Aging elicits quantitative and qualitative changes in different immune components, leading to disruption of tolerogenic circuits and development of autoimmune disorders. Galectin-1 (Gal1), an endogenous glycan-binding protein, has emerged as a regulator of immune cell homeostasis by shaping the fate of myeloid and lymphoid cells. Here, we demonstrate that aged Gal1-null mutant (Lgals1−/−) mice develop a spontaneous inflammatory process in salivary glands that resembles Sjögren’s syndrome. This spontaneous autoimmune phenotype was recapitulated in mice lacking β1,6N-acetylglucosaminyltransferase V (Mgat5), an enzyme responsible for generating β1,6-branched complex N-glycans, which serve as a major ligand for this lectin. Lack of Gal1 resulted in CD11c+dendritic cells (DCs) with higher immunogenic potential, lower frequency of Foxp3+regulatory T cells (Tregs), and increased number of CD8+T cells with greater effector capacity. Supporting its tolerogenic activity, Gal1 expression decreased with age in autoimmunity-prone nonobese diabetic (NOD) mice. Treatment with recombinant Gal1 restored tolerogenic mechanisms and reduced salivary gland inflammation. Accordingly, labial biopsies from primary Sjögren’s syndrome patients showed reduced Gal1 expression concomitant with higher number of infiltrating CD8+T cells. Thus, endogenous Gal1 serves as a homeostatic rheostat that safeguards immune tolerance and prevents age-dependent development of spontaneous autoimmunity.

The relevance of glycan-binding protein in immune tolerance and inflammation has been well established, mainly by studies of C-type lectins, siglecs and galectins both in experimental models and patient samples. Galectins, a family of evolutionarily conserved lectins, are characterized by sequence homology in the carbohydrate-recognition domain (CRD), atypical secretion via an ER-Golgi-independent pathway and the ability to recognize β-galactoside-containing saccharides. Galectin-1 (Gal-1), a prototype member of this family displays mainly anti-inflammatory and immunosuppressive activities, although, similar to many cytokines and growth factors, it may also trigger paradoxical pro-inflammatory effects under certain circumstances. These dual effects could be associated to tissue-, time- or context-dependent regulation of galectin expression and function, including particular pathophysiologic settings and/or environmental conditions influencing the structure of this lectin, as well as the availability of glycosylated ligands in immune cells during the course of inflammatory responses. Here, we discuss the tissue-specific role of Gal-1 as a master regulator of inflammatory responses across different pathophysiologic settings, highlighting its potential role as a therapeutic target. Further studies designed at analyzing the intrinsic and extrinsic pathways that control Gal-1 expression and function in different tissue microenvironments may contribute to design tailored therapeutic strategies aimed at positively or negatively modulate this glycan-binding protein in pathologic inflammatory conditions.

P5-ATPases are important for processes associated with the endosomal-lysosomal system of eukaryotic cells. In humans, the loss of function of P5-ATPases causes neurodegeneration. In the yeast Saccharomyces cerevisiae, deletion of P5-ATPase Spf1p gives rise to endoplasmic reticulum stress. The reaction cycle of P5-ATPases is poorly characterized. Here, we showed that the formation of the Spf1p catalytic phosphoenzyme was fast in a reaction medium containing ATP, Mg 2؉ , and EGTA. . Halfmaximal phosphorylation was attained at 8 M Mg 2؉, but higher concentrations partially protected from Ca 2؉ inhibition. In conditions similar to those used for phosphorylation, Ca 2؉ had a small effect accelerating dephosphorylation and minimally affected ATPase activity, suggesting that the formation of the phosphoenzyme was not the limiting step of the ATP hydrolytic cycle.P5-ATPases comprise a group of proteins that are classified as P-ATPases based on the presence of the characteristic PATPase motifs in their primary sequence (1, 2). P5-ATPases have been found only in eukaryotes and have been recently proposed to play an essential role in the endosomal-lysosomal system (3, 4). The yeast Saccharomyces cerevisiae contains two genes coding for P5-ATPases: YEL031W, coding for Spf1p (also called Cod1p), and YOR291W, coding for Ypk9. Spf1p (sensitivity to Pichia farinosa killer toxin) was initially isolated from a mutation protecting Saccharomyces from the effect of a Pichia toxin (5). The protein was also independently identified as required for the controlled degradation of 3-hydroxy-3-methylglutaryl coenzyme A reductase in the endoplasmic reticulum (ER) 3 (6). These and later studies have shown that Spf1p is located in the yeast ER and that deletion of Spf1p leads to phenotypes related to ER stress (7-9). In humans, five genes (ATP13A1-A5) code for P5-ATPases (10). Mutations in ATP13A2 have been linked to an early onset autosomal recessive form of Parkinson disease (Kufor-Rakeb syndrome) and neuronal ceroid lipofuscinosis, whereas mutations in ATP13A4 have been associated with autism spectrum disorder (11-13). P-ATPases are a large group of enzymes that couple the hydrolysis of ATP with the active transport of ions (14, 15). During the transport cycle, they transiently form a phosphoenzyme (EP) that plays a key role in the active transport mechanism. P-ATPases comprise a membrane domain (M) and a soluble portion with nucleotide binding (N), phosphorylation (P), and actuator (A) domains. These domains are involved in a kinasephosphatase reaction cycle through two major conformations, E 1 -E 2 , and the transient formation of a catalytic EP. The binding of the transported ion to the E 1 form prompts the assembly of the phosphorylation site between the ATP-bound N domain and the P domain, whereas the A domain directs the occlusion of the bound ion. When the phosphorylation reaction occurs, it initially generates the high energy E 1 ϳP intermediate and releases ADP. E 1 ϳP then changes to E 2 P, and the A domain associates with the N-...