Loss of SATB1 Induces p21-Dependent Cellular Senescence in Post-mitotic Dopaminergic Neurons.

Cellular senescence is a mechanism used by mitotic cells to prevent uncontrolled cell division. As senescent cells persist in tissues, they cause local inflammation and are harmful to surrounding cells, contributing to aging. Generally, neurodegenerative diseases, such as Parkinson's, are disorders of aging. The contribution of cellular senescence to neurodegeneration is still unclear. SATB1 is a DNA binding protein associated with Parkinson's disease. We report that SATB1 prevents cellular senescence in post-mitotic dopaminergic neurons. Loss of SATB1 causes activation of a cellular senescence transcriptional program in dopamine neurons both in human stem cell-derived dopaminergic neurons and in mice. We observed phenotypes that are central to cellular senescence in SATB1 knockout dopamine neurons in vitro and in vivo. Moreover, we found that SATB1 directly represses expression of the pro-senescence factor p21 in dopaminergic neurons. Our data implicate senescence of dopamine neurons as a contributing factor in the pathology of Parkinson's disease.

Distinct intracellular sAC-cAMP domains regulate ER Ca2+ signaling and OXPHOS function.

cAMP regulates a wide variety of physiological functions in mammals. This single second messenger can regulate multiple, seemingly disparate functions within independently regulated cell compartments. We have previously identified one such compartment inside the matrix of the mitochondria, where soluble adenylyl cyclase (sAC) regulates oxidative phosphorylation (OXPHOS). We now show that sAC knockout fibroblasts have a defect in OXPHOS activity and attempt to compensate for this defect by increasing OXPHOS proteins. Importantly, sAC knockout cells also exhibit decreased probability of endoplasmic reticulum (ER) Ca2+ release associated with diminished phosphorylation of the inositol 3-phosphate receptor. Restoring sAC expression exclusively in the mitochondrial matrix rescues OXPHOS activity and reduces mitochondrial biogenesis, indicating that these phenotypes are regulated by intramitochondrial sAC. In contrast, Ca2+ release from the ER is only rescued when sAC expression is restored throughout the cell. Thus, we show that functionally distinct, sAC-defined, intracellular cAMP signaling domains regulate metabolism and Ca2+ signaling.

cAMP and mitochondria.

Phosphorylation of mitochondrial proteins has emerged as a major regulatory mechanism for metabolic adaptation. cAMP signaling and PKA phosphorylation of mitochondrial proteins have just started to be investigated, and the presence of cAMP-generating enzymes and PKA inside mitochondria is still controversial. Here, we discuss the role of cAMP in regulating mitochondrial bioenergetics through protein phosphorylation and the evidence for soluble adenylyl cyclase as the source of cAMP inside mitochondria.

The soluble guanylyl cyclase activator YC-1 increases intracellular cGMP and cAMP via independent mechanisms in INS-1E cells.

In addition to increasing cGMP, the soluble guanylyl cyclase (sGC) activator 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1) can elevate intracellular cAMP levels. This response was assumed to be as a result of cGMP-dependent inhibition of cAMP phosphodiesterases; however, in this study, we show that YC-1-induced cAMP production in the rat pancreatic beta cell line INS-1E occurs independent of its function as a sGC activator and independent of its ability to inhibit phosphodiesterases. This YC-1-induced cAMP increase is dependent upon soluble adenylyl cyclase and not on transmembrane adenylyl cyclase activity. We previously showed that soluble adenylyl cyclase-generated cAMP can lead to extracellular signal-regulated kinase activation and that YC-1-stimulated cAMP production also stimulates extracellular signal-regulated kinase. Although YC-1 has been used as a tool for investigating sGC and cGMP-mediated pathways, this study reveals cGMP-independent pharmacological actions of this compound.