REVIEW | doi:10.20944/preprints202002.0439.v1
Subject: Life Sciences, Biochemistry Keywords: astrocytes; autophagy; hypothalamus; metabolism; obesity
Online: 28 February 2020 (13:18:35 CET)
Autophagy is an essential mechanism to maintain cellular homeostasis. Besides its role in controlling the quality of cytoplasmic components, it participates in nutrient obtaining and lipid mobilization under stressful conditions. Furthermore, autophagy is involved in the regulation of systemic metabolic, a function mainly performed by neuronal populations of the arcuate nucleus of the hypothalamus. Several studies have shown that blockade of autophagy in these neurons can affect central regulation of metabolism and impact body energy balance. Moreover, hypothalamic autophagy can be altered during obesity. However, neurons are not the only cell type involved in the central regulation of metabolism. Astrocytes, essential cells for brain homeostasis, are key metabolic regulators. They can sense metabolic signals in the hypothalamus and modulate systemic functions as glucose homeostasis and feeding response. Moreover, the response of astrocytes to obesity has been widely studied. Astrocytes are important mediators of brain inflammation and can be affected by increased levels of saturated fatty acids associated to obesity. Although autophagy plays important roles for astrocyte homeostasis and functioning, the contribution of astrocyte autophagy to systemic metabolism has not been analysed. Furthermore, how obesity can impact astrocyte autophagy is poorly understood. More studies are needed in other to understand the contribution of astrocyte autophagy to metabolism.
REVIEW | doi:10.20944/preprints201909.0314.v1
Subject: Medicine & Pharmacology, Pathology & Pathobiology Keywords: hypothalamus; endocrine; gangliocytoma; neurocytoma; pituicytoma; hormones
Online: 28 September 2019 (00:24:48 CEST)
The hypothalamus is the site of synthesis and secretion of a number of endocrine peptides that are involved in the regulation of hormonal activity of the pituitary and other endocrine targets. Tumors of the hypothalamus have been recognized to have both structural and functional effects including hormone hypersecretion. The classification of these tumors had advanced over the last few years and biomarkers are now available to classify these tumors and provide accurate structure-function correlations. This review provides an overview of tumors in this region that is critical to metabolic homeostasis with a focus on advances in the diagnosis of gangliocytomas, neurocytomas and pituicytomas that are unique to this region.
ARTICLE | doi:10.20944/preprints201807.0065.v1
Subject: Life Sciences, Endocrinology & Metabolomics Keywords: hypothalamus; insulin resistance; inflammation; docosahexaenoic acid; PI3K inhibitor; AKT
Online: 4 July 2018 (09:58:03 CEST)
Saturated fatty acids are implicated in the development of metabolic diseases, including obesity and type 2 diabetes. There is evidence, however, that polyunsaturated fatty acids can counteract the pathogenic effects of saturated fatty acids. To gain insight into the early molecular mechanisms by which fatty acids influence hypothalamic inflammation and insulin resistance, we performed time-course experiments in a hypothalamic cell line, using different durations of treatment with the saturated fatty acid palmitate, and the omega-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA). Western blot analysis revealed that palmitate elevated the protein levels of phospho(p)AKT in a time-dependent manner. This effect seems involved in the pathogenicity of palmitate, as temporary inhibition of the PI3K/AKT pathway by selective PI3K inhibitors prevented palmitate-induced insulin resistance. Similarly to palmitate, DHA also increased levels of pAKT, but to a weaker extent. Co-administration of DHA with palmitate decreased pAKT close to the basal level after 8 h, and prevented palmitate-induced insulin resistance after 12 h. Measurement of the inflammatory markers pJNK and pNFκB-p65 revealed tonic elevation of both markers in the presence of palmitate alone. DHA alone transiently induced elevation of pJNK, returning to basal levels by 12 h treatment. Co-administration of DHA with palmitate prevented palmitate-induced inflammation after 12 h, but not at earlier time points.
REVIEW | doi:10.20944/preprints201711.0026.v1
Subject: Medicine & Pharmacology, General Medical Research Keywords: Thyroid; Thyroid Hormone; Disrupting Compound; Hypothalamus Pituitary Thyroid axis; TSH
Online: 3 November 2017 (12:38:49 CET)
Endocrine disruptor compounds are exogenous agents able to interfere with a gland function, exerting their action across different functional passages, from the synthesis to the metabolism and binding to receptors of the hormone produced. Several issues such as different levels and time of exposure and different action across different ages as well as gender, make the study of endocrine disruptors still a challenge. Thyroid is very sensitive to the action of disruptors, and considering the importance of a correct thyroid function for physical and cognitive functioning, addressing this topic should be considered a priority. In this review we examined the most recent studies, many of them concentrating on maternal and child exposure, conducted to assess the impact of industrial chemicals which showed an impact on thyroid function. So far, the number of studies conducted on that topic is not sufficient to provide solid conclusions and lead to homogeneous guidelines. The lack of uniformity is certainly due to differences in areas and populations examined, the different conditions of exposures and the remarkable inter-subject variability. Nonetheless, the European Commission for Health and Food Safety is implementing recommendations to ensure that substances identified as endocrine disruptors will be withdrawn from the market.
REVIEW | doi:10.20944/preprints202107.0440.v1
Subject: Life Sciences, Biochemistry Keywords: neural stem cells; hypothalamus; circumventricular organs; limbic system; neuronal plasticity; hippocampus
Online: 20 July 2021 (10:03:05 CEST)
Evidence on adult mammalian neurogenesis and scarce studies with human brains led to the idea that adult human neurogenesis occurs in the subgranular zone (SGZ) of the dentate gyrus and in the subventricular zone (SVZ). However, findings published from 2018 rekindled controversies on adult human SGZ neurogenesis. We systematically reviewed studies published during the first decade of characterization of adult human neurogenesis (1994–2004) – when the two-neurogenic-niche concept in humans was consolidated – and compared with further studies. The synthesis of both periods is that adult human neurogenesis occurs in an intensity ranging from practically zero to a level comparable to adult mammalian neurogenesis in general, which is the prevailing conclusion. Nonetheless, Bernier and colleagues showed in 2000 intriguing indications of adult human neurogenesis in a broad area including the limbic system. Likewise, we later showed evidence that limbic and hypothalamic structures surrounding the circumventricular organs form a continuous zone expressing neurogenesis markers encompassing the SGZ and SVZ. The conclusion is that publications from 2018 on adult human neurogenesis did not bring novel findings on location of neurogenic niches. Rather, we expect that the search of neurogenesis beyond the canonical adult mammalian neurogenic niches will confirm our indications that adult human neurogenesis is orchestrated in a broad brain area. We predict that this approach may, for example, clarify that human hippocampal neurogenesis occurs mostly in the CA1-subiculum zone and that the previously identified human rostral migratory stream arising from the SVZ is indeed the column of the fornix expressing neurogenesis markers.
ARTICLE | doi:10.20944/preprints202208.0351.v1
Subject: Medicine & Pharmacology, General Medical Research Keywords: astrocytes; hypoglycemia; diabetes mellitus, type 1; mitochondria; glycemic control; hypothalamus; glutamic acid.
Online: 18 August 2022 (14:24:35 CEST)
Recurrent hypoglycaemia, a common side-effect of insulin therapy in the treatment of type 1 diabetes, induces impaired glucose-sensing. Better understanding of how astrocytes, important non-neuronal cells in the brain, function in low glucose environments may improve our understanding of recurrent hypoglycaemia-induced defective counterregulation. Astrocytes contribute to glutamatergic signalling, which is required for hypoglycaemia counterregulation and is impaired by recurrent insulin-induced hypoglcyaemia. This study examined the glutamate response of astrocytes when challenged with acute and recurrent low glucose (RLG) exposure. The metabolic responses of cortical (CRTAS) and hypothalamic (HTAS) primary rat astrocytes were measured in acute and recurrent low glucose using extracellular flux analyses. RLG caused mitochondrial adaptations in both HTAS and CRTAS, many of which were attenuated by glutamate exposure during low glucose treatments. We observed an increase in capacity of HTAS to metabolise glutamine after RLG exposure. Demonstrating astrocytic heterogeneity in the response to LG, CRTAS increased cellular acidification, a marker of glycolysis in LG, whereas this decreased in HTAS. The directional change in intracellular Ca2+ levels of each cell type, correlated with the change in extracellular acidification rate (ECAR) during LG. Further examination of glutamate-induced Ca2+ responses in low glucose treated CRTAS and HTAS identified sub-populations of glucose-excited- and glucose-inhibited-like cells with differing responses to glutamate. Lastly, release of the gliotransmitter ATP by HTAS was elevated by RLG, both with and without concurrent glutamate exposure. Therefore, hypothalamic astrocytes adapt to RLG by increasing glutamate uptake and oxidation in a manner that attenuates RLG-induced mitochondrial adaptations.
REVIEW | doi:10.20944/preprints202103.0245.v1
Subject: Life Sciences, Biochemistry Keywords: early life adversity; stress; psychosocial stress; hypothalamus-pituitary-adrenal axis; ageing; immuno-senescence; inflammageing; Developmental origins of health and disease
Online: 9 March 2021 (09:26:00 CET)
There are many ‘faces’ of early life adversity (ELA), such as childhood trauma, institutionalization, abuse or exposure to environmental toxins. These have been implicated in the onset and severity of a wide range of chronic non-communicable diseases later in life. The later-life disease risk has a well-established immunological component. This raises the question as to whether accelerated immune-ageing mechanistically links early-life adversity to the lifelong health trajectory resulting in either ‘poor’ or ‘healthy’ ageing. Here we examine observational and mechanistic studies of ELA and inflammageing, highlighting common and distinct features in these two life stages. Many biological processes appear in common including reduction in telomere length, increased immuno-senescence, metabolic distortions and chronic (viral) infections. We propose that ELA shapes the developing immune, endocrine and nervous system in a non-reversible way, creating a distinct phenotype with accelerated immuno-senescence and systemic inflammation. We believe that ELA acts as an accelerator for inflammageing and age-related diseases. Furthermore, we now have the tools and cohorts to be able to dissect the interaction between early life adversity and later life phenotype. This should, in the near future, allow us to identify the ecological and mechanistic processes that are involved in ‘healthy’ or accelerated immune-ageing.
Subject: Life Sciences, Biochemistry Keywords: glucose; glycogen; gluconeogenesis; early life adversity; acute stress; chronic stress; psychosocial stress; hypothalamus-pituitary-adrenal axis; ageing; immuno-senescence; inflamm-ageing; Developmental origins of health and disease
Online: 23 March 2021 (09:04:41 CET)
The physiological response to a psychological stressor broadly impacts energy metabolism. In-versely, changes in energy availability affect the physiological response to the stressor in terms of hypothalamus, pituitary adrenal axis (HPA) and sympathetic nervous system activation. Glu-cocorticoids, the endpoint of the HPA axis, are critical checkpoints in endocrine control of ener-gy homeostasis and have been linked to metabolic diseases including obesity, insulin resistance and type 2 diabetes. Glucocorticoids, through the glucocorticoid receptor, activate transcription of genes associated with glucose and lipid regulatory pathways and thereby control both physi-ological and pathophysiological systemic energy homeostasis. Here, we summarize the current knowledge of glucocorticoid functions in energy metabolism and systemic metabolic dysfunc-tion, particularly focusing on glucose and lipid metabolism. There are elements in the external environment that induce lifelong changes in the HPA axis stress response and glucocorticoid levels, the most prominent are early-life adversity, or exposure to traumatic stress. We hypothe-sise that when the HPA axis is so disturbed after early-life adversity, it will fundamentally alter hepatic gluconeogenesis, inducing hyperglycaemia, and hence crystalise the significant lifelong risk of developing either the metabolic syndrome, or type 2 diabetes. This gives a “Jekyll and Hyde” role to gluconeogenesis, providing the necessary energy in situations of acute stress, but driving towards pathophysiological consequences when the HPA axis has been altered.