Unexpected severe consequences ofPikfyvedeletion by aP2- or Aq-promoter-driven Cre expression for glucose homeostasis and mammary gland development

Abstract

Systemic deficiency of PIKfyve, the evolutionarily conserved phosphoinositide kinase synthesizing cellular PtdIns5P and PtdIns(3,5)P2 and implicated in insulin signaling, causes early embryonic death in mice. In contrast, mice with muscle‐specific Pikfyve disruption have normal lifespan but exhibit early‐age whole‐body glucose intolerance and muscle insulin resistance, thus establishing the key role of muscle PIKfyve in glucose homeostasis. Fat and muscle tissues control postprandial glucose clearance through different mechanisms, raising questions as to whether adipose Pikfyve disruption will also trigger whole‐body metabolic abnormalities, and if so, what the mechanism might be. To clarify these issues, here we have characterized two new mouse models with adipose tissue disruption of Pikfyve through Cre recombinase expression driven by adipose‐specific aP2‐ or adiponectin (Aq) promoters. Whereas both mouse lines were ostensibly normal until adulthood, their glucose homeostasis and systemic insulin sensitivity were severely dysregulated. These abnormalities stemmed in part from accelerated fat‐cell lipolysis and elevated serum FFA. Intriguingly, aP2‐Cre‐PIKfyvefl/fl but not Aq‐Cre‐PIKfyvefl/fl females had severely impaired pregnancy‐induced mammary gland differentiation and lactogenesis, consistent with aP2‐Cre‐mediated Pikfyve excision in nonadipogenic tissues underlying this defect. Intriguingly, whereas mammary glands from postpartum control and Aq‐Cre‐PIKfyvefl/fl mice or ex vivo mammary gland explants showed profound upregulation of PIKfyve protein levels subsequent to prolactin receptor activation, such increases were not apparent in aP2‐Cre‐PIKfyvefl/fl females. Collectively, our data identify for the first time that adipose tissue Pikfyve plays a key role in the mechanisms regulating glucose homeostasis and that the PIKfyve pathway is critical in mammary epithelial differentiation during pregnancy and lactogenesis downstream of prolactin receptor signaling.

Active vacuolar H+ ATPase and functional cycle of Rab5 are required for the vacuolation defect triggered by PtdIns(3,5)P2 loss under PIKfyve or Vps34 deficiency

“…For example, terminally differentiated 3T3L1 adipocytes in culture, as opposed to the rapidly dividing precursor 3T3L1 fibroblastic cells, do not form cytoplasmic vacuoles under pharmacological inhibition or expression of the dominantinterfering kinase-deficient mutant of PIKfyve (27,50). Likewise, fat cells, muscle cells, or glomeruli podocytes in the context of the respective adipose-specific, muscle-specific or podocytes-specific mouse model with Pikfyve inactivation through Cre recombinase expression driven by the corresponding promoters, do not exhibit cytoplasmic vacuoles in situ (22,23,28,64). Whereas in these mouse models incomplete Pikfyve inactivation might be an admissible cause for lack of vacuoles, it is remarkable that mitotic podocytes that outgrow in a culture from the very same nonvacuolating terminally differentiated glomerular podocytes exhibit the vacuolation phenomenon (64).…”

Inhibition of PIKfyve Ameliorates the Proliferation and Migration of Vascular Smooth Muscle Cells and Vascular Intima Hyperplasia By Reducing mTORC1 Activity

“…Previous study has demonstrated that PIKfyve and its downstream signaling cascade are essential for glucose homeostasis in adipocytes and participate in glucose uptake in skeletal muscle. 17 , 18 Whether PIKfyve is involved in PDGF-BB–induced metabolic switch in VSMCs remains unknown. Interestingly, the enhanced glycolysis induced by PDGF-BB was totally terminated after inhibition of PIKfyve in this study.…”

Firemaster® 550 and its components isopropylated triphenyl phosphate and triphenyl phosphate enhance adipogenesis and transcriptional activity of peroxisome proliferator activated receptor (Pparγ) on the adipocyte protein 2 (aP2) promoter

“…Furthermore, our data show that IPTP- and TPP-induced aP2 expression is mediated through direct PPARγ activation since the expression of aP2 was inhibited by the PPARγ antagonist GW9662. The functional implications of aP2 upregulation are of particular importance, as its expression is highly correlated with metabolic disorders [ 38 , 39 ].…”