Knockdown of mechanosensitive adaptor Hic-5 ameliorates post-traumatic osteoarthritis in rats through repression of MMP-13.

Osteoarthritis (OA) is the most common joint disease associated with articular cartilage destruction. Matrix metalloproteinase-13 (MMP-13) has an essential role in OA pathogenesis by degradation of collagen II, a major component of articular cartilage. Hydrogen peroxide-inducible clone-5 (Hic-5; TGFB1I1), a transforming growth factor-ß-inducible mechanosensor, has previously been reported to promote OA pathogenesis by upregulating MMP-13 expression in mouse osteoarthritic lesions. In our current study, immunohistochemical analysis showed that Hic-5 protein expression was increased in human OA cartilage compared with normal cartilage. Functional experiments demonstrated that Hic-5 and MMP-13 expression was increased by mechanical stress, and mechanical stress-induced MMP-13 expression was suppressed by Hic-5 siRNA in human chondrocytes. Moreover, intracellular localization of Hic-5 shifted to the nucleus from focal adhesions in human chondrocytes subjected to mechanical stress, and nuclear Hic-5 increased MMP-13 gene expression. In vivo, intra-articular injection of Hic-5 siRNA decreased the Osteoarthritis Research Society International score and MMP-13 protein expression in articular cartilage of OA rats. Our findings suggest that Hic-5 regulates transcription of MMP-13 in human chondrocytes, and Hic-5 may be a novel therapeutic target for OA because OA progression was suppressed by intra-articular injection of Hic-5 siRNA in rats.

CRMP4 is required for the positioning and maturation of newly generated neurons in adult mouse hippocampus.

Adult neurogenesis is a phenomenon in which neural stem cells differentiate and mature to generate new neurons in the adult brain. In mammals, the sites where adult neurogenesis occurs are limited to the subgranular zone (SGZ) of the hippocampal dentate gyrus and the subventricular zone. In the hippocampus, newly generated neurons migrate into the granule cell layer (GCL) and are integrated into neural circuits. Previous studies have revealed that CRMP4, a member of the CRMP family, is expressed in immature neurons in the hippocampal SGZ of the adult brain. However, the role of CRMP4 in adult neurogenesis is unknown. To study the role of CRMP4 in hippocampal adult neurogenesis, we compared adult neurogenesis between wild type and CRMP4-/- mice. In CRMP4-/- mice, the number of doublecortin (DCX)-positive cells was comparable to that in wild-type mice, and some DCX-positive cells were ectopically located in the granule cell layer, suggesting that CRMP4 is involved in the migration of adult neurogenesis. In addition, the number of calretinin-positive new neurons in the SGZ was significantly increased, whereas the number of EdU/NeuN-double positive neurons was decreased in CRMP4-/- mice, suggesting that CRMP4 plays an important role in neuronal maturation. Because CRMP4 is expressed in immature neurons, its expression may regulate the migration from the SGZ to the GCL during neuronal maturation in hippocampal adult neurogenesis.

Hic-5 is required for activation of pancreatic stellate cells and development of pancreatic fibrosis in chronic pancreatitis.

Accumulated evidence suggests that activated pancreatic stellate cells (PSCs) serve as the main source of the extracellular matrix proteins accumulated under the pathological conditions leading to pancreatic fibrosis in chronic pancreatitis (CP). However, little is known about the mechanisms of PSC activation. PSCs have morphologic and functional similarities to hepatic stellate cells, which are activated by hydrogen peroxide-inducible clone-5 (Hic-5), a TGF-ß1-induced protein. In this study, we investigated whether Hic-5 activates PSCs, which promote pancreatic fibrosis development in CP. Hic-5-knockout and wild type mice were subjected to caerulein injection to induce CP. Hic-5 expression was strongly upregulated in activated PSCs from human CP tissue and from mouse pancreatic fibrosis in caerulein-induced CP. Hic-5 deficiency significantly attenuated mouse pancreatic fibrosis and PSC activation in the experimental murine CP model. Mechanistically, Hic-5 knock down significantly inhibited the TGF-ß/Smad2 signaling pathway, resulting in reduced collagen production and α-smooth muscle actin expression in the activated PSCs. Taken together, we propose Hic-5 as a potential marker of activated PSCs and a novel therapeutic target in CP treatment.