Novel application of tyramide signal amplification (TSA): ultrastructural visualization of double-labeled immunofluorescent axonal profiles

Lachnum polysaccharide suppresses S180 sarcoma by boosting anti-tumor immune responses and skewing tumor-associated macrophages toward M1 phenotype

Therapeutic strategies that targeting tumor-associated macrophages (TAMs) reprogramming play a crucial role in ameliorating the immunosuppressive tumor microenvironment and boosting anti-tumor immune responses. In this study, we demonstrated that Lachnum polysaccharide (LEP) could work as an immunomodulator to reset TAMs from pro-tumor M2 to anti-tumor M1 phenotype. Mechanistically, LEP promoted Th1 polarization and the secretion of IFN-γ, which played a key role in M1 phenotype polarization. In parallel, LEP might directly activate M1 macrophages via TLR4 mediated NF-κB signaling pathway. Moreover, LEP also resulted in the accumulation of anti-tumor immune cells and decreased the infiltration of immunosuppressive cells such as myeloid-derived suppressor cells (MDSCs) and Treg cells, thereby potentiating anti-tumor immunity. In summary, these results revealed a novel mechanism of the anti-tumor effect of LEP and provided a potential new avenue targeting TAMs and cancer immunotherapy.

A novel closed-body model of spinal cord injury caused by high-pressure air blasts produces extensive axonal injury and motor impairments

Diffuse axonal injury is thought to be the basis of the functional impairments stemming from mild traumatic brain injury. To examine how axons are damaged by traumatic events, such as motor vehicle accidents, falls, sports activities, or explosive blasts, we have taken advantage of the spinal cord with its extensive white matter tracts. We developed a closed-body model of spinal cord injury in mice whereby high-pressure air blasts targeted to lower thoracic vertebral levels produce tensile, compressive, and shear forces within the parenchyma of the spinal cord and thereby cause extensive axonal injury. Markers of cytoskeletal integrity showed that spinal cord axons exhibited three distinct pathologies: microtubule breakage, neurofilament compaction, and calpain-mediated spectrin breakdown. The dorsally situated axons of the corticospinal tract primarily exhibited microtubule breakage, whereas all three pathologies were common in the lateral and ventral white matter. Individual axons typically demonstrated only one of the three pathologies during the first 24h after blast injury, suggesting that the different perturbations are initiated independently of one another. For the first few days after blast, neurofilament compaction was frequently accompanied by autophagy, and subsequent to that, by the fragmentation of degenerating axons. TuJ1 immunolabeling and mice with YFP-reporter labeling each revealed more extensive microtubule breakage than did βAPP immunolabeling, raising doubts about the sensitivity of this standard approach for assessing axonal injury. Although motor deficits were mild and largely transient, some aspects of motor function gradually worsened over several weeks, suggesting that a low level of axonal degeneration continued past the initial wave. Our model can help provide further insight into how to intervene in the processes by which initial axonal damage culminates in axonal degeneration, to improve outcomes after traumatic injury. Importantly, our findings of extensive axonal injury also caution that repeated trauma is likely to have cumulative adverse consequences for both brain and spinal cord.

Dynamic changes in fetal Leydig cell populations influence adult Leydig cell populations in mice

Testes contain two distinct Leydig cell populations during development: fetal and adult Leydig cells (FLCs and ALCs, respectively). ALCs are not derived from FLCs, and it is unknown whether these two populations share common progenitors. We discovered that hedgehog (Hh) signaling is responsible for transforming steroidogenic factor 1-positive (SF1(+)) progenitors into FLCs. However, not all SF1(+) progenitors become FLCs, and some remain undifferentiated through fetal development. We therefore hypothesized that if FLCs and ALCs share SF1(+) progenitors, increased Hh pathway activation in SF1(+) progenitor cells could change the dynamics and distribution of SF1(+) progenitors, FLCs, and ALCs. Using a genetic model involving constitutive activation of Hh pathway in SF1(+) cells, we observed reduced numbers of SF1(+) progenitor cells and increased FLCs. Conversely, increased Hh activation led to decreased ALC populations prepubertally, while adult ALC numbers were comparable to control testes. Hence, reduction in SF1(+) progenitors temporarily affects ALC numbers, suggesting that SF1(+) progenitors in fetal testes are a potential source of both FLCs and ALCs. Besides transient ALC defects, adult animals with Hh activation in SF1(+) progenitors had reduced testicular weight, oligospermia, and decreased sperm mobility. These defects highlight the importance of properly regulated Hh signaling in Leydig cell development and testicular functions.

Hypothalamic galanin-like peptide rescues the onset of puberty in food-restricted weanling rats

Galanin-like peptide (GALP) is a known mediator of metabolism and reproduction; however, the role that GALP plays in the onset of puberty is unknown. First, we tested the hypothesis that central GALP administration could rescue puberty in food-restricted weanling rats. GALP treatment in food-restricted rats of both sexes rescued the timing of the onset of puberty to that seen in ad lib. fed controls. Second, we tested whether GALP translation knocked-down in ad lib. fed, prepubertal rats would alter the timing of puberty. Knock-down females, but not males, showed a significant (P < 0.01) delay in the onset of puberty compared to controls. Third, we sought evidence that the role of GALP in pubertal onset is mediated by the kisspeptin system. In situ hybridisation analyses showed a significant (P < 0.01) reduction in Kiss1 mRNA within the hypothalamic arcuate nucleus in food-restricted rats compared to ad lib. fed controls and this reduction was prevented with i.c.v. GALP administration. Furthermore, analyses of Fos-immunoreactivity (-IR) after i.c.v. GALP treatment did not elicit Fos-IR within any kisspeptin neurones, nor are GALP and kisspeptin peptides or mRNA colocalised. These data demonstrate that hypothalamic GALP infusion maintained the onset of puberty in food-restricted weanling rats, although probably not via direct innervation of kisspeptin neurones.

Temporal assessment of traumatic axonal injury in the rat corpus callosum and optic chiasm

Impaired axoplasmic transport (IAT) and neurofilament compaction (NFC), two common axonal pathology processes involved in traumatic axonal injury (TAI), have been well characterized. TAI is found clinically and in animal models in brainstem white matter (WM) tracts and in the corpus callosum (CC), optic chiasm (Och), and internal capsule. Previous published quantitative studies of the time course of TAI expression induced by the Marmarou impact acceleration model have been limited to the brainstem. Accordingly, this study assessed the extent of IAT and NFC in the CC and Och at 8h, 28 h, 3 days and 7 days after traumatic brain injury (TBI) induction by the Marmarou impact acceleration model. IAT peak density was observed at 8h in the CC and 28 h in the Och post-TBI. NFC peak density was observed at 28 h in both structures. The density of IAT and NFC decreased with increasing survival time in both structures. The NFC density time profile followed a similar trend in both the Och and CC, whereas the IAT density time profile was variable between the Och and CC. Furthermore, a strong linear relationship was observed between IAT and NFC in the CC but not in the Och. These findings highlight the heterogeneity of TAI as evidenced by variable IAT and NFC injury time profiles in each anatomical structure. This variability indicates the requirement of multiple markers for a comprehensive TAI evaluation and multiple targeted treatments for TAI polypathology within its therapeutic window time frame.

Cellular detection of multiple antigens at single cell resolution using antibodies generated from the same species

Biology at a cellular level comes with a great amount of heterogeneity. It is now evident that even clonally propagated cells in an in vitro population do not express the same set of cellular epitopes. The vascular endothelial as well as blood cells show a very high degree of heterogeneity in expression of specific proteins. Although several methods exist for identification of genome or transcriptome from a single cell, there is still limited advancement in detection of multiple cellular antigens in a single cell. This has been mainly due to the limited availability of different antibodies. Single-cell detection methods involving the use of multiple monoclonal antibodies generated in the same species would therefore provide with an important tool for cellular detection of antigens. Here, we describe a method to assess multiple proteins in a cell using different antibodies generated in the same species.

Novel immunohistochemical techniques using discrete signal amplification systems for human cutaneous peripheral nerve fiber imaging

Confocal imaging uses immunohistochemical binding of specific antibodies to visualize tissues, but technical obstacles limit more widespread use of this technique in the imaging of peripheral nerve tissue. These obstacles include same-species antibody cross-reactivity and weak fluorescent signals of individual and co-localized antigens. The aims of this study were to develop new immunohistochemical techniques for imaging of peripheral nerve fibers. Three-millimeter punch skin biopsies of healthy individuals were fixed, frozen, and cut into 50-µm sections. Tissues were stained with a variety of antibody combinations with two signal amplification systems, streptavidin-biotin-fluorochrome (sABC) and tyramide-horseradish peroxidase-fluorochrome (TSA), used simultaneously to augment immunohistochemical signals. The combination of the TSA and sABC amplification systems provided the first successful co-localization of sympathetic adrenergic and sympathetic cholinergic nerve fibers in cutaneous human sweat glands and vasomotor and pilomotor systems. Primary antibodies from the same species were amplified individually without cross-reactivity or elevated background interference. The confocal fluorescent signal-to-noise ratio increased, and image clarity improved. These modifications to signal amplification systems have the potential for widespread use in the study of human neural tissues.

Alarin stimulates food intake in male rats and LH secretion in castrated male rats

Alarin is a newly identified member of the galanin family of neuropeptides that includes galanin-like peptide (GALP) and galanin. Alarin was discovered as an alternate transcript of the GALP gene in neuroblastoma cells, and subsequently alarin mRNA was detected in the brain of rodents. GALP and galanin are important central regulators of both feeding and reproductive behavior. We hypothesized, that, as a member of the galanin family of peptides, alarin would also have central effects on feeding and reproduction. To test this hypothesis, we treated male rats with alarin intracerebroventricularly (i.c.v.) and measured its effects on food intake and energy homeostasis as well as sexual behavior and luteinizing hormone (LH) secretion. We observed that i.c.v. injection of 1.0 nmol alarin significantly increased food intake (p<0.01) and body weight (p<0.05). Alarin did not affect sexual behavior in male rats; however, alarin did significantly (p<0.01) increase LH levels in castrated, but not intact, male rats. Alarin immunoreactive cell bodies were detected within the locus coeruleus and locus subcoeruleus of the midbrain, which is a brainstem nucleus involved in coordinating many physiological activities, including food intake and reproduction. Lastly, alarin stimulated Fos induction in hypothalamic nuclei, such as the paraventricular nucleus and the nucleus of the tractus solitarious. Our studies demonstrate that alarin, like other members of the galanin family, is a neuromediator of food intake and body weight.

Neurons that co-localize aromatase- and kisspeptin-like immunoreactivity may regulate the HPG axis of the Mallard drake (Anas platyrhynchos)

Kisspeptin is a potent regulator of the hypothalamo-pituitary-gonadal axis. The activation of several vernal and pubertal behaviors involves the action of locally synthesized estradiol by hypothalamic aromatase-expressing neurons. Little is known about kisspeptin in non-mammalian systems, and its interaction with aromatase remains unexamined. The Mallard drake is a seasonal breeder and an excellent model for studying the neural mechanisms that regulate the HPG. The goals of these studies were to determine (a) if and how kisspeptin regulates the drake HPG, (b) if kisspeptin and aromatase are expressed in the Mallard brain, and (c) if kisspeptin is co-localized or in apposition with, aromatase- and gonadotropin hormone releasing hormone (GnRH) positive neurons. Central kisspeptin administration increased plasma luteinizing hormone, an effect blocked by pretreatment with the GnRH antagonist, acyline, suggesting a conservation of kisspeptin function and mechanism of action in birds and mammals. The distribution of kisspeptin in the mallard brain was examined with immunocytochemistry (ICC). Neurons that express kisspeptin-like immunoreactive (ir) protein were observed in the medial preoptic nucleus (POM) and in ir fibers throughout the drake brain. Virtually all POM kisspeptin-ir soma also expressed aromatase-ir, suggesting that autocrine mechanisms may predominate in the interaction between steroid provision and kisspeptin expression. No co-localization was observed between KP-ir and GnRH-ir, although both were easily detected in close-proximity in the tuberoinfundibular area. Taken together, these data suggest that in the drake, estradiol synthesized by aromatase and kisspeptin co-expressing POM neurons may regulate the HPG via an effect on GnRH secretion.

Activation of the Hedgehog pathway in the mouse fetal ovary leads to ectopic appearance of fetal Leydig cells and female pseudohermaphroditism

Proper cell fate determination in mammalian gonads is critical for the establishment of sexual identity. The Hedgehog (Hh) pathway has been implicated in cell fate decision for various organs, including gonads. Desert Hedgehog (Dhh), one of the three mammalian Hh genes, has been implicated with other genes in the establishment of mouse fetal Leydig cells. To investigate whether Hh alone is sufficient to induce fetal Leydig cell differentiation, we ectopically activated the Hh pathway in Steroidogenic factor 1 (SF1)-positive somatic cell precursors of fetal ovaries. Hh activation transformed SF1-positive somatic ovarian cells into functional fetal Leydig cells. These ectopic fetal Leydig cells produced androgens and insulin-like growth factor 3 (INLS3) that cause virilization of female embryos and ovarian descent. However, the female reproductive system remained intact, indicating a typical example of female pseudohermaphroditism. The appearance of fetal Leydig cells was a direct consequence of Hh activation as evident by the absence of other testicular components in the affected ovary. This study provides not only insights into mechanisms of cell lineage specification in gonads, but also a model to understand defects in sexual differentiation.

Cardiac vanilloid receptor 1-expressing afferent nerves and their role in the cardiogenic sympathetic reflex in rats

Myocardial ischaemia causes the release of metabolites such as bradykinin, which stimulates cardiac sensory receptors to evoke a sympathoexcitatory reflex. However, the molecular identity of the afferent neurons and fibres mediating this reflex response is not clear. In this study, we tested the hypothesis that the cardiogenic sympathoexcitatory reflex is mediated by capsaicin-sensitive afferent fibres. Enhanced immunofluorescence labelling revealed that vanilloid receptor 1 (VR1)-containing afferent nerve fibres were present on the epicardial surface of the rat heart. Resiniferatoxin (RTX), a potent analogue of capsaicin, was used to deplete capsaicin-sensitive afferent fibres in rats. Depletion of these fibres was confirmed by a substantial reduction of VR1 immunoreactivity in the epicardium and dorsal root ganglia. The thermal sensitivity was also diminished in RTX-treated rats. Renal sympathetic nerve activity (RSNA) and blood pressure were recorded in anaesthetized rats during epicardial application of bradykinin or capsaicin. In vehicle-treated rats, epicardial bradykinin (10 microg ml-1) or capsaicin (10 microg ml-1) application produced a significant increase in RSNA and arterial blood pressure. The RSNA and blood pressure responses caused by bradykinin and capsaicin were completely abolished in RTX-treated rats. Furthermore, epicardial application of iodo-RTX, a highly specific antagonist of VR1 receptors, blocked capsaicin- but not bradykinin-induced sympathoexcitatory responses. Thus, these data provide important histological and functional evidence that the heart is innervated by VR1-expressing afferent nerves and these afferent nerves are essential for the cardiogenic sympathoexcitatory reflex during myocardial ischaemia.

Orexins in rat dorsal motor nucleus of the vagus potently stimulate gastric motor function

Orexins regulate food intake, arousal, and the sleep-wake cycle. They are synthesized by neurons in the lateral hypothalamus and project to autonomic areas in the hindbrain. Orexin A applied to the dorsal surface of the medulla stimulates gastric acid secretion via a vagally mediated pathway. We tested the hypothesis that orexins in the dorsal motor nucleus (DMN) of the vagus regulate gastric motor function. Multibarelled micropipette assemblies were used to administer vehicle, L-glutamate, orexins A (1 and 10 pmol) and B (10 pmol), and a dye marker into this site in anesthetized rats. When the pipette was positioned in the DMN rostral to the obex (where excitation of neurons by L-glutamate evoked an increase in contractility), orexins A and B increased intragastric pressure and antral motility. In contrast, 10 pmol orexin A microinjected into the DMN caudal to the obex (where L-glutamate evokes gastric relaxation through a vagal inhibitory pathway) did not significantly alter gastric motor function. In separate immunocytochemical studies, orexin receptor 1 was highly expressed in neurons in the DMN. Specifically, it was present in retrogradely labeled preganglionic neurons in the DMN that innervate the stomach. These data are consistent with the idea that orexin A stimulates vagal excitatory motor neurons. These are the first data to suggest that orexins in the DMN have potent and long-lasting effects to increase gastric contractility.

Site of action of GABA(B) receptor for vagal motor control of the lower esophageal sphincter in ferrets and rats

BACKGROUND & AIMS

Stimulation of gamma-aminobutyric acid B metabotropic receptors (GBRs) by baclofen reduces the incidence of transient lower esophageal sphincter (LES) relaxations. The GBR effect may be a result of a central site of action in the dorsal vagal complex, where upper gastrointestinal vagal reflexes are integrated. Therefore, we first localized GBR immunostaining in the dorsal vagal complex. Next, we tested the hypothesis that baclofen modulates LES motor tone via GBR expressed by vagal efferent neurons.

METHODS

An antibody against the human GBR1b isoform was characterized and used for immunocytochemistry in rats and ferrets. Functional studies involved microinjection of L-glutamate into the caudal dorsal motor nucleus of the vagus to evoke an LES relaxation in decerebrate unanesthetized ferrets.

RESULTS

In both species, GBR1b was expressed in preganglionic motor neurons and, in ferrets, the receptor was highly expressed in identified LES-projecting preganglionic neurons. GBR1b immunostaining was also pronounced in the subnucleus centralis of the nucleus tractus solitarius. This distribution implicates GBR in control of the esophageal phase of swallowing at the level of the central program generator. In functional studies, centrally evoked LES relaxation (-73% +/- 8% mm Hg) was significantly attenuated after 7 micromol/kg intravenous baclofen (-37% +/- 10%; N = 5).

CONCLUSIONS

These data all suggest that GBR agonists inhibit LES relaxation via a site of action associated with vagal motor outflow to the LES.

Organization and neurochemistry of vagal preganglionic neurons innervating the lower esophageal sphincter in ferrets

The motor control of the lower esophageal sphincter (LES) is critical for normal swallowing and emesis, as well as for the prevention of gastroesophageal reflux. However, there are surprisingly few data on the central organization and neurochemistry of LES-projecting preganglionic neurons. There are no such data in ferrets, which are increasingly being used to study LES relaxation. Therefore, we determined the location of preganglionic neurons innervating the ferret LES, with special attention to their relationship with gastric fundus-projecting neurons. The neurochemistry of LES-projecting neurons was also investigated using two markers of "nontraditional" neurotransmitters in vagal preganglionic neurons, nitric oxide synthase (NOS), and dopamine (tyrosine hydroxylase: TH). Injection of cholera toxin B subunit (CTB)-horseradish peroxidase (HRP) into the muscular wall of the LES-labeled profiles throughout the rostrocaudal extent of the dorsal motor nucleus of the vagus (DMN) The relative numbers of profiles in three regions of the DMN from caudal to rostral are, 43 +/- 5, 67 +/- 11, and 113 +/- 30). A similar rostrocaudal distribution occurred after injection into the gastric fundus. When CTB conjugated with different fluorescent tags was injected into the LES and fundus both labels were noted in 56 +/- 3% of LES-labeled profiles overall. This finding suggests an extensive coinnervation of both regions by vagal motor neurons. There were significantly fewer LES-labeled profiles that innervated the antrum (16 +/- 9%). In the rostral DMN, 15 +/- 4% of LES-projecting neurons also contained NADPH-diaphorase activity; however, TH immunoreactivity was never identified in LES-projecting neurons. This finding suggests that NO, but not catecholamine (probably dopamine), is synthesized by a population of LES-projecting neurons. We conclude that there are striking similarities between LES- and fundic-projecting preganglionic neurons in terms of their organization in the DMN, presence of NOS activity and absence of TH immunoreactivity. Coinnervation of the LES and gastric fundus is logical, because the LES has similar functions to the fundus, which relaxes to accommodate food during ingestion and preceding emesis, but has quite different functions from the antrum, which provides mixing and propulsion of contents for gastric emptying. The presence of NOS in some LES-projecting neurons may contribute to LES relaxation, as it does in the case of fundic relaxation. The neurologic linkage of vagal fundic and LES relaxation may have clinical relevance, because it helps explain why motor disorders of the LES and fundus frequently occur together.

Cytochrome c release and caspase activation in traumatic axonal injury

Axonal injury is a feature of traumatic brain injury (TBI) contributing to both morbidity and mortality. The traumatic axon injury (TAI) results from focal perturbations of the axolemma, allowing for calcium influx triggering local intraaxonal cytoskeletal and mitochondrial damage. This mitochondrial damage has been posited to cause local bioenergetic failure, leading to axonal failure and disconnection; however, this mitochondrial damage may also lead to the release of cytochrome c (cyto-c), which then activates caspases with significant adverse intraaxonal consequences. In the current communication, we examine this possibility. Rats were subjected to TBI, perfused with aldehydes at 15-360 min after injury, and processed for light microscopic (LM) and electron microscopic (EM) single-labeling immunohistochemistry to detect extramitochondrially localized cytochrome c (cyto-c) and the signature protein of caspase-3 activation (120 kDa breakdown product of alpha-spectrin) in TAI. Combinations of double-labeling fluorescent immunohistochemistry (D-FIHC) were also used to demonstrate colocalization of calpain activation with cyto-c release and caspase-3-induction. In foci of TAI qualitative-quantitative LM demonstrated a parallel, significant increase in cyto-c release and caspase-3 activation over time after injury. EM analysis demonstrated that cyto-c and caspase-3 immunoreactivity were associated with mitochondrial swelling-disruption in sites of TAI. Furthermore, D-IFHC revealed a colocalization of calpain activation, cyto-c release, and caspase-3 induction in these foci, which also revealed progressive TAI. The results demonstrate that cyto-c and caspase-3 participate in the terminal processes of TAI. This suggests that those factors that play a role in the apoptosis in the neuronal soma are also major contributors to the demise of the axonal appendage.