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The metabolic functions of the liver are spatially organized in a phenomenon called zonation, linked to the differential exposure of portal and central hepatocytes to nutrient-rich blood. The mTORC1 signaling pathway controls cellular metabolism in response to nutrients and insulin fluctuations. Here we show that simultaneous genetic activation of nutrient and hormone signaling to mTORC1 in hepatocytes results in impaired establishment of postnatal metabolic and zonal identity of hepatocytes. Mutant hepatocytes fail to upregulate postnatally the expression of Frizzled receptors 1 and 8, and show reduced Wnt/β-catenin activation. This defect, alongside diminished paracrine Wnt2 ligand expression by endothelial cells, underlies impaired postnatal maturation. Impaired zonation is recapitulated in a model of constant supply of nutrients by parenteral nutrition to piglets. Our work shows the role of hepatocyte sensing of fluctuations in nutrients and hormones for triggering a latent metabolic zonation program. The liver is segregated into spatially organized areas that serve distinct functions, though how these zones are patterned remains unclear. Here they show that mTORC1 controls spatial segregation of liver metabolic functions via modulation of Wnt signaling, and find that impaired zonation is also observed in pigs given total parenteral nutrition.

Connective tissue models grown from cell monolayers can be instrumental in a variety of biomedical fields such as drug screening, wound healing, and regenerative engineering. However, while connective tissues contain abundant fibrillar collagen, achieving a sufficient assembly and retention of fibrillar collagen in vitro is challenging. Unlike the dilute cell culture environment, the body’s environment is characterized by a high density of soluble macromolecules (crowding) and macromolecular networks (confinement), which contribute to extracellular matrix (ECM) assembly in vivo. Consequently, macromolecular crowding (MMC) has been successfully used to enhance the processing of type I procollagen, leading to significant increases in fibrillar collagen assembly and accumulation during in vitro culture of a variety of cell types. In this study, we developed a combination approach using a carrageenan hydrogel, which released soluble macromolecules and served as a confinement barrier. We first evaluated the local carrageenan release and then confirmed the effectiveness of this combination approach on collagen accumulation by the human MG-63 bone cell line. Additionally, computational modeling of oxygen and glucose transport within the culture system showed no negative effects of the hydrogel and its releasates on cell viability.

Background: Total parenteral nutrition (TPN) provides all nutritional needs intravenously. Although lifesaving, enthusiasm is significantly tempered due to side effects of liver and gut injury, as well as lack of mechanistic understanding into drivers of TPN injury. We hypothesized that the state of luminal nutritional deprivation with TPN drives alterations in gut–systemic signaling, contributing to injury, and tested this hypothesis using our ambulatory TPN model. Methods: A total of 16 one-week-old piglets were allocated randomly to TPN (n = 8) or enteral nutrition (EN, n = 8) for 3 weeks. Liver, gut, and serum were analyzed. All tests were two-sided, with a significance level of 0.05. Results: TPN resulted in significant hyperbilirubinemia and cholestatic liver injury, p = 0.034. Hepatic inflammation (cluster of differentiation 3 (CD3) immunohistochemistry) was higher with TPN (p = 0.021). No significant differences in alanine aminotransferase (ALT) or bile ductular proliferation were noted. TPN resulted in reduction of muscularis mucosa thickness and marked gut atrophy. Median and interquartile range for gut mass was 0.46 (0.30–0.58) g/cm in EN, and 0.19 (0.11–0.29) g/cm in TPN (p = 0.024). Key gut–systemic signaling regulators, liver farnesoid X receptor (FXR; p = 0.021), liver constitutive androstane receptor (CAR; p = 0.014), gut FXR (p = 0.028), G-coupled bile acid receptor (TGR5) (p = 0.003), epidermal growth factor (EGF; p = 0.016), organic anion transporter (OAT; p = 0.028), Mitogen-activated protein kinases-1 (MAPK1) (p = 0.037), and sodium uptake transporter sodium glucose-linked transporter (SGLT-1; p = 0.010) were significantly downregulated in TPN animals, whereas liver cholesterol 7 alpha-hydroxylase (CyP7A1) was substantially higher with TPN (p = 0.011). Conclusion: We report significant alterations in key hepatobiliary receptors driving gut–systemic signaling in a TPN piglet model. This presents a major advancement to our understanding of TPN-associated injury and suggests opportunities for strategic targeting of the gut–systemic axis, specifically, FXR, TGR5, and EGF in developing ameliorative strategies.

Successful development of tissue-engineered osteochondral replacements for joint tissue regeneration will address a significant clinical need. Current in vitro approaches produce a tissue that is deficient in collagen-rich extracellular matrices and has insufficient tissue properties. Research has shown that the in vitro accumulation of fibrillar collagen in tissues can be enhanced through the use of cellular confinement, where an impermeable barrier is overlain atop a 2-dimensional (2D) cell layer, and also through use of an extracellular macromolecular crowding (MMC) approach, where soluble macromolecules are added to culture medium. A study that evaluated cellular confinement with keratocytes reported that type I collagen accumulation was increased significantly by an agarose gel overlaid atop the cell layer following 20 days of treatment. Recent studies have evaluated MMC using carrageenan (CR) on dermal and corneal fibroblasts as well as mesenchymal stem cells and have shown increases in collagen deposition compared to untreated cultures. The objective of this study was to evaluate the effects on collagen deposition of a CR-based hydrogel overlay when suspended above cell layers and MMC using various CR isoforms in 2D human MG-63 osteosarcoma cell culture. After 7 days in expansion medium +/- the CR gel, cultures were enzymatically digested and evaluated for DNA & hydroxyproline content, which were used as indirect measures of cell number & deposited collagen, respectively. The kappa-CR and mixed (kappa & lambda) CR confinement barrier supported a 3.46- and 2.68-fold increase in collagen deposition by the cells when normalized to total cells in culture, respectively. Total cell number was reduced by about half for both conditions. Adding soluble CR to the culture medium promoted a 2.69-, 2.40- and 1.82-fold increase in collagen deposition per cell in mixed, lambda, and kappa cultures, respectively, with DNA content not significantly reduced in kappa or mixed cultures. The kappa-CR gel + soluble and mixed (kappa & lambda) CR gel + soluble cultures supported a 3.05- and 3.13-fold increase in collagen deposition by the cells when normalized to total cells in culture, respectively, but the increase was not additive. This study showed that crowding and confinement can used as an effective strategy for enhancing collagen deposition in vitro. Further developments are required for an optimized system without cell loss. Crowding and confinement are promising approaches for successfully treating common yet debilitating orthopedic diseases without the need for invasive surgical methods.

Parenteral nutrition (PN) is a life-saving nutritional therapy for those situations when patients are unable to receive enteral nutrition. However, despite a multitude of benefits offered by PN, it is associated with a variety of side effects, most notably parenteral nutrition-associated liver disease (PNALD). Adverse effects of PN on other organ systems, such as brain and cardiovascular system, have been poorly studied. There have been several case reports, studies, and a recent animal study highlighting cardiotoxic effects of PN; however, much remains unclear about the underlying mechanisms causing cardiac damage. In this review, we propose a series of potential mechanisms behind PN-associated heart injury, and we provide an overview of therapeutic strategies and recent scientific advances.

Background: Male sex is a risk factor for developing severe COVID-19 illness, hospitalization, and mortality. It is possible that the male sex hormone, testosterone, contributes to the morbidity from COVID-19. SARS-CoV2 viruses use cell membrane protein Angiotensin-Converting Enzyme 2 (ACE2) receptor and undergo S protein priming by the Type II Transmembrane Serine Protease (TMPRSS2) to enter the cells. Hence, the expression level of ACE2 and TMPRSS2 may affect disease susceptibility and possible severity. TMPRSS2 is regulated by the androgen receptor. We, therefore, examined if an association exists between serum testosterone concentrations and ACE2 or TMPRSS2 expression level in men. Methods: We analyzed fasting serum samples and peripheral blood mononuclear cells (MNC) from 42 men. Total and free testosterone and estradiol were measured by liquid chromatography/equilibrium dialysis. Sex hormone binding globulin (SHBG) was measured by chemiluminescence. mRNA was prepared from MNC. Quantitative RT-PCR was conducted using commercially available, pre-designed TaqMan primers and probes targeting ACE2. The ACE2 relative level was calculated after normalization to beta Actin and GAPDH, with lowest ACE2 level being set to 1. Results: Subjects’ age ranged from 20 to 65 years. Type 2 diabetes was present in 74% of the men and the mean HbA1 was 7.2±1.6% (mean ± S.D.). Fifteen subjects had subnormal free testosterone (<50 pg/ml). Compared to the 27 subjects with normal free testosterone, they were older (49±12 vs 40±13 years, p=0.03) but had similar BMI (36±10, 35±10 kg/m2, p=0.71). As expected, they had lower total testosterone (Median [25th, 75th percentile]; 222 [171-266] vs 431 [335, 618] ng/dl, p<0.001) and free testosterone concentrations (39 [21, 44] vs 72 [59, 92], p<0.001). Total estradiol was also lower in this group (19±1 vs 29±13 pg/ml, p=0.03) but free estradiol (0.44±0.33 vs 0.56±0.34 pg/ml, p=0.44) and SHBG (27 [19, 33] vs 30 [21, 39] nmol/L, p=0.52) were similar. Quantitative PCR data showed there was a large inter-individual variation of ACE2 expression level, up to 15-fold difference. Average ACE2 level did not differ between subnormal and normal testosterone groups (3.4 [2.7, 5.0] vs 3.9 [2.5, 5.7] arbitrary units). ACE2 expression was not related to free testosterone (r=0.11), free estradiol (r=0.18) or sex hormone binding globulin (r=0.15) on linear regression analyses (p>0.30 for all). ACE2 expression was also not related to age (r= -0.15, p=0.34), BMI (r= -0.2, p=0.23) or presence of diabetes. We were not able to detect a significant expression of TMPRSS2 in MNC. Conclusion: Our results do not support a role for testosterone or estradiol as regulators of ACE2 expression in peripheral blood MNC in males.

Ballistic and hydrodynamic electron flow can develop in materials when carrier momentum is conserved over long distance and time scales. These non-Ohmic transport regimes are characterized by distinctive spatial distributions of the current density and electrochemical potential. In this thesis, I will show scanning tunneling potentiometry (STP) measurements of the electrochemical potential induced by DC transport in graphene as a function of carrier density, temperature, and magnetic field. First, STP images are recorded as current flows through electrostatic constrictions with gate-tunable width that are \"drawn\" with the STM tip. The electrochemical potential drop through these constrictions determines the wavevector-dependent conductivity σ(k) of the electron fluid. Upon heating the system from 4.5 K to 77 K, enhanced electron-electron scattering leads to a crossover from ballistic to hydrodynamic flow, identified by superballistic conductance through the constrictions and a suppression of Landauer residual-resistivity dipoles. When increasing the magnetic field from 0 to 1.4 T at 4.5 K, the STP data reveals a diffusive-to-ballistic crossover in the flow of current resulting from Landau level quantization. In the ballistic regime of magnetotransport, the local Hall field is enhanced one cyclotron diameter away from scattering surfaces.

Antibody 43C9 accelerates the hydrolysis of a p-nitroanilide by a factor of 2.5 x 105over the background rate in addition to catalyzing the hydrolysis of a series of aromatic esters. Since this represents one of the largest rate accelerations achieved with an antibody, we have undertaken a series of studies aimed at uncovering the catalytic mechanism of 43C9. The immunogen, a phosphonamidate, was designed to mimic the geometric and electronic characteristics of the tetrahedral intermediate that forms upon nucleophilic attack by hydroxide on the amide substrate. Further studies, however, revealed that the catalytic mechanism is more complex and involves the fortuitous formation of a covalent acyl-antibody intermediate as a consequence of complementary side chain residues at the antibody-binding site. Several lines of evidence indicate that the catalytic mechanism involves two key residues: His-L91, which acts as a nucleophile to form the acyl-antibody intermediate, and Arg-L96, which stabilizes the anionic tetrahedral moieties. Support for this mechanism derives from the results of site-directed mutagenesis experiments and solvent deuterium isotope effects as well as direct detection of the acyl-antibody by electrospray mass spectrometry. Despite its partial recapitulation of the course of action of enzymic counterparts, the reactivity of 43C9, like other antibodies, is apparently limited by its affinity for the inducing immunogen. To go beyond this level, one must introduce additional catalytic functionality, particularly general acid-base catalysis, through either improvements in transition-state analog design or site-specific mutagenesis.

Emerging evidence suggests that an amplifiable protease cascade consisting of multiple aspartatespecific cysteine proteases (ASCPs) is responsible for the apoptotic changes observed in mammalian cells undergoing programmed cell death. Here we describe the cloning of two novel ASCPs from human Jurkat T-lymphocytes. Like other ASCPs, the new proteases, named Mch4 and Mch5, are derived from single chain proenzymes. However, their putative active sites contain a QACQG pentapeptide instead of the QACRG present in all known ASCPs. Also, their N termini contain FADD-like death effector domains, suggesting possible interaction with FADD. Expression of Mch4 in Escherichia coli produced an active protease that, like other ASCPs, was potently inhibited (Ki = 14 nM) by the tetrapeptide aldehyde DEVD-CHO. Interestingly, both Mch4 and the serine protease granzyme B cleave recombinant proCPP32 and proMch3 at a conserved IXXD-S sequence to produce the large and small subunits of the active proteases. Granzyme B also cleaves proMch4 at a homologous IXXD-A processing sequence to produce mature Mch4. These observations suggest that CPP32 and Mch3 are targets of mature Mch4 protease in apoptotic cells. The presence of the FADD-like domains in Mch4 and Mch5 suggests a role for these proteases in the Fas-apoptotic pathway. In addition, these proteases could participate in the granzyme B apoptotic pathway.