The purity of adeno-associated virus (AAV) vector preparations has important implications for both safety and efficacy of clinical gene transfer. Early-stage screening of candidates for AAV-based therapeutics ideally requires a purification method that is flexible and also provides vectors comparable in purity and potency to the prospective investigational product manufactured for clinical studies. The use of cesium chloride (CsCl) gradient-based protocols provides the flexibility for purification of different serotypes; however, a commonly used first-generation CsCl-based protocol was found to result in AAV vectors containing large amounts of protein and DNA impurities and low transduction efficiency in vitro and in vivo. Here, we describe and characterize an optimized, secondgeneration CsCl protocol that incorporates differential precipitation of AAV particles by polyethylene glycol, resulting in higher yield and markedly higher vector purity that correlated with better transduction efficiency observed with several AAV serotypes in multiple tissues and species. Vectors purified by the optimized CsCl protocol were found to be comparable in purity and functional activity to those prepared by more scalable, but less flexible serotype-specific purification processes developed for manufacture of clinical vectors, and are therefore ideally suited for pre-clinical studies supporting translational research.

Amyloid forms within pancreatic islets in type 2 diabetes from aggregates of the β-cell peptide islet amyloid polypeptide (IAPP). These aggregates are toxic to β-cells, inducing β-cell death and dysfunction, as well as inciting islet inflammation. The β-cell is subject to a number of other stressors, including insulin resistance and hyperglycaemia, that may contribute to amyloid formation by increasing IAPP production by the β-cell. β-Cell dysfunction, evident as impaired glucose-stimulated insulin secretion and defective prohormone processing and exacerbated by metabolic stress, is also a likely prerequisite for islet amyloid formation to occur in type 2 diabetes. Islet transplants in patients with type 1 diabetes face similar stressors, and are subject to rapid amyloid formation and impaired proinsulin processing associated with progressive loss of β-cell function and mass. Declining β-cell mass is predicted to increase metabolic demand on remaining β-cells, promoting a feed-forward cycle of β-cell decline.

Type 1 diabetes is characterized by destruction of insulin-producing β cells in the pancreatic islets by effector T cells. Tregs, defined by the markers CD4 and FoxP3, regulate immune responses by suppressing effector T cells and are recruited to sites of action by the chemokine CCL22. Here, we demonstrate that production of CCL22 in islets after intrapancreatic duct injection of double-stranded adeno-associated virus encoding CCL22 recruits endogenous Tregs to the islets and confers long-term protection from autoimmune diabetes in NOD mice. In addition, adenoviral expression of CCL22 in syngeneic islet transplants in diabetic NOD recipients prevented β cell destruction by autoreactive T cells and thereby delayed recurrence of diabetes. CCL22 expression increased the frequency of Tregs, produced higher levels of TGF-β in the CD4 + T cell population near islets, and decreased the frequency of circulating autoreactive CD8 + T cells and CD8 + IFN-γ-producing T cells. The protective effect of CCL22 was abrogated by depletion of Tregs with a CD25-specific antibody. Our results indicate that islet expression of CCL22 recruits Tregs and attenuates autoimmune destruction of β cells. CCL22-mediated recruitment of Tregs to islets may be a novel therapeutic strategy for type 1 diabetes.

Diabetes is associated with severe secondary complications, largely caused by poor glycemic control. Treatment with exogenous insulin fails to prevent these complications completely, leading to significant morbidity and mortality. We previously demonstrated that it is possible to generate a “glucose sensor” in skeletal muscle through coexpression of glucokinase and insulin, increasing glucose uptake and correcting hyperglycemia in diabetic mice. Here, we demonstrate long-term efficacy of this approach in a large animal model of diabetes. A one-time intramuscular administration of adeno-associated viral vectors of serotype 1 encoding for glucokinase and insulin in diabetic dogs resulted in normalization of fasting glycemia, accelerated disposal of glucose after oral challenge, and no episodes of hypoglycemia during exercise for >4 years after gene transfer. This was associated with recovery of body weight, reduced glycosylated plasma proteins levels, and long-term survival without secondary complications. Conversely, exogenous insulin or gene transfer for insulin or glucokinase alone failed to achieve complete correction of diabetes, indicating that the synergistic action of insulin and glucokinase is needed for full therapeutic effect. This study provides the first proof-of-concept in a large animal model for a gene transfer approach to treat diabetes.

Type 2 diabetes (T2D) is a complex metabolic disorder characterized by hyperglycemia in the context of insulin resistance, which precedes insulin deficiency as a result of β-cell failure. Accumulating evidence indicates that β-cell loss in T2D results as a response to the combination of oxidative stress and endoplasmic reticulum (ER) stress. Failure of the ER’s adaptive capacity and further activation of the unfolded protein response may trigger macroautophagy (hereafter referred as autophagy) as a process of self-protection and inflammation. Many studies have shown that inflammation plays a very important role in the pathogenesis of T2D. Inflammatory mechanisms and cytokine production activated by stress via the inflammasome may further alter the normal structure of β-cells by inducing pancreatic islet cell apoptosis. Thus, the combination of oxidative and ER stress, together with autophagy insufficiency and inflammation, may contribute to β-cell death or dysfunction in T2D. Therapeutic approaches aimed at ameliorating stress and inflammation may therefore prove to be promising targets for the development of new diabetes treatment methods. Here, we discuss different mechanisms involved in stress and inflammation, and the role of antioxidants, endogenous and chemical chaperones, and autophagic pathways, which may shift the tendency from ER stress and apoptosis toward cell survival. Strategies targeting cell survival can be essential for relieving ER stress and reestablishing homeostasis, which may diminish inflammation and prevent pancreatic β-cell death associated with T2D.

In type 2 diabetes, beta-cell dysfunction is thought to be due to several causes, one being the formation of toxic protein aggregates called islet amyloid, formed by accumulations of misfolded human islet amyloid polypeptide (hIAPP). The process of hIAPP misfolding and aggregation is one of the factors that may activate the unfolded protein response (UPR), perturbing endoplasmic reticulum (ER) homeostasis. Molecular chaperones have been described to be important in regulating ER response to ER stress. In the present work, we evaluate the role of chaperones in a stressed cellular model of hIAPP overexpression. A rat pancreatic beta-cell line expressing hIAPP exposed to thapsigargin or treated with high glucose and palmitic acid, both of which are known ER stress inducers, showed an increase in ER stress genes when compared to INS1E cells expressing rat IAPP or INS1E control cells. Treatment with molecular chaperone glucose-regulated protein 78 kDa (GRP78, also known as BiP) or protein disulfite isomerase (PDI), and chemical chaperones taurine-conjugated ursodeoxycholic acid (TUDCA) or 4-phenylbutyrate (PBA), alleviated ER stress and increased insulin secretion in hIAPP-expressing cells. Our results suggest that the overexpression of hIAPP induces a stronger response of ER stress markers. Moreover, endogenous and chemical chaperones are able to ameliorate induced ER stress and increase insulin secretion, suggesting that improving chaperone capacity can play an important role in improving beta-cell function in type 2 diabetes.

Type 1 diabetic patients develop severe secondary complications because insulin treatment does not guarantee normoglycemia. Thus, efficient regulation of glucose homeostasis is a major challenge in diabetes therapy. Skeletal muscle is the most important tissue for glucose disposal after a meal. However, the lack of insulin during diabetes impairs glucose uptake. To increase glucose removal from blood, skeletal muscle of transgenic mice was engineered both to produce basal levels of insulin and to express the liver enzyme glucokinase. After streptozotozin (STZ) administration of double-transgenic mice, a synergic action in skeletal muscle between the insulin produced and the increased glucose phosphorylation by glucokinase was established, preventing hyperglycemia and metabolic alterations. These findings suggested that insulin and glucokinase might be expressed in skeletal muscle, using adeno-associated viral 1 (AAV1) vectors as a new gene therapy approach for diabetes. AAV1-Ins؉GK-treated diabetic mice restored and maintained normoglycemia in fed and fasted conditions for >4 months after STZ administration. Furthermore, these mice showed normalization of metabolic parameters, glucose tolerance, and food and fluid intake. Therefore, the joint action of basal insulin production and glucokinase activity may generate a "glucose sensor" in skeletal muscle that allows proper regulation of glycemia in diabetic animals and thus prevents secondary complications. Diabetes 55: 1546 -1553, 2006

The pancreatic β-cell transcriptome is highly sensitive to external signals such as glucose oscillations and stress cues. MicroRNAs (miRNAs) have emerged as key factors in gene expression regulation. Here, we aimed to identify miRNAs that are modulated by glucose in mouse pancreatic islets. We identified miR-708 as the most upregulated miRNA in islets cultured at low glucose concentrations, a setting that triggers a strong stress response. miR-708 was also potently upregulated by triggering endoplasmic reticulum (ER) stress with thapsigargin and in islets of / mice. Low-glucose induction of miR-708 was blocked by treatment with the chemical chaperone 4-phenylbutyrate, uncovering the involvement of ER stress in this response. An integrative analysis identified neuronatin () as a potential glucose-regulated target of miR-708. Indeed, expression was inversely correlated with miR-708 in islets cultured at different glucose concentrations and in/ mouse islets and was reduced after miR-708 overexpression. Consistent with the role of Nnat in the secretory function of β-cells, miR-708 overexpression impaired glucose-stimulated insulin secretion (GSIS), which was recovered by overexpression. Moreover, miR-708 inhibition recovered GSIS in islets cultured at low glucose. Finally, miR-708 overexpression suppressed β-cell proliferation and induced β-cell apoptosis. Collectively, our results provide a novel mechanism of glucose regulation of β-cell function and growth by repressing stress-induced miR-708.