Liraglutide ameliorates hepatic steatosis via retinoic acid receptor-related orphan receptor α-mediated autophagy pathway.

Liraglutide, an analog of human glucagon-like peptide-1 (GLP-1), has been found to improve hepatic steatosis in clinical practice. However, the underlying mechanism remains to be fully defined. Increasing evidence suggests that retinoic acid receptor-related orphan receptor α (RORα) is involved in hepatic lipid accumulation. In the current study, we investigated whether the ameliorating impact of liraglutide on lipid-induced hepatic steatosis is dependent on RORα activity and examined the underlying mechanisms. Cre-loxP-mediated, liver-specific Rorα knockout (Rora LKO) mice, and littermate controls with a Roraloxp/loxp genotype were established. The effects of liraglutide on lipid accumulation were evaluated in mice challenged with a high-fat diet (HFD) for 12 weeks. Moreover, mouse AML12 hepatocytes expressing small interfering RNA (siRNA) of Rora were exposed to palmitic acid to explore the pharmacological mechanism of liraglutide. The results showed that liraglutide treatment significantly alleviated HFD-induced liver steatosis, marked by reduced liver weight and triglyceride accumulation, improved glucose tolerance and serum levels of lipid profiles and aminotransferase. Consistently, liraglutide also ameliorated lipid deposits in a steatotic hepatocyte model in vitro. In addition, liraglutide treatment reversed the HFD-induced downregulation of Rora expression and autophagic activity in mouse liver tissues. However, the beneficial effect of liraglutide on hepatic steatosis was not observed in Rora LKO mice. Mechanistically, the ablation of Rorα in hepatocytes diminished liraglutide-induced autophagosome formation and the fusion of autophagosomes and lysosomes, resulting in weakened autophagic flux activation. Thus, our findings suggest that RORα is essential for the beneficial impact of liraglutide on lipid deposition in hepatocytes and regulates autophagic activity in the underlying mechanism.

Report of PRPF19 as a novel partner of RARG and the recurrence of interposition-type fusion in variant acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia (AML) which is characterized by specific clinical and biological features. Typical APL cases are caused by PML::RARA fusion gene and are exquisitely sensitive to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). Rarely, APLs are caused by atypical fusions involving RARA or, in fewer cases still, fusions involving other members of the retinoic acid receptors (RARB or RARG). To date, seven partner genes of RARG have been reported in a total of 18 cases of variant APL. Patients with RARG fusions showed distinct clinical resistance to ATRA and had poor outcomes. Here, we report PRPF19 gene as a novel partner of RARG and identify a rare interposition-type gene fusion in a variant APL patient with a rapidly fatal clinical course. The incomplete ligand-binding domain of RARG in the fusion protein may account for the clinical ATRA resistance in this patient. These results broaden the spectrum of variant APL associated molecular aberrations. Accurately and timely identification of these rare gene fusions in variant APL is essential to guide therapeutic decisions.

The immunomodulatory role of all-trans retinoic acid in tumor microenvironment.

Retinoids are essential nutrients for human beings. Among them, all-trans retinoic acid (ATRA), considered one of the most active metabolites, plays important roles in multiple biological processes. ATRA regulates the transcription of target genes by interacting with nuclear receptors bonded to retinoic acid response elements (RAREs). Besides its differentiation-inducing effect in the treatment of acute promyelocytic leukemia and some solid tumor types, its immunoregulatory role in tumor microenvironment (TME) has attracted considerable attention. ATRA not only substantially abrogates the immunosuppressive effect of tumor-infiltrating myeloid-derived suppressor cells but also activates the anti-tumor effect of CD8 + T cells. Notably, the combination of ATRA with other therapeutic approaches, including immune checkpoint inhibitors (ICIs), tumor vaccines, and chemotherapy, has been extensively investigated in a variety of tumor models and clinical trials. In this review, we summarize the current understanding of the role of ATRA in cancer immunology and immunotherapy, dissect the underlying mechanisms of ATRA-mediated activation or differentiation of different types of immune cells, and explore the potential clinical significance of ATRA-based cancer therapy.

The pancreatic clock is a key determinant of pancreatic fibrosis progression and exocrine dysfunction.

Chronic pancreatitis (CP) is characterized by progressive fibrosis and exocrine dysregulation, which have long been considered irreversible. As a peripheral oscillator, the pancreas harbors autonomous and self-sustained timekeeping systems in both its endocrine and exocrine compartments, although the role of the latter remains poorly understood. By using different models of CP established in mice with dysfunctional pancreatic clocks, we found that the local clock played an important role in CP pathology, and genetic or external disruption of the pancreatic clock exacerbated fibrogenesis and exocrine insufficiency. Mechanistically, an impaired retinoic acid receptor-related orphan receptor A (Rora)/nuclear receptor subfamily 1, group D, member 1 (Nr1d1)/aryl hydrocarbon receptor nuclear translocator-like (Arntl or Bmal1) loop, called the circadian stabilizing loop, resulted in the deficiency of pancreatic Bmal1, which was responsible for controlling the fibrogenic properties of pancreatic stellate cells (PSCs) and for rewiring the function of acinar cells in a clock-TGF signaling-IL-11/IL-11RA axis-dependent manner. During PSC activation, the antagonistic interaction between Nr1d1 and Rora was unbalanced in response to the loss of cytoplasmic retinoid-containing lipid droplets. Patients with CP also exhibited reduced production of endogenous melatonin. Enhancing the clock through pharmacological restoration of the circadian stabilizing loop using a combination of melatonin and the Rora agonist SR1078 attenuated intrapancreatic pathological changes in mouse models of CP. Collectively, this study identified a protective role of the pancreatic clock against pancreatic fibrosis and exocrine dysfunction. Pancreatic clock-targeted therapy may represent a potential strategy to treat CP.

[Future treatment strategies for cryptorchidism to improve spermatogenesis].

Orchiopexy is one of the most frequently used surgical procedures for cryptorchidism and has been shown to have a beneficial effect on fertility. However, orchiopexy, especially for bilateral cryptorchidism, does not always guarantee subsequent fertility and paternity. Compared with a control group, paternity was significantly compromised in men with previous bilateral, but not unilateral cryptorchidism. Recent techniques of assisted reproductive technology, especially testicular sperm extraction with intracytoplasmic sperm injection (TESE-ICSI), have brought revolutionary changes in clinical therapy for infertiliy. If spermatozoa exists in testis of infertile men, logically there is a possibility of paternity. However, our study demonstrated that about 20% of pubertal boys who had had orchiopexy, were predicted to have lost their future paternity potential even if TESE-ICSI were conducted, because they were predicted to have no spermatozoa in the testis. To prevent or reverse the damage of spermatogenesis at prepuberty or puberty, we should not take a wait-and-see attitude but should consider a countermeasure for the pubertal boys who had had bilateral orchiopexy in childhood, especially when the serum follicle stimulating hormone level is elevated and testicular volume is lowered, before paternity is lost. In this review, we discuss the potential approaches including epidermal growth facter therapy, gene therapy and stem-cell therapy for cryptorchid patients in the future.

AML bearing the translocation t(11;17)(q23;q21): involvement of MLL and a region close to RARA, with no differentiation response to retinoic acid.

We describe a case of acute myeloid leukemia (AML) bearing the translocation t(11;17)(q23;q21). The morphological phenotype represented a monoblastic leukemia, AML French-American-British (FAB) M5a. Further analysis of the translocation revealed an involvement of the mixed-lineage leukemia (MLL) gene and a region closely proximal to the retinoic acid (RA) receptor alpha (RARA) gene. AMLs involving both a rearranged MLL and the 17q21 region, in which the RARA gene is located, have only been described in some individual cases. The functional role of this translocation is still unknown. Rearrangements of the MLL (11q23) gene in AML are usually related to the morphological phenotype FAB M5. In general, they are associated with an adverse prognosis. In acute promyelocytic leukemia, the translocation (15;17)(q22;q11-21) involving the RARA leads to a maturation arrest that can be overcome by RA, often inducing remission. In other forms of AML, however, the effects of RA are limited and diverse. To study whether RA might have a therapeutical potential in our case, we performed an in vitro analysis of RA effects on AML cells. We found that RA leads to enhanced cell death and up-regulation of CD38 and CD117. However, no hints of RA-induced in vitro differentiation were visible. Our data indicate that in AML cells bearing the t(11;17)(q23;q21), a differentiation arrest that is overcome by RA is not present. On the contrary, RA induces alterations in cellular regulation that are similar to the RA-induced changes observed in early hematogenic progenitors; thus, a possible therapeutical benefit of RA in such cases remains open.

Leukemia: beneficial actions of retinoids and rexinoids.

Acute promyelocytic leukemia (APL), a subtype of acute myeloid leukemia, is the prototype of a cancer that can be cured by differentiation therapy using combined retinoic acid (RA) and chemotherapy. Acute promyelocytic leukemia is caused by chromosomal translocations, which in the large majority of cases generate the prototypic promyelocytic leukemia-retinoic-acid receptor alpha (PML-RARalpha) an oncogenic fusion protein formed from the retinoic-acid receptor alpha and the so-called PML protein. The fusion protein leads to the deregulation of wild type PML and RARalpha function, thus inducing the differentiation block and an altered survival capacity of promyelocytes of affected patients. A plethora of studies have revealed molecular details that account for the oncogenic properties of acute promyelocytic leukemia fusion proteins and the events that contribute to the therapy-induced differentiation and apoptosis of patients' blasts. Illustrating the beneficial mechanisms of action of retinoids for acute promyelocytic leukemia patients this review goes on to discuss a plethora of recently recognized molecular paradigms by which retinoids and rexinoids, alone or in combination with other compounds, regulate growth, differentiation and apoptosis also in non-acute promyelocytic leukemia cells, highlighting their potential as drugs for cancer therapy and prevention.

Retinoids in chemoprevention of cancer.

Retinoic acid (RA), a natural metabolite of circulating Vitamin A (retinol) and an irreversible oxidation product of retinol, is essential in maintaining the normal pathway of differentiation of epithelial tissues. RA and a number of its analogs, both natural and synthetic (retinoids), have been shown to be effective in the prevention of a variety of cancers in experimental animals, and in reversing preneoplastic lesions in humans. The retinoids exhibit a high degree of specificity in cancer chemoprevention. Diverse effects of retinoids are mediated by retinoid nuclear receptors, the ligand-inducible trans-acting transcription factors. The receptor-selective retinoids may be more effective and less toxic in cancer prevention. Our chemoprevention study with retinoids using the mouse skin carcinogenesis model indicated that retinoids are anti-tumor promoters. One of the mechanisms by which retinoids inhibit promotion of mouse skin tumor formation involves their property to inhibit the induction of ornithine decarboxylase by the phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate. RARalpha and RARgamma, but not RXRs, may mediate mouse skin anti-tumor promotion activity of retinoids. Retinoids are highly selective chemopreventive agents and are toxic at high pharmacological doses. Clinical trials with retinoids should be conducted with a carefully evaluated, appropriate patient population and perhaps at low doses in combination with other chemopreventive agents with mechanisms of action different from retinoids.

Chemoprevention of tumors: the role of RAR-beta.

Chemoprevention can be defined as the use of specific natural or synthetic chemical agents to reverse, suppress, or prevent carcinogenic progression to invasive cancer. The knowledge of carcinogenic mechanisms provides the scientific rationale for chemoprevention. Epithelial carcinogenesis proceeds through multiple discernible stages of molecular and cellular alterations. Understanding of the multistep nature of carcinogenesis has evolved through highly controlled animal carcinogenesis studies, and these studies have identified three distinct phases: initiation, promotion and progression. Animal model studies have provided evidence that the development of cancer involves many different factors, including alterations in the structures and functions of different genes. Transitions between successive stages can be enhanced or inhibited in the laboratory by different types of agents, such activities providing the fundamental basis for chemoprevention.

A library construction of 2,5-disubstituted pyrrole compounds by using solid/solution-phase syntheses.

Using solid- and solution-phase synthesis, a library of 2,5-disubstituted pyrrole compounds was constructed. This is the first report that Stetter reaction was applied to the solid-phase synthesis for C-C bond formation. Some of 2,5-disubstituted pyrrole compounds showed the inhibitory activity of LPS-induced mouse B-lymphocyte proliferation.