The Rho-guanine nucleotide exchange factor PDZ-RhoGEF governs susceptibility to diet-induced obesity and type 2 diabetes.

Adipose tissue is crucial for the maintenance of energy and metabolic homeostasis and its deregulation can lead to obesity and type II diabetes (T2D). Using gene disruption in the mouse, we discovered a function for a RhoA-specific guanine nucleotide exchange factor PDZ-RhoGEF (Arhgef11) in white adipose tissue biology. While PDZ-RhoGEF was dispensable for a number of RhoA signaling-mediated processes in mouse embryonic fibroblasts, including stress fiber formation and cell migration, it's deletion led to a reduction in their proliferative potential. On a whole organism level, PDZ-RhoGEF deletion resulted in an acute increase in energy expenditure, selectively impaired early adipose tissue development and decreased adiposity in adults. PDZ-RhoGEF-deficient mice were protected from diet-induced obesity and T2D. Mechanistically, PDZ-RhoGEF enhanced insulin/IGF-1 signaling in adipose tissue by controlling ROCK-dependent phosphorylation of the insulin receptor substrate-1 (IRS-1). Our results demonstrate that PDZ-RhoGEF acts as a key determinant of mammalian metabolism and obesity-associated pathologies.

Pax6 and Pdx1 are required for production of glucose-dependent insulinotropic polypeptide in proglucagon-expressing L cells.

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are incretin hormones that play important roles in maintaining glucose homeostasis and are being actively pursued as novel therapeutic agents for diabetes. GIP is produced by dispersed enteroendocrine cells and interestingly at times is coexpressed with GLP-1. We sought to determine the factors that selectively define GIP- vs. GLP-1-expressing cells. We performed comparative immunostaining of Pax6 and Pdx1 in GIP- and GLP-1-secreting cells. We investigated whether Pax6 and Pdx1 activate the human GIP promoter in control IEC-6 cells and GIP-expressing STC-1 cells. EMSA was performed to assess the binding of these transcription factors to the GIP promoter. Pax6 and Pdx1 consistently colocalized in GIP-immunoreactive cells. Cells that coexpress GIP and GLP-1 were Pax6 and Pdx1 positive, whereas cells expressing only GLP-1 were Pax6 positive but did not express Pdx1. GIP promoter activity was enhanced in IEC-6 cells by exogenous Pax6 or Pdx1 and diminished in STC-1 cells by inhibition of endogenous Pax6 or Pdx1 by dominant-negative forms. Promoter truncation analysis revealed a major loss of promoter activity when the sequence between -184 to -145 bp was deleted. EMSA studies indicated that Pax6 and Pdx1 bind to this proximal sequence of the human GIP promoter. Our findings indicate that concomitant expression of Pax6 and Pdx1 is important for GIP expression. Our results also suggest that the presence of Pdx1 defines whether GLP-1-expressing gastrointestinal L cells also coexpress GIP.

Caspase recruitment domain protein 6 is a microtubule-interacting protein that positively modulates NF-kappaB activation.

Proteins containing a caspase recruitment domain (CARD) play pivotal roles in signal transduction leading to apoptosis and NF-kappaB activation and inflammation. Here we identify and characterize human and mouse CARD protein 6 (CARD6), CARD-containing proteins of unique structure. CARD6 associates with microtubules and interacts with receptor-interacting protein (RIP)-like interacting caspase-like apoptosis regulatory protein kinase (RICK), a CARD-containing member of the RIP family of protein kinases. These kinases are involved in multiple NF-kappaB signaling pathways important for innate and adaptive immune responses. Surprisingly, the CARDs of CARD6 and RICK were not required for their interaction; instead, mutational analysis revealed that the CARD of CARD6 negatively controls the association of these molecules. CARD6 also binds to RIP1, a RIP kinase homologue that lacks a CARD but contains a C-terminal death domain. Coexpression of RICK targets CARD6 to aggresomes via a mechanism that requires the CARD of RICK. Importantly, CARD6 expression has a synergistic effect on NF-kappaB activation induced by several independent signal transduction pathways. In summary, our results indicate that CARD6 is a regulator of NF-kappaB activation that modulates the functions of RIP kinase family members.

Hypersensitivity of DJ-1-deficient mice to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine (MPTP) and oxidative stress.

Mutations of the DJ-1 (PARK7) gene are linked to familial Parkinson's disease. We used gene targeting to generate DJ-1-deficient mice that were viable, fertile, and showed no gross anatomical or neuronal abnormalities. Dopaminergic neuron numbers in the substantia nigra and fiber densities and dopamine levels in the striatum were normal. However, DJ-1-/- mice showed hypolocomotion when subjected to amphetamine challenge and increased striatal denervation and dopaminergic neuron loss induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine. DJ-1-/-embryonic cortical neurons showed increased sensitivity to oxidative, but not nonoxidative, insults. Restoration of DJ-1 expression to DJ-1-/- mice or cells via adenoviral vector delivery mitigated all phenotypes. WT mice that received adenoviral delivery of DJ-1 resisted 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine-induced striatal damage, and neurons overexpressing DJ-1 were protected from oxidative stress in vitro. Thus, DJ-1 protects against neuronal oxidative stress, and loss of DJ-1 may lead to Parkinson's disease by conferring hypersensitivity to dopaminergic insults.