Hemodynamic stress-induced cardiac remodelling is not modulated by ablation of phosphodiesterase 4D interacting protein.

Adrenergic stimulation in the heart activates the protein kinase A (PKA), which phosphorylates key proteins involved in intracellular Ca2+ handling. PKA is held in proximity to its substrates by protein scaffolds, the A kinase anchoring proteins (AKAPs). We have previously identified the transcript of phosphodiesterase 4D interacting protein (Pde4dip; also known as myomegalin), one of the sarcomeric AKAPs, as being differentially expressed following hemodynamic overload, a condition inducing hyperadrenergic state in the heart. Here, we addressed whether PDE4DIP is involved in the adverse cardiac remodelling following hemodynamic stress. Homozygous Pde4dip knockout (KO) mice, generated by CRISPR-Cas9 technology, and wild-type (WT) littermates were exposed to aortocaval shunt (shunt) or transthoracic aortic constriction (TAC) to induce hemodynamic volume overload (VO) or pressure overload (PO), respectively. The mortality, cardiac structure, function and pathological cardiac remodelling were followed up after hemodynamic injuries. The PDE4DIP protein level was markedly downregulated in volume-overloaded- but upregulated in pressure-overloaded-WT hearts. Following shunt or TAC, mortality rates were comparably increased in both genotypes. Twelve weeks after shunt or TAC, Pde4dip-KO animals showed a similar degree of cardiac hypertrophy, dilatation and dysfunction as WT mice. Cardiomyocyte hypertrophy, myocardial fibrosis, reactivation of cardiac stress genes and downregulation of ATPase, Ca2+ transporting, cardiac muscle, slow twitch 2 transcript did not differ between WT and Pde4dip-KO hearts following shunt or TAC. In summary, despite a differential expression of PDE4DIP protein in remodelled WT hearts, Pde4dip deficiency does not modulate adverse cardiac remodelling after hemodynamic VO or PO.

The Hippo kinase LATS2 impairs pancreatic ß-cell survival in diabetes through the mTORC1-autophagy axis.

Diabetes results from a decline in functional pancreatic ß-cells, but the molecular mechanisms underlying the pathological ß-cell failure are poorly understood. Here we report that large-tumor suppressor 2 (LATS2), a core component of the Hippo signaling pathway, is activated under diabetic conditions and induces ß-cell apoptosis and impaired function. LATS2 deficiency in ß-cells and primary isolated human islets as well as ß-cell specific LATS2 ablation in mice improves ß-cell viability, insulin secretion and ß-cell mass and ameliorates diabetes development. LATS2 activates mechanistic target of rapamycin complex 1 (mTORC1), a physiological suppressor of autophagy, in ß-cells and genetic and pharmacological inhibition of mTORC1 counteracts the pro-apoptotic action of activated LATS2. We further show a direct interplay between Hippo and autophagy, in which LATS2 is an autophagy substrate. On the other hand, LATS2 regulates ß-cell apoptosis triggered by impaired autophagy suggesting an existence of a stress-sensitive multicomponent cellular loop coordinating ß-cell compensation and survival. Our data reveal an important role for LATS2 in pancreatic ß-cell turnover and suggest LATS2 as a potential therapeutic target to improve pancreatic ß-cell survival and function in diabetes.

Inhibition of PHLPP1/2 phosphatases rescues pancreatic ß-cells in diabetes.

Pancreatic ß-cell failure is the key pathogenic element of the complex metabolic deterioration in type 2 diabetes (T2D); its underlying pathomechanism is still elusive. Here, we identify pleckstrin homology domain leucine-rich repeat protein phosphatases 1 and 2 (PHLPP1/2) as phosphatases whose upregulation leads to ß-cell failure in diabetes. PHLPP levels are highly elevated in metabolically stressed human and rodent diabetic ß-cells. Sustained hyper-activation of mechanistic target of rapamycin complex 1 (mTORC1) is the primary mechanism of the PHLPP upregulation linking chronic metabolic stress to ultimate ß-cell death. PHLPPs directly dephosphorylate and regulate activities of ß-cell survival-dependent kinases AKT and MST1, constituting a regulatory triangle loop to control ß-cell apoptosis. Genetic inhibition of PHLPPs markedly improves ß-cell survival and function in experimental models of diabetes in vitro, in vivo, and in primary human T2D islets. Our study presents PHLPPs as targets for functional regenerative therapy of pancreatic ß cells in diabetes.

Neratinib protects pancreatic beta cells in diabetes.

The loss of functional insulin-producing ß-cells is a hallmark of diabetes. Mammalian sterile 20-like kinase 1 (MST1) is a key regulator of pancreatic ß-cell death and dysfunction; its deficiency restores functional ß-cells and normoglycemia. The identification of MST1 inhibitors represents a promising approach for a ß-cell-protective diabetes therapy. Here, we identify neratinib, an FDA-approved drug targeting HER2/EGFR dual kinases, as a potent MST1 inhibitor, which improves ß-cell survival under multiple diabetogenic conditions in human islets and INS-1E cells. In a pre-clinical study, neratinib attenuates hyperglycemia and improves ß-cell function, survival and ß-cell mass in type 1 (streptozotocin) and type 2 (obese Leprdb/db) diabetic mouse models. In summary, neratinib is a previously unrecognized inhibitor of MST1 and represents a potential ß-cell-protective drug with proof-of-concept in vitro in human islets and in vivo in rodent models of both type 1 and type 2 diabetes.

Loss of Deubiquitinase USP1 Blocks Pancreatic ß-Cell Apoptosis by Inhibiting DNA Damage Response.

Impaired pancreatic ß-cell survival contributes to the reduced ß-cell mass in diabetes, but underlying regulatory mechanisms and key players in this process remain incompletely understood. Here, we identified the deubiquitinase ubiquitin-specific protease 1 (USP1) as an important player in the regulation of ß-cell apoptosis under diabetic conditions. Genetic silencing and pharmacological suppression of USP1 blocked ß-cell death in several experimental models of diabetes in vitro and ex vivo without compromising insulin content and secretion and without impairing ß-cell maturation/identity genes in human islets. Our further analyses showed that USP1 inhibition attenuated DNA damage response (DDR) signals, which were highly elevated in diabetic ß-cells, suggesting a USP1-dependent regulation of DDR in stressed ß-cells. Our findings highlight a novel function of USP1 in the control of ß-cell survival, and its inhibition may have a potential therapeutic relevance for the suppression of ß-cell death in diabetes.

Ageing potentiates diet-induced glucose intolerance, ß-cell failure and tissue inflammation through TLR4.

Ageing and obesity are two major risk factors for the development of type 2 diabetes (T2D). A chronic, low-grade, sterile inflammation contributes to insulin resistance and ß-cell failure. Toll-like receptor-4 (TLR4) is a major pro-inflammatory pathway; its ligands as well as downstream signals are increased systemically in patients with T2D and at-risk individuals. In the present study we investigated the combined effects of high fat/high sucrose diet (HFD) feeding, ageing and TLR4-deficiency on tissue inflammation, insulin resistance and ß-cell failure. In young mice, a short-term HFD resulted in a mildly impaired glucose tolerance and reduced insulin secretion, together with a ß-cell mass compensation. In older mice, HFD further deteriorated insulin secretion and induced a significantly impaired glucose tolerance and augmented tissue inflammation in adipose, liver and pancreatic islets, all of which was attenuated by TLR4 deficiency. Our results show that ageing exacerbates HFD-induced impairment of glucose homeostasis and pancreatic ß-cell function and survival, and deteriorates HFD-induced induction of mRNA expression of inflammatory cytokines and pro-inflammatory macrophage markers. TLR4-deficiency protects against these combined deleterious effects of a high fat diet and ageing through a reduced expression of inflammatory products in both insulin sensitive tissues and pancreatic islets.