Malou Friederich-Persson

Background and aims: Abdominal aortic aneurysm (AAA) is a vascular disease characterized by the progressive dilation of the aorta, culminating in rupture. At present, there are no pharmacological treatments to prevent AAA development or reduce rupture rate. A recent study showed that patients prescribed Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have significantly lower risks of mortality, AAA repair, and acute abdominal aortic syndrome. Semaglutide is a GLP-1RA with increased agonist capacity and longer half-life, compared to earlier generations of GLP-1RAs. In this study, we aimed to investigate the role and mechanisms of semaglutide in the prevention of AAA development and rupture in a murine model. Methods: AAA was induced in apolipoprotein-E-deficient mice, by continuous subcutaneous infusion of angiotensin II. Treatment with semaglutide (12 µg/kg) began seven days after disease induction (rescue trial) or simultaneously with disease induction (prophylactic trial). At experimental endpoint, aortic diameter was measured by high-frequency ultrasound and the aortic tissue was collected for histological analysis. Results: Prophylactic treatment with semaglutide drastically reduced mortality by dissection and rupture during the first seven days of disease development, but did not affect AAA formation at 28 days. Histological evaluation of the aorta at day seven showed a normal vessel wall thickness with a trend for a higher content of collagen in the aortic wall in mice treated with semaglutide, compared to controls. Conclusions: Semaglutide prevents aortic rupture and dissection in the early phases of AAA development in the angiotensin II mouse model, likely by promoting the maintenance of an adequate proportion of collagen in the vessel wall.

Background: The pathophysiological mechanisms of Abdominal Aortic Aneurysm (AAA) are not elucidated. Alterations in mitochondrial function, such as a reduction in oxidative phosphorylation (OXPHOS), have been observed at genome level and functionally in vascular smooth muscle cells. Metformin reduces AAA development and growth in diabetic patients, but the precise mechanisms are not known. In this paper we aim to demonstrate the feasibility of measuring mitochondrial functional capacity ex vivo in intact murine aneurysmal tissue and confirm a decrease in OXPHOS, and to determine if the protective effect of metformin on AAA is mediated by mitochondrial function. Methods: AAA was induced in ApoE KO mice by administration of angII (1000 ng/kg/min) through osmotic minipumps. Metformin was administered in drinking water at a dose of 100 mg/kg/day. The abdominal aorta was isolated in situ and mitochondrial functional capacity was analyzed ex vivo in whole permeabilized tissue by high-resolution respirometry. Results: Mitochondrial respiration was successfully measured ex vivo in whole aneurysmal tissue. Mitochondrial function was impaired in angII-treated mice, with decreased fold change in Complex I and Complex I+II oxygen consumption, relative to basal levels. Complex II oxygen consumption was also decreased in angII-treated mice. Rescue treatment of mice with metformin did not affect or restore mitochondrial function. Conclusions: Mitochondrial function can be evaluated in murine whole aneurysmal tissue, providing a method for a physiological approach to the study of mitochondrial function in AAA. Mitochondrial function is impaired in AAA. However, rescue treatment with metformin is not sufficient to recover mitochondrial function and seems not to be the mechanism behind prevention of aneurysm.

Hypertension is a world-leading cause of cardiovascular disease and premature deaths. Vascular tone is in part regulated by perivascular adipose tissue (PVAT) that releases pro and anticontractile factors. In hypertension, dysfunctional PVAT is observed and studies have indicated a causal relationship between dysfunctional PVAT and vascular damage in hypertension. The phenotype of PVAT on resistance vessels is primarily white adipose tissue. The present study investigates the impact of a changed phenotype, i.e., browning of PVAT, on vascular function and the development of hypertension. Browning was induced by β₃-adrenergic agonist in control and angiotensin II-induced hypertensive mice. Studied parameters included blood pressure by tail-cuff plethysmography and vascular function by wire myography. Browning was confirmed through an immunohistochemical and gene analysis approach. The anticontractile effect of PVAT is lost in untreated hypertensive mice and vascular tone and blood pressure are increased. Browning of PVAT resulted in a maintained anticontractile effect, improved endothelial function, and reduced development of hypertension. Phenotype of PVAT is a major determinant of PVAT health during hypertensive conditions. Our data clearly demonstrates that browning of PVAT, i.e. changing the phenotype of PVAT, protects the vascular function and counteract the development of hypertension. This study provides novel insights into how PVAT can be protected in pathologies and thus limit the development of hypertension.

Mineralocorticoid receptor (MR) expression is increased in the adipose tissue (AT) of obese patients and animals. We previously demonstrated that adipocyte-MR overexpression in mice (Adipo-MROE mice) is associated with metabolic alterations. Moreover, we showed that MR regulates mitochondrial dysfunction and cellular senescence in the visceral AT of obese db/db mice. Our hypothesis is that adipocyte-MR overactivation triggers mitochondrial dysfunction and cellular senescence, through increased mitochondrial oxidative stress (OS). Using the Adipo-MROE mice with conditional adipocyte-MR expression, we evaluated the specific effects of adipocyte-MR on global and mitochondrial OS, as well as on OS-induced damage. Mitochondrial function was assessed by high throughput respirometry. Molecular mechanisms were probed in AT focusing on mitochondrial quality control and senescence markers. Adipo-MROE mice exhibited increased mitochondrial OS and altered mitochondrial respiration, associated with reduced biogenesis and increased fission. This was associated with OS-induced DNA-damage and AT premature senescence. In conclusion, targeted adipocyte-MR overexpression leads to an imbalance in mitochondrial dynamics and regeneration, to mitochondrial dysfunction and to ageing in visceral AT. These data bring new insights into the MR-dependent AT dysfunction in obesity.

Aim: Uncoupling protein‐2 (UCP‐2) can induce mitochondrial uncoupling in the diabetic kidney. Although mitochondrial uncoupling reduces oxidative stress originating from the mitochondria and can be regarded as a protective mechanism, the increased oxygen consumption occurring secondarily to increased mitochondria uncoupling, that is leak respiration, may contribute to kidney tissue hypoxia. Using UCP‐2^−/− mice, we tested the hypothesis that UCP‐2‐mediated leak respiration is important for the development of diabetes‐induced intrarenal hypoxia and proteinuria.Methods: Kidney function, in vivo oxygen metabolism, urinary protein leakage and mitochondrial function were determined in wild‐type and UCP‐2^−/− mice during normoglycaemia and 2 weeks after diabetes induction.Results: Diabetic wild‐type mice displayed mitochondrial leak respiration, pronounced intrarenal hypoxia, proteinuria and increased urinary KIM‐1 excretion. However, diabetic UCP‐2^−/− mice did not develop increased mitochondrial leak respiration and presented with normal intrarenal oxygen levels, urinary protein and KIM‐1 excretion.Conclusion: Although functioning as an antioxidant system, mitochondria uncoupling is always in co‐occurrence with increased oxygen consumption, that is leak respiration; a potentially detrimental side effect as it can result in kidney tissue hypoxia; an acknowledged unifying pathway to nephropathy. Indeed, this study demonstrates a novel mechanism in which UCP‐2‐mediated mitochondrial leak respiration is necessary for the development of diabetes‐induced intrarenal tissue hypoxia and proteinuria.

The content of hyaluronan (HA) in the interstitium of the renal medulla changes in relation to body hydration status. We investigated if hormones of central importance for body fluid homeostasis affect HA production by renomedullary interstitial cells in culture (RMICs). Simultaneous treatment with vasopressin and angiotensin II (Ang II) reduced HA by 69%. No change occurred in the mRNA expressions of hyaluronan synthase 2 (HAS2) or hyaluronidases (Hyals), while Hyal activity in the supernatant increased by 67% and CD44 expression reduced by 42%. The autocoid endothelin (ET-1) at low concentrations (10⁻¹⁰ and 10⁻⁸ M) increased HA 3-fold. On the contrary, at a high concentration (10⁻⁶ M) ET-1 reduced HA by 47%. The ET-A receptor antagonist BQ123 not only reversed the reducing effect of high ET-1 on HA, but elevated it to the same level as low concentration ET-1, suggesting separate regulating roles for ET-A and ET-B receptors. This was corroborated by the addition of ET-B receptor antagonist BQ788 to low concentration ET-1, which abolished the HA increase. HAS2 and Hyal2 mRNA did not alter, while Hyal1 mRNA was increased at all ET-1 concentrations tested. Hyal activity was elevated the most by high ET-1 concentration, and blockade of ET-A receptors by BQ123 prevented about 30% of this response. The present study demonstrates an important regulatory influence of hormones involved in body fluid balance on HA handling by RMICs, thereby supporting the concept of a dynamic involvement of interstitial HA in renal fluid handling.

The underlying mechanisms in the development of diabetic nephropathy are currently unclear and likely consist of a series of dynamic events from the early to late stages of the disease. Diabetic nephropathy is currently without curative treatments and it is acknowledged that even the earliest clinical manifestation of nephropathy is preceded by an established morphological renal injury that is in turn preceded by functional and metabolic alterations. An early manifestation of the diabetic kidney is the development of kidney hypoxia that has been acknowledged as a common pathway to nephropathy. There have been reports of altered mitochondrial function in the diabetic kidney such as altered mitophagy, mitochondrial dynamics, uncoupling and cellular signaling through hypoxia inducible factors and AMP-kinase. These factors are also likely to be intertwined in a complex manner. In this review we discuss how these pathways are connected to mitochondrial production of reactive oxygen species (ROS) and how they may relate to the development of kidney hypoxia in diabetic nephropathy. From available literature, it is evident that early correction and/or prevention of mitochondrial dysfunction may be pivotal in the prevention and treatment of diabetic nephropathy.

The proposed pathways for the development of nephropathy are many and likely to be complex and overlapping. Recent literature strongly supports a role of renal tissue hypoxia as a pathway to nephropathy but the evidence remains inconclusive as the role of hypoxia cannot be separated from confounding factors such as hyperglycemia, hypertension and oxidative stress. By increasing kidney oxygen consumption (QO2) using triodothyronine (T3) we aimed to investigate the role of renal hypoxia per se for the development of nephropathy. Normoglycemic Sprague‐Dawley rats were treated with T3 (10 mg/kg bw/day) for 56 days. Thereafter, glomerular filtration rate (GFR), renal blood flow (RBF), total kidney QO2, kidney oxygen tension (pO2, Clark‐type oxygen electrodes) proteinuria, oxidative stress and histological alterations were evaluated and compared to corresponding controls. T3 increased kidney QO2 (18±2 vs. 11±1 µmol/min/kidney, p<0.05) and decreased kidney pO2 (27±1 vs. 44±1 mmHg, p<0.05). Furthermore, T3 resulted in proteinuria (74±6 vs. 54±5 µg/min/kidney, p<0.05) and four of eight T3‐treated rats, but none of the controls, presented with focal tubulointerstitial fibrosis. GFR (1.4±0.2 vs. 1.5±0.2 ml/min), RBF (12.7±1.6 vs. 11.1±0.8 ml/min), TBARS (15±2 vs. 16±3 fmol/min/kidney) and blood glucose (4.8±0.2 vs. 5.1±0.2 mM) were unaffected by T3. The detected mitochondrial uncoupling and increased ATP synthesis provide a mechanistic explanation for the increased kidney QO2. In conclusion, the present study adds further evidence in support of renal tissue hypoxia as an independent pathway to nephropathy.

Oxidative stress is closely associated with renal dysfunction following diabetes and hypertension. Angiotensin II (Ang II) can activate the NADPH-oxidase, increasing oxidative stress that is thought to blunt proximal tubular electrolyte transport and thereby oxygen consumption (QO₂). We investigated the effect of Ang II on QO₂ in immortalized mouse proximal tubular cells over-expressing the NADPH oxidase subunit p22^phox; a model of increased oxidative stress. Cultured cells were exposed to either Ang II or H₂O₂ for 48 h. QO₂ was determined during baseline (113 mmol/l NaCl; transport-dependent QO₂) and during sodium-free conditions (transport-independent QO₂). Ang II reduced transport-dependent QO₂ in wild-types, but not in p22^phox which also displayed increased QO₂ at baseline. Transport-independent QO₂ was increased in p22^phox and Ang II had no additional effect, whereas it increased QO₂ in wild-type. Addition of H₂O₂ reduced transport-dependent QO₂ in wild-types, but not in p22^phox. Transport-independent QO₂ was unaffected by H₂O₂. The similar effects of Ang II and H₂O₂ to reduce transport-dependent QO₂ suggest a direct regulatory role of oxidative stress. In accordance, the transport-dependent QO₂ was reduced in p22^phox already during baseline. The effects of Ang II on transport-independent QO₂ was not replicated by H₂O₂, indicating direct regulation via Ang II-receptors independently of oxidative stress. However, the Ang II effect was absent in p22^phox, suggesting that oxidative stress also modulates normal Ang II signaling. In conclusion, Ang II affects both transport-dependent and transport-independent QO₂ in proximal tubular cells and may be an important pathway modulating renal QO₂.

Diabetic nephropathy is strongly associated with both increased oxidative stress and kidney tissue hypoxia. The increased oxidative stress causes increased kidney oxygen consumption resulting in kidney tissue hypoxia. To date, it has been difficult to determine the role of kidney hypoxia, per se, for the development of nephropathy. We tested the hypothesis that kidney hypoxia, without confounding factors such as hyperglycemia or elevated oxidative stress, results in nephropathy. To induce kidney hypoxia, dinitrophenol (30 mg per day per kg bodyweight by gavage), a mitochondrial uncoupler that increases oxygen consumption and causes kidney hypoxia, was administered for 30 consecutive days to rats. Thereafter, glomerular filtration rate, renal blood flow, kidney oxygen consumption, kidney oxygen tension, kidney concentrations of glucose and glycogen, markers of oxidative stress, urinary protein excretion, and histological findings were determined and compared with vehicle-treated controls. Dinitrophenol did not affect arterial blood pressure, renal blood flow, glomerular filtration rate, blood glucose, or markers of oxidative stress but increased kidney oxygen consumption, and reduced cortical and medullary concentrations of glucose and glycogen, and resulted in intrarenal tissue hypoxia. Furthermore, dinitrophenol treatment increased urinary protein excretion, kidney vimentin expression, and infiltration of inflammatory cells. In conclusion, increased mitochondrial oxygen consumption results in kidney hypoxia and subsequent nephropathy. Importantly, these results demonstrate that kidney tissue hypoxia, per se, without confounding hyperglycemia or oxidative stress, may be sufficient to initiate the development of nephropathy and therefore demonstrate a new interventional target for treating kidney disease.