Increased Levels of cAMP by the Calcium-Dependent Activation of Soluble Adenylyl Cyclase in Parkin-Mutant Fibroblasts

Abstract

Almost half of autosomal recessive early-onset parkinsonism has been associated with mutations in PARK2, coding for parkin, which plays an important role in mitochondria function and calcium homeostasis. Cyclic adenosine monophosphate (cAMP) is a major second messenger regulating mitochondrial metabolism, and it is strictly interlocked with calcium homeostasis. Parkin-mutant (Pt) fibroblasts, exhibiting defective mitochondrial respiratory/OxPhos activity, showed a significant higher value of basal intracellular level of cAMP, as compared with normal fibroblasts (CTRL). Specific pharmacological inhibition/activation of members of the adenylyl cyclase- and of the phosphodiesterase-families, respectively, as well as quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis, indicate that the higher level of cAMP observed in Pt fibroblasts can contribute to a higher level of activity/expression by soluble adenylyl cyclase (sAC) and to low activity/expression of the phosphodiesterase isoform 4 (PDE4). As Ca2+ regulates sAC, we performed quantitative calcium-fluorimetric analysis, showing a higher level of Ca2+ in the both cytosol and mitochondria of Pt fibroblasts as compared with CTRL. Most notably, inhibition of the mitochondrial Ca2+ uniporter decreased, specifically the cAMP level in PD fibroblasts. All together, these findings support the occurrence of an altered mitochondrial Ca2+-mediated cAMP homeostasis in fibroblasts with the parkin mutation.

Bicarbonate, carbon dioxide and pH sensing via mammalian bicarbonate-regulated soluble adenylyl cyclase

“…sAC has additional functions which have been demonstrated both genetically and pharmacologically, but which have not, at least by currently available findings, been directly ascribed to its CO 2 /HCO 3 − /pH-sensing capabilities. In addition to CO 2 /HCO 3 − /pH, sAC activity can be regulated by Ca 2+ , ATP and multiple regulatory domains located in the C-terminus of the protein [35,36,[44][45][46][47][48][49]. A recent role for sAC has been uncovered in the liver.…”

“…1 mM) and an overall stimulation of sAC activity at cellular levels of ATP [41–43]. This effect is physiologically relevant, as activation of sAC in response to an increase in intracellular levels of Ca 2+ was observed in several systems [44–48]. Even when sAC is fully activated, its affinity for ATP ( K m of approx.…”

PGC-1s in the Spotlight with Parkinson’s Disease

“…Indeed, complex I represents a sensitive target in neuronal bioenergetic metabolism, due to its controlling role in mitochondrial oxidative phosphorylation (OXPHOS) efficiency and capacity, especially during aging [ 31 , 32 , 33 ]. Thereafter, numerous other compounds have been utilized in animal models to induce motor symptoms of PD, mainly via the inhibition of the respiratory chain complexes with the consequent generation of oxidative stress and impaired calcium homeostasis which cause cell death in the DA neuronal population [ 34 , 35 ].…”

Multitasking guardian of mitochondrial quality: Parkin function and Parkinson’s disease

“…Moreover, an increase in ROS production [ 147 ], higher levels of protein oxidation [ 144 ] and lower activity of the antioxidant enzymes (MnSOD, GPx and catalase) [ 147 ] have been observed in addition to higher levels of cytosolic and mitochondrial Ca 2+ [ 151 ].…”