Prevalence of type 2 diabetes (T2D) and obesity is increasing worldwide. Currently available therapies are not suited for all patients in the heterogeneous obese/T2D population, hence the need for novel treatments. Fibroblast growth factor 21 (FGF21) is considered a promising therapeutic agent for T2D/obesity. Native FGF21 has, however, poor pharmacokinetic properties, making gene therapy an attractive strategy to achieve sustained circulating levels of this protein. Here, adeno‐associated viral vectors (AAV) were used to genetically engineer liver, adipose tissue, or skeletal muscle to secrete FGF21. Treatment of animals under long‐term high‐fat diet feeding or of ob/ob mice resulted in marked reductions in body weight, adipose tissue hypertrophy and inflammation, hepatic steatosis, inflammation and fibrosis, and insulin resistance for > 1 year. This therapeutic effect was achieved in the absence of side effects despite continuously elevated serum FGF21. Furthermore, FGF21 overproduction in healthy animals fed a standard diet prevented the increase in weight and insulin resistance associated with aging. Our study underscores the potential of FGF21 gene therapy to treat obesity, insulin resistance, and T2D. Synopsis This study describes the use of adeno‐associated viral (AAV) vectors to achieve long‐term production of fibroblast growth factor 21 (FGF21) to treat obesity and insulin resistance. AAV‐FGF21 gene transfer to healthy animals also prevented age‐associated weight gain and insulin resistance. A one‐time administration of an AAV vector encoding FGF21 counteract obesity and insulin resistance for more than a year. The approach works in two different animal models of obesity, induced either by diet or genetic mutations. Administration of AAV‐FGF21 to healthy animals promotes healthy aging. AAV‐FGF21 pharmacological effects are demonstrated after genetic engineering of 3 different tissues (liver, adipose tissue and skeletal muscle). FGF21 gene therapy holds great translational potential in the fight against insulin resistance, T2D, obesity and related comorbidities.

The human insulin-like growth factor 2 (IGF2) and insulin genes are located within the same genomic region. Although human genomic studies have demonstrated associations between diabetes and the INS/IGF2 locus or the IGF2 mRNA binding protein 2 (IGF2BP2), the role of IGF2 in diabetes pathogenesis is not fully understood. We previously described that transgenic mice overexpressing IGF2 specifically in β-cells (Tg-IGF2) develop a pre-diabetic state. Here, we characterized the effects of IGF2 on β-cell functionality. Overexpression of IGF2 led to β-cell dedifferentiation and endoplasmic reticulum stress causing islet dysfunction in vivo. Both adenoviral-mediated overexpression of IGF2 and treatment of adult wild-type islets with recombinant IGF2 in vitro further confirmed the direct implication of IGF2 on β-cell dysfunction. Treatment of Tg-IGF2 mice with subdiabetogenic doses of streptozotocin or crossing these mice with a transgenic model of islet lymphocytic infiltration promoted the development of overt diabetes, suggesting that IGF2 makes islets more susceptible to β-cell damage and immune attack. These results indicate that increased local levels of IGF2 in pancreatic islets may predispose to the onset of diabetes. This study unravels an unprecedented role of IGF2 on β-cells function.

Eicosanoids, such as leukotriene B4 (LTB4) and lipoxin A4 (LXA4), may play a key role during obesity. While LTB4 is involved in adipose tissue inflammation and insulin resistance, LXA4 may exert anti-inflammatory effects and alleviate hepatic steatosis. Both lipid mediators derive from the same pathway, in which arachidonate 5-lipoxygenase (ALOX5) and its partner, arachidonate 5-lipoxygenase–activating protein (ALOX5AP), are involved. ALOX5 and ALOX5AP expression is increased in humans and rodents with obesity and insulin resistance. We found that transgenic mice overexpressing ALOX5AP in adipose tissue had higher LXA4 rather than higher LTB4 levels, were leaner, and showed increased energy expenditure, partly due to browning of white adipose tissue (WAT). Upregulation of hepatic LXR and Cyp7a1 led to higher bile acid synthesis, which may have contributed to increased thermogenesis. In addition, transgenic mice were protected against diet-induced obesity, insulin resistance, and inflammation. Finally, treatment of C57BL/6J mice with LXA4, which showed browning of WAT, strongly suggests that LXA4 is responsible for the transgenic mice phenotype. Thus, our data support that LXA4 may hold great potential for the future development of therapeutic strategies for obesity and related diseases.

Mucopolysaccharidosis type II (MPSII) is an X-linked lysosomal storage disease characterized by severe neurologic and somatic disease caused by deficiency of iduronate-2-sulfatase (IDS), an enzyme that catabolizes the glycosaminoglycans heparan and dermatan sulphate. Intravenous enzyme replacement therapy (ERT) currently constitutes the only approved therapeutic option for MPSII. However, the inability of recombinant IDS to efficiently cross the blood-brain barrier (BBB) limits ERT efficacy in treating neurological symptoms. Here, we report a gene therapy approach for MPSII through direct delivery of vectors to the CNS. Through a minimally invasive procedure, we administered adeno-associated virus vectors encoding IDS (AAV9- Ids ) to the cerebrospinal fluid of MPSII mice with already established disease. Treated mice showed a significant increase in IDS activity throughout the encephalon, with full resolution of lysosomal storage lesions, reversal of lysosomal dysfunction, normalization of brain transcriptomic signature, and disappearance of neuroinflammation. Moreover, our vector also transduced the liver, providing a peripheral source of therapeutic protein that corrected storage pathology in visceral organs, with evidence of cross-correction of nontransduced organs by circulating enzyme. Importantly, AAV9- Ids -treated MPSII mice showed normalization of behavioral deficits and considerably prolonged survival. These results provide a strong proof of concept for the clinical translation of our approach for the treatment of Hunter syndrome patients with cognitive impairment.

Iron is essential in the retina because the heme-containing enzyme guanylate cyclase modulates phototransduction in rods and cones. Transferrin endocytosis is the classical pathway for obtaining iron from the blood circulation in the retina. However, the iron storage protein ferritin has been also recently proposed as an iron carrier. In this study, the presence of Scara5 and its binding to L-ferritin was investigated in the retina. Our results showed that Scara5, the specific receptor for L-ferritin, was expressed in mouse and human retinas in many cell types, including endothelial cells. Furthermore, we showed that intravenously injected ferritin crossed the blood retinal barrier through L-ferritin binding to Scara5 in endothelial cells. Thus, suggesting the existence of a new pathway for iron delivery and trafficking in the retina. In a murine model of photoreceptor degeneration, Scara5 was downregulated, pointing out this receptor as a potential player implicated in retinopathy and also as a possible therapeutic target.