In the integrin family, the collagen receptors form a structurally and functionally distinct subgroup. Two members of this subgroup, ␣ 1 ␤ 1 and ␣ 2 ␤ 1 integrins, are known to bind to monomeric form of type I collagen. However, in tissues type I collagen monomers are organized into large fibrils immediately after they are released from cells. Here, we studied collagen fibril recognition by integrins. By an immunoelectron microscopy method we showed that integrin ␣ 2 I domain is able to bind to classical D-banded type I collagen fibrils. However, according to the solid phase binding assay, the collagen fibril formation appeared to reduce integrin ␣ 1 I and ␣ 2 I domain avidity to collagen and to lower the number of putative ␣I domain binding sites on it. Respectively, cellular ␣ 1 ␤ 1 integrin was able to mediate cell spreading significantly better on monomeric than on fibrillar type I collagen matrix, whereas ␣ 2 ␤ 1 integrin appeared still to facilitate both cell spreading on fibrillar type I collagen matrix and also the contraction of fibrillar type I collagen gel. Additionally, ␣ 2 ␤ 1 integrin promoted the integrin-mediated formation of long cellular projections typically induced by fibrillar collagen. Thus, these findings suggest that ␣ 2 ␤ 1 integrin is a functional cellular receptor for type I collagen fibrils, whereas ␣ 1 ␤ 1 integrin may only effectively bind type I collagen monomers. Furthermore, when the effect of soluble ␣I domains on type I collagen fibril formation was tested in vitro, the observations suggest that integrin type collagen receptors might guide or even promote pericellular collagen fibrillogenesis.A fibril-forming type I collagen, a ubiquitous protein in all vertebrates, is known to provide mechanical stability for tissues and serve as a functional environment for cells (1). Depending on the physical properties of the tissue, type I collagen fibrils are arranged with different suprafibrillar architectures and diameters. Thus, narrow fibrils (ϳ20 nm) in highly ordered arrangement occur in the cornea, where optical transparency is important, whereas large diameter fibrils (ϳ500 nm) provide high tensile strength in mature tendon (2).The mechanism of type I collagen fibril formation has been under extensive research for decades. In tissues, type I collagen is synthesized as a monomeric precursor, which is secreted by exocytosis into the extracellular space. In addition to the triple helical collagenous domain, the precursor contains noncollagenous C-and N-propeptides, which are linked to the triple helical domain by short sequences called telopeptides (3). After the enzymatic removal of propeptides, the solubility of collagen monomers decreases, and they spontaneously form fibrils, assisted by remaining nonhelical telopeptides (1, 4). Evidently, collagen molecules themselves contain all the information needed for fibril assembly. Therefore, in physiological conditions, acid-solubilized collagen monomers form tissue-type long fibrils with characteristic axial periodic structure also in v...

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Changes occur in gene expression during aging in vivo and in replicative senescence in vitro, suggesting that aging can affect gene regulation. We have recently observed age-related changes in ubiquitously expressed, oxidative stress-responsive nuclear factor-kappa B (NF-kappa B) pathway during aging. Here we report a significant age-related increase in nuclear NF-kappa B binding activity together with increased protein levels of p52 and p65 components in rat liver. An additional, higher molecular weight protein band seen in their western blots suggests that their post-translational modification (but not phosphorylation) occurs in liver, which might affect their nuclear localization and binding activity during aging. However, aging did not affect the protein levels of the main I kappa B inhibitors (I kappa B alpha and I kappa B beta) or I kappa B kinase (IKK)-complex subunits (IKK alpha, -beta, and -gamma) involved in NF-kappa B activation. In addition, the level of Ser32-phosphorylated I kappa B alpha was unaffected by age, suggesting that neither the IKK complex nor altered level of the main inhibitors is involved in the observed up-regulation of NF-kappa B binding activity. Furthermore, the expression of NF-kappa B mRNAs (p50, p52, p65, and c-rel) and the mRNAs of their inhibitors (I kappa B alpha and I kappa B beta) did not show any statistically significant age-related changes. These results indicate that the expression level of NF-kappa B genes is not significantly affected by aging. The up-regulation of constitutive nuclear NF-kappa B binding activity and increased levels of nuclear p52 and p65 proteins might affect the expression of some NF-kappa B target genes in the aging liver.

In amyotrophic lateral sclerosis (ALS), mitochondrial dysfunction is recognized as one of the key elements contributing to the pathology. Mitochondria are the major source of intracellular reactive oxygen species (ROS). Increased production of ROS as well as oxidative damage of proteins and lipids have been demonstrated in many models of ALS. Moreover, these changes were also observed in tissues of ALS patients indicative of important role for oxidative stress in the disease pathology. However, the origin of oxidative stress in ALS has remained unclear. ALS linked mutant Cu/Zn-superoxide dismutase 1 (SOD1) has been shown to significantly associate with mitochondria, especially in the spinal cord. In animal models, increased recruitment of mutant SOD1 (mutSOD1) to mitochondria appears already before the disease onset, suggestive of causative role for the manifestation of pathology. Recently, substantial in vitro and in vivo evidence has accumulated demonstrating that localization of mutSOD1 to the mitochondrial intermembrane space (IMS) inevitably leads to impairment of mitochondrial functions. However, the exact mechanisms of the selectivity and toxicity have remained obscure. Here we discuss the current knowledge on the role of mutSOD1 in mitochondrial dysfunction in ALS from the novel perspective emphasizing the misregulation of dismutase activity in IMS as a major mechanism for the toxicity.