Brian P. Boerner

Hippo Signaling Regulates Pancreas Development through Inactivation of Yap

ABSTRACT The mammalian pancreas is required for normal metabolism, with defects in this vital organ commonly observed in cancer and diabetes. Development must therefore be tightly controlled in order to produce a pancreas of correct size, cell type composition, and physiologic function. Through negative regulation of Yap-dependent proliferation, the Hippo kinase cascade is a critical regulator of organ growth. To investigate the role of Hippo signaling in pancreas biology, we deleted Hippo pathway components in the developing mouse pancreas. Unexpectedly, the pancreas from Hippo-deficient offspring was reduced in size, with defects evident throughout the organ. Increases in the dephosphorylated nuclear form of Yap are apparent throughout the exocrine compartment and correlate with increases in levels of cell proliferation. However, the mutant exocrine tissue displays extensive disorganization leading to pancreatitis-like autodigestion. Interestingly, our results suggest that Hippo signaling does not directly regulate the pancreas endocrine compartment as Yap expression is lost following endocrine specification through a Hippo-independent mechanism. Altogether, our results demonstrate that Hippo signaling plays a crucial role in pancreas development and provide novel routes to a better understanding of pathological conditions that affect this organ.

Type 1 diabetes: role of intestinal microbiome in humans and mice

Type 1 diabetes is a disease involving autoimmune destruction of pancreatic beta cells in genetically predisposed individuals. Identifying factors that trigger initiation and progression of autoimmunity may provide opportunities for directed prophylactic and therapeutic measures to prevent and/or treat type 1 diabetes. The human intestinal microbiome is a complex, symbiotic ecological community that influences human health and development, including the development and maintenance of the human immune system. The role of the intestinal microbiome in autoimmunity has garnered significant attention, and evidence suggests a particular role for intestinal microbiome alterations in autoimmune disease development, including type 1 diabetes. This review will examine the role of the intestinal microbiome in the development and function of the immune system and how this relates to the development of autoimmunity. Data from animal and human studies linking alterations in the intestinal microbiome and intestinal integrity with type 1 diabetes will be closely examined. Finally, we will examine the interactions between the intestinal microbiome and dietary exposures and how these interactions may further influence autoimmunity and type 1 diabetes development.

Post-Transplant Diabetes Mellitus: Causes, Treatment, and Impact on Outcomes

Post-transplant diabetes mellitus (PTDM) is a frequent consequence of solid organ transplantation. PTDM has been associated with greater mortality and increased infections in different transplant groups using different diagnostic criteria. An international consensus panel recommended a consistent set of guidelines in 2003 based on American Diabetes Association glucose criteria but did not exclude the immediate post-transplant hospitalization when many patients receive large doses of corticosteroids. Greater glucose monitoring during all hospitalizations has revealed significant glucose intolerance in the majority of recipients immediately after transplant. As a result, the international consensus panel reviewed its earlier guidelines and recommended delaying screening and diagnosis of PTDM until the recipient is on stable doses of immunosuppression after discharge from initial transplant hospitalization. The group cautioned that whereas hemoglobin A1C has been adopted as a diagnostic criterion by many, it is not reliable as the sole diabetes screening method during the first year after transplant. Risk factors for PTDM include many of the immunosuppressant medications themselves as well as those for type 2 diabetes. The provider managing diabetes and associated dyslipidemia and hypertension after transplant must be careful of the greater risk for drug-drug interactions and infections with immunosuppressant medications. Treatment goals and therapies must consider the greater risk for fluctuating and reduced kidney function, which can cause hypoglycemia. Research is actively focused on strategies to prevent PTDM, but until strategies are found, it is imperative that immunosuppression regimens are chosen based on their evidence to prolong graft survival, not to avoid PTDM.

Diabetes and Cardiovascular Disease Following Kidney Transplantation

Kidney transplantation is being performed more frequently for individuals with end stage renal disease (ESRD) due to improved survival and quality of life compared to long-term dialysis. Though rates decrease after transplant, cardiovascular disease (CVD) remains the most common cause of death after kidney transplant. New-onset diabetes after transplant (NODAT), a common complication following kidney transplantation, and pre-transplant diabetes both significantly increase the risk for CVD. Several other risk factors for CVD in kidney transplant recipients have been identified; however, optimal therapy for controlling the risk factors of CVD after kidney transplantation, including NODAT and pre-transplant diabetes, is not well defined. In the following review we will discuss the role of traditional and non-traditional risk factors in CVD after kidney transplant and the mechanisms involved therein. We will also examine the current literature regarding treatment of these risk factors for the prevention of CVD. Finally, we will review the current recommendations for pre- and post-transplant cardiovascular evaluation and management.

Single-dose rATG induction at renal transplantation: superior renal function and glucoregulation with less hypomagnesemia.

Stevens RB, Lane JT, Boerner BP, Miles CD, Rigley TH, Sandoz JP, Nielsen KJ, Skorupa JY, Skorupa AJ, Kaplan B, Wrenshall LE. Single‐dose rATG induction at renal transplantation: superior renal function and glucoregulation with less hypomagnesemia. 
Clin Transplant 2012: 26: 123–132. 
© 2011 John Wiley & Sons A/S.

Exploiting Expression of Hippo Effector, Yap, for Expansion of Functional Islet Mass.

Loss of pancreas β-cell function is the precipitating factor in all forms of diabetes. Cell replacement therapies, such as islet transplantation, remain the best hope for a cure; however, widespread implementation of this method is hampered by availability of donor tissue. Thus, strategies that expand functional β-cell mass are crucial for widespread usage in diabetes cell replacement therapy. Here, we investigate the regulation of the Hippo-target protein, Yes-associated protein (Yap), during development of the endocrine pancreas and its function after reactivation in human cadaveric islets. Our results demonstrate that Yap expression is extinguished at the mRNA level after neurogenin-3-dependent specification of the pancreas endocrine lineage, correlating with proliferation decreases in these cells. Interestingly, when a constitutively active form of Yap was expressed in human cadaver islets robust increases in proliferation were noted within insulin-producing β-cells. Importantly, proliferation in these cells occurs without negatively affecting β-cell differentiation or functional status. Finally, we show that the proproliferative mammalian target of rapamycin pathway is activated after Yap expression, providing at least one explanation for the observed increases in β-cell proliferation. Together, these results provide a foundation for manipulating Yap activity as a novel approach to expand functional islet mass for diabetes regenerative therapy.

TGF-β superfamily member nodal stimulates human β-cell proliferation while maintaining cellular viability

In an effort to expand human islets and enhance allogeneic islet transplant for the treatment of type 1 diabetes, identifying signaling pathways that stimulate human β-cell proliferation is paramount. TGF-β superfamily members, in particular activin-A, are likely involved in islet development and may contribute to β-cell proliferation. Nodal, another TGF-β member, is present in both embryonic and adult rodent islets. Nodal, along with its coreceptor, Cripto, are pro-proliferative factors in certain cell types. Although Nodal stimulates apoptosis of rat insulinoma cells (INS-1), Nodal and Cripto signaling have not been studied in the context of human islets. The current study investigated the effects of Nodal and Cripto on human β-cell proliferation, differentiation, and viability. In the human pancreas and isolated human islets, we observed Nodal mRNA and protein expression, with protein expression observed in β and α-cells. Cripto expression was absent from human islets. Furthermore, in cultured human islets, exogenous Nodal stimulated modest β-cell proliferation and inhibited α-cell proliferation with no effect on cellular viability, apoptosis, or differentiation. Nodal stimulated the phosphorylation of mothers against decapentaplegic (SMAD)-2, with no effect on AKT or MAPK signaling, suggesting phosphorylated SMAD signaling was involved in β-cell proliferation. Cripto had no effect on human islet cell proliferation, differentiation, or viability. In conclusion, Nodal stimulates human β-cell proliferation while maintaining cellular viability. Nodal signaling warrants further exploration to better understand and enhance human β-cell proliferative capacity.

Management of the hospitalized transplant patient.

Significant hyperglycemia is commonly observed immediately after solid organ and bone marrow transplant as well as with subsequent hospitalizations. Surgery and procedures are well known to cause pain and stress leading to secretion of cytokines and other hormones known to aggravate insulin action. Immunosuppression required for transplant and preexisting risk are also major factors. Glucose control improves outcomes for all hospitalized patients, including transplant patients, but is often more challenging to achieve because of frequent and sometimes unpredictable changes in immunosuppression doses, renal function, and nutrition. As a result, risk of hypoglycemia can be greater in this patient group when trying to achieve glucose control goals for hospitalized patients. Key to successful management of hyperglycemia is regular communication between the members of the care team as well as anticipating and rapidly implementing a new treatment paradigm in response to changes in immunosuppression, nutrition, renal function, or evidence of changing insulin resistance.

WS6 induces both alpha and beta cell proliferation without affecting differentiation or viability

Agents that stimulate human pancreatic beta cell proliferation are needed to improve diabetes mellitus treatment. Recently, a small molecule, WS6, was observed to stimulate human beta cell proliferation. However, little is known about its other effects on human islets. To better understand the role of WS6 as a possible beta cell regenerative therapy, we carried out in-depth phenotypic analysis of WS6-treated human islets, exploring its effects on non-beta cell proliferation, beta cell differentiation, and islet cell viability. WS6 not only stimulated beta cell proliferation in cultured human islets (in agreement with previous reports), but also human alpha cell proliferation, indicating that WS6 is not a beta cell-specific mitogen. WS6 did not change the proportion of insulin-positive beta cells or the expression of beta cell-specific transcription factors, suggesting that WS6 does not alter beta cell differentiation, and WS6 had no effect on human islet cell apoptosis or viability. In conclusion, WS6 stimulates proliferation of both human beta and alpha cells while maintaining cellular viability and the beta cell differentiated phenotype. These findings expand the literature on WS6 and support the suggestion that WS6 may help increase human islet mass needed for successful treatment of diabetes.

Post-transplant diabetes: Diagnosis and management

Post-transplant diabetes mellitus (PTDM) is common after most types of solid organ transplantation, though the actual incidence is as yet unknown because of the use of different diagnostic criteria. PTDM is the result of individual risk factors as well as risk factors associated with the transplant itself, particularly immunosuppressants. Previously called New Onset Diabetes, in many cases inadequate screening for diabetes before transplant cannot assure that the diabetes is new after transplant. The most recent international consensus guidelines suggest diagnosis should be delayed until the patient is taking maintenance doses of immunosuppressants even if they require treatment in the immediate hospitalization. Criteria for diagnosis follow those of the American Diabetes Association and the World Health Organization, although hemoglobin A1C should not be used as the only screening test at least until one year after transplant because of its insensitivity for significant glucose intolerance in the transplant patient and setting. Management of PTDM is best done in a team setting, with an emphasis on glycemic control, dyslipidemia, and hypertension, and taking into consideration immunosuppressant regimens and potential drug side effects and interactions. While PTDM has been associated with changes in outcomes, these have and may continue to improve with improved diabetes care in and out of the hospital, and other changes in post-transplant care.