Characterization of the dynamics of fat cell turnover in different bovine adipose tissue depots S. Häussler a,⇑ , D. Germeroth a , K. Friedauer a , S.H. Akter a,b , S. Dänicke c , H. Sauerwein a a Institute of Animal Science, Physiology and Hygiene Group, University of Bonn, 53115 Bonn, Germany b Faculty of Veterinary Science, Department of Anatomy and Histology, Bangladesh Agricultural University, Mymensing 2202, Bangladesh c Institute of Animal Nutrition, Friedrich-Loeffler-Institute (FLI), Federal Research Institute for Animal Health, 38116 Braunschweig, Germany article info Article history: Received 26 September 2012 Accepted 8 July 2013 Keywords: Adipose tissue Apoptosis Cattle Cell proliferation Conjugated linoleic acids Preadipocytes abstract In many but not all high producing cows, the energy requirements for milk yield and maintenance exceed energy intake by voluntary feed intake during early lactation. Prioritizing milk secretion, body reserves mainly from adipose tissue are mobilized and imply an increased risk for metabolic diseases. Reducing the energy output via milk by decreasing the milk fat content through feed supplements containing con- jugated linoleic acids (CLAs) may attenuate the negative energy balance during this period. In two sep- arate trials, variables characterizing fat cell turnover were investigated in different subcutaneous and visceral fat depots from primiparous heifers (n = 25) during early lactation, and subcutaneous fat from non-lactating, over-conditioned heifers (n = 12) by immunohistochemistry. The portion of apoptotic adi- pocytes was consistently greater than that of proliferating cells and preadipocytes; the sporadically observed effects of CLA were limited to visceral fat. Lactating heifers had more apoptosis and less preadi- pocytes than non-lactating heifers. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Early lactation is classified as the most metabolically stressful period in dairy cows, because the energetic needs for the rapidly increasing milk synthesis cannot be covered by voluntary feed in- take, resulting in a state of negative energy balance (NEB; Grum- mer, 1995). During this period, high-yielding dairy cows are susceptible to metabolic disorders, compromised immune re- sponse and reduced fertility (Butler and Smith, 1989; Mallard et al., 1998). The energy deficit during early lactation is accompa- nied by fat mobilization from adipose tissue (AT): during the NEB lipogenesis is decreased and lipolysis is increased (McNamara and Hillers, 1989). When the energy balance reaches positive val- ues, the energy stores in AT are increasingly refilled by lipogenesis and possibly also by adipogenesis thus preparing the organism for the upcoming energy deficit in the subsequent lactation. The cellu- lar components of AT comprise not only mature adipocytes but also other cell types e.g. endothelial cells, adipocyte progenitors (preadipocytes), fibroblasts, and immune cells, that are commonly summarized as the stromal vascular fraction (SVF; Eto et al., 2009). The major processes involved in adipogenesis are proliferation and differentiation of preadipocytes into mature adipocytes (Hausman et al., 2009), whereby the dynamic balance between both processes causes changes in adipocyte size (Prins and O‘Rahilly, 1997). In dairy cows, changes in adipocyte size generally appear after 120 days of lactation (Smith and McNamara, 1989). Adipocyte homeostasis and turnover processes include cell proliferation, dif- ferentiation of preadipocytes as well as programmed cell death (apoptosis). Conjugated linoleic acids (CLA) designate a group of positional and geometric isomers of linoleic acid. CLA has been reported to have many health benefits, including anti-obesity, anti-carcinogenic, anti-atherogenic, anti-diabetogenic, and immu- nomodulating properties in certain animal models (Belury, 2002; McLeod et al., 2004). In dairy cows, dietary CLA supplementation alters lipid metabolism and causes a decrease in milk fat secretion during lactation (Loor and Herbein, 1998). Commercially available CLA preparations for supplementing cows‘ diets mainly contain the cis-9, trans-11 (c9,t11) and the trans-10, cis-12 (t10,c12) isomer in equal portions. In cultured adipocytes and AT from rodents, anti- lipogenic and/or lipolytic effects of dietary CLA are described (Bro- die et al., 1999; Azain et al., 2000; Miner et al., 2001). The milk fat reducing effect of CLA is mainly attributed to the t10,c12 isomer (Baumgard et al., 2001), whereas the c9,t11 isomer had less effects (Perfield et al., 2007). Furthermore, body fat accretion in growing animals was decreased through decreasing de novo lipogenesis by the t10,c12 isomer (Bauman et al., 2000). In dairy cattle, we re- cently observed that adipocyte size is decreased at varying degrees in different fat depots from animals receiving a 1:1 mixture of the t10,c12 and the c9,t11 isomer when compared with a control group 0034-5288/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.rvsc.2013.07.004 ⇑ Corresponding author. Address: Institute of Animal Science, Physiology and Hygiene Group, University of Bonn, Katzenburgweg 7 – 9, 53115 Bonn, Germany. Tel.: +49 228739669; fax: +49 228737938. E-mail address: susanne.haeussler@uni-bonn.de (S. Häussler). Research in Veterinary Science 95 (2013) 1142–1150 Contents lists available at SciVerse ScienceDirect Research in Veterinary Science journal homepage: www.elsevier.com/locate/rvsc