Effects of phorbol ester-sensitive PKC (c/nPKC) activation on the production of adiponectin in 3T3-L1 adipocytes

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Stem cell transplantation impairs dendritic cell trafficking and herpesvirus immunity

Long-term survivors after hematopoietic stem cell transplantation are at high risk of infection, which accounts for one-third of all deaths related to stem cell transplantation. Little is known about the cause of inferior host defense after immune cell reconstitution. Here, we exploited a murine syngeneic BM transplantation (BMT) model of late infection with murine gammaherpesvirus 68 (MHV-68) to determine the role of conventional DC (cDC) trafficking in adaptive immunity in BMT mice. After infection, the expression of chemokine Ccl21 in the lung is reduced and the migration of cDCs into lung draining lymph nodes (dLNs) is impaired in BMT mice, limiting the opportunity for cDCs to prime Th cells in the dLNs. While cDC subsets are redundant in priming Th1 cells, Notch2 functions in cDC2s are required for priming increased Th17 responses in BMT mice, and cDC1s can lessen this activity. Importantly, Th17 cells can be primed both in the lungs and dLNs, allowing for increased Th17 responses without optimum cDC trafficking in BMT mice. Taken together, impaired cDC trafficking in BMT mice reduces protective Th1 responses and allows increased pathogenic Th17 responses. Thus, we have revealed a previously unknown mechanism for BMT procedures to cause long-term inferior immune responses to herpes viral infection.

Elevated mitochondrial biogenesis in skeletal muscle is associated with testosterone-induced body weight loss in male mice

Androgen reduces fat mass, although the underlying mechanisms are unknown. Here, we examined the effect of testosterone on heat production and mitochondrial biogenesis. Testosterone-treated mice exhibited elevated heat production. Treatment with testosterone increased the expression level of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), ATP5B and Cox4 in skeletal muscle, but not that in brown adipose tissue and liver. mRNA levels of genes involved in mitochondrial biogenesis were elevated in skeletal muscle isolated from testosterone-treated male mice, but were down-regulated in androgen receptor deficient mice. These results demonstrated that the testosterone-induced increase in energy expenditure is derived from elevated mitochondrial biogenesis in skeletal muscle.

Dehydroepiandrosterone reduces preadipocyte proliferation via androgen receptor

Several studies have suggested that both testosterone and dehydroepiandrosterone (DHEA) have weight-reducing and antidiabetic effects, especially in rodent studies; however, the precise mechanism of their action remains unclear. Here, we investigated the effect of DHEA on cell growth in adipose tissue. The appearance of senescence-associated β-galactosidase in stromal vascular fraction (SVF) isolated from Otsuka Long-Evans Tokushima fatty rats, an animal model of inherent obese type 2 diabetes, was prevented by DHEA administration. Next, the effects of DHEA and testosterone were compared in vivo and in vitro to evaluate whether these hormones influence cell growth in adipose tissue. Both DHEA and testosterone reduced body weight and epididymal fat weight equivalently when administered for 4 wk. To assess the effect of DHEA and testosterone on cell growth in adipose tissue, 5-bromo-2'-deoxyuridine (BrdU) uptake by SVF was measured. Quantification analysis of BrdU uptake by examining DNA isolated from each SVF revealed that treatment with DHEA and testosterone reduced cell replication. These results indicated that DHEA- and testosterone-induced decreased adiposity was associated with reduced SVF growth. Incubation with DHEA and testosterone equally decreased BrdU uptake by 3T3-L1 preadipocytes. Pretreatment with the androgen receptor (AR) inhibitor flutamide, but not the estrogen receptor inhibitor fulvestrant, abolished these effects. Knockdown of AR with siRNA also inhibited DHEA-induced decreases in BrdU uptake. These results suggest that DHEA-induced growth suppression of preadipocytes is mediated via AR. Therefore, both DHEA and testosterone similarly decrease adipocyte growth possibly via a common mechanism.

Neutral sphingomyelinase 2 (nSMase2) is a phosphoprotein regulated by calcineurin (PP2B)

We previously reported that exposure of human airway epithelial cells to oxidative stress increased ceramide generation via specific activation of neutral sphingomyelinase2 (nSMase2). Here we show that nSMase2 is a phosphoprotein exclusively phosphorylated at serine residues. The level of nSMase2 phosphorylation can be modulated by treatment with anisomycin or phorbol 12-myristate 13-acetate (PMA/12-O-tetradecanoylphorbol-13-acetate), suggesting that p38 mitogen-activated protein kinase (MAPK) and protein kinases Cs are upstream of nSMase2 phosphorylation. Oxidative stress enhances both the activity and phosphorylation of nSMase2. Strikingly, we show here that nSMase2 is bound directly by the phosphatase calcineurin (CaN), which acts as an on/off switch for nSMase2 phosphorylation in the presence or absence of oxidative stress. Specifically, CaN is being inhibited/degraded and therefore does not bind nSMase2 under oxidative stress, and a mutant nSMase2 that lacks the CaN binding site exhibits constitutively elevated phosphorylation and increased activity relative to wild type nSMase2. Importantly, the phosphorylation and activity of the mutant no longer responds to oxidative stress, confirming that CaN is the critical link that allows oxidative stress to modulate nSMase2 phosphorylation and function.