A practical protocol to prepare paraffin-embedded whole tick histology sections

Ticks are important ectoparasites that are capable of transmitting multiple classes of pathogens and are currently linked with many emerging tick-borne diseases worldwide. With increasing occurrences of tick-borne diseases in both humans and veterinary species, there is a continuous need to further our understanding of ticks and the pathogens they transmit. Whole tick histology provides a full scope of the tick internal anatomy, allowing researchers to examine multiple organs of interest in a single section. This is in contrast to other techniques that are more commonly utilized in tick-borne disease research, such as electron microscopy and light microscopy of individual organs. There is a lack of literature describing a practical technique to process whole tick histologic sections. Therefore, the current study aims to provide researchers with a workable protocol to prepare high quality paraffin-embedded whole tick histology sections. Amblyomma americanum adults were used as an example species for this study. After a series of pilot experiments using a combination of various fixatives, softening agents and processing techniques, we elected to compare two common fixatives, 10% neutral-buffered formalin (NBF) and Bouin's solution for whole ticks. Equal numbers of A. americanum unfed adults (n = 10/fixative) were processed identically and their whole tick histology coronal sections were individually scored. Higher scores were assigned to whole tick sections that contained more internal organs that are crucial for tick-borne disease research (e.g. salivary glands and midgut), high integrity of tissues and exoskeleton on the section, and good fixation and staining quality of the tissues. The mean total scores for Bouin's-fixed ticks were significantly higher compared to NBF-fixed ticks (p = 0.001). To further assess our preferred technique, we also demonstrated the feasibility of producing high quality whole tick sections for three other common tick species of medical importance (Rhipicephalus sanguineus, Ixodes scapularis, and Dermacentor variabilis) using Bouin's solution. While this technique may require further optimization for other tick species, we described a feasible protocol that uses commonly available tools, reagents and standard histologic equipment. This should allow any investigator to easily make adjustments to this protocol as needed based on their experimental goals.

Transmission of Cytauxzoon felis by injection of Amblyomma americanum salivary glands

BACKGROUND

Cytauxzoonosis is a life-threatening disease of cats, caused by the tick-borne piroplasmid hemoparasite, Cytauxzoon felis. Current experimental models for cytauxzoonosis rely on either tick transmission or direct injection of infected cat tissues. These models require researchers to directly work with infected ticks or use cats with acute cytauxzoonosis. To improve the feasibility and accessibility, there is a need to establish sharable resources among researchers. In related piroplasmid parasites, sporozoite-based inoculums are routinely produced from tick salivary glands, cryopreserved and distributed to other investigators and facilities. For these parasites, sporozoites have been the basis for vaccine development and in vitro cultivation, both of which remain lacking for C. felis research. If infectious sporozoites can be similarly isolated for C. felis, it would significantly broaden our capabilities to study this parasite. Aims of this study was to determine if C. felis sporozoites inoculums collected from the salivary glands of Amblyomma americanum ticks were capable of inducing cytauxzoonosis in naïve cats.

MATERIALS AND METHODS

A. americanum nymphs were acquisition-fed on a donor cat chronically infected with C. felis and allowed to molt to adults. Four groups of adult ticks (n = 50/group) were either stimulation-fed for 4 days on naïve cats or were heated at 37 °C for 4 days. After these treatments, salivary glands (SG) of each group of ticks were collected to create inoculums. Infectivity of these inoculums was then tested by subcutaneous injection into naïve cats.

RESULTS

The two naïve cats used for stimulation feeding and as controls both developed cytauxzoonosis, indicating these groups of ticks were capable of producing infectious sporozoites. Of the 2 cats that were injected with SGs from the stimulation-fed ticks, one cat developed cytauxzoonosis and C. felis infection was confirmed by both light microscopy and PCR. The other cat did not develop cytauxzoonosis and only had equivocal evidence of infection. Neither cat injected with SGs from the heated ticks developed cytauxzoonosis. One of these cats had equivocal evidence of infection and one had no evidence of infection.

CONCLUSION

This study validates the feasibility of collecting infectious sporozoites from C. felis-infected ticks that can be used to infect naïve cats. While this model requires further optimization, it has the potential to expand resources to study C. felis and further advance research in this field.

Cytauxzoon felis in salivary glands of Amblyomma americanum

Cytauxzoon felis is a tick-borne piroplasmid hemoparasite that causes life-threatening disease in cats. Despite the critical role that ticks play in pathogen transmission, our knowledge regarding the C. felis life cycle remains limited to the feline hosts. Specific life stages of C. felis within the tick host have never been visualized microscopically and previous investigations have been limited to molecular detection by polymerase chain reaction (PCR). Sporozoites are the infectious stage of piroplasmids that are transmitted by ticks. In other tick-borne piroplasmids, sporozoite-based vaccines play a key role in disease prevention and management. We believe sporozoites have similar potential for cytauxzoonosis. Therefore, the objective of this study was to use different molecular and microscopic techniques to detect and evaluate C. felis sporozoites in tick salivary glands (SG). A total of 140 Amblyomma americanum adults that were fed on C. felis-infected cats as nymphs were included for this study. Specifically, dissected SGs were quartered and subjected to C. felis RT-PCR, RNAscope® in situ hybridization (ISH), histology, direct azure staining, and transmission electron microscopy (TEM). Cytauxzoon felis RT-PCR was also performed on half tick (HT) carcasses after SG dissection. Cytauxzoon felis RNA was detected in SGs of 17/140 ticks. Of these, 7/17 ticks had microscopic visualization via ISH and/or TEM. The remaining 10/17 ticks had only molecular detection of C. felis in SGs via RT-PCR without visualization. Cytauxzoon felis RNA was detected solely in HT carcasses via RT-PCR in 9/140 ticks. In ISH-positive tick SGs, hybridization signals were present in cytoplasms of SG acinar cells. TEM captured rare C. felis organisms with characteristic ultrastructural features of sporozoites. This study describes the first direct visualization of any developing stage of C. felis in ticks. Forthcoming studies should employ a combination of molecular and microscopic techniques to investigate the C. felis life cycle in A. americanum.

Relative Abundance of the Stink Bug (Hemiptera: Pentatomidae) Complex Infesting Rice in the Everglades Agricultural Area of Florida

Florida's rice stink bug complex comprises three species; Oebalus pugnax (F.), O. insularis (Stal), and O. ypsilongriseus (DeGeer), the latter two of which are invasive and exclusive to Florida within the United States. A series of surveys were conducted in 2017 and 2018 to determine the relative abundance of the three species throughout Florida's rice growing region within the Everglades Agricultural Area, in addition to comparing their seasonality within crop and noncrop habitats. Sampling occurred in commercial rice fields and adjacent transects of graminaceous noncrop hosts using sweep nets. Oebalus pugnax (52.7%) and O. insularis (61.7%) were the most abundant species in 2017 and 2018, respectively. Both species were more prevalent in rice fields compared to transects of noncrop hosts. Oebalus ypsilongriseus remained in low abundance relative to O. pugnax and O. insularis, and did not differ in numbers collected among rice and noncrop hosts. Of the noncrop hosts in transects, Panicum dichotomiflorum (fall panicum) was the most abundant across both years. This study is the first report of Oebalus species feeding on Echinochloa crus-galli (common barnyardgrass) in Florida. This study shows that the invasive O. insularis continues to increase in abundance, and has surpassed O. pugnax in terms of regional populations. These results emphasize the need for additional studies to assess the interactions among O. insularis and other Oebalus species in addition to its feeding behavior in Florida rice.

Coplanar polychlorinated biphenyls impair glucose homeostasis in lean C57BL/6 mice and mitigate beneficial effects of weight loss on glucose homeostasis in obese mice

BACKGROUND

Previous studies demonstrated that coplanar polychlorinated biphenyls (PCBs) promote proinflammatory gene expression in adipocytes. PCBs are highly lipophilic and accumulate in adipose tissue, a site of insulin resistance in persons with type 2 diabetes.

OBJECTIVES

We investigated the in vitro and in vivo effects of coplanar PCBs on adipose expression of tumor necrosis factor α (TNF-α) and on glucose and insulin homeostasis in lean and obese mice.

METHODS

We quantified glucose and insulin tolerance, as well as TNF-α levels, in liver, muscle, and adipose tissue of male C57BL/6 mice administered vehicle, PCB-77, or PCB-126 and fed a low fat (LF) diet. Another group of mice administered vehicle or PCB-77 were fed a high fat (HF) diet for 12 weeks; the diet was then switched from HF to LF for 4 weeks to induce weight loss. We quantified glucose and insulin tolerance and adipose TNF-α expression in these mice. In addition, we used in vitro and in vivo studies to quantify aryl hydrocarbon receptor (AhR)-dependent effects of PCB-77 on parameters of glucose homeostasis.

RESULTS

Treatment with coplanar PCBs resulted in sustained impairment of glucose and insulin tolerance in mice fed the LF diet. In PCB-77-treated mice, TNF-α expression was increased in adipose tissue but not in liver or muscle. PCB-77 levels were strikingly higher in adipose tissue than in liver or serum. Antagonism of AhR abolished both in vitro and in vivo effects of PCB-77. In obese mice, PCB-77 had no effect on glucose homeostasis, but glucose homeostasis was impaired after weight loss.

CONCLUSIONS

Coplanar PCBs impaired glucose homeostasis in lean mice and in obese mice following weight loss. Adipose-specific elevations in TNF-α expression by PCBs may contribute to impaired glucose homeostasis.

Deficiency of angiotensin type 1a receptors in adipocytes reduces differentiation and promotes hypertrophy of adipocytes in lean mice

Adipocytes express angiotensin receptors, but the direct effects of angiotensin II (AngII) stimulating this cell type are undefined. Adipocytes express angiotensin type 1a receptor (AT1aR) and AT2R, both of which have been implicated in obesity. In this study, we determined the effects of adipocyte AT1aR deficiency on adipocyte differentiation and the development of obesity in mice fed low-fat (LF) or high-fat (HF) diets. Mice expressing Cre recombinase under the control of the aP2 promoter were bred with AT1aR-floxed mice to generate mice with adipocyte AT1aR deficiency (AT1aR(aP2)). AT1aR mRNA abundance was reduced significantly in both white and brown adipose tissue from AT1aR(aP2) mice compared with nontransgenic littermates (AT1aR(fl/fl)). Adipocyte AT1aR deficiency did not influence body weight, glucose tolerance, or blood pressure in mice fed either LF or high-fat diets. However, LF-fed AT1aR(aP2) mice exhibited striking adipocyte hypertrophy even though total fat mass was not different between genotypes. Stromal vascular cells from AT1aR(aP2) mice differentiated to a lesser extent to adipocytes compared with controls. Conversely, incubation of 3T3-L1 adipocytes with AngII increased Oil Red O staining and increased mRNA abundance of peroxisome proliferator-activated receptor γ (PPARγ) via AT1R stimulation. These results suggest that reductions in adipocyte differentiation in LF-fed AT1aR(aP2) mice resulted in increased lipid storage and hypertrophy of remaining adipocytes. These results demonstrate that AngII regulates adipocyte differentiation and morphology through the adipocyte AT1aR in lean mice.

Abstract 399: Deficiency of Angiotensin Type 1a Receptors in Adipocytes Increases Fat Mass in Angiotensin II-Infused LDLR-Deficient Mice but Has No Effect on Vascular Pathologies

Objectives: Angiotensin II (AngII) promotes atherosclerosis and abdominal aortic aneurysms (AAA) through the angiotensin type 1a receptor (AT1aR). However, the cell type mediating these effects has not been defined. Adipose tissue surrounding the aorta may influence the inflammatory milieu within the vessel wall and thus contribute to disease progression. The purpose of this study was to determine the effect of adipocyte-AT1aR deficiency on development of AngII and diet-induced vascular pathologies in low density lipoprotein receptor deficient (LDLR-/-) mice.

Methods and results: LDLR -/- mice with adipocyte-AT1aR deficiency (AT1aRaP2, n = 21) and littermates (AT1aRfl/fl, n=17) were fed a high-fat diet (HF, 42% kcal fat; 0.15 cholesterol) for 1 week prior to, and throughout, 28 days of AngII infusion (1,000 ng/kg/min). Adipocyte-AT1aR deficiency had no effect on AAA incidence (external diameter of aorta; AT1aRfl/fl 1.4±0.1 vs. AT1aRaP2 1.5±0.1 mm, p=0.41) and atherosclerotic lesion areas in the aortic arch (AT1aRfl/fl 7.1±0.8 vs. AT1aRaP2 8.3+0.8% lesion area, p=0.49). Serum cholesterol (AT1aRfl/fl 1981±109 vs. AT1aRaP2 2044±85 mg/dL, p=0.65) and triglyceride (AT1aRfl/fl 450±31 vs. AT1aRaP2 496±33 mg/dL, p=0.32) concentrations were also unaffected by adipocyte-AT1aR deficiency. Interestingly, body weight was significantly increased in AngII-infused AT1aRaP2 mice (AT1aRfl/fl 26.8±0.5 vs. AT1aRaP2 28.0±0.5 g, p=0.013 for interaction between genotype and time), due to increases in adipose mass (retroperitoneal fat; AT1aRfl/fl 0.26±0.03 vs. AT1aRaP2 0.36±0.02 g, p=0.017). Mice fed the HF diet for 3 months without AngII infusion did not exhibit any changes in atherosclerotic lesion area in the aortic arch (AT1aRfl/fl 14.3±1% vs. AT1aRaP2 11.7±1%, p=0.14).

Conclusions: Adipocyte-AT1aR deficiency has no effect on development of diet- or AngII-induced atherosclerosis or AAAs in hypercholesterolemic mice. Interestingly, body weight and fat mass were increased in AngII-infused adipocyte AT1aR deficient mice. Future studies will elucidate the mechanisms through which AngII regulates body weight and fat mass under these conditions.

Angiotensin converting enzyme 2 contributes to sex differences in the development of obesity hypertension in C57BL/6 mice

OBJECTIVE

Obesity promotes hypertension, but it is unclear if sex differences exist in obesity-related hypertension. Angiotensin converting enzyme 2 (ACE2) converts angiotensin II (AngII) to angiotensin-(1-7) (Ang-[1-7]), controlling peptide balance. We hypothesized that tissue-specific regulation of ACE2 by high-fat (HF) feeding and sex hormones contributes to sex differences in obesity-hypertension.

METHODS AND RESULTS

HF-fed females gained more body weight and fat mass than males. HF-fed males exhibiting reduced kidney ACE2 activity had increased plasma angiotensin II levels and decreased plasma Ang-(1-7) levels. In contrast, HF-fed females exhibiting elevated adipose ACE2 activity had increased plasma Ang-(1-7) levels. HF-fed males had elevated systolic and diastolic blood pressure that were abolished by losartan. In contrast, HF-fed females did not exhibit increased systolic blood pressure until females were administered the Ang-(1-7) receptor antagonist, D-Ala-Ang-(1-7). Deficiency of ACE2 increased systolic blood pressure in HF-fed males and females, which was abolished by losartan. Ovariectomy of HF-fed female mice reduced adipose ACE2 activity and plasma Ang-(1-7) levels, and promoted obesity-hypertension. Finally, estrogen, but not other sex hormones, increased adipocyte ACE2 mRNA abundance.

CONCLUSIONS

These results demonstrate that tissue-specific regulation of ACE2 by diet and sex hormones contributes to sex differences in obesity-hypertension.

Adipocyte-specific deficiency of angiotensinogen decreases plasma angiotensinogen concentration and systolic blood pressure in mice

Previous studies demonstrated that overexpression of angiotensinogen (AGT) in adipose tissue increased blood pressure. However, the contribution of endogenous AGT in adipocytes to the systemic renin-angiotensin system (RAS) and blood pressure control is undefined. To define a role of adipocyte-derived AGT, mice with loxP sites flanking exon 2 of the AGT gene (Agt(fl/fl)) were bred to transgenic mice expressing Cre recombinase under the control of an adipocyte fatty acid-binding protein 4 promoter (aP2) promoter to generate mice with adipocyte AGT deficiency (Agt(aP2)). AGT mRNA abundance in adipose tissue and AGT secretion from adipocytes were reduced markedly in adipose tissues of Agt(aP2) mice. To determine the contribution of adipocyte-derived AGT to the systemic RAS and blood pressure control, mice were fed normal laboratory diet for 2 or 12 mo. In males and females of each genotype, body weight and fat mass increased with age. However, there was no effect of adipocyte AGT deficiency on body weight, fat mass, or adipocyte size. At 2 and 12 mo of age, mice with deficiency of AGT in adipocytes had reduced plasma concentrations of AGT (by 24-28%) compared with controls. Moreover, mice lacking AGT in adipocytes exhibited reduced systolic blood pressures compared with controls (Agt(fl/fl), 117 ± 2; Agt(aP2), 110 ± 2 mmHg; P < 0.05). These results demonstrate that adipocyte-derived AGT contributes to the systemic RAS and blood pressure control.

Polychlorinated biphenyl 77 augments angiotensin II-induced atherosclerosis and abdominal aortic aneurysms in male apolipoprotein E deficient mice

Infusion of angiotensin II (AngII) to hyperlipidemic mice augments atherosclerosis and causes formation of abdominal aortic aneurysms (AAAs). Each of these AngII-induced vascular pathologies exhibit pronounced inflammation. Previous studies demonstrated that coplanar polychlorinated biphenyls (PCBs) promote inflammation in endothelial cells and adipocytes, two cell types implicated in AngII-induced vascular pathologies. The purpose of this study was to test the hypothesis that administration of PCB77 to male apolipoprotein E (ApoE) -/- mice promotes AngII-induced atherosclerosis and AAA formation. Male ApoE-/- mice were administered vehicle or PCB77 (49 mg/kg, i.p.) during week 1 and 4 (2 divided doses/week) of AngII infusion. Body weights and total serum cholesterol concentrations were not influenced by administration of PCB77. Systolic blood pressure was increased in AngII-infused mice administered PCB77 compared to vehicle (156±6 vs 137±5 mmHg, respectively). The percentage of aortic arch covered by atherosclerotic lesions was increased in AngII-infused mice administered PCB77 compared to vehicle (2.0±0.4 vs 0.9±0.1%, respectively). Lumen diameters of abdominal aortas determined by in vivo ultrasound and external diameters of excised suprarenal aortas were increased in AngII-infused mice administered PCB77 compared to vehicle. In addition, AAA incidence increased from 47 to 85% in AngII-infused mice administered PCB77. Adipose tissue in close proximity to AAAs from mice administered PCB77 exhibited increased mRNA abundance of proinflammatory cytokines and elevated expression of components of the renin-angiotensin system (angiotensinogen, angiotensin type 1a receptor (AT1aR)). These results demonstrate that PCB77 augments AngII-induced atherosclerosis and AAA formation.