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Objective: Understanding the regulation of adipocyte differentiation by cellular and extracellular factors is crucial for better management of chronic conditions such as obesity, insulin resistance and lipodystrophy. Experimental infection of rats with a human adenovirus type 36 (Ad-36) improves insulin sensitivity and promotes adipogenesis, reminiscent of the effect of thiozolinediones. Therefore, we investigated the role of Ad-36 as a novel regulator of the adipogenic process., Design and Results: Even in the absence of adipogenic inducers, infection of 3T3-L1 preadipocytes and human adipose-derived stem cells (hASC) by Ad-36, but not Ad-2 that is another human adenovirus, modulated regulatory points that spanned the entire adipogenic cascade ranging from the upregulation of cAMP, phosphatidylinositol 3-kinase and p38 signaling pathways, downregulation of Wnt10b expression, and increased expression of CCAAT/enhancer binding protein-beta and peroxisome proliferator-activated receptor gamma2 and consequential lipid accumulation. Next, we identified that E4 open reading frame (orf)-1 gene of the virus is necessary and sufficient for Ad-36-induced adipogenesis. Selective knockdown of E4 orf-1 by RNAi abrogated Ad-36-induced adipogenic signaling cascade in 3T3-L1 cells and hASC. Compared to the null vector, selective expression of Ad-36 E4 orf-1 in 3T3-L1 induced adipogenesis, which was abrogated when the PDZ-binding domain of the protein was deleted., Conclusion: Thus, Ad-36 E4 orf-1 is a novel inducer of rodent and human adipocyte differentiation process.

Objective: Human adenovirus Ad-36 causes adiposity in animal models and shows association with human obesity. Ad-36 enhances differentiation of 3T3-L1 and human preadipocytes, without cell lysis, a characteristic that may contribute to its adipogenic effect observed in vivo. Ad-2, another human adenovirus is nonadipogenic in animals and in 3T3-L1 cells and shows no correlation with human obesity. The objective of this study was to determine the adipogenic roles of viral mRNA and DNA, which may explain the differential effects of Ad-36 and Ad-2 on preadipocyte differentiation., Methods: This study determined the duration of selected Ad-36 gene expression in 3T3-L1 cells, and the effect on preadipocytes differentiation, when Ad-36 gene expression was attenuated by Cidofovir, an antiadenoviral agent., Results: The results showed that Ad-36, but not Ad-2, expresses viral mRNA. Ad-36 gene expression peaked at 2-4 days postinoculation and very low levels persisted after day 7. Despite the viral mRNA expression, Ad-36 infection of 3T3-L1 cells was abortive as indicated by a progressive decrease in viral DNA quantity. Attenuation of Ad-36 mRNA expression by Cidofovir reduced the adipogenic effect of the virus., Conclusion: In conclusion, viral mRNA expression, although transient, is a prerequisite for enhancing differentiation of preadipocytes by Ad-36. Viral DNA replication was not required for the effect. This is the first evidence for the role of gene expression of an adipogenic human virus in enhancing preadipocytes differentiation. This study provides the basis for further understanding novel regulatory modulators of preadipocytes differentiation.

Objective: Adenovirus 36 (Ad-36) has been shown to increase adiposity in experimentally infected chickens, mice, and marmosets (nonhuman primates). Neutralizing antibodies to Ad-36 are associated with obesity in humans. The metabolic and molecular mechanisms responsible for Ad-36-induced adipogenesis are unknown. As a potential adipogenic mechanism, this study examined if Ad-36 enhanced differentiation of preadipocytes., Research Methods and Procedures: To determine the suitability of 3T3-L1 cells (murine preadipocyte cell line) as a model, the first experiment determined if Ad-36 attaches and initiates replication in the cells. Next, effects of Ad-36 on the number of differentiated adipocytes, glycerol 3-phosphate dehydrogenase (GPDH) levels, and cellular lipid accumulation were determined. The last experiment determined the effect of Ad-36 on human primary preadipocyte differentiation. Ad-2, a known nonadipogenic human adenovirus, was used as a negative control in these experiments., Results: Immunofluorescence studies showed adenoviral attachment to 3T3-L1 cells, and reverse transcriptase-polymerase chain reaction showed expression of the Ad-36 E1A gene in the infected cells. Ad-36, but not Ad-2, increased the number of differentiated adipocytes, GPDH enzyme levels, and the total cellular lipid content. Also, Ad-36, but not Ad-2, increased GPDH levels in human preadipocytes., Discussion: Taken together, these experiments showed that Ad-36 enhanced differentiation of preadipocytes, which may be a contributory mechanism to its adipogenic effect in vivo. The lack of effect of Ad-2 on differentiation demonstrated that the observed findings were not a common characteristic of all adenoviruses. Future understanding of the molecular interactions of cellular and viral genes responsible for enhanced differentiation may reveal novel signaling pathways and controls of preadipocyte differentiation., (Copyright 2004 NAASO)