Background and Aim: Patients with polycystic kidney disease (PKD), the most common inherited form of chronic kidney disease, have a 2-fold higher risk of developing cognitive impairment and dementia. The mechanisms underlying the pathogenesis of cognitive impairment in PKD are unclear but peripheral inflammation has been suggested to play a role. We aimed to establish the first rat model of PKD-induced cognitive impairment and elucidate potential contributing mechanisms.

Methods: Male and female Lewis wild-type (WT) and Lewis polycystic kidney (LPK) rats were studied at 6, 12 and 18 weeks of age. Blood pressure was measured by tail cuff plethysmography. Cognitive parameters, including recognition and spatial working memory, were assessed using the novel object recognition and Y-maze tests. Renal inflammation was assessed using flow cytometry.

Results: LPK rats had higher blood pressure than WT from 6 weeks of age (178±1 mmHg vs 132±1 mmHg, n=10, P<0.05). At 6 and 12 weeks of age, recognition memory (n=5-9) was not different between LPK and WT rats. LPK rats had intact spatial working memory at 6 weeks (spontaneous alternations= 66% vs 72%, n=9, P>0.05) but it was impaired at 12 weeks of age (spontaneous alternations= 53% vs 79%, n=5-8, P<0.05) as indicated by the lower percentage of spontaneous alternations compared to WT. Flow cytometric analysis revealed that at 6 weeks of age, there were 32% more infiltrating T cells and 33% more M1-like macrophages in the kidneys of LPK rats compared to WT (n=10, P<0.05). The renal inflammation increased with age where at 12 weeks, there were 70% more infiltrating T cells and 53% more M1-like macrophages in the kidneys of LPK rats (n=5-10, P<0.05). Experiments are currently underway to study 18 week-old LPK and WT rats.

Conclusions: Cognitive impairment was observed in a rat model of PKD from 12 weeks of age. Hypertension and renal inflammation appears to precede the development of these cognitive changes and future studies will investigate the mechanistic links between these different parameters.

Background and Aim: Currently, there are no pharmacological treatments for abdominal aortic aneurysms (AAA), and AAA rupture is fatal in ~90% of patients. Aortic inflammation and recently the NLRP3 inflammasome has been implicated in the development of AAA. Interleukin (IL)-18, an inflammasome-derived cytokine, exerts pro-inflammatory responses when bound to its cognate IL-18 receptor (IL-18Rα). The current project aimed to determine the effect of IL-18-deficiency on the incidence of angiotensin (Ang) II-induced AAA.

Methods: Ten-week-old male C57BL/6 (WT) and IL-18-deficient (Il18-/-) mice were infused with Ang II (1.44 mg/kg/day, s.c.) for 28 days via osmotic minipump. SBP detection via tail cuff plethysmography and in vivo ultrasound imaging (Vevo 2100) of abdominal aorta was performed weekly. At endpoint, the incidence of AAA which included mortality due to AAA rupture was recorded. Single cell RNA sequencing was used to determine IL-18Rα expressing cells which was validated using flow cytometry.

Results: While 52% of WT mice developed AAA (including premature deaths due to rupture), no AAAs were detected in Il18-/- mice (P<0.05, n=20-23). Consistent with this finding, in vivo ultrasound imaging revealed dilation of the abdominal aorta beginning at d7 in WT mice with 50% expansion by endpoint (1.5 ± 0.1mm; P<0.05; n=20) with no change in aortic diameter observed in Il18-/- mice throughout the treatment period (1.1 ± 0.1mm; n=23). Single cell RNA-sequencing of Ang II-infused mouse aorta revealed Il18r1 gene expression was limited to T cells, with the greatest expression in gamma-delta T cells, suggesting that they may be primary cellular targets of IL-18 that drive AAA formation. These findings were further validated with flow cytometry where T cells were the main cells expressing IL-18Rα in the aorta. Semi-quantitative analysis of IL-18Rα (mean fluorescence intensity) showed ~2-fold greater expression in gamma-delta T cells compared to other T cells. Preliminary AAA studies in gamma-delta T cell-deficient mice have revealed delayed AAA expansion at d7 following Ang II-infusion.

Conclusions: IL-18-deficiency profoundly protects against Ang II-induced AAA formation with gamma-delta T cells representing a possible cellular target for IL-18 signaling. Neutralisation of IL-18 may represent a novel therapeutic strategy to halt the progression of AAA.

Background and Aim

Short-chain fatty acids (SCFAs) are produced from the digestion of dietary fibre by the gut microbiome. SCFA supplementation reduces blood pressure (BP) in hypertensive animals and patients, potentially through SCFA receptors expressed by immune cells. Mice lacking SCFA-receptors GPR41/43 (whole-body) exhibit more severe hypertension when treated with angiotensin II. However, whether SCFA-receptors in immune cells contribute to hypertension remains unclear.

Methods

To investigate if SCFA-receptors in immune cells contribute to hypertension, reciprocal bone marrow chimeras were generated with GPR41/43 knockout (KO) and Ly5.1 wildtype (WT) mice carrying a variant facilitating identification of donor immune cells (n=10/group). After chimerism was established, pro-hypertensive angiotensin II (0.5 mg/kg/day) was administered via a subcutaneous minipump for 28 days. BP was measured weekly by tail cuff. The heart, kidney, spleen, and liver were weighed at the endpoint, and immune cells were quantified in aortic tissue, kidney, and spleen using flow cytometry.

Results

At baseline, there was no difference in systolic BP between the groups (p=0.2182). Following angiotensin II treatment, at week 4, WT mice that received KO immune cells developed significantly higher systolic BP compared to KO mice with WT immune cells (138.2 mmHg vs 123.7 mmHg, p=0.0037). No differences were found in body, kidney, heart, spleen, and liver weights. Intriguingly, WT mice that received KO immune cells had more CD45+CD11c+MHCII+CD11b- dendritic cells in the aorta (565,935 vs 62,093 cells, p=0.0473) and kidney (41,083 vs 18,310 cells, p=0.0067).

Conclusions

Our findings suggest that GPR41/43 signalling in immune cells, particularly in dendritic cells, contribute to the development of hypertension

Background and Aim. Ischaemic stroke is a debilitating cardiovascular disease that currently has no treatment option that targets cell death mechanisms. Thus, identifying new therapeutic targets that can prevent neuronal cell death is urgently needed. There are two main relaxin receptor subtypes expressed in the central nervous system (CNS): Relaxin Family Peptide Receptor (RXFP)1 and RXFP3. Whilst targeting RXFP1 with the major circulating and stored form of relaxin, human gene-2 (H2) relaxin, improved functional outcomes and reduced neuronal cell death when given 6 h post-photothrombotic stroke (Truong et al, 2023), the effects of targeting RXFP3 in this model are unknown. Therefore, the aim of this study was to examine the efficacy of the RXFP3-selective agonist, Analogue 2 (A2) (Shabanpoor et al, 2012), as a treatment for ischaemic stroke.
Methods. Male C57Bl/6 mice (8-10 weeks, n=8/group) underwent photothrombotic stroke or sham surgery. At 6-, 24- and 48-h post-stroke, mice were treated with vehicle (saline) or A2 at 0.2mg/kg or 0.8mg/kg i.v. Infarct volume was assessed via thionin staining at 72 h after stroke onset and motor function assessed via the hanging wire test at 24 and 72 h post-stroke. Immunofluorescence was used to measure brain inflammation and apoptosis.
Results. The highest dose of A2 improved motor function on the hanging wire test by 88% compared to vehicle-treated mice at 72 h. There was a trend for mice treated with A2 to have fewer astrocytes within the peri-infarct area but there was no difference between treatment groups in infarct size, apoptotic cells and neutrophils.
Conclusions. Targeting RXFP3 using A2 improved motor function following stroke; however, the mechanism behind the improvement is unclear due to a lack of change in many histological outcomes in mice treated with A2 compared to vehicle. Future studies should examine the use of other RXFP3-selective agonists to determine if activating RXFP3 following stroke is able to improve a wider range of markers and if the improvement in motor function by A2 is indeed mediated by RXFP3.

Truong S et al (2023) Pharmacol Res 187:106611; Shabanpoor F et al (2012) J Med Chem 55:1671-81.