Highly vascularized complex liver tissue is generally divided into lobes, lobules, hepatocytes, and sinusoids, which can be viewed under different types of lens from the micro‐ to macro‐scale. To engineer multiscaled heterogeneous tissues, a sophisticated and rapid tissue engineering approach is required, such as advanced 3D bioprinting. In this study, a preset extrusion bioprinting technique, which can create heterogeneous, multicellular, and multimaterial structures simultaneously, is utilized for creating a hepatic lobule (≈1 mm) array. The fabricated hepatic lobules include hepatic cells, endothelial cells, and a lumen. The endothelial cells surround the hepatic cells, the exterior of the lobules, the lumen, and finally, become interconnected with each other. Compared to hepatic cell/endothelial cell mixtures, the fabricated hepatic lobule shows higher albumin secretion, urea production, and albumin, MRP2, and CD31 protein levels, as well as, cytochrome P450 enzyme activity. It is found that each cell type with spatial cell patterning in bioink accelerates cellular organization, which could preserve structural integrity and improve cellular functions. In conclusion, preset extruded hepatic lobules within a highly vascularized construct are successfully constructed, enabling both micro‐ and macro‐scale tissue fabrication, which can support the creation of large 3D tissue constructs for multiscale tissue engineering.
Brain renin angiotensin system within the paraventricular nucleus plays a critical role in balancing excitatory and inhibitory inputs to modulate sympathetic output and blood pressure regulation. We previously identified ACE2 and ADAM17 as a compensatory enzyme and a sheddase, respectively, involved in brain renin angiotensin system regulation. Here, we investigated the opposing contribution of ACE2 and ADAM17 to hypothalamic presympathetic activity and ultimately neurogenic hypertension. New mouse models were generated where ACE2 and ADAM17 were selectively knocked down from all neurons (AC-N) or Sim1 neurons (SAT), respectively. Neuronal ACE2 deletion revealed a reduction of inhibitory inputs to AC-N presympathetic neurons relevant to blood pressure regulation. Primary neuron cultures confirmed ACE2 expression on GABAergic neurons synapsing onto excitatory neurons within the hypothalamus but not on glutamatergic neurons. ADAM17 expression was shown to colocalize with angiotensin-II type 1 receptors on Sim1 neurons, and the pressor relevance of this neuronal population was demonstrated by photoactivation. Selective knockdown of ADAM17 was associated with a reduction of FosB gene expression, increased vagal tone, and prevented the acute pressor response to centrally administered angiotensin-II. Chronically, SAT mice exhibited a blunted blood pressure elevation and preserved ACE2 activity during development of salt-sensitive hypertension. Bicuculline injection in those models confirmed the supporting role of ACE2 on GABAergic tone to the paraventricular nucleus. Together, our study demonstrates the contrasting impact of ACE2 and ADAM17 on neuronal excitability of presympathetic neurons within the paraventricular nucleus and the consequences of this mutual regulation in the context of neurogenic hypertension.
Type A gamma-aminobutyric acid (GABA(A)) receptors expressed in the dorsal motor nucleus of vagus (DMV) critically regulate the activity of vagal motor neurons and, by inference, the gastrointestinal (GI) tract. Two types of GABA(A) receptor-mediated inhibition have been identified in the brain, represented by phasic (I(phasic)) and tonic (I(tonic)) inhibitory currents. The hypothesis that I(tonic) regulates neuron activity was tested in the DMV using whole cell patch-clamp recordings in transverse brain stem slices from rats. An I(tonic) was present in a subset of DMV neurons, which was determined to be mediated by different receptors than those mediating fast, synaptic currents. Preapplication of tetrodotoxin significantly decreased the resting I(tonic) amplitude in DMV neurons, suggesting that most of the current was due to action potential (AP)-dependent GABA release. Blocking GABA transport enhanced I(tonic) and multiple GABA transporters cooperated to regulate I(tonic). The I(tonic) was composed of both a gabazine-insensitive component that was nearly saturated under basal conditions and a gabazine-sensitive component that was activated when extracellular GABA concentration was elevated. Perfusion of THIP (10 muM) significantly increased I(tonic) amplitude without increasing I(phasic) amplitude. The I(tonic) played a major role in determining the overall excitability of DMV neurons by contributing to resting membrane potential and AP frequency. Our results indicate that I(tonic) contributes to DMV neuron membrane potential and activity and is thus an important regulator of vagally mediated GI function.
Emerging data indicate that central neurons participate in diabetic processes by modulating autonomic output from neurons in the dorsal motor nucleus of the vagus (DMV). We tested the hypothesis that synaptic modulation by transient receptor potential vanilloid type 1 (TRPV1) receptors is reduced in the DMV in slices from a murine model of type 1 diabetes. The TRPV1 agonist, capsaicin robustly enhanced glutamate release onto DMV neurons by acting at preterminal receptors in slices from intact mice, but failed to do so in slices from diabetic mice. TRPV1 receptor protein expression in the vagal complex was unaltered. Brief insulin pre-application restored TRPV1-dependent modulation of glutamate release in a PKC- and PI3K-dependent manner. The restorative effect of insulin was prevented by brefeldin A, suggesting insulin induced TRPV1 receptor trafficking to the terminal membrane. Central vagal circuits critical to the autonomic regulation of metabolism undergo insulin-dependent synaptic plasticity involving TRPV1 receptor modulation in diabetic mice after several days of chronic hyperglycemia.
The paraventricular nucleus (PVN) of the hypothalamus controls the autonomic neural output to the liver, thereby participating in the regulation of hepatic glucose production (HGP); nevertheless, mechanisms controlling the activity of liver-related PVN neurons are not known. Transient receptor potential vanilloid type 1 (TRPV1) is involved in glucose homeostasis and colocalizes with liver-related PVN neurons; however, the functional role of TRPV1 regarding liver-related PVN neurons has to be elucidated. A retrograde viral tracer was used to identify liver-related neurons within the brain-liver circuit in control, type 1 diabetic, and insulin-treated mice. Our data indicate that TRPV1 regulates liver-related PVN neurons. This TRPV1-dependent excitation diminished in type 1 diabetic mice. In vivo and in vitro insulin restored TRPV1 activity in a phosphatidylinositol 3-kinase/protein kinase C–dependent manner and stimulated TRPV1 receptor trafficking to the plasma membrane. There was no difference in total TRPV1 protein expression; however, increased phosphorylation of TRPV1 receptors was observed in type 1 diabetic mice. Our data demonstrate that TRPV1 plays a pivotal role in the regulation of liver-related PVN neurons. Moreover, TRPV1-dependent excitation of liver-related PVN neurons diminishes in type 1 diabetes, thus indicating that the brain-liver autonomic circuitry is altered in type 1 diabetes and may contribute to the autonomic dysfunction of HGP.
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