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Abstract Chronic kidney disease (CKD) affects 850 million people worldwide and is associated with significant cardiovascular morbidity and mortality. Routine laboratory tests do not reflect early stages of microcirculatory changes and vascular rarefaction that characterise kidney fibrosis, the common endpoint of CKD. Imaging techniques that detect CKD in early stages could promote timely treatment with new drugs like SGLT2 inhibitors, thus, decreasing CKD progression and the cardiovascular disease burden. Ultrasound is the most used imaging modality in CKD, as it is non-invasive and radiation free. Initially, ultrasound imaging was applied to assess kidney macro-morphology and to rule out ureteral obstruction. The development of higher frequency probes allowed for more detailed imaging of kidney parenchyma, and advances in Doppler ultrasound provided insights into segmental arterial flow patterns including resistive indices as an indirect measure of microcirculatory impedance, elevated values of which correlated with progressive organ failure and fibrosis. Today, low-flow detection methods and matrix probes better resolve organ parenchyma and smaller vascular beds, and contrast-enhanced ultrasound allows perfusion measurement. Particularly, super-resolution ultrasound imaging, a technology currently being in clinical translation, can characterise the microcirculation morphologically and functionally in unrivalled detail. This is accompanied by rapid developments in radiomics and machine learning supporting ultrasound image acquisition and processing, as well as lesion detection and characterisation. This perspective article introduces emerging ultrasound methods for the diagnosis of CKD and discusses how the promising technical and analytical advancements can improve disease management after successful translation to clinical application.

Summary Virus detection methods are important to cope with the SARS‐CoV‐2 pandemics. Apart from the lung, SARS‐CoV‐2 was detected in multiple organs in severe cases. Less is known on organ tropism in patients developing mild or no symptoms, and some of such patients might be missed in symptom‐indicated swab testing. Here, we tested and validated several approaches and selected the most reliable RT‐PCR protocol for the detection of SARS‐CoV‐2 RNA in patients’ routine diagnostic formalin‐fixed and paraffin‐embedded (FFPE) specimens available in pathology, to assess (i) organ tropism in samples from COVID‐19‐positive patients, (ii) unrecognized cases in selected tissues from negative or not‐tested patients during a pandemic peak, and (iii) retrospectively, pre‐pandemic lung samples. We identified SARS‐CoV‐2 RNA in seven samples from confirmed COVID‐19 patients, in two gastric biopsies, one small bowel and one colon resection, one lung biopsy, one pleural resection and one pleural effusion specimen, while all other specimens were negative. In the pandemic peak cohort, we identified one previously unrecognized COVID‐19 case in tonsillectomy samples. All pre‐pandemic lung samples were negative. In conclusion, SARS‐CoV‐2 RNA detection in FFPE pathology specimens can potentially improve surveillance of COVID‐19, allow retrospective studies, and advance our understanding of SARS‐CoV‐2 organ tropism and effects.

Donor organ-shortage has resulted in the increased use of marginal grafts; however, normothermic machine perfusion (NMP) holds the potential for organ viability assessment and restoration of marginal grafts prior to transplantation. Additionally, cell-, oxygen carrier-free and antioxidants-supplemented solutions could potentially prevent adverse effects (transfusion reactions, inflammation, hemolysis), associated with the use of autologous packed red blood cell (pRBC)-based perfusates. This study compared 6 h NMP of porcine kidneys, using an established pRBC-based perfusate (pRBC, n = 7), with the novel cell- and oxygen carrier-free organ preservation solution Ecosol, containing taurine (Ecosol, n = 7). Despite the enhanced tissue edema and tubular injury in the Ecosol group, related to a suboptimal molecular mass of polyethylene glycol as colloid present in the solution, functional parameters (renal blood flow, intrarenal resistance, urinary flow, pH) and oxygenation (arterial pO2, absence of hypoxia-inducible factor 1-alpha) were similar to the pRBC group. Furthermore, taurine significantly improved the antioxidant capacity in the Ecosol group, reflected in decreased lactate dehydrogenase, urine protein and tubular vacuolization compared to pRBC. This study demonstrates the feasibility of 6 h NMP using a taurine containing, cell- and oxygen carrier-free perfusate, achieving a comparable organ quality to pRBC perfused porcine kidneys.

Abstract Kidney fibrosis is characterized by expansion and activation of platelet‐derived growth factor receptor‐β (PDGFR‐β)‐positive mesenchymal cells. To study the consequences of PDGFR‐β activation, we developed a model of primary renal fibrosis using transgenic mice with PDGFR‐β activation specifically in renal mesenchymal cells, driving their pathological proliferation and phenotypic switch toward myofibroblasts. This resulted in progressive mesangioproliferative glomerulonephritis, mesangial sclerosis, and interstitial fibrosis with progressive anemia due to loss of erythropoietin production by fibroblasts. Fibrosis induced secondary tubular epithelial injury at later stages, coinciding with microinflammation, and aggravated the progression of hypertensive and obstructive nephropathy. Inhibition of PDGFR activation reversed fibrosis more effectively in the tubulointerstitium compared to glomeruli. Gene expression signatures in mice with PDGFR‐β activation resembled those found in patients. In conclusion, PDGFR‐β activation alone is sufficient to induce progressive renal fibrosis and failure, mimicking key aspects of chronic kidney disease in humans. Our data provide direct proof that fibrosis per se can drive chronic organ damage and establish a model of primary fibrosis allowing specific studies targeting fibrosis progression and regression.

Multiorgan tropism of SARS-CoV-2 has previously been shown for several major organs. We have comprehensively analyzed 25 different formalin-fixed paraffin-embedded (FFPE) tissues/organs from autopsies of fatal COVID-19 cases (n = 8), using histopathological assessment, detection of SARS-CoV-2 RNA using polymerase chain reaction and RNA in situ hybridization, viral protein using immunohistochemistry, and virus particles using transmission electron microscopy. SARS-CoV-2 RNA was mainly localized in epithelial cells across all organs. Next to lung, trachea, kidney, heart, or liver, viral RNA was also found in tonsils, salivary glands, oropharynx, thyroid, adrenal gland, testicles, prostate, ovaries, small bowel, lymph nodes, skin and skeletal muscle. Viral RNA was predominantly found in cells expressing ACE2, TMPRSS2, or both. The SARS-CoV-2 replicating RNA was also detected in these organs. Immunohistochemistry and electron microscopy were not suitable for reliable and specific SARS-CoV-2 detection in autopsies. These findings were validated using in situ hybridization on external COVID-19 autopsy samples (n = 9). Apart from the lung, correlation of viral detection and histopathological assessment did not reveal any specific alterations that could be attributed to SARS-CoV-2. In summary, SARS-CoV-2 and its replication could be observed across all organ systems, which co-localizes with ACE2 and TMPRSS2 mainly in epithelial but also in mesenchymal and endothelial cells. Apart from the respiratory tract, no specific (histo-)morphologic alterations could be assigned to the SARS-CoV-2 infection.

Macrophage migration inhibitory factor (MIF) is a pleiotropic inflammatory cytokine with anti-fibrotic properties in toxic liver injury models and anti-steatotic functions in non-alcoholic fatty liver disease (NAFLD) attributed to the CD74/AMPK signaling pathway. As NAFLD progression is associated with fibrosis, we studied MIF function during NAFLD-associated liver fibrogenesis in mice and men by molecular, histological and immunological methods in vitro and in vivo. After NASH diet feeding, hepatic Mif expression was strongly induced, an effect which was absent in Mif∆hep mice. In contrast to hepatotoxic fibrosis models, NASH diet-induced fibrogenesis was significantly abrogated in Mif−/− and Mif∆hep mice associated with a reduced accumulation of the pro-fibrotic type-I NKT cell subpopulation. In vitro, MIF skewed the differentiation of NKT cells towards the type-I subtype. In line with the murine results, expression of fibrosis markers strongly correlated with MIF, its receptors, and markers of NKT type-I cells in NASH patients. We conclude that MIF expression is induced during chronic metabolic injury in mice and men with hepatocytes representing the major source. In NAFLD progression, MIF contributes to liver fibrogenesis skewing NKT cell polarization toward a pro-fibrotic phenotype highlighting the complex, context-dependent role of MIF during chronic liver injury.