Defects in the DNA repair mechanism nucleotide excision repair (NER) may lead to tumors in xeroderma pigmentosum (XP) or to premature aging with loss of subcutaneous fat in Cockayne syndrome (CS). Mutations of mitochondrial (mt)DNA play a role in aging, but a link between the NER-associated CS proteins and base excision repair (BER)-associated proteins in mitochondrial aging remains enigmatic. We show functional increase of CSA and CSB inside mt and complex formation with mtDNA, mt human 8-oxoguanine glycosylase (mtOGG)-1, and mt single-stranded DNA binding protein (mtSSBP)-1 upon oxidative stress. MtDNA mutations are highly increased in cells from CS patients and in subcutaneous fat of aged Csbm/m and Csa−/− mice. Thus, the NER-proteins CSA and CSB localize to mt and directly interact with BER-associated human mitochondrial 8-oxoguanine glycosylase-1 to protect from aging- and stress-induced mtDNA mutations and apoptosis-mediated loss of subcutaneous fat, a hallmark of aging found in animal models, human progeroid syndromes like CS and in normal human aging.

SummaryThe free radical theory of aging postulates that the production of mitochondrial reactive oxygen species is the major determinant of aging and lifespan. Its role in aging of the connective tissue has not yet been established, even though the incidence of aging-related disorders in connective tissue-rich organs is high, causing major disability in the elderly. We have now addressed this question experimentally by creating mice with conditional deficiency of the mitochondrial manganese superoxide dismutase in fibroblasts and other mesenchymederived cells of connective tissues in all organs. Here, we have shown for the first time that the connective tissuespecific lack of superoxide anion detoxification in the mitochondria results in reduced lifespan and premature onset of aging-related phenotypes such as weight loss, skin atrophy, kyphosis (curvature of the spine), osteoporosis and muscle degeneration in mutant mice. Increase in p16 INK4a , a robust in vivo marker for fibroblast aging, may contribute to the observed phenotype. This novel model is particularly suited to decipher the underlying mechanisms and to develop hopefully novel connective tissuespecific anti-aging strategies.

Chemotherapy-induced alopecia represents one of the major unresolved problems of clinical oncology. The underlying molecular pathogenesis in humans is virtually unknown because of the lack of adequate research models. Therefore, we have explored whether microdissected, organ-cultured, human scalp hair follicles (HFs) in anagen VI can be exploited for dissecting and manipulating the impact of chemotherapy on human HFs. Here, we show that these organ-cultured HFs respond to a key cyclophosphamide metabolite, 4-hydroperoxycyclophosphamide (4-HC), in a manner that resembles chemotherapy-induced HF dystrophy as it occurs in vivo: namely, 4-HC induced melanin clumping and melanin incontinence, down-regulated keratinocyte proliferation, massively up-regulated apoptosis of hair matrix keratinocytes, prematurely induced catagen, and up-regulated p53. In addition, 4-HC induced DNA oxidation and the mitochondrial DNA common deletion. The organ culture system facilitated the identification of new molecular targets for chemotherapyinduced HF damage by microarray technology (eg, interleukin-8, fibroblast growth factor-18, and glypican 6). It was also used to explore candidate chemotherapy protectants, for which we used the cytoprotective cytokine keratinocyte growth factor as exemplary pilot agent. Thus, this novel system serves as a powerful yet pragmatic tool for dissecting and manipulating the impact of chemotherapy on the human HF. (Am J Pathol

The role of ultraviolet radiation (UV) in the pathogenesis has been discussed controversially for many decades. Studies in mice (SCID, HGF ⁄ SF, SV40T) which develop malignant melanoma, show a role of UVB in melanomagenesis. In contrast to this, the role of UVA is less clear. We will review the recent in vitro and in vivo data in support of the hypothesis that UVA is also involved in the development of malignant melanoma. The role of UVA in p53 activation, apoptosis, cell cycle arrest and photoproduct formation is discussed.

The genetic diagnosis in inherited optic neuropathies often remains challenging, and the emergence of complex neurological phenotypes that involve optic neuropathy is puzzling. Here we unravel two novel principles of genetic mechanisms in optic neuropathies: deep intronic OPA1 mutations, which explain the disease in several so far unsolved cases; and an intralocus OPA1 modifier, which explains the emergence of syndromic 'optic atrophy plus' phenotypes in several families. First, we unravelled a deep intronic mutation 364 base pairs 3' of exon 4b in OPA1 by in-depth investigation of a family with severe optic atrophy plus syndrome in which conventional OPA1 diagnostics including gene dosage analyses were normal. The mutation creates a new splice acceptor site resulting in aberrant OPA1 transcripts with retained intronic sequence and subsequent translational frameshift as shown by complementary DNA analysis. In patient fibroblasts we demonstrate nonsense mediated messenger RNA decay, reduced levels of OPA1 protein, and impairment of mitochondrial dynamics. Subsequent site-specific screening of >360 subjects with unexplained inherited optic neuropathy revealed three additional families carrying this deep intronic mutation and a base exchange four nucleotides upstream, respectively, thus confirming the clinical significance of this mutational mechanism. Second, in all severely affected patients of the index family, the deep intronic mutation occurred in compound heterozygous state with an exonic OPA1 missense variant (p.I382M; NM_015560.2). The variant alone did not cause a phenotype, even in homozygous state indicating that this long debated OPA1 variant is not pathogenic per se, but acts as a phenotypic modifier if it encounters in trans with an OPA1 mutation. Subsequent screening of whole exomes from >600 index patients identified a second family with severe optic atrophy plus syndrome due to compound heterozygous p.I382M, thus confirming this mechanism. In summary, we provide genetic and functional evidence that deep intronic mutations in OPA1 can cause optic atrophy and explain disease in a substantial share of families with unsolved inherited optic neuropathies. Moreover, we show that an OPA1 modifier variant explains the emergence of optic atrophy plus phenotypes if combined in trans with another OPA1 mutation. Both mutational mechanisms identified in this study-deep intronic mutations and intragenic modifiers-might represent more generalizable mechanisms that could be found also in a wide range of other neurodegenerative and optic neuropathy diseases.