Single-cell transcriptomic analysis identifies downregulated phosphodiesterase 8B as a novel oncogene in IDH-mutant glioma.

Introduction: Glioma, a prevalent and deadly brain tumor, is marked by significant cellular heterogeneity and metabolic alterations. However, the comprehensive cell-of-origin and metabolic landscape in high-grade (Glioblastoma Multiforme, WHO grade IV) and low-grade (Oligoastrocytoma, WHO grade II) gliomas remains elusive. Methods: In this study, we undertook single-cell transcriptome sequencing of these glioma grades to elucidate their cellular and metabolic distinctions. Following the identification of cell types, we compared metabolic pathway activities and gene expressions between high-grade and low-grade gliomas. Results: Notably, astrocytes and oligodendrocyte progenitor cells (OPCs) exhibited the most substantial differences in both metabolic pathways and gene expression, indicative of their distinct origins. The comprehensive analysis identified the most altered metabolic pathways (MCPs) and genes across all cell types, which were further validated against TCGA and CGGA datasets for clinical relevance. Discussion: Crucially, the metabolic enzyme phosphodiesterase 8B (PDE8B) was found to be exclusively expressed and progressively downregulated in astrocytes and OPCs in higher-grade gliomas. This decreased expression identifies PDE8B as a metabolism-related oncogene in IDH-mutant glioma, marking its dual role as both a protective marker for glioma grading and prognosis and as a facilitator in glioma progression.

Inhibition of phosphodiesterase PDE8B reduces activation of primordial follicles in mouse ovaries.

In the ovaries, cyclic adenosine 3',5'-monophosphate (cAMP) is a second messenger supporting the generation of steroids. Phosphodiesterases (PDEs) are regulators of intracellular cAMP, and therefore, potential regulators of ovarian function. Interestingly, the family of PDE genes are differentially expressed in human oocytes and granulosa cells from primordial and primary follicles, suggesting diverse roles. In this study, we addressed the functions of PDE3B and PDE8B in primordial follicle regulation using inhibitors of PDE3B and PDE8B in murine ovary primary in vitro cultures. Inhibition of PDE8B in ovarian cultures prevented primordial follicle activation, while inhibition of PDE3B had no effect on follicle distribution in the ovary, under the tested conditions. As cAMP levels may increase steroid levels, we assessed the protein levels of the steroidogenic acute regulatory protein (StAR) and aromatase enzymes, and found that inhibition of PDE3B reduced StAR protein levels, whereas inhibition of PDE8 did not alter StAR expression in our murine ovary culture system conditions. Our results showed that ketotifen-induced inhibition of PDE8B can decrease primordial follicle activation, whereas we observed no effect of follicle distribution, when PDE3B was inhibited. Expression of the StaR enzyme was not altered when PDE8B was inhibited, which might reflect not sufficient inhibition by ketotifen to induce StAR alterations, or redundant mechanisms.

cAMP-specific phosphodiesterase 8A and 8B isoforms are differentially expressed in human testis and Leydig cell tumor.

Cyclic adenosine monophosphate/Protein kinase A (cAMP/PKA) signaling pathway is the master regulator of endocrine tissue function. The level, compartmentalization and amplitude of cAMP response are finely regulated by phosphodiesterases (PDEs). PDE8 is responsible of cAMP hydrolysis and its expression has been characterized in all steroidogenic cell types in rodents including adrenal and Leydig cells in rodents however scarce data are currently available in humans. Here we demonstrate that human Leydig cells express both PDE8A and PDE8B isoforms. Interestingly, we found that the expression of PDE8B but not of PDE8A is increased in transformed Leydig cells (Leydig cell tumors-LCTs) compared to non-tumoral cells. Immunofluorescence analyses further reveals that PDE8A is also highly expressed in specific spermatogenic stages. While the protein is not detected in spermatogonia it accumulates nearby the forming acrosome, in the trans-Golgi apparatus of spermatocytes and spermatids and it follows the fate of this organelle in the later stages translocating to the caudal part of the cell. Taken together our findings suggest that 1) a specific pool(s) of cAMP is/are regulated by PDE8A during spermiogenesis pointing out a possible new role of this PDE8 isoform in key events governing the differentiation and maturation of human sperm and 2) PDE8B can be involved in Leydig cell transformation.

Pde8b haploinsufficiency in mice is associated with modest adrenal defects, impaired steroidogenesis, and male infertility, unaltered by concurrent PKA or Wnt activation.

PDE8B, PRKAR1A and the Wnt/ß-catenin signaling are involved in endocrine disorders. However, how PDEB8B interacts with both Wnt and protein kinase A (PKA) signaling in vivo remains unknown. We created a novel Pde8b knockout mouse line (Pde8b-/-); Pde8b haploinsufficient (Pde8b+/-) mice were then crossed with mice harboring: (1) constitutive beta-catenin activation (Pde8b+/-;ΔCat) and (2) Prkar1a haploinsufficieny (Pde8b+/-;Prkar1a+/-). Adrenals and testes from mice (3-12-mo) were evaluated in addition to plasma corticosterone, aldosterone and Dkk3 concentrations, and the examination of expression of steroidogenesis-, Wnt- and cAMP/PKA-related genes. Pde8b-/- male mice were infertile with down-regulation of the Wnt/ß-catenin pathway which did not change significantly in the Pde8b+/-;ΔCat mice. Prkar1a haploinsufficiency also did not change the phenotype significantly. In vitro studies showed that PDE8B knockdown upregulated the Wnt pathway and increased proliferation in CTNNB1-mutant cells, whereas it downregulated the Wnt pathway in PRKAR1A-mutant cells. These data support an overall weak, if any, role for PDE8B in adrenocortical tumorigenesis, even when co-altered with Wnt signaling or PKA upregulation; on the other hand, PDE8B appears to play a significant role in male fertility.

PDE8B mutation is not associated with Parkinson's disease in a Taiwanese population.

Mutations in the phosphodiesterase 8B gene (PDE8B) were recently linked to autosomal-dominant striatal degeneration clinically presenting as slowly progressive parkinsonism. PDE8B degrades cyclic adenosine monophosphate (cAMP), a second messenger involved in dopamine signaling. Dopamine deficiency is the pathognomonic feature of Parkinson's disease (PD). Few studies have explored the role of PDE8B in PD. We aim to address the genetic contribution of PDE8B in early-onset and familial PD in a Taiwanese population. Among 642 participants, we sequenced the exon containing previously reported mutations and exon-intron boundaries of PDE8B in 196 PD pedigrees without known PD-causative gene mutations, 207 patients with early-onset PD (age of onset <50 years), and 239 ethnicity-matched controls. We did not find any coding variants or previously reported mutations, suggesting that PDE8B mutations are not a common cause of familial or early-onset PD in this Taiwanese population.