based biomarker analysis of inflammatory markers indicative of dementia could serve as a minimally invasive and easy-to-administer diagnostic tool in primary care.

MATERIAL AND METHODS

The authors quantified 6 markers (brain-derived neurotrophic factor, insulin-like growth factor 1, vascular endothelial growth factor, transforming growth factor-beta type 1, monocyte chemoattractant protein 1, and interleukin-18) in blood serum of 68 healthy blood donors (controls), 42 patients with AD at the dementia stage, 55 patients with AD at the stage of mild cognitive impairment (MCI-AD), and 25 patients with MCI non-AD. All patients have been fully characterized, including AD biomarker analyses in cerebrospinal fluid. Data were analyzed in an algorithm that was trained, validated, and then used for dichotomous classification of unknown data into data sets suspicious and not suspicious of AD.

RESULTS

Using this algorithm, 47 of 55 MCI-AD (85.5%) and 20 of 25 MCI non-AD (80%) cases were classified as suspicious of AD.

CONCLUSIONS

This panel of 6 markers in blood serum may indicate underlying neurodegenerative processes in patients with AD at the MCI stage. The authors assume that a deranged equilibrium of neuroprotective and inflammatory processes is an overall major cause for neurodegeneration and cognitive decline.

Definition and quantification of six immune- and neuroregulatory serum proteins in healthy and demented elderly

Aim: Blood-based biomarkers related to immune- and neuroregulatory processes may be indicative of dementia but lack standardization and proof-of-principle studies. Materials & methods: The blood serum collection protocol as well as the analytic procedure to quantify the markers BDNF, IGF-1, VEGF, TGF-β 1, MCP-1 and IL-18 in blood serum were standardized and their concentrations were compared between groups of 81 Alzheimer’s disease patients and 79 healthy controls. Results: Applying standardized methods, results for the quantification of the six markers in blood serum are stable and their concentrations significantly differ for all analytes except VEGF between patients diagnosed with Alzheimer’s disease and healthy controls. Conclusion: Analyzing a panel of six markers in blood serum under standardized conditions may serve as a diagnostic tool in primary dementia care in the future.

The Cross-Talk Between Sphingolipids and Insulin-Like Growth Factor Signaling: Significance for Aging and Neurodegeneration

Bioactive sphingolipids: sphingosine, sphingosine-1-phosphate (S1P), ceramide, and ceramide-1-phosphate (C1P) are increasingly implicated in cell survival, proliferation, differentiation, and in multiple aspects of stress response in the nervous system. The opposite roles of closely related sphingolipid species in cell survival/death signaling is reflected in the concept of tightly controlled sphingolipid rheostat. Aging has a complex influence on sphingolipid metabolism, disturbing signaling pathways and the properties of lipid membranes. A metabolic signature of stress resistance-associated sphingolipids correlates with longevity in humans. Moreover, accumulating evidence suggests extensive links between sphingolipid signaling and the insulin-like growth factor I (IGF-I)-Akt-mTOR pathway (IIS), which is involved in the modulation of aging process and longevity. IIS integrates a wide array of metabolic signals, cross-talks with p53, nuclear factor κB (NF-κB), or reactive oxygen species (ROS) and influences gene expression to shape the cellular metabolic profile and stress resistance. The multiple connections between sphingolipids and IIS signaling suggest possible engagement of these compounds in the aging process itself, which creates a vulnerable background for the majority of neurodegenerative disorders.

IGF1 Gene Therapy Modifies Microglia in the Striatum of Senile Rats

Microglial cells become dystrophic with aging; this phenotypic alteration contributes to basal central nervous system (CNS) neuroinflammation being a risk factor for age related neurodegenerative diseases. In previous studies we have observed that insulin like growth factor 1 (IGF1) gene therapy is a feasible approach to target brain cells, and that is effective to modify inflammatory response in vitro and to ameliorate cognitive or motor deficits in vivo. Based on these findings, the main aim of the present study is to investigate the effect of IGF1 gene therapy on microglia distribution and morphology in the senile rat. We found that IGF1 therapy leads to a region-specific modification of aged microglia population.

The insulin-like growth factor-1 system in the adult mammalian brain and its implications in central maternal adaptation

Our knowledge on the bioavailability and actions of insulin-like growth factor-1 (IGF-1) has markedly expanded in recent years as novel mechanisms were discovered on IGF binding proteins (IGFBPs) and their ability to release IGF-1. The new discoveries allowed a better understanding of the endogenous physiological actions of IGF-1 and also its applicability in therapeutics. The focus of the present review is to summarize novel findings on the neuronal, neuroendocrine and neuroplastic actions of IGF-1 in the adult brain. As most of the new regulatory mechanisms were described in the periphery, their implications on brain IGF system will also be covered. In addition, novel findings on the effects of IGF-1 on lactation and maternal behavior are described. Based on the enormous neuroplastic changes related to the peripartum period, IGF-1 has great but largely unexplored potential in maternal adaptation of the brain, which is highlighted in the present review.

The Therapeutic Potential of Metformin in Neurodegenerative Diseases

The search for treatments for neurodegenerative diseases is a major concern in light of today's aging population and an increasing burden on individuals, families, and society. Although great advances have been made in the last decades to understand the underlying genetic and biological cause of these diseases, only some symptomatic treatments are available. Metformin has long since been used to treat Type 2 Diabetes and has been shown to be beneficial in several other conditions. Metformin is well-tested in vitro and in vivo and an approved compound that targets diverse pathways including mitochondrial energy production and insulin signaling. There is growing evidence for the benefits of metformin to counteract age-related diseases such as cancer, cardiovascular disease, and neurodegenerative diseases. We will discuss evidence showing that certain neurodegenerative diseases and diabetes are explicitly linked and that metformin along with other diabetes drugs can reduce neurological symptoms in some patients and reduce disease phenotypes in animal and cell models. An interesting therapeutic factor might be how metformin is able to balance survival and death signaling in cells through pathways that are commonly associated with neurodegenerative diseases. In healthy neurons, these overarching signals keep energy metabolism, oxidative stress, and proteostasis in check, avoiding the dysfunction and neuronal death that defines neurodegenerative disease. We will discuss the biological mechanisms involved and the relevance of neuronal vulnerability and potential difficulties for future trials and development of therapies.

The Therapeutic Potential of Metformin in Neurodegenerative Diseases

The search for treatments for neurodegenerative diseases is a major concern in light of today's aging population and an increasing burden on individuals, families, and society. Although great advances have been made in the last decades to understand the underlying genetic and biological cause of these diseases, only some symptomatic treatments are available. Metformin has long since been used to treat Type 2 Diabetes and has been shown to be beneficial in several other conditions. Metformin is well-tested in vitro and in vivo and an approved compound that targets diverse pathways including mitochondrial energy production and insulin signaling. There is growing evidence for the benefits of metformin to counteract age-related diseases such as cancer, cardiovascular disease, and neurodegenerative diseases. We will discuss evidence showing that certain neurodegenerative diseases and diabetes are explicitly linked and that metformin along with other diabetes drugs can reduce neurological symptoms in some patients and reduce disease phenotypes in animal and cell models. An interesting therapeutic factor might be how metformin is able to balance survival and death signaling in cells through pathways that are commonly associated with neurodegenerative diseases. In healthy neurons, these overarching signals keep energy metabolism, oxidative stress, and proteostasis in check, avoiding the dysfunction and neuronal death that defines neurodegenerative disease. We will discuss the biological mechanisms involved and the relevance of neuronal vulnerability and potential difficulties for future trials and development of therapies.

A Putative Mechanism of Age-Related Synaptic Dysfunction Based on the Impact of IGF-1 Receptor Signaling on Synaptic CaMKIIα Phosphorylation

Insulin-like growth factor 1 receptor (IGF-1R) signaling regulates the activity and phosphorylation of downstream kinases linked to inflammation, neurodevelopment, aging and synaptic function. In addition to the control of Ca2+ currents, IGF-1R signaling modulates the activity of calcium-calmodulin-dependent kinase 2 alpha (CaMKIIα) and mitogen activated protein kinase (MAPK/ErK) through multiple signaling pathways. These proteins (CaMKIIα and MAPK) regulate Ca2+ movement and long-term potentiation (LTP). Since IGF-1R controls the synaptic activity of Ca2+, CaMKIIα and MAPK signaling, the possible mechanism through which an age-dependent change in IGF-1R can alter the synaptic expression and phosphorylation of these proteins in aging needs to be investigated. In this study, we evaluated the relationship between an age-dependent change in brain IGF-1R and phosphorylation of CaMKIIα/MAPK. Furthermore, we elucidated possible mechanisms through which dysregulated CaMKIIα/MAPK interaction may be linked to a change in neurotransmitter processing and synaptic function. Male C57BL/6 VGAT-Venus mice at postnatal days 80 (P80), 365 and 730 were used to study age-related neural changes in two brain regions associated with cognitive function: hippocampus and prefrontal cortex (PFC). By means of high throughput confocal imaging and quantitative immunoblotting, we evaluated the distribution and expression of IGF-1, IGF-1R, CaMKIIα, p-CaMKIIα, MAPK and p-MAPK in whole brain lysate, hippocampus and cortex. Furthermore, we compared protein expression patterns and regional changes at P80, P365 and P730. Ultimately, we determined the relative phosphorylation pattern of CaMKIIα and MAPK through quantification of neural p-CaMKIIα and p-MAPK/ErK, and IGF-1R expression for P80, P365 and P730 brain samples. In addition to a change in synaptic function, our results show a decrease in neural IGF-1/IGF-1R expression in whole brain, hippocampus and cortex of aged mice. This was associated with a significant upregulation of phosphorylated neural MAPK (p-MAPK) and decrease in total brain CaMKIIα (i.e., CaMKIIα and p-CaMKIIα) in the aged brain. Taken together, we showed that brain aging is associated with a change in neural IGF-1/IGF-1R expression and may be linked to a change in phosphorylation of synaptic kinases (CaMKIIα and MAPK) that are involved in the modulation of LTP.

Analysis of Association of Genetic Markers in the LUZP2 and FBXO40 Genes with the Normal Variability in Cognitive Performance in the Elderly

Cognitive performance is an important endophenotype for various neurodegenerative and neuropsychiatric traits. In the present study two genetic variants in the leucine-zipper protein (LUZP2) and the F-box 40 protein (FBXO40) genes, previously reported to be genome-wide significant for Alzheimer's diseases and schizophrenia, were examined for an association with cognitive abilities in normal elderly from the Russian population. Rs1021261 in the LUZP2 and rs3772130 in the FBXO40 were genotyped by multiplex PCR and MALDI-TOF mass spectrometry in a sample of 708 normal elderly subjects tested for cognitive performance using the Montreal Cognitive Assessment (MoCA). Association of genetic variability with the MoCA scores was estimated by parametric and nonparametric analysis of variance and by the frequency comparison between upper and lower quartiles of MoCA distribution. Significantly higher frequency of "TT" genotype of rs1021261 in the LUZP2 gene as well as "A" allele and "AA" genotype of rs3772130 in the FBXO40 gene was found in a subsample of individuals with the MoCA score less than 20 comparing to the fourth quartile's subsample (MoCA > 25). The data of the present study suggests that genetic variability in the LUZP2 and FBXO40 loci associated with neurodegenerative and neuropsychiatric diseases is also contributed to the normal variability in cognitive performance in the elderly.

Insulin-like Growth Factor 1 (IGF-1) as a marker of cognitive decline in normal ageing: A review

Insulin-like Growth Factor 1 (IGF-1) and its signaling pathway play a primary role in normal growth and ageing, however serum IGF-1 is known to reduce with advancing age. Recent findings suggest IGF-1 is essential for neurogenesis in the adult brain, and this reduction of IGF-1 with ageing may contribute to age-related cognitive decline. Experimental studies have shown manipulation of the GH/GF-1 axis can slow rates of cognitive decline in animals, making IGF-1 a potential biomarker of cognition, and/or its signaling pathway a possible therapeutic target to prevent or slow age-related cognitive decline. A systematic literature review and qualitative narrative summary of current evidence for IGF-1 as a biomarker of cognitive decline in the ageing brain was undertaken. Results indicate IGF-1 concentrations do not confer additional diagnostic information for those with cognitive decline, and routine clinical measurement of IGF-1 is not currently justified. In cases of established cognitive impairment, it remains unclear whether increasing circulating or brain IGF-1 may reverse or slow down the rate of further decline. Advances in neuroimaging, genetics, neuroscience and the availability of large well characterized biobanks will facilitate research exploring the role of IGF-1 in both normal ageing and age-related cognitive decline.

Crosstalk between insulin-like growth factor-1 and angiotensin-II in dopaminergic neurons and glial cells: role in neuroinflammation and aging

The local renin-angiotensin system (RAS) and insulin-like growth factor 1 (IGF-1) have been involved in longevity, neurodegeneration and aging-related dopaminergic degeneration. However, it is not known whether IGF-1 and angiotensin-II (AII) activate each other. In the present study, AII, via type 1 (AT1) receptors, exacerbated neuroinflammation and dopaminergic cell death. AII, via AT1 receptors, also increased the levels of IGF-1 and IGF-1 receptors in microglial cells. IGF-1 inhibited RAS activity in dopaminergic neurons and glial cells, and also inhibited the AII-induced increase in markers of the M1 microglial phenotype. Consistent with this, IGF-1 decreased dopaminergic neuron death induced by the neurotoxin MPP⁺ both in the presence and in the absence of glia. Intraventricular administration of AII to young rats induced a significant increase in IGF-1 expression in the nigral region. However, aged rats showed decreased levels of IGF-1 relative to young controls, even though RAS activity is known to be enhanced in aged animals. The study findings show that IGF-1 and the local RAS interact to inhibit or activate neuroinflammation (i.e. transition from the M1 to the M2 phenotype), oxidative stress and dopaminergic degeneration. The findings also show that this mechanism is impaired in aged animals.

Glial contributions to neuronal health and disease: new insights from Drosophila

Glial cells are essential for proper formation and maintenance of the nervous system. During development, glia keep neuronal cell numbers in check and ensure that mature neural circuits are appropriately sculpted by engulfing superfluous cells and projections. In the adult brain, glial cells offer metabolic sustenance and provide critical immune support in the face of acute and chronic challenges. Dysfunctional glial immune activity is believed to contribute to age-related cognitive decline, as well as neurodegenerative disease risk, but we still know surprisingly little about the specific molecular pathways that govern glia-neuron communication in the healthy or diseased brain. Drosophila offers a versatile in vivo model to explore the conserved molecular underpinnings of glial cell biology and glial cell contributions to brain function, health, and disease susceptibility. This review addresses recent findings describing how Drosophila glial cells influence neuronal activity in the adult fly brain to support optimal brain function and, importantly, highlights new insights into specific glial defects that may contribute to neuronal demise.

Opening up the DNA methylome of dementia

Dementia is a complex clinical condition characterized by several cognitive impairments that interfere with patient independence in executing everyday tasks. Various neurodegenerative disorders have dementia in common among their clinical manifestations. In addition, these diseases, such as Alzheimer's disease, Parkinson's disease, dementia with Lewy bodies and frontotemporal dementia, share molecular alterations at the neuropathological level. In recent years, the field of neuroepigenetics has expanded massively and it is now clear that epigenetic processes, such as DNA methylation, are mechanisms involved in both normal and pathological brain function. Despite the persistent methodological and conceptual caveats, it has been reported that several genes fundamental to the development of neurodegenerative disorders are deregulated by aberrant methylation patterns of their promoters, and even common epigenetic signatures for some dementia-associated pathologies have been identified. Therefore, understanding the epigenetic mechanisms that are altered in dementia, especially those associated with the initial phases, will allow us not only to understand the etiopathology of dementia and its progression but also to design effective therapies to reduce this global public health problem. This review provides an in-depth summary of our current knowledge about DNA methylation in dementia, focusing exclusively on the analyses performed in human brain.

Sirtuins and Their Roles in Brain Aging and Neurodegenerative Disorders

Sirtuins (SIRT1-SIRT7) are unique histone deacetylases (HDACs) whose activity depends on NAD⁺ levels and thus on the cellular metabolic status. SIRTs regulate energy metabolism and mitochondrial function. They orchestrate the stress response and damage repair. Through these functions sirtuins modulate the course of aging and affect neurodegenerative diseases. SIRTSs interact with multiple signaling proteins, transcription factors (TFs) and poly(ADP-ribose) polymerases (PARPs) another class of NAD⁺-dependent post-translational protein modifiers. The cross-talk between SIRTs TFs and PARPs is a highly promising research target in a number of brain pathologies. This review describes updated results on sirtuins in brain aging/neurodegeneration. It focuses on SIRT1 but also on the roles of mitochondrial SIRTs (SIRT3, 4, 5) and on SIRT6 and SIRT2 localized in the nucleus and in cytosol, respectively. The involvement of SIRTs in regulation of insulin-like growth factor signaling in the brain during aging and in Alzheimer's disease was also focused. Moreover, we analyze the mechanism(s) and potential significance of interactions between SIRTs and several TFs in the regulation of cell survival and death. A critical view is given on the application of SIRT activators/modulators in therapy of neurodegenerative diseases.

Discrepancies in insulin-like growth factor signaling? No, not really

Why do studies on insulin-like growth factors (IGFs) and IGF signaling seem so contradictory? The answer is "It depends". This mini- review will explore a few of the factors that are likely to contribute to a seemingly confusing message. Most of the evidence comes from experimental animal models.

Insulin-like Signaling Promotes Glial Phagocytic Clearance of Degenerating Axons through Regulation of Draper

Neuronal injury triggers robust responses from glial cells, including altered gene expression and enhanced phagocytic activity to ensure prompt removal of damaged neurons. The molecular underpinnings of glial responses to trauma remain unclear. Here, we find that the evolutionarily conserved insulin-like signaling (ILS) pathway promotes glial phagocytic clearance of degenerating axons in adult Drosophila. We find that the insulin-like receptor (InR) and downstream effector Akt1 are acutely activated in local ensheathing glia after axotomy and are required for proper clearance of axonal debris. InR/Akt1 activity, it is also essential for injury-induced activation of STAT92E and its transcriptional target draper, which encodes a conserved receptor essential for glial engulfment of degenerating axons. Increasing Draper levels in adult glia partially rescues delayed clearance of severed axons in glial InR-inhibited flies. We propose that ILS functions as a key post-injury communication relay to activate glial responses, including phagocytic activity.

Exercise-induced neuroprotective effects on neurodegenerative diseases: the key role of trophic factors

Age-related neurodegenerative disorders, like Alzheimer's or Parkinson's disease, are becoming a major issue to public health care. Currently, there is no effective pharmacological treatment to address cognitive impairment in these patients. Here, we aim to explore the role of exercise-induced trophic factor enhancement in the prevention or delay of cognitive decline in patients with neurodegenerative diseases. There is a significant amount of evidence from animal and human studies that links neurodegenerative related cognitive deficits with changes on brain and peripheral trophic factor levels. Several trials with elderly individuals and patients with neurodegenerative diseases report exercise induced cognitive improvements and changes on trophic factor levels including BDNF, IGF-I, among others. Further studies with healthy aging and clinical populations are needed to understand how diverse exercise interventions produce different variations in trophic factor signaling. Genetic profiles and potential confounders regarding trophic factors should also be addressed in future trials.

Central insulin-like growth factor-1 (IGF-1) restores whole-body insulin action in a model of age-related insulin resistance and IGF-1 decline

Low insulin‐like growth factor‐1 (IGF‐1) signaling is associated with improved longevity, but is paradoxically linked with several age‐related diseases in humans. Insulin‐like growth factor‐1 has proven to be particularly beneficial to the brain, where it confers protection against features of neuronal and cognitive decline. While aging is characterized by central insulin resistance in the face of hyperinsulinemia, the somatotropic axis markedly declines in older humans. Thus, we hypothesized that increasing IGF‐1 in the brain may prove to be a novel therapeutic alternative to overcome central insulin resistance and restore whole‐body insulin action in aging. Utilizing hyperinsulinemic‐euglycemic clamps, we show that old insulin‐resistant rats with age‐related declines in IGF‐1 level demonstrate markedly improved whole‐body insulin action, when treated with central IGF‐1, as compared to central vehicle or insulin (P < 0.05). Furthermore, central IGF‐1, but not insulin, suppressed hepatic glucose production and increased glucose disposal rates in aging rats (P < 0.05). Taken together, IGF‐1 action in the brain and periphery provides a ‘balance’ between its beneficial and detrimental actions. Therefore, we propose that strategies aimed at ‘tipping the balance’ of IGF‐1 action centrally are the optimal approach to achieve healthy aging and longevity in humans.

Insulin-like growth factor-1 and insulin-like growth factor binding protein 3 and risk of postoperative cognitive dysfunction

Insulin-like growth factor (IGF)-1 is implicated in learning and memory. Experimental studies have suggested that the IGF-1 system is beneficial in cognition, especially in Alzheimer’s disease (AD), by opposing Aβ amyloid processing and hyperphosphorylated tau toxicity. Low IGF-I and insulin-like growth factor binding protein (IGFBP)-3 serum levels are significantly associated with AD. To assess the relationship between circulating IGF-I and IGFBP3 levels and change of postoperative cognition. The study was performed in patients scheduled for elective head and neck carcinoma surgery under general anesthesia. On the day before the operation and postoperative days 1, 3 and 7, mini-mental state examination (MMSE) was performed by the same doctor, and blood samples were collected at 08:00 h after overnight fasting. The circulating levels of IGF-1 and IGFBP3 were measured by enzyme-linked immunosorbent assay. One hundred and two patients completed all four MMSE tests and forty-four of them completed all the four blood samples collection. Postoperative circulating IGF-1 level, ratio of IGF-1/IGFBP3 and MMSE score significantly decreased, whereas IGFBP3 level significantly increased compared with preoperative values in total patients. The change trends of circulating IGF-1 level and MMSE score were similar. Preoperative circulating IGF-1 level, ratio and MMSE score were significantly lower in POCD group compared to non-POCD group. There was no significant difference in preoperative level of circulating IGFBP3 between the two groups. Preoperative circulating IGF-1 level was negatively correlated with age and positively with MMSE. Logistic regression analysis revealed that lower preoperative IGF-1 level and elderly patients increased the odds of POCD. Down-regulation of circulating IGF-1 level may be involved in the mechanism of postoperative cognitive dysfunction. Older patients had lower circulating IGF-1 levels and were more susceptible to POCD.

Monomeric ß-amyloid interacts with type-1 insulin-like growth factor receptors to provide energy supply to neurons

ß-amyloid (Aß₁₋₄₂) is produced by proteolytic cleavage of the transmembrane type-1 protein, amyloid precursor protein. Under pathological conditions, Aß₁₋₄₂self-aggregates into oligomers, which cause synaptic dysfunction and neuronal loss, and are considered the culprit of Alzheimer's disease (AD). However, Aß₁₋₄₂ is mainly monomeric at physiological concentrations, and the precise role of monomeric Aß₁₋₄₂ in neuronal function is largely unknown. We report that the monomer of Aß₁₋₄₂ activates type-1 insulin-like growth factor receptors and enhances glucose uptake in neurons and peripheral cells by promoting the translocation of the Glut3 glucose transporter from the cytosol to the plasma membrane. In neurons, activity-dependent glucose uptake was blunted after blocking endogenous Aß production, and re-established in the presence of cerebrospinal fluid Aß. APP-null neurons failed to enhance depolarization-stimulated glucose uptake unless exogenous monomeric Aß₁₋₄₂ was added. These data suggest that Aß₁₋₄₂ monomers were critical for maintaining neuronal glucose homeostasis. Accordingly, exogenous Aß₁₋₄₂ monomers were able to rescue the low levels of glucose consumption observed in brain slices from AD mutant mice.

The Novel Functions of High-Molecular-Mass Complexes Containing Insulin Receptor Substrates in Mediation and Modulation of Insulin-Like Activities: Emerging Concept of Diverse Functions by IRS-Associated Proteins

Insulin-like peptides, such as insulin-like growth factors (IGFs) and insulin, induce a variety of bioactivities, such as growth, differentiation, survival, increased anabolism, and decreased catabolism in many cell types and in vivo. In general, IGFs or insulin bind to IGF-I receptor (IGF-IR) or insulin receptor (IR), activating the receptor tyrosine kinase. Insulin receptor substrates (IRSs) are known to be major substrates of receptor kinases, mediating IGF/insulin signals to direct bioactivities. Recently, we discovered that IRSs form high-molecular-mass complexes (referred to here as IRSomes) even without IGF/insulin stimulation. These complexes contain proteins (referred to here as IRSAPs; IRS-associated proteins), which modulate tyrosine phosphorylation of IRSs by receptor kinases, control IRS stability, and determine intracellular localization of IRSs. In addition, in these complexes, we found not only proteins that are involved in RNA metabolism but also RNAs themselves. Thus, IRSAPs possibly contribute to modulation of IGF/insulin bioactivities. Since it is established that disorder of modulation of insulin-like activities causes various age-related diseases including cancer, we could propose that the IRSome is an important target for treatment of these diseases.

Alterations in function and expression of ABC transporters at blood-brain barrier under diabetes and the clinical significances

Diabetes is a systematic metabolic disease, which often develops a number of well-recognized vascular complications including brain complications which may partly result from the dysfunction of blood-brain barrier (BBB). BBB is generally considered as a mechanism for protecting the brain from unwanted actions resulting from substances in the blood and maintaining brain homeostasis via monitoring the entry or efflux of compounds. ATP-binding cassette (ABC) family of transporters including P-glycoprotein (P-GP) and breast cancer-related protein (BCRP), widely expressed in the luminal membrane of the microvessel endothelium and in the apical membrane of the choroids plexus epithelium, play important roles in the function of BBB. However, these transporters are easily altered by some diseases. The present article was focused on the alteration in expression and function of both P-GP and BCRP at BBB by diabetes and the clinical significances.

Cerebral ageing-the role of insulin and insulin-like growth factor signalling: A review

Cerebral ageing is a complex biological process associated with progressing cerebrovascular disease and neuronal death. It does not always, however, associate with a functional decline, as the ageing mammalian brain retains considerable functional plasticity which supports successful cerebral ageing where age-related cognitive decline is modest. On the contrary, pathological cerebral ageing results in memory impairment and cognitive deterioration, with Alzheimer’s disease (AD) being a florid example. Trophic/growth factors promote brain plasticity; among them are peptides which belong to the insulin family. Preclinical research suggests that the evolutionarily conserved brain insulin/insulin-like growth factor-1 (IGF-1) signalling system controls lifespan and protects against some features of AD such as neurodegeneration-related accumulation of toxic proteins and cognitive deficiencies, as observed in animal models. Insulin and IGF-1 activate cell signalling mechanisms which play protective and regenerative roles; abnormalities in the insulin/IGF-1 system may trigger a cascade of neurodegeneration in AD. AD patients show cerebral resistance to insulin which associates with IGF-I resistance and dysregulation of insulin/IGF-1 receptors as well as cognitive deterioration. This review is focused on the roles of the insulin/IGF-1 signalling system in cerebral ageing and its potential involvement in neurodegeneration in the human brain as seen against the background of preclinical evidence.

Physical activity, inflammation, and volume of the aging brain

Physical activity influences inflammation, and both affect brain structure and Alzheimer's disease (AD) risk. We hypothesized that older adults with greater reported physical activity intensity and lower serum levels of the inflammatory marker tumor necrosis factor α (TNFα) would have larger regional brain volumes on subsequent magnetic resonance imaging (MRI) scans. In 43 cognitively intact older adults (79.3±4.8 years) and 39 patients with AD (81.9±5.1 years at the time of MRI) participating in the Cardiovascular Health Study, we examined year-1 reported physical activity intensity, year-5 blood serum TNFα measures, and year-9 volumetric brain MRI scans. We examined how prior physical activity intensity and TNFα related to subsequent total and regional brain volumes. Physical activity intensity was measured using the modified Minnesota Leisure Time Physical Activities questionnaire at year 1 of the study, when all subjects included here were cognitively intact. Stability of measures was established for exercise intensity over 9 years and TNFα over 3 years in a subset of subjects who had these measurements at multiple time points. When considered together, more intense physical activity intensity and lower serum TNFα were both associated with greater total brain volume on follow-up MRI scans. TNFα, but not physical activity, was associated with regional volumes of the inferior parietal lobule, a region previously associated with inflammation in AD patients. Physical activity and TNFα may independently influence brain structure in older adults.