Murine HSD17ß13 does not control liver steatosis and modestly impacts fibrosis in a sex- and diet-specific manner.

Human genetic studies show that loss of function mutations in 17-Beta hydroxysteroid dehydrogenase (HSD17ß13) are associated with protection from non-alcoholic steatohepatitis (NASH). As a result, therapies which reduce HSD17ß13 are being pursued for the treatment of NASH. However, inconsistent effects on steatosis, inflammation and fibrosis pathogenesis have been reported in murine Hsd17b13 knockdown or knockout models. To clarify whether murine Hsd17b13 loss regulates liver damage and fibrosis, we characterized Hsd17b13 knockout mice subjected to pro-NASH diets or pro-inflammatory chemical-induced liver injury. There were no effects of Hsd17b13 loss on liver injury, inflammation, fibrosis or lipids after 28 weeks on the Gubra-Amylin NASH (GAN) diet or 12 weeks on a 45% choline deficient high fat diet (CDAHFD). However, AAV-mediated re-expression of murine Hsd17b13 in KO mice increased liver macrophage abundance in both sexes fed the 45% CDAHFD. In contrast, there was a modest reduction in liver fibrosis, but not lipids or inflammation within Hsd17b13 null female, but not male, mice after 12 weeks of a 60% CDAHFD compared to WT littermates. Fibrosis and the abundance of liver macrophages were increased in Hsd17b13 KO females upon adenoviral re-expression of mouse HSD17ß13, but this was not reflected in inflammatory markers. Additionally, we found minimal differences in liver injury, lipids, or inflammatory and fibrotic markers 48 hours after acute CCl4 exposure. In summary, murine Hsd17b13 loss has modest diet- and sex-specific effects on liver fibrosis which contrasts with human genetic studies. This suggests a disconnect between the biological function of HSD17ß13 in mice and humans.

A fluorogenic near-infrared imaging agent for quantifying plasma and local tissue renin activity in vivo and ex vivo.

The renin-angiotensin system (RAS) is well studied for its regulation of blood pressure and fluid homeostasis, as well as for increased activity associated with a variety of diseases and conditions, including cardiovascular disease, diabetes, and kidney disease. The enzyme renin cleaves angiotensinogen to form angiotensin I (ANG I), which is further cleaved by angiotensin-converting enzyme to produce ANG II. Although ANG II is the main effector molecule of the RAS, renin is the rate-limiting enzyme, thus playing a pivotal role in regulating RAS activity in hypertension and organ injury processes. Our objective was to develop a near-infrared fluorescent (NIRF) renin-imaging agent for noninvasive in vivo detection of renin activity as a measure of tissue RAS and in vitro plasma renin activity. We synthesized a renin-activatable agent, ReninSense 680 FAST (ReninSense), using a NIRF-quenched substrate derived from angiotensinogen that is cleaved specifically by purified mouse and rat renin enzymes to generate a fluorescent signal. This agent was assessed in vitro, in vivo, and ex vivo to detect and quantify increases in plasma and kidney renin activity in sodium-sensitive inbred C57BL/6 mice maintained on a low dietary sodium and diuretic regimen. Noninvasive in vivo fluorescence molecular tomographic imaging of the ReninSense signal in the kidney detected increased renin activity in the kidneys of hyperreninemic C57BL/6 mice. The agent also effectively detected renin activity in ex vivo kidneys, kidney tissue sections, and plasma samples. This approach could provide a new tool for assessing disorders linked to altered tissue and plasma renin activity and to monitor the efficacy of therapeutic treatments.

Noninvasive in vivo quantification of neutrophil elastase activity in acute experimental mouse lung injury.

We developed a neutrophil elastase-specific near-infrared fluorescence imaging agent, which, combined with fluorescence molecular tomographic imaging, allowed us to detect and quantify neutrophil elastase activity in vivo, in real time, and noninvasively in an acute model of lung injury (ALI). Significantly higher fluorescent signal was quantified in mice with LPS/fMLP-induced ALI as compared to healthy controls, correlating with increases in the number of bronchoalveolar lavage cells, neutrophils, and elastase activity. The agent was significantly activated ex vivo in lung sections from ALI but not from control mice, and this activation was ablated by the specific inhibitor sivelestat. Treatment with the specific inhibitor sivelestat significantly reduced lung signal in mice with ALI. These results underscore the unique ability of fluorescence molecular imaging to quantify specific molecular processes in vivo, crucial for understanding the mechanisms underlying disease progression and for assessing and monitoring novel pharmacological interventions.