Proteomic analysis of rat hypothalamus revealed the role of ubiquitin-proteasome system in the genesis of DR or DIO

Comparative Hypothalamic Proteomic Analysis Between Diet-Induced Obesity and Diet-Resistant Rats

Obesity arises from a complex interplay of genetic and environmental factors. Even among individuals with the same genetic predisposition, diet-induced obesity (DIO) exhibits varying degrees of susceptibility, which are categorized as DIO and diet-induced obesity resistance (DR). The hypothalamus plays a pivotal role in regulating energy homeostasis. This study performed a comparative hypothalamic proteomic analysis in DIO and DR rats to identify differentially expressed proteins (DEPs) associated with alterations in body weight. Male Sprague Dawley rats were fed either a standard chow diet or a high-fat diet for 12 weeks. DIO rats exhibited the most rapid weight gain compared to both the control and DR rats. Despite consuming similar caloric intake, DR rats exhibited less weight gain relative to DIO rats. Proteomic analysis revealed 31 DEPs in the hypothalamus of DR rats compared to DIO rats (with a false discovery rate (FDR) < 1%). Notably, 14 proteins were upregulated and 17 proteins were downregulated in DR rats. Gene ontology analysis revealed an enrichment of ion-binding proteins, such as those binding to Fe2+, Zn2+, Ca2+, and Se, as well as proteins involved in neuronal activity and function, potentially enhancing neuronal development and cognition in DR rats. The DEPs pathway analysis via the Kyoto Encyclopedia of Genes and Genomes (KEGG) implicated starch and sucrose metabolism, antigen processing and presentation, and the regulation of inflammatory mediator affecting TRP channels. Western blotting confirmed the proteomic findings for TRPV4, CaMKV, RSBN1, and BASP1, which were consistent with those obtained from Tandem Mass tag (TMT) proteomic analysis. In conclusion, our study highlights the hypothalamic proteome as a critical determinant in the susceptibility to DIO and provides novel targets for obesity prevention and treatment.

Short-term exposure to an obesogenic diet causes dynamic dysregulation of proteasome-mediated protein degradation in the hypothalamus of female rats

OBJECTIVES

Previous work has shown that exposure to a high fat diet dysregulates the protein degradation process in the hypothalamus of male rodents. However, whether this occurs in a sex-independent manner is unknown. The objective of this study was to determine the effects of a short-term obesogenic diet on the ubiquitin-proteasome mediated protein degradation process in the hypothalamus of female rats.

METHODS

We fed young adult female rats a high fat diet or standard rat chow for 7 weeks. At the end of the 7th week, animals were euthanized and hypothalamus nuclear and cytoplasmic fractions were collected. Proteasome activity and degradation-specific (K48) ubiquitin signaling were assessed. Additionally, we transfected female rats with CRISPR-dCas9-VP64 plasmids in the hypothalamus prior to exposure to the high fat diet in order to increase proteasome activity and determine the role of reduced proteasome function on weight gain from the obesogenic diet.

RESULTS

We found that across the diet period, females gained weight significantly faster on the high fat diet than controls and showed dynamic downregulation of proteasome activity, decreases in proteasome subunit expression and an accumulation of degradation-specific K48 polyubiquitinated proteins in the hypothalamus. Notably, while our CRISPR-dCas9 manipulation was able to selectively increase some forms of proteasome activity, it was unable to prevent diet-induced proteasome downregulation or abnormal weight gain.

CONCLUSIONS

Collectively, these results reveal that acute exposure to an obesogenic diet causes reductions in the protein degradation process in the hypothalamus of females.

A novel c.-652C>T mutation in UCHL1 gene is associated with the growth performance in Yangzhou goose

As a member of the ubiquitin-dependent proteasome degradation pathway, Ubiquitin carboxyl-terminal hydrolase-L1 (UCHL1) plays a key role in post-translational modification and protein degradation, and it is extensive and important for the regulation of various biological functions of the organism. However, its function remains unclear in goose growth performance. In this study, the full-length genomic DNA and coding region of UCHL1 gene was firstly cloned and characterized in Yangzhou goose. Tissue expression profile revealed that UCHL1 was exclusively expressed in brain and gonads. A novel single nucleotide polymorphisms c.-652C>T which is significantly related to 64-d body weight of Yangzhou goose was found in UCHL1 promoter region by comparative sequencing. Correlation analysis in a population of 405 geese showed that TT genotype individuals had higher body weight than CC individuals in male, but not in female geese. Dual-luciferase reporter assay indicated that the single nucleotide polymorphisms c.-652C>T is located at the core promoter region of UCHL1, and the promoter transcription activity was significantly increased (P < 0.01) when allele C changed to T. Geese with TT genotype had higher mRNA level of UCHL1 in brain tissue than those of CC genotype (P < 0.01). Compared with CC individuals, neuropeptide Y and AdipoR1 mRNA level was significantly higher in TT individuals (P < 0.05), while FAS mRNA level was lower in the TT individuals (P < 0.05). In summary, we identify a novel mutation in the promoter of UCHL1 gene, which can alter transcriptional activity of UCHL1 gene, and affect the growth performance of male goose.

Dysregulation of protein degradation in the hippocampus is associated with impaired spatial memory during the development of obesity

Studies have shown that long-term exposure to high fat and other obesogenic diets results in insulin resistance and altered blood brain barrier permeability, dysregulation of intracellular signaling mechanisms, changes in DNA methylation levels and gene expression, and increased oxidative stress and neuroinflammation in the hippocampus, all of which are associated with impaired spatial memory. The ubiquitin-proteasome system controls the majority of protein degradation in cells and is a critical regulator of synaptic plasticity and memory formation. Yet, whether protein degradation in the hippocampus becomes dysregulated following weight gain and is associated with obesity-induced memory impairments is unknown. Here, we used a high fat diet procedure in combination with behavioral and subcellular fractionation protocols and a variety of biochemical assays to determine if ubiquitin-proteasome activity becomes altered in the hippocampus during obesity development and whether this is associated with impaired spatial memory. We found that only 6 weeks of exposure to a high fat diet was sufficient to impair performance on an object location task in rats and resulted in dynamic dysregulation of ubiquitin-proteasome activity in the nucleus and cytoplasm of cells in the hippocampus. Furthermore, these changes in the protein degradation process extended into cortical regions also involved in spatial memory formation. Collectively, these results indicate that weight gain-induced memory impairments may be due to altered ubiquitin-proteasome signaling that occurs during the early stages of obesity development.

Cerebrocortical proteome profile of female rats subjected to the western diet and chronic social stress

The energy-dense western diet significantly increases the risk of obesity, type 2 diabetes, cardiovascular episodes, stroke, and cancer. Recently more attention has been paid to the contribution of an unhealthy lifestyle on the development of central nervous system disorders. Exposure to long-lasting stress is one of the key lifestyle modifications associated with the increased prevalence of obesity and metabolic diseases. The main goal of the present study was to verify the hypothesis that exposure to chronic stress modifies alterations in the brain proteome induced by the western diet. Female adult rats were fed with the prepared chow reproducing the human western diet and/or subjected to chronic stress induced by social instability for 6 weeks. A control group of lean rats were fed with a standard diet. Being fed with the western diet resulted in an obese phenotype and induced changes in the serum metabolic parameters. The combination of the western diet and chronic stress exposure induced more profound changes in the rat cerebrocortical proteome profile than each of these factors individually. The down-regulation of proteins involved in neurotransmitter secretion (Rph3a, Snap25, Syn1) as well as in learning and memory processes (Map1a, Snap25, Tnr) were identified, while increased expression was detected for 14-3-3 protein gamma (Ywhag) engaged in the modulation of the insulin-signaling cascade in the brain. An analysis of the rat brain proteome reveals important changes that indicate that a combination of the western diet and stress exposure may lead to impairments of neuronal function and signaling.

Downregulation of HIF complex in the hypothalamus exacerbates diet-induced obesity

Hypothalamic hypoxia-inducible factor-1 (HIF-1) can regulate whole-body energy homeostasis in response to changes in blood glucose, suggesting that it acts as a sensor for systemic energy stores. Here, we hypothesized that hypothalamic HIF-1 could be affected by diet-induced obesity (DIO). We used eight-week old, male C57Bl6 mice, fed normal chow diet or with high fat diet for 1, 3, 7, 14 and 28 days. The expression of HIF-1alpha and HIF-1beta was measured by PCR and western blotting and its hypothalamic distribution was evaluated by fluorescence microscopy. Inhibition of HIF-1beta in arcuate nucleus of hypothalamus was performed using stereotaxic injection of shRNA lentiviral particles and animals were grouped under normal chow diet or high fat diet for 14 days. Using bioinformatics, we show that in humans, the levels of HIF-1 transcripts are directly correlated with those of hypothalamic transcripts for proteins involved in inflammation, regulation of apoptosis, autophagy, and the ubiquitin/proteasome system; furthermore, in rodents, hypothalamic HIF-1 expression is directly correlated with the phenotype of increased energy expenditure. In mice, DIO was accompanied by increased HIF-1 expression. The inhibition of hypothalamic HIF-1 by injection of an shRNA resulted in a further increase in body mass, a decreased basal metabolic rate, increased hypothalamic inflammation, and glucose intolerance. Thus, hypothalamic HIF-1 is increased during DIO, and its inhibition worsens the obesity-associated metabolic phenotype. Thus, hypothalamic HIF-1 emerges as a target for therapeutic intervention against obesity.

Mapping Molecular Datasets Back to the Brain Regions They are Extracted from: Remembering the Native Countries of Hypothalamic Expatriates and Refugees

This article focuses on approaches to link transcriptomic, proteomic, and peptidomic datasets mined from brain tissue to the original locations within the brain that they are derived from using digital atlas mapping techniques. We use, as an example, the transcriptomic, proteomic and peptidomic analyses conducted in the mammalian hypothalamus. Following a brief historical overview, we highlight studies that have mined biochemical and molecular information from the hypothalamus and then lay out a strategy for how these data can be linked spatially to the mapped locations in a canonical brain atlas where the data come from, thereby allowing researchers to integrate these data with other datasets across multiple scales. A key methodology that enables atlas-based mapping of extracted datasets-laser-capture microdissection-is discussed in detail, with a view of how this technology is a bridge between systems biology and systems neuroscience.

The pathophysiology of defective proteostasis in the hypothalamus - from obesity to ageing

Hypothalamic dysfunction has emerged as an important mechanism involved in the development of obesity and its comorbidities, as well as in the process of ageing and age-related diseases, such as type 2 diabetes mellitus, hypertension and Alzheimer disease. In both obesity and ageing, inflammatory signalling is thought to coordinate many of the cellular events that lead to hypothalamic neuronal dysfunction. This process is triggered by the activation of signalling via the toll-like receptor 4 pathway and endoplasmic reticulum stress, which in turn results in intracellular inflammatory signalling. However, the process that connects inflammation with neuronal dysfunction is complex and includes several regulatory mechanisms that ultimately control the homeostasis of intracellular proteins and organelles (also known as 'proteostasis'). This Review discusses the evidence for the key role of proteostasis in the control of hypothalamic neurons and the involvement of this process in regulating whole-body energy homeostasis and lifespan.

Nutritional conditions regulate transcriptional activity of SF-1 by controlling sumoylation and ubiquitination

Steroidogenic factor 1 (SF-1) is a transcription factor expressed in the ventral medial nucleus of the hypothalamus that regulates energy homeostasis. However, the molecular mechanisms of SF-1 in the control of energy balance are largely unknown. Here, we show that nutritional conditions, such as the presence or absence of serum, affect SF-1 action. Serum starvation significantly decreased hypothalamic SF-1 levels by promoting ubiquitin-dependent degradation, and sumoylation was required for this process. SF-1 transcriptional activity was also differentially regulated by nutritional status. Under normal conditions, the transcriptional activity of hypothalamic SF-1 was activated by SUMO, but this was attenuated during starvation. Taken together, these results indicate that sumoylation and ubiquitination play crucial roles in the regulation of SF-1 function and that these effects are dependent on nutritional conditions, further supporting the importance of SF-1 in the control of energy homeostasis.

Proteomic profiling of the rat hypothalamus

Background

The hypothalamus plays a pivotal role in numerous mechanisms highly relevant to the maintenance of body homeostasis, such as the control of food intake and energy expenditure. Impairment of these mechanisms has been associated with the metabolic disturbances involved in the pathogenesis of obesity. Since rodent species constitute important models for metabolism studies and the rat hypothalamus is poorly characterized by proteomic strategies, we performed experiments aimed at constructing a two-dimensional gel electrophoresis (2-DE) profile of rat hypothalamus proteins.

Results

As a first step, we established the best conditions for tissue collection and protein extraction, quantification and separation. The extraction buffer composition selected for proteome characterization of rat hypothalamus was urea 7 M, thiourea 2 M, CHAPS 4%, Triton X-100 0.5%, followed by a precipitation step with chloroform/methanol. Two-dimensional (2-D) gels of hypothalamic extracts from four-month-old rats were analyzed; the protein spots were digested and identified by using tandem mass spectrometry and database query using the protein search engine MASCOT. Eighty-six hypothalamic proteins were identified, the majority of which were classified as participating in metabolic processes, consistent with the finding of a large number of proteins with catalytic activity. Genes encoding proteins identified in this study have been related to obesity development.

Conclusion

The present results indicate that the 2-DE technique will be useful for nutritional studies focusing on hypothalamic proteins. The data presented herein will serve as a reference database for studies testing the effects of dietary manipulations on hypothalamic proteome. We trust that these experiments will lead to important knowledge on protein targets of nutritional variables potentially able to affect the complex central nervous system control of energy homeostasis.