Mitochondrial DNA (mtDNA) copy number plays a key role in the pathophysiology of metabolic syndrome-related phenotypes, but its role in non-alcoholic fatty liver disease (NAFLD) is not well understood. We evaluated the molecular mechanisms that may be involved in the regulation of liver mtDNA content in a high-fat-induced rat model of NAFLD. In particular, we tested the hypothesis that liver mtDNA copy number is associated with liver expression of HIF-1α. Rats were given either standard chow diet (SCD, n= 10) or high-fat diet (HFD, n= 15) for 20 weeks. Subsequently, mtDNA quantification using nuclear DNA (nDNA) as a reference was carried out using real time quantitative PCR. HFD induced a significant increase in liver mtDNA/nDNA ratio, which significantly correlated with the liver triglyceride content (R: 0.29, P < 0.05). The liver mtDNA/nDNA ratio significantly correlated with the hepatic expression of HIF-1α mRNA (R: 0.37, P < 0.001); liver HIF-1α mRNA was significantly higher in the HFD group. In addition, liver cytochrome c oxidase subunit IV isoform 1 (COX4I1) mRNA expression was also positively correlated with liver mtDNA content. The hepatic expression of mRNA of transcriptional factors that regulate mitochondrial biogenesis, including peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) and PGC-1β, nuclear respiratory factor-1 (NRF-1), peroxisome proliferator-activated receptor δ and Tfam, was not associated with the liver mtDNA content. Neither hepatocyte apoptosis nor oxidative stress was involved in the HIF-1α-mediated increase in mtDNA copy number. In conclusion, we found that HFD promotes an increase in liver mitochondrial biogenesis in response to hypoxia via HIF-1α, probably to enhance the mitochondrial function as well as to accommodate the metabolic load.

Galectins, a family of mammalian lectins, have emerged as key regulators of the immune response. We previously demonstrated that galectin (Gal)-8, from the tandem-repeat subgroup, exerts two well-defined effects on mouse naive peripheral CD4 T cells: Ag-specific costimulation and Ag-independent proliferation. These stimulatory signals on naive T cells have not been described for any other Gal. Therefore, we investigated whether Gal-1 and Gal-3, two prominent members of the Gal family, share the stimulatory effects exerted by Gal-8 on naive T cells. We found that Gal-1 costimulated Ag-specific T cell responses similarly to Gal-8, as evaluated in the DO11.10 TCROVA-transgenic mouse model, by acting simultaneously on APCs and target CD4 T cells. In contrast, Gal-3 failed to costimulate Ag-specific T cell responses; moreover, it antagonized both Gal-1 and Gal-8 signals. We observed that both Gal-1 and Gal-3 were unable to induce Ag-independent proliferation; however, when two Gal-1 molecules were covalently fused, the resulting chimeric protein efficiently promoted proliferation. This finding indicates that Gal-1 might eventually induce proliferation and, moreover, stresses the requirement of a tandem-repeat structure. Remarkably, a single dose of recombinant Gal-1 or Gal-8 administered together with a suboptimal Ag dose to DO11.10 mice strengthened weak responses in vivo. Taken together, these findings argue for the participation of Gals in the initiation of the immune response and allow the postulation of these lectins as enhancers of borderline Ag responses, thus representing potential adjuvants for vaccine formulations.

Galectins (Gals), a family of mammalian lectins, play diverse roles under physiological and pathological conditions. Here, we analyzed the tandem-repeat Gal-8 synthesis, secretion and effects on the endothelium physiology. Gal-8M and Gal-8L isoforms were secreted under basal conditions by human microvascular endothelial cells (HMEC-1). However, expression and secretion of the Gal-8M isoform, but not Gal-8L, were increased in response to bacterial lipopolysaccharide (LPS) stimulus and returned to control values after LPS removal. Similarly, cell surface Gal-8 exposure was increased after stimulation with LPS. To evaluate Gal-8 effects on the endothelium physiology, HMEC-1 cells were incubated in the presence of recombinant Gal-8M. Pretreated HMEC-1 cells became proadhesive to human normal platelets, indicating that Gal-8 actually activates endothelial cells. This effect was specific for lectin activity as it was prevented by the simultaneous addition of lactose, but not by sucrose. Endothelial cells also increased their exposition of von Willebrand factor after Gal-8 treatment, which constitutes another feature of cell activation that could be, in turn, responsible for the observed platelet adhesion. Several pro-inflammatory molecules were abundantly produced by Gal-8 stimulated endothelial cells: CXCL1 (GRO-α), GM-CSF, IL-6 and CCL5 (RANTES), and in a lower degree CCL2 (MCP-1), CXCL3 (GRO-γ) and CXCL8 (IL-8). In agreement, Gal-8M induced nuclear factor kappa B phosphorylation. Altogether, these results not only confirm the pro-inflammatory role we have already proposed for Gal-8 in other cellular systems but also suggest that this lectin is orchestrating the interaction between leukocytes, platelets and endothelial cells.