Publications

Heme oxygenase 1 (Hmox1), a ubiquitous enzyme degrading heme to carbon monoxide, iron, and biliverdin, is one of the cytoprotective enzymes induced in response to a variety of stimuli, including cellular oxidative stress. Gangliosides, sialic acid‐containing glycosphingolipids expressed in all cells, are involved in cell recognition, signalling, and membrane stabilization. Their expression is often altered under many pathological and physiological conditions including cell death, proliferation, and differentiation. The aim of this study was to assess the possible role of Hmox1 in ganglioside metabolism in relation to oxidative stress. The content of liver and brain gangliosides, their cellular distribution, and mRNA as well as protein expression of key glycosyltransferases were determined in Hmox1 knockout mice as well as their wild‐type littermates. To elucidate the possible underlying mechanisms between Hmox1 and ganglioside metabolism, hepatoblastoma HepG2 and neuroblastoma SH‐SY5Y cell lines were used for in vitro experiments. Mice lacking Hmox1 exhibited a significant increase in concentrations of liver and brain gangliosides and in mRNA expression of the key enzymes of ganglioside metabolism. A marked shift of GM1 ganglioside from the subsinusoidal part of the intracellular compartment into sinusoidal membranes of hepatocytes was shown in Hmox1 knockout mice. Induction of oxidative stress by chenodeoxycholic acid in vitro resulted in a significant increase in GM3, GM2, and GD1a gangliosides in SH‐SY5Y cells and GM3 and GM2 in the HepG2 cell line. These changes were abolished with administration of bilirubin, a potent antioxidant agent. These observations were closely related to oxidative stress‐mediated changes in sialyltransferase expression regulated at least partially through the protein kinase C pathway. We conclude that oxidative stress is an important factor modulating synthesis and distribution of gangliosides in vivo and in vitro which might affect ganglioside signalling in higher organisms.

We have tested cultured human microvascular endothelial cells (HMEC-1) for their ability to synthesize cyclic adenosine 3',5'-monophosphate (cAMP) in the absence or presence of various drugs. The accumulation of cAMP was only slightly affected by the addition of a phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) to the incubation medium. A direct stimulator of adenylyl cyclase forskolin and adrenergic drugs, such as adrenaline and noradrenaline, strongly increased cAMP accumulation in IBMX-treated HMEC-1 cells, whereas some other drugs known to stimulate the nucleotide synthesis in different cell/tissues were inactive (dopamine, histamine). Adrenaline was significantly more potent than noradrenaline. The effect of adrenaline on cyclic AMP production was reproduced by a selective beta-adrenoceptor agonist isoprenaline, antagonized by beta-blocker propranolol, and was not influenced by both alpha(1) and alpha(2)-selective antagonists, prazosin and yohimbine, respectively. Adrenaline did not significantly affect the ability of HMEC-1 cells to produce vascular endothelial growth factor (VEGF) or interleukin-8 (IL-8), the major angiogenic mediators. The results indicate that under basal (non-stimulated) conditions, the cAMP generating system of HMEC-1 cells maintained in culture remains rather quiescent, yet it can strongly respond to the hormone adrenaline acting on beta-adrenergic receptors.

Abstract Heme oxygenase-1 (HO-1, encoded by Hmox1 ) is a cytoprotective enzyme with well-established roles in defending against oxidative stress. Global Hmox1 deficiency in mice accelerates hematopoietic stem cell (HSC) exhaustion and aging, effects previously attributed primarily to loss of HO-1 activity within the bone marrow (BM) niche. However, the cell-intrinsic contribution of HO-1 to HSC regulation has remained unclear. Here, we show that global Hmox1 deficiency results in accumulation of an expanded but largely quiescent HSC pool characterized by compromised genome maintenance, altered apoptotic signaling, and defective cell-cycle checkpoint control. We further demonstrate that HO-1 protein is expressed in HSCs and exhibits a predominantly nuclear, non-canonical localization. Using Hoxb5 -CreERT2-mediated conditional deletion of Hmox1 in HSCs, we uncover an intrinsic requirement for HO-1 in controlling early hematopoietic differentiation. HSC-specific loss of HO-1 skews stem cell output toward short-term progenitors and increases colony-forming capacity. Transcriptomic profiling of Hmox1 fl/fl ; Hoxb5 -CreERT2 HSCs revealed broad dysregulation of pathways involved in translation and RNA metabolism, together with aberrant expression of key transcription factors controlling hematopoietic differentiation. Collectively, these findings identify a non-canonical, cell-intrinsic role for HO-1 in regulating HSC homeostasis, differentiation, and aging.

Both MSC Hmox1^+/+ and Hmox1^-/- showed similar phenotype, differentiation capacities, and production of cytokines or growth factors. Hmox1^+/+ and Hmox1^-/- cells showed similar survival in response to 50 μmol/L hemin even in increased glucose concentration, conditions that were unfavorable for Hmox1^-/- bone marrow-derived proangiogenic cells (BDMC). Hmox1^+/+ MSCs but not fibroblasts retained low ROS levels even after prolonged incubation with 50 μmol/L hemin, although both cell types have a comparable Hmox1 expression and similarly increase its levels in response to hemin. MSCs Hmox1^-/- treated with hemin efficiently induced expression of a vast panel of antioxidant genes, especially enzymes of the glutathione pathway. Innovation and Conclusion: Hmox1 overexpression is a popular strategy to enhance viability and performance of MSCs after the transplantation. However, murine MSCs Hmox1^-/- do not differ from wild-type MSCs in phenotype and functions. MSC Hmox1^-/- show better resistance to hemin than fibroblasts and BDMCs and rapidly react to the stress by upregulation of quintessential genes in antioxidant response. Antioxid. Redox Signal. 00, 000-000.

Cytokines such as interleukin-6 induce tyrosine and serine phosphorylation of Stat3 that results in activation of Stat3-responsive genes. We provide evidence that Stat3 is present in the mitochondria of cultured cells and primary tissues, including the liver and heart. In Stat3 –/– cells, the activities of complexes I and II of the electron transport chain (ETC) were significantly decreased. We identified Stat3 mutants that selectively restored the protein's function as a transcription factor or its functions within the ETC. In mice that do not express Stat3 in the heart, there were also selective defects in the activities of complexes I and II of the ETC. These data indicate that Stat3 is required for optimal function of the ETC, which may allow it to orchestrate responses to cellular homeostasis.

Heme oxygenase-1 (HO1) degrades heme to carbon monoxide (CO), biliverdin, and ferrous iron. Through these<br /> products, HO1 mitigates cellular injury by exerting anti-oxidant, anti-apoptotic, and anti-inflammatory effects.<br /> Several lines of evidence indicate that angiogenic factors, such as vascular endothelial growth factor A (VEGF)<br /> and stromal cell-derived factor 1 (SDF1), mediate their proangiogenic action in endothelial cells and endothelial<br /> progenitor cells through induction of HO1, and reciprocally, VEGF and SDF1 are enhanced by HO1 overexpression.<br /> Ferrous iron released during the breakdown of free heme by HO1 is an extremely pro-oxidative molecule<br /> that can be rapidly removed by ferritin. Of note, this iron sequestering protein also has been shown to exert some<br /> proangiogenic effects. Moreover, our recent data indicate that HO1 is an important mediator of differentiation<br /> and function of stem cells, including endothelial and myoblasts progenitors. All of this makes HO1 a promising<br /> target for novel cardiovascular therapies. The aim of this review is to discuss the existing knowledge and to propose<br /> the therapeutic approaches, which have to consider the necessity of tight regulation of HO1 expression.

<p>Effect of co-culture of SMS-CTR eRMS cell line and mesenchymal stromal cells (MSC) with normal HO-1 expression (MSC WT) or lacking HO-1 (MSC HO-1 KO).</p>

Adeno-associated viral (AAV) vectors are characterised by low immunogenicity, although humoral and cellular responses may be triggered upon infection. Following systemic administration high levels of vector particles accumulate within the liver. Kupffer cells (KCs) are liver resident macrophages and an important part of the liver innate immune system. Decreased functional activity of KCs can contribute to exaggerated inflammatory response upon antigen exposure. Heme oxygenase-1 (HO-1) deficiency is associated with considerably reduced numbers of KCs. In this study we aimed to investigate the inflammatory responses in liver and to characterise two populations of hepatic macrophages in adult wild type (WT) and HO-1 knockout (KO) mice following systemic administration of one or two doses (separated by 3 months) of self-complementary (sc)AAV9 vectors. At steady state, the livers of HO-1 KO mice contained significantly higher numbers of monocyte-derived macrophages (MDMs), but significantly less KCs than their WT littermates. Three days after re-administration of scAAV9 we observed increased mRNA level of monocyte chemoattractant protein-1 (Mcp-1) in the livers of both WT and HO-1 KO mice, but the protein level and the macrophage infiltration were not affected. Three days after the 1st and 3 days after the 2nd vector dose the numbers of AAV genomes in the liver were comparable between both genotypes indicating similar transduction efficiency, but the percentage of transgene-expressing MDMs and KCs was higher in WT than in HO-1 KO mice. In the primary culture, KCs were able to internalize AAV9 particles without induction of TLR9-mediated immune responses, but no transgene expression was observed. In conclusion, in vivo and in vitro cultured KCs have different susceptibility to scAAV9 vectors. Regardless of the presence or absence of HO-1 and initial numbers of KCs in the liver, scAAV9 exhibits a low potential to stimulate inflammatory response at the analysed time points.

Endothelium has an immense impact on the tissue regeneration, regulation of atherosclerosis and tumour growth. Therefore, modification of endothelial cell differentiation and function seems a promising target for many therapies. MicroRNAs are small RNA molecules, which recognize and inhibit specific mRNAs. In that way, they can regulate and orchestrate whole signalling pathways. It has been shown that microRNAs can fine-tune endothelial cell functions since they have either pro- and antiangiogenic activity, regulate expression of e.g. adhesion molecules or nitric oxide synthase. Furthermore, microRNAs modulate differentiation of embryonic stem cells to endothelial cells and their further specialization towards specific vascular bed. This review focuses mainly on the influence of microRNA on the angiogenesis and endothelial cell differentiation.