Notch-mediated hepatocyte MCP-1 secretion causes liver fibrosis

Patients with nonalcoholic steatohepatitis (NASH) have increased expression of liver monocyte chemoattractant protein-1 (MCP-1), but its cellular source and contribution to various aspects of NASH pathophysiology remain debated. We demonstrated increased liver CCL2 (which encodes MCP-1) expression in patients with NASH, and commensurately, a 100-fold increase in hepatocyte Ccl2 expression in a mouse model of NASH, accompanied by increased liver monocyte-derived macrophage (MoMF) infiltrate and liver fibrosis. To test repercussions of increased hepatocyte-derived MCP-1, we generated hepatocyte-specific Ccl2-knockout mice, which showed reduced liver MoMF infiltrate as well as decreased liver fibrosis. Forced hepatocyte MCP-1 expression provoked the opposite phenotype in chow-fed wild-type mice. Consistent with increased hepatocyte Notch signaling in NASH, we observed a close correlation between markers of Notch activation and CCL2 expression in patients with NASH. We found that an evolutionarily conserved Notch/recombination signal binding protein for immunoglobulin kappa J region binding site in the Ccl2 promoter mediated transactivation of the Ccl2 promoter in NASH diet-fed mice. Increased liver MoMF infiltrate and liver fibrosis seen in opposite gain-of-function mice was ameliorated with concomitant hepatocyte Ccl2 knockout or CCR2 inhibitor treatment. Hepatocyte Notch activation prompts MCP-1-dependent increase in liver MoMF infiltration and fibrosis.

Acetylation of PPARγ in macrophages promotes visceral fat degeneration in obesity

Obesity is characterized by chronic, low-grade inflammation, which is driven by macrophage infiltration of adipose tissue. PPARγ is well established to have an anti-inflammatory function in macrophages, but the mechanism that regulates its function in these cells remains to be fully elucidated. PPARγ undergoes post-translational modifications (PTMs), including acetylation, to mediate ligand responses, including on metabolic functions. Here, we report that PPARγ acetylation in macrophages promotes their infiltration into adipose tissue, exacerbating metabolic dysregulation. We generated a mouse line that expresses a macrophage-specific, constitutive acetylation-mimetic form of PPARγ (K293Qflox/flox:LysM-cre, mK293Q) to dissect the role of PPARγ acetylation in macrophages. Upon high-fat diet feeding to stimulate macrophage infiltration into adipose tissue, we assessed the overall metabolic profile and tissue-specific phenotype of the mutant mice, including responses to the PPARγ agonist Rosiglitazone. Macrophage-specific PPARγ K293Q expression promotes proinflammatory macrophage infiltration and fibrosis in epididymal white adipose tissue, but not in subcutaneous or brown adipose tissue, leading to decreased energy expenditure, insulin sensitivity, glucose tolerance, and adipose tissue function. Furthermore, mK293Q mice are resistant to Rosiglitazone-induced improvements in adipose tissue remodeling. Our study reveals that acetylation is a new layer of PPARγ regulation in macrophage activation, and highlights the importance and potential therapeutic implications of such PTMs in regulating metabolism.

The schizophrenia- and autism-associated gene, transcription factor 4 regulates the columnar distribution of layer 2/3 prefrontal pyramidal neurons in an activity-dependent manner

Disruption of the laminar and columnar organization of the brain is implicated in several psychiatric disorders. Here, we show in utero gain-of-function of the psychiatric risk gene transcription factor 4 (TCF4) severely disrupts the columnar organization of medial prefrontal cortex (mPFC) in a transcription- and activity-dependent manner. This morphological phenotype was rescued by co-expression of TCF4 plus calmodulin in a calcium-dependent manner and by dampening neuronal excitability through co-expression of an inwardly rectifying potassium channel (Kir2.1). For we believe the first time, we show that N-methyl-d-aspartate (NMDA) receptor-dependent Ca²⁺ transients are instructive to minicolumn organization because Crispr/Cas9-mediated mutation of NMDA receptors rescued TCF4-dependent morphological phenotypes. Furthermore, we demonstrate that the transcriptional regulation by the psychiatric risk gene TCF4 enhances NMDA receptor-dependent early network oscillations. Our novel findings indicate that TCF4-dependent transcription directs the proper formation of prefrontal cortical minicolumns by regulating the expression of genes involved in early spontaneous neuronal activity, and thus our results provides insights into potential pathophysiological mechanisms of TCF4-associated psychiatric disorders.

Neurodevelopmental models of transcription factor 4 deficiency converge on a common ion channel as a potential therapeutic target for Pitt Hopkins syndrome

The clinically pleiotropic gene, Transcription Factor 4 (TCF4), is a broadly expressed basic helix-loop-helix (bHLH) transcription factor linked to multiple neurodevelopmental disorders, including schizophrenia, 18q deletion syndrome, and Pitt Hopkins syndrome (PTHS). In vivo suppression of Tcf4 by shRNA or mutation by CRISPR/Cas9 in the developing rat prefrontal cortex resulted in attenuated action potential output. To explain this intrinsic excitability deficit, we demonstrated that haploinsufficiency of TCF4 lead to the ectopic expression of two ion channels, Scn10a and Kcnq1. These targets of TCF4 regulation were identified through molecular profiling experiments that used translating ribosome affinity purification to enrich mRNA from genetically manipulated neurons. Using a mouse model of PTHS (Tcf4+/tr), we observed a similar intrinsic excitability deficit, however the underlying mechanism appeared slightly different than our rat model - as Scn10a expression was similarly increased but Kcnq1 expression was decreased. Here, we show that the truncated TCF4 protein expressed in our PTHS mouse model binds to wild-type TCF4 protein, and we suggest the difference in Kcnq1 expression levels between these two rodent models appears to be explained by a dominant-negative function of the truncated TCF4 protein. Despite the differences in the underlying molecular mechanisms, we observed common underlying intrinsic excitability deficits that are consistent with ectopic expression of Scn10a. The converging molecular function of TCF4 across two independent rodent models indicates SCN10a is a potential therapeutic target for Pitt-Hopkins syndrome.