cDNA cloning and chromosomal mapping of rat Smad2 and Smad4 and their expression in cultured rat articular chondrocytes

Musculoskeletal gene therapy and its potential use in the treatment of complicated musculoskeletal infection

Tissue repair is a major issue in orthopedics. Many musculoskeletal tissues, including cartilage, meniscus, and the anterior cruciate ligament, heal poorly after injury. Recent studies have led to the identification of numerous growth factors and other gene products that can promote the regeneration of damaged musculoskeletal tissues. In the last century, the discovery and evolving use of antibiotics has significantly decreased the prevalence and severity of infectious diseases. In many orthopedic scenarios, however, treatment of infections can be difficult, and often involves a prolonged course of antibiotics with concomitant surgical interventions and loss of tissue. Although studies have demonstrated the successful transfer of target genes and the associated manipulation of the musculoskeletal tissue environment, researchers have made few attempts designed to use gene therapy to treat infectious musculoskeletal diseases in animal models. Before it is possible to use gene-based approaches to treat such diseases effectively, researchers must perform more studies to investigate the potential problems that may arise when using gene therapy in an infectious environment.

Cloning of Smad2, Smad3, Smad4, and Smad7 from the goldfish pituitary and evidence for their involvement in activin regulation of goldfish FSHbeta promoter activity

Follicle-stimulating hormone (FSH), a glycoprotein consisting of an alpha subunit and a unique beta subunit, is essential for gonadal development and function in vertebrates including teleosts. FSH is regulated by a variety of neuroendocrine and endocrine factors, and its biosynthesis is primarily determined by the expression of the beta subunit. Although the regulation of FSH biosynthesis has been well documented in mammals, the molecular mechanisms underlying the regulation are poorly understood. Our previous studies demonstrated that activin stimulated goldfish FSHbeta expression in the primary pituitary cell culture and enhanced its promoter activity in the mouse gonadotrope cell line LbetaT-2 cells. However, little is known about the signal transduction pathway involved in the transcriptional activation of this gene by activin. To assess the involvement of intracellular signaling protein Smads in regulating goldfish FSHbeta promoter, we first cloned full-length cDNAs for goldfish Smad2, Smad3, Smad4, and Smad7 from the pituitary. All Smads cloned show high sequence conservation with their mammalian counterparts. The spatial expression of these Smads overlapped with that of activin subunits and its receptors in various tissues examined. In addition, we demonstrated that activin induced Smad3 and Smad7 expression, but not Smad2 and Smad4. Co-transfection of Smad2 or Smad3 cDNA into the LbetaT-2 cells with the reporter construct of goldfish FSHbeta promoter significantly enhanced basal and activin-stimulated reporter (SEAP, secreted alkaline phosphatase) expression, while Smad7 completely blocked basal and Smad2/3-stimulated FSHbeta activity. Interestingly, the effect of Smad3 was much higher than that of Smad2, suggesting that Smad3 is likely the principal signal transducing molecule involved in activin stimulation of FSHbeta expression in the goldfish. This work lays a foundation for further analysis of goldfish FSHbeta promoter for the cis-regulatory elements involved in activin signaling.

Gene-based approaches for the repair of articular cartilage

Gene transfer technology has opened novel treatment avenues toward the treatment of damaged musculoskeletal tissues, and may be particularly beneficial to articular cartilage. There is no natural repair mechanism to heal damaged or diseased cartilage. Existing pharmacologic, surgical and cell based treatments may offer temporary relief but are incapable of restoring damaged cartilage to its normal phenotype. Gene transfer provides the capability to achieve sustained, localized presentation of bioactive proteins or gene products to sites of tissue damage. A variety of cDNAs have been cloned which may be used to stimulate biological processes that could improve cartilage healing by (1) inducing mitosis and the synthesis and deposition of cartilage extracellular matrix components by chondrocytes, (2) induction of chondrogenesis by mesenchymal progenitor cells, or (3) inhibiting cellular responses to inflammatory stimuli. The challenge is to adapt this technology into a useful clinical treatment modality. Using different marker genes, the principle of gene delivery to synovium, chondrocytes and mesenchymal progenitor cells has been convincingly demonstrated. Following this, research efforts have begun to move to functional studies. This involves the identification of appropriate gene or gene combinations, incorporation of these cDNAs into appropriate vectors and delivery to specific target cells within the proper biological context to achieve a meaningful therapeutic response. Methods currently being explored range from those as simple as direct delivery of a vector to a cartilage defect, to synthesis of cartilaginous implants through gene-enhanced tissue engineering. Data from recent efficacy studies provide optimism that gene delivery can be harnessed to guide biological processes toward both accelerated and improved articular cartilage repair.

Retinoic acid stimulates chondrocyte differentiation and enhances bone morphogenetic protein effects through induction of Smad1 and Smad5

Whereas bone morphogenetic protein (BMP)-signaling events induce maturational characteristics in vitro, recent evidence suggests that the effects of other regulators might be mediated through BMP-signaling events. The present study examines the mechanism through which retinoic acid (RA) stimulates differentiation in chicken embryonic caudal sternal chondrocyte cultures. Both RA and BMP-2 induced expression of the chondrocyte maturational marker, colX, in chondrocyte cultures by 8 d. Though the RA effect was small, it synergistically enhanced the effect of BMP-2 on colX and phosphatase activity. Inhibition of either RA or BMP signaling, with selective inhibitors, interfered with the inductive effects of these agents but also inhibited the complementary pathway, demonstrating a codependence of RA and BMP signaling during chondrocyte maturation. BMP-2 did not enhance the effects of RA on an RA-responsive reporter construct, but RA enhanced basal activity and synergistically enhanced BMP-2 stimulation of the BMP-responsive chicken type X collagen reporter. A similar synergistic interaction between RA and BMP-2 was observed on colX expression. RA did not increase the expression of the type IA BMP receptor but did markedly up-regulate the expression of Smad1 and Smad5 proteins, important participants in the BMP pathway. Inhibition of RA signaling, with the selective inhibitor AGN 193109, blocked RA-mediated induction of the Smad proteins and chondrocyte differentiation. These findings demonstrate that RA induces the expression of BMP-signaling molecules and enhances BMP effects in chondrocytes.

Transcriptional regulation of Smad2 is required for enhancement of TGF?/Smad signaling by TGF? inducible early gene

TGFbeta inducible early gene (TIEG) is a novel Krüppel-like transcriptional repressor that was recently shown to increase the activity of the TGFbeta/Smad signal transduction pathway by relieving negative feedback through repression of the inhibitory Smad7. Interestingly, while Smad7 is required for maximal enhancement of TGFbeta/Smad signaling, we observe that TIEG is still capable of increasing Smad pathway activity in the absence of Smad7. Furthermore, while Smad7 is known to block both TGFbeta and bone morphogenetic protein (BMP) signaling, we observe that TIEG specifically enhances only the TGFbeta pathway. Similarly, while both TIEG and the related Krüppel-like factor, FKLF2, repress Smad7 transcription, only TIEG is capable of enhancing Smad signaling. In order to identify additional regulatory targets of TIEG important for this enhancement of the Smad pathway activity, we performed microarray analysis and identified Smad2 as a TIEG target gene. We now show evidence that TIEG increases transcription of the Smad2 gene but not the Smad3 or Smad4 genes. Furthermore, while the TGFbeta/Smad pathway remains intact in Smad2 null cells, TIEG enhancement of Smad signaling is dramatically reduced. Thus we propose a new model whereby TIEG enhances Smad signaling by a dual mechanism involving both the repression of the inhibitory Smad7 as well as the activation of Smad2.