Conversion of mesenchymal stem cells into a canine hepatocyte-like cells by Foxa1 and Hnf4a

Introduction

Hepatocytes, which account for the majority of liver tissue, are derived from the endoderm and become hepatocytes via differentiation of hepatic progenitor cells. Induced hepatocyte-like (iHep) cells and artificial liver tissues are expected to become useful, efficient therapies for severe and refractory liver diseases and to contribute to drug discovery research. The establishment of iHep cell lines are needed to carry out liver transplants and assess liver toxicity in the rising number of dogs affected by liver disease. Recently, direct conversion of non-hepatocyte cells into iHep cells was achieved by transfecting mouse adult fibroblasts with the Forkhead box protein A1 (Foxa1) and hepatocyte nuclear factor 4 homeobox alpha (Hnf4α) genes. Here, we applied this conversion process for the differentiation of canine bone marrow stem cells (cBMSCs) into hepatocyte-like cells.

Methods

Bone marrow specimens were collected from four healthy Beagle dogs and used to culture cBMSCs in Dulbecco's Modified Eagle's Medium (DMEM). The cBMSCs displayed the following characteristic features: plastic adherence; differentiation into adipocytes, osteoblasts and chondrocytes; and a cell surface antigen profile of CD29 (+), CD44 (+), CD90 (+), CD45 (−), CD34 (−) and CD14 (−), or CD11b (−) and CD79a (−), or CD19 (−) and HLA class II(−). The cBMSCs were seeded in a collagen I-coated plate and cultured in DMEM with 10% fetal bovine serum and transfected with retroviruses expressing Foxa1 and Hnf4α the following day. Canine iHep cells were differentiated from cBMSCs in culture on day 10, and were analyzed for morphology, RNA expression, immunocytochemistry, urea production, and low-density lipoprotein (LDL) metabolism.

Results

The cBMSCs expressed CD29 (98.06 ± 1.14%), CD44 (99.59 ± 0.27%) and CD90 (92.78 ± 4.89%), but did not express CD14 (0.47 ± 0.29%), CD19 (0.44 ± 0.39%), CD34 (0.33 ± 0.25%), CD45 (0.46 ± 0.34%) or MHC class II (0.54 ± 0.40%). The iHep cells exhibited morphology that included circular to equilateral circular shapes, and the formation of colonies that adhered to each other 10 days after Foxa1 and Hnf4α transfection. Quantitative RT-PCR analysis showed that the expression levels of the genes encoding albumin (ALB) and cadherin (CDH) in iHep cells on day 10 were increased approximately 100- and 10,000-fold, respectively, compared with cBMSCs. Corresponding protein expression of ALB and epithelial-CDH was confirmed by immunocytochemistry. Important hepatic functions, including LDL metabolic ability and urea production, were increased in iHep cells on day 10.

Conclusion

We successfully induced cBMSCs to differentiate into functional iHep cells. To our knowledge, this is the first report of canine liver tissue differentiation using Foxa1 and Hnf4α gene transfection. Canine iHep cells are expected to provide insights for the construction of liver models for drug discovery research and may serve as potential therapeutics for canine liver disease.

[Regulation of Ca2+ sensitivity of contractile elements in cardiac muscle]

Contraction of cardiac muscle is regulated by changes in the concentration of intracellular Ca(2+) . An increase in the Ca(2+) concentration results in enhanced contractility of cardiac muscle. It is also known that cardiac contractility is influenced by changes in Ca(2+) sensitivity of contractile elements. Recent studies at the molecular level have revealed the complexity of the regulation of Ca(2+) sensitivity of contractile elements.

Spread of Ca2+ in the sarcomere during fast and slow activation of mammalian cardiac myocytes

A multi-compartment model was used to estimate Ca2+ gradients in a sarcomere of a cardiac myocyte. The mathematical model assumed Ca2+ release from the sarcoplasmic reticulum as a driving function, and calculated Ca2+ binding to myoplasmic buffers, Ca2+ uptake by the sarcoplasmic reticulum, and diffusion of Ca2+ (and the buffers). During the fast Ca2+ transient similar to those observed during a twitch, the model predicted a large Ca2+ gradient in the sarcomere. A trajectory of the instantaneous relation between spatially averaged concentrations of Ca2+ and the Ca2+-troponin complex showed a counterclockwise loop, indicating non-equilibrium Ca2+ binding to troponin. During slow changes in [Ca2+] with time to peaks of approximately 500 ms or longer, the gradient of [Ca2+] was largely dissipated and the apparent equilibrium of the Ca2+-troponin binding reaction was suggested with little hysteresis of the trajectory. We conclude that a steady-state relation between [Ca2+] and mechanical activity can be achieved uniformly in the sarcomere by slowing the rate of Ca2+ release from the sarcoplasmic reticulum.

Estimation of myofibrillar responsiveness to Ca2+ in isolated rat ventricular myocytes

To estimate myofibrillar responsiveness to Ca2+, we used the relation between cell length and intracellular [Ca2+] ([Ca2+]i) during tetanic contractions of isolated ventricular myocytes. Enzymatically isolated rat ventricular myocytes were loaded with fura-2 AM (4 microM for 10 min) and excited alternately at 340 nm and 380 nm. The ratio (R) of fura-2 fluorescence at these wavelengths [F(340)/F(380), an index of [Ca2+]i] and cell length (L) were measured simultaneously. Following treatment with thapsigargin (0.2 microM), myocytes were stimulated at 10 Hz for 10 s to produce a tetanic contraction every min and an instantaneous plot of R vs L (R-L trajectory) was constructed. The R-L trajectory followed the same path during cell shortening and re-lengthening, suggesting that dynamic equilibrium between R and L was achieved during tetanus. Increasing the extracellular [Ca2+] from 1 to 8 mM extended the R-L trajectory without a substantial shift of the relation. The Ca2+-sensitizing thiadiazinone derivative, EMD57033 (1 microM), shifted the R-L trajectory to the left (sensitization of the myofibrils to Ca2+), whereas the non-selective phosphodiesterase inhibitor, 3-isobutyl-1-methylxantine (200 microM), shifted the R-L trajectory to the right (desensitization of the myofibrils to Ca2+), in agreement with previous results obtained using skinned preparations. We conclude that the R-L trajectory is useful for estimating the myofibrillar responsiveness to Ca2+ in isolated myocytes and may be beneficial for the evaluation of inotropic agents.

Histidine-like immunoreactivity in the rat retina

PURPOSE

Histidine is an indispensable amino acid with an imidazole ring and it is a precursor of histamine, carnosine, and anserine. Histidine has been proposed to act as a neurotransmitter or neuromodulator in mammalian central nervous system (CNS), including retina. In this study, we report histidine-like immunoreactivity in the rat retina with the use of antibodies raised against histidine coupled to bovine serum albumin (BSA) with glutaraldehyde.

METHODS

In order to confirm the specificity of the antiserum toward histidine, immunodots were carried out. Only the histidine conjugate showed immunoreactivity. The rat retinas fixed with glutaraldehyde were used for immunocytochemistry.

RESULTS

Histidine immunoreactivity was identified in the ganglion cell layer (GCL), inner nuclear layer (INL), inner plexiform layer (IPL), and Müller cells of rat retina.

CONCLUSIONS

Histidine may be a precursor of histamine in the inner retina, and Müller cells may play some role in the metabolism of histidine.