Highly efficient adenovirus-mediated gene transfer into renal cells in culture

MURC, a muscle-restricted coiled-coil protein, is involved in the regulation of skeletal myogenesis

Skeletal myogenesis is a multistep process by which multinucleated mature muscle fibers are formed from undifferentiated, mononucleated myoblasts. However, the molecular mechanisms of skeletal myogenesis have not been fully elucidated. Here, we identified muscle-restricted coiled-coil (MURC) protein as a positive regulator of myogenesis. In skeletal muscle, MURC was localized to the cytoplasm with accumulation in the Z-disc of the sarcomere. In C2C12 myoblasts, MURC expression occurred coincidentally with myogenin expression and preceded sarcomeric myosin expression during differentiation into myotubes. RNA interference (RNAi)-mediated knockdown of MURC impaired differentiation in C2C12 myoblasts, which was accompanied by impaired myogenin expression and ERK activation. Overexpression of MURC in C2C12 myoblasts resulted in the promotion of differentiation with enhanced myogenin expression and ERK activation during differentiation. During injury-induced muscle regeneration, MURC expression increased, and a higher abundance of MURC was observed in immature myofibers compared with mature myofibers. In addition, ERK was activated in regenerating tissue, and ERK activation was detected in MURC-expressing immature myofibers. These findings suggest that MURC is involved in the skeletal myogenesis that results from modulation of myogenin expression and ERK activation. MURC may play pivotal roles in the molecular mechanisms of skeletal myogenic differentiation.

The cyclin-dependent kinase inhibitor p21 is required for TGF-beta1-induced podocyte apoptosis

BACKGROUND

Reduced podocyte number is a critical determinant in the development of glomerulosclerosis. Transforming growth factor-beta1 (TGF-beta1) induces podocyte apoptosis, but the cell cycle events are not known. The cyclin-dependent kinase (CDK) inhibitor p21 increases in podocytes in diseases where TGF-beta increases. Accordingly, we studied the role of p21 in podocyte apoptosis.

METHODS

Immortalized and primary p21+/+ and p21-/- mouse podocytes were used. Apoptosis was measured by Hoechst 33342 staining and caspase-3 activity following the exposure to TGF-beta1 or puromycin aminonucleoside. p21 and specific Bcl-2-related family proteins levels were measured by Western blot analysis. To prove a role for p21, we reconstituted p21 expression in p21-/- podocytes utilizing an adenovirus vector.

RESULTS

TGF-beta1 increased the protein levels of p21 in p21+/+ podocytes, and this coincided with apoptosis. In contrast, TGF-beta1 did not induce apoptosis in p21-/- podocytes. Restoring p21 expression increased apoptosis in p21-/- podocytes following exposure to TGF-beta1. TGF-beta1 increased the protein levels of an anti-apoptotic Bcl-2 in p21-/- podocytes, but not in p21+/+ podocytes. Moreover, TGF-beta1 did not increase Bcl-2 expression in p21-/- podocytes in which p21 expression was restored. Finally, puromycin aminonucleoside also induced apoptosis in p21+/+ podocytes, but not in p21-/- podocytes.

CONCLUSION

Podocyte apoptosis induced by TGF-beta1 and puromycin aminonucleoside requires p21, and Bcl-2 plays a crucial role downstream of p21 in mediating this effect. These results suggest that p21 may play a critical role in the decrease in podocyte number in disease status accompanied by increased TGF-beta1.

Effects of suppressing intrarenal angiotensinogen on renal transforming growth factor-beta1 expression in acute ureteral obstruction

BACKGROUND

Angiotensin II (Ang II) mediates the up-regulation of fibrogenic factors such as transforming growth factor-beta1 (TGF-beta1) in chronic renal diseases. In addition, it has been proposed that the intrarenal renin-angiotensin system (RAS) is as important as the systemic RAS in kidney disease progression.

METHODS

We suppressed angiotensinogen (AGT) gene expression in the kidney by transferring recombinant adenoviral vectors carrying a transgene expressing AGT antisense mRNA, and determined the effect of the local inhibition of the RAS on TGF-beta1 synthesis in the kidneys of rats with unilateral ureteral obstruction (UUO). Immediately after UUO, recombinant adenovirus vectors were injected intraparenchymally into the cortex of obstructed kidneys.

RESULTS

beta-galactosidase (beta-gal)-stained kidney sections revealed the efficient transduction of the recombinant adenoviral vectors into tubular epithelial cells. Kidney cortex injected with AGT antisense showed significantly lower native AGT mRNA and protein expressions than control UUO kidneys at 24 hours and 5 days post-UUO. TGF-beta1 was significantly up-regulated in the renal cortex 24 hours and 5 days post-UUO, whereas AGT antisense-injected UUO rats showed significantly reduced TGF-beta1 expression compared to control UUO rats. Both fibronectin and collagen type I expressions were increased 24 hours and 5 days post-UUO, and these augmentations were considerably reduced by AGT antisense RNA treatment.

CONCLUSION

This study demonstrates that the suppression of intrarenal RAS prevents the formation of renal cortical TGF-beta1, and of related fibrogenic factors, in early UUO.

Dopa-producing astrocytes generated by adenoviral transduction of human tyrosine hydroxylase gene: in vitro study and transplantation to hemiparkinsonian model rats

Astrocytes secreting a large amount of 3,4-dihydroxyphenylalanine (dopa) were generated by adenoviral transduction of the human tyrosine hydroxylase (TH) gene. After characterizing in vitro, the effect of transplantation of these astrocytes to the striatum of hemiparkinsonian model rats was investigated. Subconfluent cortical astrocytes were infected by replication-defect adenovirus type 5 carrying the human TH-1 gene or the LacZ reporter gene under the promoter of the glial fibrillary acidic protein (AdexGFAP-HTH-1, AdexGFAP-NL-LacZ). Dopa secretion was not evident at 3 days after the transduction of the HTH-1 gene but it increased from 7 days up to at least 4 months. The secretion was substrate (tyrosine)-dependent, and was enhanced by loading tetrahydrobioputerin (BH4) concentration-dependently. One-third of the hemiparkinsonian model rats, that were transplanted the HTH-1 gene-transduced astrocytes or introduced the direct injection of the viral vector to the striatum, showed a reduction of methamphetamine-induced rotations for at least 6 weeks. Apomorphine-induced rotation was decreased to the 50% level of the control's, but the reduction was obtained equally by the transplantation of HTH-1 gene-transduced or LacZ reporter gene-transduced astrocytes, or by the introduction of HTH-1 or LacZ gene carrying adenovirus. Treatment with FK506 for 3 weeks improved the late-phase apomorphine-induced rotations following the introduction of the HTH-1 gene carrying adenovirus. Histological examination revealed that, in animals that showed a reduction of methamphetamine-rotation, the TH positive astrocytes-like cells were distributed widely in the host striatum for at least 4 weeks. The number of TH positive astrocytes-like cells and their immunoreactivity decreased after 6 weeks when OX-41 positive microglias/macrophages were infiltrated. Data indicate that the adenoviral transduction of the human TH gene to astrocytes and its introduction to the striatum is a promising approach for the treatment of Parkinson's disease. However, the further technical improvements are required to optimize the adenoviral gene delivery, such as the control of viral toxicity and the regulation of the immune response.

Molecular aspects of vasopressin receptor function

The molecular mechanisms governing the G protein coupling selectivity of different members of the vasopressin receptor family were studied by using a combined molecular genetic/biochemical approach. While the V1a and V1b vasopressin receptors are selectively linked to G proteins of the Gq/11 class, the V2 vasopressin receptor is preferentially coupled to Gs. Systematic functional analysis of V1a/V2 hybrid receptors showed that the second intracellular loop of the V1a receptor is required and sufficient for efficient coupling to Gq/11, whereas the third intracellular loop of the V2 receptor is required and sufficient for coupling to Gs. By using a strategy involving the coexpression of the wild type V1a receptor with chimeric G protein alpha s/alpha q subunits, two C-terminal alpha q/11 residues were identified that are critical for proper receptor recognition. We previously demonstrated -in transiently transfected COS-7 cells- that selected mutant V2 vasopressin receptors (all of which have been identified in X-linked nephrogenic diabetes insipidus patients) containing inactivating mutations in the C-terminal third of the receptor protein (including missense, frameshift, or nonsense mutations) can be functionally rescued by coexpression with a C-terminal V2 receptor fragment (V2-tail) spanning the region where the various mutations occur. Co-immunoprecipitation experiments and a newly developed sandwich ELISA revealed that the V2-tail polypeptide directly interacts with the mutant V2 receptors thus creating a functional receptor protein. To study the potential therapeutic usefulness of these findings, CHO cell lines stably expressing low levels of functionally inactive mutant V2 vasopressin receptors (E242stop, Y280C, and W284stop) were created and infected with a recombinant adenovirus coding for the V2-tail polypeptide. Following adenovirus infection, arginine vasopressin (AVP) gained the ability to stimulate cAMP formation in all CHO cell clones studied. Adenovirus-mediated gene transfer also proved to be a highly efficient method to achieve expression of the V2-tail fragment (as well as of the wild type V2 vasopressin receptor) in MDCK renal tubular cells. We therefore speculate that the targeted expression of receptor fragments in vivo may represent a novel strategy in the treatment of human diseases caused by inactivating mutations in distinct G protein-coupled receptors.

Reconstitution of mutant V2 vasopressin receptors by adenovirus-mediated gene transfer. Molecular basis and clinical implication

Recent studies with transfected COS-7 cells have shown that functionally inactive mutant V2 vasopressin receptors (occurring in patients with nephrogenic diabetes insipidus) can be functionally rescued by coexpression of a carboxy-terminal V2 receptor fragment (V2-tail) spanning the region where various mutations occur [Schöneberg, T., J. Yun, D. Wenkert, and J. Wess. 1996. EMBO (Eur. Mol. Biol. Organ.) J. 15:1283-1291]. In this study, we set out to characterize the underlying molecular mechanism. Using a coimmunoprecipitation strategy and a newly developed sandwich ELISA system, a direct and highly specific interaction between the mutant V2 vasopressin receptor proteins and the V2-tail polypeptide was demonstrated. To study the potential therapeutic usefulness of these findings, Chinese hamster ovary (CHO) cell lines stably expressing low levels of functionally inactive mutant V2 vasopressin receptors were created and infected with a recombinant adenovirus carrying the V2-tail gene fragment. After adenovirus infection, vasopressin gained the ability to stimulate cAMP formation with high potency and efficacy in all CHO cell clones studied. Moreover, adenovirus-mediated gene transfer also proved to be a highly efficient method for achieving expression of the V2-tail fragment (as well as the wild-type V2 receptor) in Madin-Darby canine kidney tubular cells. Taken together, these studies clarify the molecular mechanisms by which receptor fragments can restore function of mutationally inactivated G protein-coupled receptors and suggest that adenovirus-mediated expression of receptor fragments may lead to novel strategies for the treatment of a variety of human diseases.

A neural cell-type-specific expression system using recombinant adenovirus vectors

We demonstrated neural cell-type-specific gene expression using an adenovirus vector, which is useful for delivering foreign genes into quiescent neural cells. We produced eight recombinant replication-defective adenoviruses carrying the lacZ reporter gene driven by various promoters, including those of the L7/PCP2 gene (highly restricted expression in cerebellar Purkinje cells), and the myelin basic protein (in oligodendrocytes) gene. We demonstrated in vitro and in vivo promoter-driven, neural cell-type-specific gene expression by recombinant adenoviruses. The genes were transferred into these recombinant adenoviruses and expressed with high levels of efficiency in vitro and in vivo. In primary culture, the recombinant adenoviruses AdexL7-NL-LacZ and AdexMBP-NL-LacZ appeared to be expressed in a Purkinje cell and oligodendrocyte-specific manner. Introduction of 10(8) pfu of these viruses into the adult rat cerebellum by stereotactic injection yielded neural cell-type-specific expression without apparent toxicity to the animals. Thus, adenovirus vectors are useful for cell-type-specific therapeutic uses and in studies requiring neural cell-type-specific gene expression.