Studies from several laboratories have generated evidence suggesting that oxidative stress is involved in the pathogenesis of Alzheimer's disease (AD). The finding that the amyloid ␤ protein (A␤) has neurotoxic properties and that such effects are, in part, mediated by free radicals has provided insights into mechanisms of cell death in AD and an avenue to explore new therapeutic approaches. In this study we demonstrate that melatonin, a pineal hormone with recently established antioxidant properties, is remarkably effective in preventing death of cultured neuroblastoma cells as well as oxidative damage and intracellular Ca 2ϩ increases induced by a cytotoxic fragment of A␤. The effects of melatonin were extremely reproducible and corroborated by multiple quantitative methods, including cell viability studies by confocal laser microscopy, electron microscopy, and measurements of intracellular calcium levels. The importance of this finding is that, in contrast to conventional antioxidants, melatonin has a proposed physiological role in the aging process. Secretion levels of this hormone are decreased in aging and more severely reduced in AD. The reported phenomenon may be of therapeutic relevance in AD.

The transcription factor CCAAT enhancer binding protein ␣ (C͞ EBP␣) is expressed at high levels in liver and adipose tissue. Cell culture studies show that C͞EBP␣ is sufficient to trigger differentiation of preadipocytes into mature adipocytes, suggesting a central role for C͞EBP␣ in the development of adipose tissue. C͞EBP␣ knockout mice die within 7-12 h after birth. Defective gluconeogenesis of the liver and subsequent hypoglycemia contribute to the early death of these animals. This short life span impairs investigation of the development of adipose tissue in these mice. To improve the survival of C͞EBP␣؊͞؊ animals, we generated a transgenic line that expresses C͞EBP␣ under the control of the albumin enhancer͞promoter. This line was bred into the knockout strain to generate animals that express C͞EBP␣ in the liver but in no other tissue. The presence of the transgene improved survival of C͞EBP␣؊͞؊ animals almost 3-fold. Transgenic C͞EBP␣؊͞؊ animals at 7 days of age show an absence of s.c., perirenal, and epididymal white fat despite excess lipid substrate in the serum, whereas brown adipose tissue is somewhat hypertrophied and shows minimal biochemical alterations. Interestingly, mammary gland fat tissue is present and exhibits normal morphology. The absence of white adipose tissue in many depots in the presence of high serum lipid levels shows that C͞EBP␣ is required for the in vivo development of this tissue. In contrast, brown adipose tissue differentiation is independent of C͞EBP␣ expression. The presence of lipid in brown adipose tissue serves as an internal nutritional control, indicating that neither nutritional intake nor lipoprotein composition is likely responsible for the absence of white fat.

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Cartilage oligomeric matrix protein (COMP) is a pentameric extracellular protein expressed in cartilage and other musculoskeletal tissues. Mutations in the COMP gene cause pseudoachondroplasia (PSACH), a severe dwarfing condition that has a growth plate chondrocyte pathology. PSACH is characterized by intracellular retention of COMP and other extracellular matrix (ECM) proteins, which form an ordered matrix within large rough endoplasmic reticulum cisternae. This accumulation is cytotoxic and causes premature chondrocyte cell death, thereby depleting chondrocytes needed for normal long bone growth. Research to define the underlying molecular mechanisms of PSACH has been hampered by the lack of a suitable model system. In this study, we achieved robust expression of human mutant (MT) or wild-type (WT) COMP in mice by using a tetracycline-inducible promoter. Normal growth plate distribution of ECM proteins was observed in 1-month-old WT-COMP and C57BL\6 control mice. In contrast, the structure of the MT-COMP growth plate recapitulated the findings of human PSACH growth plate morphology, including (1) retention of ECM proteins, (2) intracellular matrix formation in the rER cisternae, and (3) increased chondrocyte apoptosis. Therefore, we have generated the first mouse model to show extensive intracellular retention of ECM proteins recapitulating the human PSACH disease process at the cellular level.