The large intestine is a home for trillions of microbiota, which confer many benefits on the host, including production of vitamins, absorption of nutrients, pathogen displacement, and development of the immune system. For several decades, germ-free animals have been used to study the interaction between the host and its microbiota. This minireview describes the technical aspects for establishing and maintaining germ-free animals and highlights the advantages and disadvantages for germ-free animals as experimental models.

Mammalian brain development is initiated in utero and internal and external environmental signals can affect this process all the way until adulthood. Recent observations suggest that one such external cue is the indigenous microbiota which has been shown to affect developmental programming of the brain. This may have consequences for brain maturation and function that impact on cognitive functions later in life. This review discusses these recent findings from a developmental perspective.

Growth Hormone is essential for the regulation of growth and the homeostatic control of intermediary metabolism. GH actions are mediated by the Growth Hormone Receptor; a member of the cytokine receptor super family that signals chiefly through the JAK2/STAT5 pathway. Target tissue responsiveness to GH is under regulatory control to avoid excessive and off-target effects upon GHR activation. The suppressor of cytokine signalling 2 (SOCS) is a key regulator of GHR sensitivity. This is clearly shown in mice where the SOCS2 gene has been inactivated, which show 30–40% increase in body length, a phenotype that is dependent on endogenous GH secretion. SOCS2 is a GH-stimulated, STAT5b-regulated gene that acts in a negative feedback loop to downregulate GHR signalling. Since the biochemical basis for these actions is poorly understood, we studied the molecular function of SOCS2. We demonstrated that SOCS2 is part of a multimeric complex with intrinsic ubiquitin ligase activity. Mutational analysis shows that the interaction with Elongin B/C controls SOCS2 protein turnover and affects its molecular activity. Increased GHR levels were observed in livers from SOCS2^−/− mice and in the absence of SOCS2 in in vitro experiments. We showed that SOCS2 regulates cellular GHR levels through direct ubiquitination and in a proteasomally dependent manner. We also confirmed the importance of the SOCS-box for the proper function of SOCS2. Finally, we identified two phosphotyrosine residues in the GHR to be responsible for the interaction with SOCS2, but only Y487 to account for the effects of SOCS2. The demonstration that SOCS2 is an ubiquitin ligase for the GHR unveils the molecular basis for its physiological actions.

Hepatic steatosis is a prominent feature in patients with growth hormone (GH) deficiency. The ubiquitin ligase SOCS2 attenuates hepatic GH signaling by inhibiting the Janus kinase 2 (JAK2)‐signal transducer and activator of transcription 5b (STAT5b) axis. Here, we investigated the role of SOCS2 in the development of diet‐induced hepatic steatosis and insulin resistance. SOCS2‐knockout (SOCS2 ^−/− ) mice and wild‐type littermates were fed for 4 mo with control or high‐fat diet, followed by assessment of insulin sensitivity, hepatic lipid content, and expression of inflammatory cytokines. SOCS2 ^−/− mice exhibited increased hepatic TG secretion by 77.6% ( P < 0.001) as compared with wild‐type control mice and were protected from high‐fat‐diet (HFD)‐induced hepatic steatosis, showing 49.3% ( P <0.01) reduction in liver TG levels compared to HFD‐fed wild‐type littermates. In contrast, we found that HFD‐triggered attenuation of systemic insulin sensitivity was more marked in SOCS2 ^−/− mice. Livers from the HFD‐fed SOCS2 ^−/− mice showed increased NF‐κB activity as well as elevated expression of genes for the inflammatory cytokines IFN‐γ and IL‐6. An inhibitory role of SOCS2 on Toll‐like receptor 4 signaling was demonstrated in macrophages obtained from the SOCS2 ^−/− and wild‐type mice. This study identified SOCS2 as an important regulator of hepatic homeostasis under conditions of high‐fat dietary stress.—Zadjali, F., Santana‐Farre, R., Vesterlund, M., Carow, B., Mirecki‐Garrido, M., Hernandez‐Hernandez, I., Flodström‐Tullberg, M., Parini, P., Rottenberg, M., Norstedt, G., Fernandez‐Perez, L., Flores‐Morales, A. SOCS2 deletion protects against hepatic steatosis but worsens insulin resistance in high‐fat‐diet‐fed mice. FASEB J. 26, 3282–3291 (2012). www.fasebj.org