We have recently identified a tachykinin-related peptide (AmTRP) from the mushroom bodies (MBs) of the brain of the honeybee Apis mellifera L. by using direct matrix-assisted laser desorption/ionization with time-of-flight mass spectometry and have isolated its cDNA. Here, we have examined prepro-AmTRP gene expression in the honeybee brain by using in situ hybridization. The prepro-AmTRP gene is expressed predominantly in the MBs and in some neurons located in the optic and antennal lobes. cDNA microarray studies have revealed that AmTRP expression is enriched in the MBs compared with other brain regions. There is no difference in AmTRP-expressing cells among worker, queen, and drone brains, suggesting that the cell types that express the prepro-AmTRP gene do not change according to division of labor, sex, or caste. The unique expression pattern of the prepro-AmTRP gene suggests that AmTRPs function as neuromodulators in the MBs of the honeybee brain.

Peptidergic hormones, neurotransmitters, and neuromodulators are extracellular signaling molecules that play central roles in physiological signal transmissions between various cells, tissues, and organs. These factors are primarily translated as inactive precursor proteins according to the genetic information. These precursor proteins are then cleaved by various proteases including signal peptidases and processing enzymes to produce matured bioactive factors. During these processes, various fragmented peptides are also produced from the same precursor proteins. Such fragmented peptides may have various unexpected biological activities that have not been identified yet because these peptides are considered to be produced and released along with mature factors at the same secretary pathways. Recently, we found that various fragmented peptides of mitochondrial proteins that are produced during the maturation processes, such as fragments of cytochrome c oxidase, activate neutrophils whose functions are distinct from their parent proteins. These findings suggest the existence of many different functional peptides whose functions have not been identified yet. These unidentified peptides may play a variety of roles in various regulatory mechanisms, and therefore, they are expected to provide novel regulatory and signaling mechanisms, "Peptide World".

To clarify the molecular basis underlying the neural function of the honeybee mushroom bodies (MBs), we identified three genes preferentially expressed in MB using cDNA microarrays containing 480 differential display-positive candidate cDNAs expressed locally or differentially, dependent on caste/aggressive behavior in the honeybee brain. One of the cDNAs encodes a putative type I inositol 1,4,5-trisphosphate (IP 3 ) 5-phosphatase and was expressed preferentially in one of two types of intrinsic MB neurons, the large-type Kenyon cells, suggesting that IP 3 -mediated Ca 2+ signaling is enhanced in these neurons. ß

Background Based on epidemiological and experimental studies, type 2 diabetes mellitus (T2DM), especially insulin resistance that comprises the core mechanism of T2DM, has been recognized as a significant risk factor for Alzheimer’s disease (AD). Studies in humans and diabetic AD model mice have indicated a correlation between insulin resistance and increased amyloid deposition in the brain. Paradoxically, mice with targeted disruption of genes involved in the insulin signaling pathway showed protective effects against the AD-related pathology. These conflicting observations raise an issue as to the relationship between dysregulation of insulin signaling and AD pathophysiology. Methods To study the causal relations and molecular mechanisms underlying insulin resistance-induced exacerbation of amyloid pathology, we investigated the chronological changes in the development of insulin resistance and amyloid pathology in two independent insulin-resistant AD mouse models, i.e., long-term high-fat diet (HFD) feeding and genetic disruption of Irs2 , in combination with dietary interventions. In addition to biochemical and histopathological analyses, we examined the in vivo dynamics of brain amyloid-β (Aβ) and insulin by microdialysis technique. Results HFD-fed diabetic AD model mice displayed a reduced brain response to peripheral insulin stimulation and a decreased brain to plasma ratio of insulin during the hyperinsulinemic clamp. Diet-induced defective insulin action in the brain was accompanied by a decreased clearance of the extracellular Aβ in vivo and an exacerbation of brain amyloid pathology. These noxious effects of the HFD both on insulin sensitivity and on Aβ deposition in brains were reversibly attenuated by dietary interventions. Importantly, HFD feeding accelerated Aβ deposition also in the brains of IRS-2-deficient AD mice. Conclusions Our results suggested a causal and reversible association of brain Aβ metabolism and amyloid pathology by diet-dependent, but not genetically-induced, insulin-resistance. These observations raise the possibility that the causal factors of insulin resistance, e.g., metabolic stress or inflammation induced by HFD feeding, but not impaired insulin signaling per se, might be directly involved in the acceleration of amyloid pathology in the brain. Electronic supplementary material The online version of this article (10.1186/s13024-019-0315-7) contains supplementary material, which is available to authorized users.

Although neutrophils are known to migrate in response to various chemokines and complement factors, the substances involved in the early stages of their transmigration and activation have been poorly characterized to date. Here we report the discovery of a peptide isolated from healthy porcine hearts that activated neutrophils. Its primary structure is HLeu-Ser-Phe-Leu-Ile-Pro-Ala-Gly-Trp-Val-Leu-Ser-HisLeu-Asp-His-Tyr-Lys-Arg-Ser-Ser-Ala-Ala-OH, and it was indicated to originate from mitochondrial cytochrome c oxidase subunit VIII. This peptide caused chemotaxis at concentrations lower than that inducing ␤-hexosaminidase release. Such responses were observed in neutrophilic/granulocytic differentiated HL-60 cells but not in undifferentiated cells, and G i2 -type G proteins were suggested to be involved in the peptide signaling. Moreover the peptide activated human neutrophils to induce ␤-hexosaminidase secretion. A number of other amphipathic neutrophil-activating peptides presumably originating from mitochondrial proteins were also found. The present results suggest that neutrophils monitor such amphipathic peptides including the identified peptide as an initiation signal for inflammation at injury sites.Neutrophils are a type of leukocyte involved in the innate defense system. Once tissue injury occurs because of an infection or toxic cell debris resulting from cell necrosis, these cells migrate from the bloodstream to the injury sites. They are then activated to produce superoxide and digestive enzymes and to phagocytose toxic cell debris and the infectious microorganisms (1, 2). Chemokines, such as interleukin 8, are produced at tissue injury sites where they induce the migration and activation of neutrophils (3). Most of these chemokines are synthesized after the inflammatory stimuli, suggesting that they might not be the substances promoting the initial migration and activation of neutrophils because the transmigration of these cells is often observed immediately after tissue injury. Thus, it is likely that there are neutrophil-activating substances inducing the initial phase of migration. Some of these substances may be present in mitochondria because the contents of disrupted mitochondria, which are thought to be released immediately after necrosis in damaged tissues, promote neutrophilic migration (4). The responsible proteins or peptides, however, have not yet been purified. In the present study, we purified and identified a novel class of neutrophil-activating peptides from healthy porcine hearts that activate primary human neutrophils and neutrophilic/granulocytic differentiated HL-60 cells (HL-60-derived neutrophilic/granulocytic cells). 5 EXPERIMENTAL PROCEDURESPeptides that activated HL-60-derived neutrophilic/granulocytic cells were purified from healthy porcine hearts (outlined in Fig. 1) by monitoring the activity of fractions that induce ␤-hexosaminidase release from the cells. This enzyme can be easily assayed and is known to be quantitatively released from * This study was supported by a re...