Manipulating fenestrations in young and old liver sinusoidal endothelial cells

Abstract

Fenestrations are pores within liver sinusoidal endothelial cells (LSECs) that enable the transfer of substrates (particularly insulin and lipoproteins) between blood and hepatocytes. With increasing age, there are marked reductions in fenestrations, referred to as pseudocapillarization. Currently, fenestrations are thought to be regulated by vascular endothelial growth factor and nitric oxide (NO) pathways promoting remodeling of the actin cytoskeleton and cell membrane lipid rafts. We investigated the effects of drugs that act on these pathways on fenestrations in old (18–24 mo) and young mice (3–4 mo). Isolated LSECs were incubated with either cytochalasin 7-ketocholesterol, sildenafil, amlodipine, simvastatin, 2, 5-dimethoxy-4-iodoamphetamine (DOI), bosentan, TNF-related apoptosis-inducing ligand (TRAIL) or nicotinamide mononucleotide (NMN). LSECs were visualized under scanning electron microscopy to quantify fenestration porosity, diameter, and frequency, as well as direct stochastic optical reconstruction microscopy to examine actin and NO synthase. In young and old LSECs, fenestration porosity, diameter and frequency were increased by 7-ketocholesterol, while porosity and/or frequency were increased with NMN, sildenafil, amlodipine, TRAIL, and cytochalasin D. In old mice only, bosentan and DOI increased fenestration porosity and/or frequency. Modification of the actin cytoskeleton was observed with all agents that increased fenestrations, while NO synthase was only increased by sildenafil, amlodipine, and TRAIL. In conclusion, agents that target NO, actin, or lipid rafts promote changes in fenestrations in mice LSECs. Regulation of fenestrations occurs via both NO-dependent and independent pathways. This work indicates that age-related defenestration can be reversed pharmacologically, which has potential translational relevance for dyslipidemia and insulin resistance.NEW & NOTEWORTHY We demonstrate the effects of multiple nitric oxide-dependent and -independent pharmaceutical agents on fenestrations of the liver sinusoidal endothelium. Fenestrations are reorganized in response to nicotinamide mononucleotide, sildenafil, amlodipine, and TNF-related apoptosis-inducing ligand. This work indicates that age-related defenestration can be reversed pharmacologically, which has potential translational relevance for dyslipidemia and insulin resistance in old age.

Cost-efficient nanoscopy reveals nanoscale architecture of liver cells and platelets

“…F-actin in the sildenafil-treated cells appears to be generally more condensed, and the actin rings (arrows, Figure 4E and F) that typically delineate fenestrations [47] are more pronounced in both NMN and sildenafil-treated cells. We also noted similar changes in fenestration size ( Figure 4H, I, K, L) as reported in [15]. NMN and sildenafil increased the median fenestration diameter by 5% and 30%, respectively ( Figure 4N).…”

“…Recently, a number of agents (NMN and sildenafil among others) were demonstrated to enhance fenestrations size and number in LSECs from aging mice, as visualized with scanning EM [15]. We tested these agents in our optical super-resolution microscope ( Figure 4) and visualized changes in the actin cytoskeleton in cells treated with NMN ( Figure 4B and E) and sildenafil ( Figure 4C and F).…”

“…Sildenafil is a medication used to remedy erectile dysfunction and pulmonary arterial hypertension [14]. A previous LSEC study showed increased frequency of fenestrations with NMN and sildenafil treatment, as well as an increased proportion of small fenestrations, suggesting the formation of new fenestrations [15].…”

Novel targets for delaying aging: The importance of the liver and advances in drug delivery

“…The ef fects of DOI were shown to be mod u lated by both VEGF de pen dent and in de pen dent mech a nisms. Re cent data [159] have demon strated the util ity of mul ti ple phar ma ceu ti cal agents in pro mot ing in creased fen es tra tion di am e ter and fre quency in isolated LSECs from both young and old mice. These agents all act via the path ways pre vi ously dis cussed in this re view: ni tric ox ide de pendent path ways (silde nafil and am lodip ine); NAD pro mo tion (nicotinamide mononu cleotide); and cell sur face death re cep tor ac ti va tion (TRAIL) [159].…”

CTRP13 attenuates the expression of LN and CAV-1 Induced by high glucose via CaMKKβ/AMPK pathway in rLSECs

“…Previous studies demonstrate that hepatic sinusoidal capillarization undergo increased laminin (LN) and caveolin-1 (CAV-1) expression [10]. However, the exact mechanism responsible for hepatic sinusoidal capillarization induced by T2DM remains to be elucidated [11].…”