Sustained delivery of activated Rho GTPases and BDNF promotes axon growth in CSPG-rich regions following spinal cord injury

BACKGROUND

Spinal cord injury (SCI) often results in permanent functional loss. This physical trauma leads to secondary events, such as the deposition of inhibitory chondroitin sulfate proteoglycan (CSPG) within astroglial scar tissue at the lesion.

METHODOLOGY/PRINCIPAL FINDINGS

We examined whether local delivery of constitutively active (CA) Rho GTPases, Cdc42 and Rac1 to the lesion site alleviated CSPG-mediated inhibition of regenerating axons. A dorsal over-hemisection lesion was created in the rat spinal cord and the resulting cavity was conformally filled with an in situ gelling hydrogel combined with lipid microtubes that slowly released constitutively active (CA) Cdc42, Rac1, or Brain-derived neurotrophic factor (BDNF). Treatment with BDNF, CA-Cdc42, or CA-Rac1 reduced the number of GFAP-positive astrocytes, as well as CSPG deposition, at the interface of the implanted hydrogel and host tissue. Neurofilament 160kDa positively stained axons traversed the glial scar extensively, entering the hydrogel-filled cavity in the treatments with BDNF and CA-Rho GTPases. The treated animals had a higher percentage of axons from the corticospinal tract that traversed the CSPG-rich regions located proximal to the lesion site.

CONCLUSION

Local delivery of CA-Cdc42, CA-Rac1, and BDNF may have a significant therapeutic role in overcoming CSPG-mediated regenerative failure after SCI.

HMG-CoA Reductase Inhibitors Decrease Angiotensin II–Induced Vascular Fibrosis

3-hydroxy-3-methylglutaryl (HMG)-coenzyme A (CoA) reductase inhibitors (statins) present beneficial effects in cardiovascular diseases. Angiotensin II (Ang II) contributes to cardiovascular damage through the production of profibrotic factors, such as connective tissue growth factor (CTGF). Our aim was to investigate whether HMG-CoA reductase inhibitors could modulate Ang II responses, evaluating CTGF expression and the mechanisms underlying this process. In cultured vascular smooth muscle cells (VSMCs) atorvastatin and simvastatin inhibited Ang II–induced CTGF production. The inhibitory effect of statins on CTGF upregulation was reversed by mevalonate and geranylgeranylpyrophosphate, suggesting that RhoA inhibition could be involved in this process. In VSMCs, statins inhibited Ang II–induced Rho membrane localization and activation. In these cells Ang II regulated CTGF via RhoA/Rho kinase activation, as shown by inhibition of Rho with C3 exoenzyme, RhoA dominant-negative overexpression, and Rho kinase inhibition. Furthermore, activation of p38MAPK and JNK, and redox process were also involved in Ang II–mediated CTGF upregulation, and were downregulated by statins. In rats infused with Ang II (100 ng/kg per minute) for 2 weeks, treatment with atorvastatin (5 mg/kg per day) diminished aortic CTGF and Rho activation without blood pressure modification. Rho kinase inhibition decreased CTGF upregulation in rat aorta, mimicking statin effect. CTGF is a vascular fibrosis mediator. Statins diminished extracellular matrix (ECM) overexpression caused by Ang II in vivo and in vitro. In summary, HMG-CoA reductase inhibitors inhibit several intracellular signaling systems activated by Ang II (RhoA/Rho kinase and MAPK pathways and redox process) involved in the regulation of CTGF. Our results may explain, at least in part, some beneficial effects of statins in cardiovascular diseases.

Src tyrosine kinase activity down-regulates Rho-dependent responses during Shigella entry into epithelial cells and stress fibre formation

Invasion of epithelial cells by Shigella, the causative agent of bacillary dysentery, is dependent upon the formation of characteristic membrane ruffles that engulf the bacteria in a macropinocytic-like process. We show here that Cdc42 and Rac GTPases, but not Rho;, are critical for actin polymerisation, whereas Rho; is necessary for the recruitment of ezrin and Src at the site of entry. Remarkably, cells expressing constitutively active Src did not show ezrin recruitment at Shigella entry foci. In these cells, formation of stress fibres induced by LPA stimulation, or microinjection of activated Rho; (V14Rho), was inhibited. Src-mediated tyrosyl-phosphorylation of p190RhoGAP correlated with changes in the ability of p190RhoGAP to interact with Rho;, suggesting that Src regulates Rho; function via p190RhoGAP. We propose that Rho; activation is required for proper organisation of Shigella entry foci and for Src recruitment, and that Src tyrosine kinase activity, in turn, down-regulates the function of Rho; at the site of Shigella entry. The significance of this negative regulatory loop on Rho;-dependent responses is discussed.