Saturated Fat-Mediated Upregulation of IL-32 and CCL20 in Hepatocytes Contributes to Higher Expression of These Fibrosis-Driving Molecules in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) comprises a spectrum of liver diseases, ranging from liver steatosis to metabolic dysfunction-associated steatohepatitis (MASH), increasing the risk of developing cirrhosis and hepatocellular carcinoma (HCC). Fibrosis within MASLD is critical for disease development; therefore, the identification of fibrosis-driving factors is indispensable. We analyzed the expression of interleukin 32 (IL-32) and chemokine CC ligand 20 (CCL20), which are known to be linked with inflammation and fibrosis, and for their expression in MASLD and hepatoma cells. RT-PCR, ELISA and Western blotting analyses were performed in both human liver samples and an in vitro steatosis model. IL-32 and CCL20 mRNA expression was increased in tissues of patients with NASH compared to normal liver tissue. Stratification for patatin-like phospholipase domain-containing protein 3 (PNPLA3) status revealed significance for IL-32 only in patients with I148M (rs738409, CG/GG) carrier status. Furthermore, a positive correlation was observed between IL-32 expression and steatosis grade, and between IL-32 as well as CCL20 expression and fibrosis grade. Treatment with the saturated fatty acid palmitic acid (PA) induced mRNA and protein expression of IL-32 and CCL20 in hepatoma cells. This induction was mitigated by the substitution of PA with monounsaturated oleic acid (OA), suggesting the involvement of oxidative stress. Consequently, analysis of stress-induced signaling pathways showed the activation of Erk1/2 and p38 MAPK, which led to an enhanced expression of IL-32 and CCL20. In conclusion, cellular stress in liver epithelial cells induced by PA enhances the expression of IL-32 and CCL20, both known to trigger inflammation and fibrosis.

Interleukin-1ß Attenuates Expression of Augmenter of Liver Regeneration (ALR) by Regulating HNF4α Independent of c-Jun

Inflammasomes and innate immune cells have been shown to contribute to liver injury, thereby activating Kupffer cells, which release several cytokines, including IL-6, IL-1ß, and TNFα. Augmenter of liver regeneration (ALR) is a hepatotropic co-mitogen that was found to have anti-oxidative and anti-apoptotic properties and to attenuate experimental non-alcoholic fatty liver disease (NAFLD) and cholestasis. Additionally, hepatic ALR expression is diminished in patients with NAFLD or cholestasis, but less is known about the mechanisms of its regulation under these conditions. Therefore, we aimed to investigate the role of IL-1ß in ALR expression and to elucidate the molecular mechanism of this regulation in vitro. We found that ALR promoter activity and mRNA and protein expression were reduced upon treatment with IL-1ß. Early growth response protein-1 (Egr-1), an ALR inducer, was induced by IL-1ß but could not activate ALR expression, which may be attributed to reduced Egr-1 binding to the ALR promoter. The expression and nuclear localization of hepatocyte nuclear factor 4 α (HNF4α), another ALR-inducing transcription factor, was reduced by IL-1ß. Interestingly, c-Jun, a potential regulator of ALR and HNF4α, showed increased nuclear phosphorylation levels upon IL-1ß treatment but did not change the expression of ALR or HNF4α. In conclusion, this study offers evidence regarding the regulation of anti-apoptotic and anti-oxidative ALR by IL-1ß through reduced Egr-1 promoter binding and diminished HNF4α expression independent of c-Jun activation. Low ALR tissue levels in NAFLD and cholestatic liver injury may be caused by IL-1ß and contribute to disease progression.

A polycystin-2 protein with modified channel properties leads to an increased diameter of renal tubules and to renal cysts

Mutations in the PKD2 gene cause autosomal-dominant polycystic kidney disease but the physiological role of polycystin-2, the protein product of PKD2, remains elusive. Polycystin-2 belongs to the transient receptor potential (TRP) family of non-selective cation channels. To test the hypothesis that altered ion channel properties of polycystin-2 compromise its putative role in a control circuit controlling lumen formation of renal tubular structures, we generated a mouse model in which we exchanged the pore loop of polycystin-2 with that of the closely related cation channel polycystin-2L1 (encoded by PKD2L1), thereby creating the protein polycystin-2^poreL1. Functional characterization of this mutant channel in Xenopus laevis oocytes demonstrated that its electrophysiological properties differed from those of polycystin-2 and instead resembled the properties of polycystin-2L1, in particular regarding its permeability for Ca²⁺ ions. Homology modeling of the ion translocation pathway of polycystin-2^poreL1 argues for a wider pore in polycystin-2^poreL1 than in polycystin-2. In Pkd2^poreL1 knock-in mice in which the endogenous polycystin-2 protein was replaced by polycystin-2^poreL1 the diameter of collecting ducts was increased and collecting duct cysts developed in a strain-dependent fashion.

Summary: Replacement of the pore region of polycystin-2 with that of polycystin-2L1 results in wider renal tubules and polycystic kidney disease, thus demonstrating the essential function of its ion channel properties.

LMX1B is essential for the maintenance of differentiated podocytes in adult kidneys

Mutations of the LMX1B gene cause nail-patella syndrome, a rare autosomal-dominant disorder affecting the development of the limbs, eyes, brain, and kidneys. The characterization of conventional Lmx1b knockout mice has shown that LMX1B regulates the development of podocyte foot processes and slit diaphragms, but studies using podocyte-specific Lmx1b knockout mice have yielded conflicting results regarding the importance of LMX1B for maintaining podocyte structures. In order to address this question, we generated inducible podocyte-specific Lmx1b knockout mice. One week of Lmx1b inactivation in adult mice resulted in proteinuria with only minimal foot process effacement. Notably, expression levels of slit diaphragm and basement membrane proteins remained stable at this time point, and basement membrane charge properties also did not change, suggesting that alternative mechanisms mediate the development of proteinuria in these mice. Cell biological and biophysical experiments with primary podocytes isolated after 1 week of Lmx1b inactivation indicated dysregulation of actin cytoskeleton organization, and time-resolved DNA microarray analysis identified the genes encoding actin cytoskeleton-associated proteins, including Abra and Arl4c, as putative LMX1B targets. Chromatin immunoprecipitation experiments in conditionally immortalized human podocytes and gel shift assays showed that LMX1B recognizes AT-rich binding sites (FLAT elements) in the promoter regions of ABRA and ARL4C, and knockdown experiments in zebrafish support a model in which LMX1B and ABRA act in a common pathway during pronephros development. Our report establishes the importance of LMX1B in fully differentiated podocytes and argues that LMX1B is essential for the maintenance of an appropriately structured actin cytoskeleton in podocytes.

The vertebrate homolog of sulfide-quinone reductase is expressed in mitochondria of neuronal tissues

Hydrogen sulfide (H₂S) can be consumed by both invertebrates and vertebrates as an inorganic substrate. The pathway metabolizing H₂S probably involves three mitochondrial enzymes, one of which is sulfide-quinone oxidoreductase (SQR), known as sulfide-quinone reductase-like protein (SQRDL) in vertebrates. Evidence from fission yeast suggests that SQR might have a role in regulating sulfide levels in the cell. Regulation might be essential for H₂S to act as a gaseous transmitter (gasotransmitter). The brain is an organ with high activity of gasotransmitters, like nitric oxide (NO) and H₂S, which are known to affect synaptic transmission. In this study, we provide evidence that SQRDL is expressed in the mammalian brain. Real-time polymerase chain reaction (PCR) showed an increase in the number of Sqrdl transcripts in the brain with increasing age. Cellular fractionation and subsequent analysis by Western blotting indicated that the protein is located in mitochondria, which is the site of sulfide consumption in the cell. With an immunohistochemical approach, we demonstrated that the SQRDL protein is expressed in neurons, oligodendrocytes, and endothelial cells. Taken together, our data suggest that brain tissue harbors the machinery required for local regulation of sulfide levels.

Expression of pigment-epithelium-derived factor during kidney development and aging

Inhibitors and stimulators of endothelial cell growth are essential for the coordination of blood vessel formation during organ growth and development. In the adult kidney, one of the major inhibitors of angiogenesis is pigment-epithelium-derived factor (PEDF). We have analyzed the expression and distribution of PEDF during various stages of renal development and aging with particular emphasis on the formation of functional glomeruli. We show that PEDF gene expression and protein levels in the kidney significantly increase with age. We have detected PEDF in the mesenchyme and endothelial cells at all developmental stages studied, in all regions of the nephrogenic zone in which the formation of new blood vessels is associated with the development of nephrons and collecting ducts, and in mature podocytes in the adult kidney. Our results are the first to suggest that PEDF is important in early renal postnatal development, that it could be relevant to the maturation of glomerular function and the filtration barrier formed by these cells, and that it may serve as an anti-angiogenic modulator during kidney development.

ICAM-1 and VCAM-1 expression following aneurysmal subarachnoid hemorrhage and their possible role in the pathophysiology of subsequent ischemic deficits

BACKGROUND

The pathophysiology of ischemic cerebral lesions following aneurysmal subarachnoid hemorrhage (SAH) is poorly understood. There is growing evidence that inflammatory reactions could be involved in the pathogenesis of such delayed occurring ischemic lesions. The aim of this study was to evaluate adhesion molecules with regard to these lesions following SAH.

METHODS

Serum and cerebrospinal fluid (CSF) samples were taken daily from 15 patients up to day 9 after SAH and evaluated for intercellular adhesion molecule-1 (ICAM-1) and vascular adhesion molecule-1 (VCAM-1).

RESULTS

CSF and serum samples correlated well during nearly the whole time course (p < 0.0001). A secondary increase in ICAM-1 and VCAM-1 in the serum and CSF correlated with an increase in flow velocity in the transcranial Doppler (p > 0.0001 and p < 0.007) but not to a delayed lesion in the CT scan.

CONCLUSION

We believe that inflammatory processes are involved in the pathogenesis of cerebral vasospasm but they might only be a part of a multifactorial pathogenesis.

Expression of hypoxia-inducible carbonic anhydrases in brain tumors

Malignant brain tumors exhibit distinct metabolic characteristics. Despite high levels of lactate, the intracellular pH of brain tumors is more alkaline than normal brain. Additionally, with increasing malignancy, brain tumors display intratumoral hypoxia. Carbonic anhydrase (CA) IX and XII are transmembrane isoenzymes that are induced by tissue hypoxia. They participate in regulation of pH homeostasis by catalyzing the reversible hydration of carbon dioxide. The aim of our study was to investigate whether brain tumors of different histology and grade of malignancy express elevated levels of CA IX and XII as compared to normal brain. We analyzed 120 tissue specimens from brain tumors (primary and metastatic) and normal brain for CA IX and XII expression by immunohistochemistry, Western blot, and in situ hybridization. Whereas normal brain tissue showed minimal levels of CA IX and XII expression, expression in tumors was found to be upregulated with increased level of malignancy. Hemangioblastomas, from patients with von Hippel-Lindau disease, also displayed high levels of CA IX and XII expression. Comparison of CA IX and XII staining with HIF-1alpha staining revealed a similar microanatomical distribution, indicating hypoxia as a major, but not the only, induction factor. The extent of CA IX and XII staining correlated with cell proliferation, as indicated by Ki67 labeling. The results demonstrate that CA IX and XII are upregulated in intrinsic and metastatic brain tumors as compared to normal brain tissue. This may contribute to the management of tumor-specific acid load and provide a therapeutic target.

PV-1 is a component of the fenestral and stomatal diaphragms in fenestrated endothelia

PV-1 is a novel endothelial protein shown by immunocytochemical tests to be specifically associated with the stomatal diaphragms of caveolae in lung endothelium. Although the highest expression levels of both mRNA and protein are in the lung, PV-1 also has been found to be expressed in other organs. Using a specific antibody to the extracellular domain of PV-1, we have extended the survey on the presence of this protein at light and electron microscope level in several rat organs. Here we show that by immunofluorescence the antibody recognizes with high specificity the endothelium of the fenestrated peritubular capillaries of the kidney and those of the intestinal villi, pancreas, and adrenals. By immunolocalization at electron microscope level, the antibody recognizes specifically the diaphragms of the fenestrae and the stomatal diaphragms of caveolae and transendothelial channels in the endothelia of these vascular beds. No signal was detected in the continuous endothelium of the heart, skeletal muscle, intestinal muscularis, or brain capillaries or the nondiaphragmed fenestrated endothelium of kidney glomeruli. Taken together, our findings define the only antigen to be localized thus far in fenestral diaphragms. They also show that the stomatal diaphragms of caveolae and transendothelial channels and the fenestral diaphragms might be biochemically related, in addition to being morphologically similar structures.

Influence of host microvascular environment on tumour vascular endothelium

This review will focus on the tumour microvascular endothelium; how it is derived, modulated by angiogenic factors, and how the structure and function is influenced by the host tissue microenvironment.

Tonic neurogenic inhibition of interleukin-6 secretion from murine spleen caused by opioidergic transmission

The peripheral nervous system and the immune system were shown to have neurohumoral interactions. This study extends observations that demonstrated neuronal modulation of spontaneous interleukin-6 (IL-6) secretion in the spleen by norepinephrine (NE) and beta-endorphin. Spontaneous IL-6 secretion in vivo was markedly reduced by removal of macrophages with the clodronate technique. Furthermore, spontaneous IL-6 secretion was significantly inhibited at physiological concentrations of cortisol (10(-7) M). In the presence of 10(-7) M cortisol, addition of norepinephrine (NE; 10(-5) M) and isoproterenol (10(-6) and 10(-5) M) significantly increased spontaneous IL-6 secretion (+20%; P = 0.0280, P = 0.0005, and P = 0.0050, respectively). In contrast, addition of beta-endorphin significantly inhibited spontaneous IL-6 secretion in the presence of 10(-7) M cortisol (-40%; 10(-11) M, P = 0.0410; 10(-10) M, P = 0.0005). To study the effect of endogenously released transmitters on spontaneous IL-6 secretion, spleen slices were electrically stimulated with 1, 5, 10, 50, and 100 Hz. Spontaneous IL-6 secretion was markedly reduced at a frequency of 10 Hz with 10(-7) M cortisol present (P < 0.0001). This indicates that the combination of nerve firing at 5-10 Hz and physiological cortisol conditions inhibits spontaneous IL-6 secretion. Inhibition of spontaneous IL-6 secretion from spleen macrophages is most probably due to a net inhibitory effect of opioidergic transmission under these conditions.

Development of renal podocytes cultured under medium perifusion

BACKGROUND

In the past, podocytes have been described as highly susceptible to dedifferentiation under cell culture. Whether this process resulted from insufficient culture conditions or whether it was a consequence of missing cellular interactions remained unclear. A further reason could be that podocytes within the maturing kidney are irreversibly growth-arrested at a very early point of development because proliferating cells have been detected at the S-shaped body stage but not at the capillary loop stage or in the maturing glomeruli. These were important reasons that hindered the establishment of podocyte cell culture systems.

EXPERIMENTAL DESIGN

The aim of our present study was to culture podocytes under the most organotypic conditions possible to maintain typical cellular characteristics. Cortex explants of neonatal rabbit kidneys consisting of nephrogenic tissue were used as a source for podocytes. No serum additives were given for the whole culture period of 13 days. An organ-specific environment was obtained by keeping the podocytes within the surrounding renal tissue and by ensuring a permanent exchange of medium.

RESULTS

mAb were used to characterize podocytes and the other glomerular cell types. Cultured podocytes and parietal cells of Bowman's capsule were identified by EnPo 1. Ks 19.2.105, a marker for cytokeratin 19, was used to discriminate among these epithelial cells because cytokeratin 19 is expressed by the parietal cells of Bowman's capsule but not by podocytes. The Ab EC1 specifically detected endothelial cells. Glomerular endothelium cultured under medium perifusion expressed these typical Ag and thus could be unequivocally discriminated. Furthermore, by means of the proliferation marker Ki-67, it could be demonstrated that glomerulus-like structures developed under culture by proliferation of visceral and parietal cells of Bowman's capsule.

CONCLUSIONS

A culture model is presented that allows the maintenance of developing podocytes within the organ-specific tissue environment and under permanent medium perifusion.

Stimulation of renal microvascular development under organotypic culture conditions

The development of the renal vascular system requires the coordinated action of soluble morphogenic factors and specific extracellular matrix components. Despite intensive research it remains unknown whether the humoral or the environmental component is more important in the development of renal microvessels. The prolonged serum-free culture of embryonic kidney cortex explants was achieved by means of a newly developed perfusion culture system. This system made the investigation of renal vascular development under defined organotypic conditions possible. Thus, growth factors such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and hormones (aldosterone, vitamin D3) could be applied without the interference with serum components. Medium supplementation with VEGF or aldosterone in combination with vitamin D3 resulted in the coordinated proliferation of endothelial cells in the explant. A well-developed collecting duct epithelium and numerous tubular structures were always observed. In contrast, only a uniform cell layer was found between fibrous organ capsule and the collecting duct epithelium after bFGF application, but neither tubular structures nor endothelial cells. Thus, the experiments indicate that bFGF alone has no stimulating effect on the growth of the renal microvasculature under perfusion culture conditions.

Developing renal microvasculature can be maintained under perfusion culture conditions

The cortex corticis of the neonatal rabbit kidney consists of developing nephrons, vessels, collecting duct ampullae and the nephrogenic mesenchyme. Inductive interactions between embryonic mesenchyme and collecting duct ampullae lead to the coordinated development of the nephrons and the collecting duct system. The factors regulating nephrogenesis and vascular development within this tissue region are unknown. In order to analyze the hormonal regulation of vascular development an organotypic culture system was established. Cortex explants from neonatal rabbit kidneys were prepared, mounted in a set of holding rings and cultured under serum-free conditions for 14 days in conventional culture plates or under permanent medium perfusion in a newly developed culture container. The detection of endothelial cells was carried out by means of two monoclonal antibodies. Within the renal cortex corticis EnPo 1 detected developing vasculature as well as podocytes and a subset of mesenchymal cells. EC1 displayed exclusive specificity for endothelial cells. The antibody did not discriminate between arteries and veins. Endothelial cells of different developmental stages were labeled with the same intensity. A combination of both antibodies allowed the discrimination between developing endothelial cells and podocytes. Following 14 days of culture under permanent medium exchange, excellent tissue preservation as well as endothelial cell proliferation was observed in cortex explants. In contrast, tissue kept in stationary culture revealed a high degree of disintegration. Endothelial antigen expression was also severely disturbed. Tissue maintenance under stationary conditions was improved by the application of a hormone mixture consisting of aldosterone and 1,25-hydroxyvitamin D3. However, the high degree of spatial organization shown by developing endothelial cells in vivo was maintained exclusively in explants cultured in the presence of hormone under permanent perfusion.

Aldosterone modulates PNA binding cell isoforms within renal collecting duct epithelium

To investigate the differentiation of the ampullary collecting duct cells into adult principal and intercalated cells, the embryonic cortex of newborn New Zealand rabbit kidney was isolated and brought in culture. With this culture technique the ampullary cells formed a polarized collecting duct epithelium which was kept under permanent exchange of medium and in the presence of aldosterone, arginine vasopressin and/or insulin. After 14 days of perfusion culture the epithelia showed light and dark cells resembling the principal and intercalated cells of the adult collecting duct. The differentiation from embryonic into adult collecting duct cells was controlled by applying the monoclonal antibody CD 7. Independent of the hormonal treatment all of the epithelial cells matured in culture and expressed the CD 7 antigen. This corresponded with the situation found within the adult kidney, where the CD 7 antigen was localized in all principal and intercalated (IC) cells, whereas the embryonic ampullary epithelium in the neonatal kidney remained negative. A differentiation feature of the beta-type intercalated cell was investigated by labeling the cultured epithelia with peanut agglutinin (PNA). In contrast to the CD 7 antigen the development of PNA binding was highly dependent of time and individual hormone administration. While in control epithelia only 8% of PNA positive cells were found, aldosterone induced epithelia revealed 72% PNA labeled cells. The combination of aldosterone and insulin increased the number of PNA-positive cells to 90%. By scanning electron microscopy it could further be shown that several isoforms of cells were reactive with PNA. Thus, in culture the PNA label is not restricted to the typical beta-type IC cells.