Inhibition of high-fat diet-induced inflammatory responses in adipose tissue by SF1-expressing neurons of the ventromedial hypothalamus

Inflammation and thermogenesis in white adipose tissue (WAT) at different sites influence the overall effects of obesity on metabolic health. In mice fed a high-fat diet (HFD), inflammatory responses are less pronounced in inguinal WAT (ingWAT) than in epididymal WAT (epiWAT). Here we show that ablation and activation of steroidogenic factor 1 (SF1)-expressing neurons in the ventromedial hypothalamus (VMH) oppositely affect the expression of inflammation-related genes and the formation of crown-like structures by infiltrating macrophages in ingWAT, but not in epiWAT, of HFD-fed mice, with these effects being mediated by sympathetic nerves innervating ingWAT. In contrast, SF1 neurons of the VMH preferentially regulated the expression of thermogenesis-related genes in interscapular brown adipose tissue (BAT) of HFD-fed mice. These results suggest that SF1 neurons of the VMH differentially regulate inflammatory responses and thermogenesis among various adipose tissue depots and restrain inflammation associated with diet-induced obesity specifically in ingWAT.

Neural insights into sweet taste transduction and hunger-induced taste modification in mice

Feeding is one of the most fundamental activities in the survival and reproduction of animals. During feeding, the gustatory system functions as a gate keeper to evaluate food quality. Accumulated evidence in the field of taste research has shown that five basic tastes (sweet, umami, sour, bitter, and salty) are sensed by the corresponding taste receptors expressed in taste receptor cells on the tongue. In contrast, brain mechanisms that transduce or modify taste information have been less studied. In this review, I introduce our recent findings on the sweet taste transduction in the brainstem of mice and explain the hypothalamic neuronal network regulating hunger-induced taste modification. Finally, future perspectives are discussed.

De novo transcriptome analysis and comparative expression profiling of genes associated with the taste-modifying protein neoculin in Curculigo latifolia and Curculigo capitulata fruits

Background

Curculigo latifolia is a perennial plant endogenous to Southeast Asia whose fruits contain the taste-modifying protein neoculin, which binds to sweet receptors and makes sour fruits taste sweet. Although similar to snowdrop (Galanthus nivalis) agglutinin (GNA), which contains mannose-binding sites in its sequence and 3D structure, neoculin lacks such sites and has no lectin activity. Whether the fruits of C. latifolia and other Curculigo plants contain neoculin and/or GNA family members was unclear.

Results

Through de novo RNA-seq assembly of the fruits of C. latifolia and the related C. capitulata and detailed analysis of the expression patterns of neoculin and neoculin-like genes in both species, we assembled 85,697 transcripts from C. latifolia and 76,775 from C. capitulata using Trinity and annotated them using public databases. We identified 70,371 unigenes in C. latifolia and 63,704 in C. capitulata. In total, 38.6% of unigenes from C. latifolia and 42.6% from C. capitulata shared high similarity between the two species. We identified ten neoculin-related transcripts in C. latifolia and 15 in C. capitulata, encoding both the basic and acidic subunits of neoculin in both plants. We aligned these 25 transcripts and generated a phylogenetic tree. Many orthologs in the two species shared high similarity, despite the low number of common genes, suggesting that these genes likely existed before the two species diverged. The relative expression levels of these genes differed considerably between the two species: the transcripts per million (TPM) values of neoculin genes were 60 times higher in C. latifolia than in C. capitulata, whereas those of GNA family members were 15,000 times lower in C. latifolia than in C. capitulata.

Conclusions

The genetic diversity of neoculin-related genes strongly suggests that neoculin genes underwent duplication during evolution. The marked differences in their expression profiles between C. latifolia and C. capitulata may be due to mutations in regions involved in transcriptional regulation. Comprehensive analysis of the genes expressed in the fruits of these two Curculigo species helped elucidate the origin of neoculin at the molecular level.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07674-3.

Recent Advances in Neural Circuits for Taste Perception in Hunger

Feeding is essential for survival and taste greatly influences our feeding behaviors. Palatable tastes such as sweet trigger feeding as a symbol of a calorie-rich diet containing sugar or proteins, while unpalatable tastes such as bitter terminate further consumption as a warning against ingestion of harmful substances. Therefore, taste is considered a criterion to distinguish whether food is edible. However, perception of taste is also modulated by physiological changes associated with internal states such as hunger or satiety. Empirically, during hunger state, humans find ordinary food more attractive and feel less aversion to food they usually dislike. Although functional magnetic resonance imaging studies performed in primates and in humans have indicated that some brain areas show state-dependent response to tastes, the mechanisms of how the brain senses tastes during different internal states are poorly understood. Recently, using newly developed molecular and genetic tools as well as in vivo imaging, researchers have identified many specific neuronal populations or neural circuits regulating feeding behaviors and taste perception process in the central nervous system. These studies could help us understand the interplay between homeostatic regulation of energy and taste perception to guide proper feeding behaviors.

Homeostatic versus hedonic control of carbohydrate selection

Macronutrient intake is associated with cardiometabolic health, ageing and longevity, but the mechanisms underlying its regulation have remained unclear. Most rodents increase carbohydrate selection under certain physiological and pathological conditions such as fasting. When presented with a choice between a basally preferable high-fat diet (HFD) and a high-carbohydrate diet (HCD) such as a high-sucrose diet, fasted mice first eat the HFD and then switch to the HCD during the first few hours of refeeding and continue to eat the HCD up to 24 h in the two-diet choice approach. Such consumption of an HCD after fasting reverses the fasting-induced increase in the plasma concentration of ketone bodies more rapidly than does refeeding with an HFD alone. 5'-AMP-activated protein kinase (AMPK)-regulated neurons in the paraventricular nucleus of the hypothalamus (PVH) that express corticotropin-releasing hormone (CRH) are necessary and sufficient for the fasting-induced selection of carbohydrate over an HFD in mice. These neurons appear to contribute to a fasting-induced increase in the positive valence of carbohydrate without affecting the preference for more palatable and energy-dense diets such as an HFD. Identification of the neural circuits in which AMPK-regulated CRH neurons in the PVH of mice are embedded should shed new light on the physiological and molecular mechanisms responsible for macronutrient selection.

SatB2-Expressing Neurons in the Parabrachial Nucleus Encode Sweet Taste

The gustatory system plays an important role in sensing appetitive and aversive tastes for evaluating food quality. In mice, taste signals are relayed by multiple brain regions, including the parabrachial nucleus (PBN) of the pons, before reaching the gustatory cortex via the gustatory thalamus. Recent studies show that taste information at the periphery is encoded in a labeled-line manner, such that each taste modality has its own receptors and neuronal pathway. In contrast, the molecular identity of gustatory neurons in the CNS remains unknown. Here, we show that SatB2-expressing neurons in the PBN play a pivotal role in sweet taste transduction. With cell ablation, in vivo calcium imaging, and optogenetics, we reveal that SatB2^PBN neurons encode positive valance and selectively transmit sweet taste signals to the gustatory thalamus.

Neoculin as a New Taste-modifying Protein Occurring in the Fruit ofCurculigo latifolia

A unique taste-modifying activity that converts the sense of sourness to the sense of sweetness occurs in the fruit of the plant Curculigo latifolia, intrinsic to West Malaysia. The active component, known as curculin, is a protein consisting of two identical subunits. We have found a new taste-modifying protein, named neoculin, of the same origin. Both chemical analysis and cDNA cloning characterized neoculin as a heterodimeric protein consisting of an acidic, glycosylated subunit of 113 amino acid residues and a basic subunit that is the monomeric curculin itself.

Biochemical and genomic analysis of neoculin compared to monocot mannose-binding lectins

Neoculin occurring in an edible tropical fruit is a heterodimeric protein which has both sweetness and a taste-modifying activity that converts sourness to sweetness. Both the primary and the overall tertiary structures of neoculin resemble those of monocot mannose-binding lectins. This study investigated differences in biochemical properties between neoculin and the lectins. Structural comparison between the mannose-binding sites of lectins and the corresponding regions of neoculin showed that there is at least one amino acid substitution at each site in neoculin, suggesting a reason for the lack of its mannose-binding ability. This was consistent with hemagglutination assay data demonstrating that neoculin had no detectable agglutinin activity. DNA microarray analysis indicated that neoculin had no significant influence on gene expression in Caco-2 cell, whereas kidney bean lectin (Phaseolus vulgaris agglutinin) greatly influenced various gene expressions. These data strongly suggest that neoculin has no lectin-like properties, encouraging its practical use in the food industry.

Sentinel lymph node biopsy in breast cancer using blue dye with or without isotope localization

BACKGROUND

The purpose of this study was to determine the feasibility of sentinel lymph node (SLN) biopsy using blue dye with or without isotope localization to predict the presence of axillary and internal mammary lymph node (IMN) metastases in patients with breast cancer. We also investigated whether multiple sectioning of the SLN could improve the accuracy of frozen section examination.

METHOD

One-hundred twenty-six patients underwent dye-guided or dye- and gamma probe-guided SLN biopsy followed by complete axillary lymph node dissection (ALND). No ALND was performed in the 14 patients with small tumors and a negative SLN. In addition, 69 patients underwent IMN biopsy.

RESULTS

The axillary SLN was identified in 123 of 140 (88%) patients. An accuracy rate of 90% was obtained by frozen section examination of the SLN, which increased to 100% in patients examined with a greater number of sections. Lymphatic flow to the IMN and/or a radioactive hot spot in the IMN was found in 9 of 102 (9%) patients, while a hot node was detected using a gamma probe in only 2 of these patients. No involvement of the IMNs was found histologically in these 9 patients. IMN involvement was found in 7 of 61 (11%) patients without lymphatic flow to the IMNs or a hot spot by lymphoscintigraphy or who did not undergo lymphoscintigraphy.

CONCLUSION

ALND can be avoided in patients with small breast cancers and a negative SLN. SLN biopsy guided by lymphatic mapping is unreliable for identifying metastases to IMNs.

Gastric signet ring cell adenocarcinoma metastatic to the iris

PURPOSE

To report a case of gastric signet ring cell adenocarcinoma metastatic to the iris.

METHODS

Case report. A 38-year-old man with a history of gastric signet ring cell adenocarcinoma presented with a white lacework-like mass on the iris of the left eye.

RESULTS

Systemic medical evaluation demonstrated no other metastasis. Because of increased intraocular pressure, trabeculectomy and peripheral iridectomy were performed. Histology of the iris specimen demonstrated metastasis of gastric signet ring cell adenocarcinoma to the iris.

CONCLUSION

Gastric signet ring cell carcinoma can metastasize to the iris. Ophthalmologists should include this possibility in the differential diagnosis when encountering a patient with a history of gastric adenocarcinoma and an iris mass.