Although many genes have been implicated in the pathogenesis of common neurodegenerative diseases, the genetic and cellular mechanisms that maintain neuronal integrity during normal aging remain elusive. Here we show that Caenorhabditis elegans touch receptor and cholinergic neurons display age-dependent morphological defects, including cytoskeletal disorganization, axon beading, and defasciculation. Progression of neuronal aging is regulated by DAF-2 and DAF-16 signaling, which also modulate adult life span. Mutations that disrupt touch-evoked sensory activity or reduce membrane excitability trigger accelerated neuronal aging, indicating that electrical activity is critical for adult neuronal integrity. Disrupting touch neuron attachment to the epithelial cells induces distinct neurodegenerative phenotypes. These results provide a detailed description of the age-dependent morphological defects that occur in identified neurons of C. elegans, demonstrate that the age of onset of these defects is regulated by specific genes, and offer experimental evidence for the importance of normal levels of neural activity in delaying neuronal aging. In the nematode Caenorhabditis elegans, age-dependent morphological changes are widespread in somatic tissues (2-4). However, there is little evidence for neuronal aging in C. elegans (3). The observations by Herndon et al. (3) suggest that neuronal loss or axon guidance defects do not occur in the aging C. elegans nervous system. It was also shown that whereas nuclear membranes of other somatic cell nuclei undergo drastic age-dependent deterioration, those of neuronal nuclei remain relatively intact in aging animals (4).There is, however, a clear age-dependent behavioral decline in C. elegans, including decrease in pharyngeal pumping, locomotion and chemotaxis (5). Evidence suggests that failure in neuronal activity could play a direct role in age-dependent behavioral deterioration. Cai and Sesti (6) showed that age-dependent oxidation of the C. elegans potassium channel KVS-1 causes sensory loss and that protection of neuronal KVS-1 from oxidation rescues agedependent decline in chemotaxis behavior. Electrical activity has been shown to be important for neuronal development (7) and was recently implicated in the survival or maintenance of adult mammalian and Drosophila neurons (8, 9). However, it is unclear how electrical activity promotes the integrity of adult neurons.In this paper, we address whether more subtle, subcellular changes occur in the aging C. elegans nervous system. Our results indicate that C. elegans neurons do develop age-dependent changes. Moreover, we show that electrical activity and normal attachment to the neighboring epithelial cells are required for the maintenance of adult touch receptor neurons.

Objective-The introduction of 4 transcription factors-c-MYC, OCT3/4, SOX2, and KLF4 -can reprogram somatic cells back to pluripotency. However, some of the factors used are oncogenic, making therapeutic application unfeasible. Although the use of adult stem cells expressing high endogenous levels of some of these factors allows for reprogramming with fewer exogenous genes, such cells are rare and may have accumulated genetic mutations. Our goal was to reprogram human somatic cells without oncogenic factors. We found that high endogenous expression of KLF4 in human umbilical vein endothelial cells (HUVECs) allows for generation of induced pluripotent stem cells (iPSCs) with just 2 nononcogenic factors, OCT3/4 and SOX2. Methods and Results-HUVECs were infected with lentivirus containing OCT4 and SOX2 for generation of iPSCs. These 2-factor HUVEC iPSCs were morphologically similar to embryonic stem cells, express endogenous pluripotency markers postreprogramming, and can differentiate toward lineages of all 3 germ layers both in vitro and in vivo. T he discovery that somatic cells can be reprogrammed to pluripotency with the addition of 4 transcription factorsc-Myc, Oct3/4, Sox2, and Klf4 -is revolutionary. 1,2 These induced pluripotent stem cells (iPSCs) are similar to embryonic stem cells but can be generated without ethical concern and transplanted without immune rejection. Although this method of reprogramming is straightforward, efficiency is still quite low even in the best system. 3 Subsequent reports reveal that oncogenic factors increase efficiency, 4 but in anticipation of clinical use, exclusion of such factors is necessary. Conclusion-iPSCs See accompanying article on page 1880To date, the generation of human iPSCs from adult somatic cells has been reported 5,6 but generally with 3 or more factors, because reprogramming of human cells is less efficient than reprogramming of mouse cells 3 and may require immortalization in some instances. 6 Recent reports have shown that some human adult stem cells can be reprogrammed with relatively few factors because of endogenous expression of SOX2. 7 However, the rarity of adult stem cells makes this a difficult option. Because fetal-derived cells (FDCs) are more proliferative and at an earlier stage of development than adult cells, we hypothesized that reprogramming of FDCs may require fewer factors and obviate oncogenes. As proof of principle, we used an easily obtainable source of FDCs for iPSC generation: human umbilical vein endothelial cell (HUVECs). We found that HUVECs endogenously express high levels of KLF4 and can be reprogrammed with just OCT3/4 and SOX2. Our data may have important implications in terms of providing an efficient in vitro model for human iPSCs research and possibly open up a new cell source for reprogramming. MethodsHUVECs (Bioresource Collection and Research Center, Hsinchu, Taiwan) were infected with lentivirus containing OCT3/4 and SOX2 and monitored for iPSC formation as previously reported. 1 Reprogrammed HUVECs were assayed for in...

Aging of the nervous system underlies the behavioral and cognitive decline associated with senescence. Understanding the molecular and cellular basis of neuronal aging will therefore contribute to the development of effective treatments for aging and age-associated neurodegenerative disorders. Despite this pressing need, there are surprisingly few animal models that aim at recapitulating neuronal aging in a physiological context. We recently developed a C. elegans model of neuronal aging, and showed that age-dependent neuronal defects are regulated by insulin signaling. We identified electrical activity and epithelial attachment as two critical factors in the maintenance of structural integrity of C. elegans touch receptor neurons. These findings open a new avenue for elucidating the molecular mechanisms that maintain neuronal structures during the course of aging.

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