Ding Xie

Impact of Glucose-Dependent Insulinotropic Peptide on Age-Induced Bone Loss†

GIP is an important hormonal link between nutrition and bone formation. We show for the first time that BMSCs express functional GIP receptors, that expression decreases with aging, and that elevations in GIP can prevent age‐associated bone loss.

Effects of glucose-dependent insulinotropic peptide on behavior

Glucose-dependent insulinotropic peptide (GIP) is an incretin hormone that rises rapidly in response to nutrient ingestion. The GIP receptor is widely expressed in the brain including the brain stem, telencephalon, diencephalon, olfactory bulb, pituitary, and cerebellum. Until recently it was not clear what the endogenous ligand for this receptor was because no GIP expression had been demonstrated in the brain. GIP synthesis has now been documented in the dentate gyrus of the hippocampus. To define GIP effects on behavior we utilized a mouse model a GIP-overexpressing transgenic mouse (GIP Tg). Specifically, anxiety-related behavior, exploration, memory, and nociception were examined. Compared to age-matched adult male C57BI/6 controls GIP Tg mice displayed enhanced exploratory behavior in the open-field locomotor activity test. GIP Tg mice also demonstrated increased performance in some of the motor function tests. These data suggest that the GIP receptor plays a role in the regulation of locomotor activity and exploration. To our knowledge, this is the first report of effects of GIP on behavior.

Obesity, hypertension and aldosterone: is leptin the link?

Obesity is a serious health hazard with rapidly increasing prevalence in the United States. In 2014, the World Health Organization estimated that nearly 2 billion people worldwide were overweight with an estimated 600 million of these obese. Obesity is associated with many chronic diseases, including cardiovascular disease and hypertension. Data from the Framingham Heart study suggest that approximately 78% of the risk for hypertension in men and 65% in women is related to excess body weight, a relationship that is further supported by studies showing increases in blood pressure with weight gain and decreases with weight loss. However, the exact mechanism by which excess body fat induces hypertension remains poorly understood. Several clinical studies have demonstrated elevated plasma aldosterone levels in obese individuals, especially those with visceral adiposity, with decreased aldosterone levels measured in concert with reduced blood pressure following weight loss. Since aldosterone is a mineralocorticoid hormone that regulates blood volume and pressure, serum aldosterone levels may link obesity and hypertension. Nevertheless, the mechanism by which obesity induces aldosterone production is unclear. A recent study by Belin de Chantemele and coworkers suggests that one adipose-released factor, leptin, is a direct agonist for aldosterone secretion; other adipose-related factors may also contribute to elevated aldosterone levels in obesity, such as very low-density lipoprotein (VLDL), the levels of which are elevated in obesity and which also directly stimulates aldosterone biosynthesis. This focused review explores the possible roles of leptin and VLDL in modulating aldosterone secretion to underlie obesity-associated hypertension.

The effect of pioglitazone on aldosterone and cortisol production in HAC15 human adrenocortical carcinoma cells.

Pioglitazone belongs to the class of drugs called thiazolidinediones (TZDs), which are widely used as insulin sensitizers in the treatment of diabetes. A major side effect of TZDs is fluid retention. The steroid hormone aldosterone also promotes sodium and fluid retention; however, the effect of pioglitazone on aldosterone production is controversial. We analyzed the effect of pioglitazone alone and in combination with angiotensin II (AngII) on the late rate-limiting step of adrenocortical steroidogenesis in human adrenocortical carcinoma HAC15 cells. Treatment with pioglitazone for 24 h significantly increased the expression of CYP11B2 and enhanced AngII-induced CYP11B2 expression. Despite the observed changes in mRNA levels, pioglitazone significantly inhibited AngII-induced aldosterone production and CYP11B2 protein levels. On the other hand, pioglitazone stimulated the expression of the unfolded protein response (UPR) marker DDIT3, with this effect occurring at early times and inhibitable by the PPARγ antagonist GW9962. The levels of DDIT3 (CHOP) and phospho-eIF2α (Ser51), a UPR-induced event that inhibits protein translation, were also increased. Thus, pioglitazone promotes CYP11B2 expression but nevertheless inhibits aldosterone production in AngII-treated HAC15 cells, likely by blocking global protein translation initiation through DDIT3 and phospho-eIF2α. In contrast, pioglitazone promoted AngII-induced CYP11B1 expression and cortisol production. Since cortisol enhances lipolysis, this result suggests the possibility that PPARs, activated by products of fatty acid oxidation, stimulate cortisol secretion to promote utilization of fatty acids during fasting. In turn, the ability of pioglitazone to stimulate cortisol production could potentially underlie the effects of this drug on fluid retention.

Pine Oil Effects on Chemical and Thermal Injury in Mice and Cultured Mouse Dorsal Root Ganglion Neurons

A commercial resin‐based pine oil (PO) derived from Pinus palustris and Pinus elliottii was the major focus of this investigation. Extracts of pine resins, needles, and bark are folk medicines commonly used to treat skin ailments, including burns. The American Burn Association estimates that 500,000 people with burn injuries receive medical treatment each year; one‐half of US burn victims are children, most with scald burns. This systematic study was initiated as follow‐up to personal anecdotal evidence acquired over more than 10 years by MH Bhattacharyya regarding POs efficacy for treating burns. The results demonstrate that PO counteracted dermal inflammation in both a mouse ear model of contact irritant‐induced dermal inflammation and a second degree scald burn to the mouse paw. Furthermore, PO significantly counteracted the tactile allodynia and soft tissue injury caused by the scald burn. In mouse dorsal root ganglion neuronal cultures, PO added to the medium blocked adenosine triphosphate‐activated, but not capsaicin‐activated, pain pathways, demonstrating specificity. These results together support the hypothesis that a pine‐oil‐based treatment can be developed to provide effective in‐home care for second degree burns. Copyright

Distinct Effects of Different Phosphatidylglycerol Species on Mouse Keratinocyte Proliferation

We have previously shown that liposomes composed of egg-derived phosphatidylglycerol (PG), with a mixed fatty acid composition (comprising mainly palmitate and oleate), inhibit the proliferation and promote the differentiation of rapidly dividing keratinocytes, and stimulate the growth of slowly proliferating epidermal cells. To determine the species of PG most effective at modulating keratinocyte proliferation, primary mouse keratinocytes were treated with different PG species, and proliferation was measured. PG species containing polyunsaturated fatty acids were effective at inhibiting rapidly proliferating keratinocytes, whereas PG species with monounsaturated fatty acids were effective at promoting proliferation in slowly dividing cells. Thus, palmitoyl-arachidonyl-PG (16∶0/20∶4), palmitoyl-linoleoyl-PG (16∶0/18∶2), dilinoleoyl-PG (18∶2/18∶2) and soy PG (a PG mixture with a large percentage of polyunsaturated fatty acids) were particularly effective at inhibiting proliferation in rapidly dividing keratinocytes. Conversely, palmitoyl-oleoyl-PG (16∶0/18∶1) and dioleoyl-PG (18∶1/18∶1) were especially effective proproliferative PG species. This result represents the first demonstration of opposite effects of different species of a single class of phospholipid and suggests that these different PG species may signal to diverse effector enzymes to differentially affect keratinocyte proliferation and normalize keratinocyte proliferation. Thus, different PG species may be useful for treating skin diseases characterized by excessive or insufficient proliferation.

The potential use of protein kinase D inhibitors for prevention/treatment of epidermal tumors

BACKGROUND The serine/threonine kinase protein kinase D (PKD) has been proposed to be a pro-proliferative, anti-differentiative signal in epidermal keratinocytes. Indeed, the phorbol ester tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA) induces biphasic PKD activation, which mirrors the biphasic response of initial differentiation followed by proliferation and tumor promotion seen in TPA-treated keratinocytes in vitro and epidermis in vivo. OBJECTIVE Our objective was to test the idea that PKDs pro-proliferative and/or anti-differentiative effects in keratinocytes contribute to TPA-induced tumorigenesis. METHODS Using western analysis and assays of keratinocyte proliferation and differentiation, we investigated the effect of inhibitors of PKD on keratinocyte function. RESULTS We found that overexpression of a constitutively active PKD mutant increased, and of a dominant-negative PKD mutant decreased, keratinocyte proliferation. A recently described selective PKD inhibitor showed low potency to inhibit keratinocyte proliferation or PKD activation. Therefore, we tested the ability of known only relatively selective PKD inhibitors on keratinocyte function and protein kinase activation. H89 {N-[2-(p-bromocinnamylamino) ethyl]-5-isoquinoline-sulfonamide}, a reported inhibitor of PKD and cAMP-dependent protein kinase, enhanced the effect of a differentiating agent on a marker of keratinocyte differentiation. Another reported non-selective PKD inhibitor, resveratrol stimulated differentiation and inhibited proliferation. The protein kinase C/PKD inhibitor Gö6976 blocked the increase in proliferation (as measured by DNA specific activity) induced by chronic TPA without affecting the initial TPA-elicited differentiation. CONCLUSION Our results support the idea that relatively selective PKD inhibitors, such as Gö6976, H89 and resveratrol, might be useful for preventing/treating epidermal tumorigenesis without affecting keratinocyte differentiation.

Carboxy-terminal PTH fragments stimulate [3H]thymidine incorporation in vascular endothelial cells

We have previously reported that the intact PTH molecule (1-84) stimulates proliferation of human umbilical vein endothelial cells (HUVECs). To define the bioactive portion of the PTH molecule we utilized amino, mid and carboxy-terminal PTH fragments. Carboxy- but not amino-terminal fragments were equivalent to the intact PTH molecule in stimulating [3H]thymidine incorporation in HUVEC. Carboxy- but not amino-terminal PTH fragments increased intracellular calcium. Blocking the rise in intracellular calcium with calcium chelators abolished PTHs proliferative effect on HUVEC. In contrast to PTH 1-84, the carboxy-terminal fragment effect on [3H]thymidine incorporation was blocked by KN-93 an inhibitor of CaM kinase II. Taken together, these data suggest that the carboxy-terminal PTH is (or contains) the bioactive fragment responsible for the changes in intracellular calcium and thymidine incorporation in HUVEC stimulated with the intact PTH molecule.

Soy Phosphatidylglycerol Reduces Inflammation in a Contact Irritant Ear Edema Mouse Model In Vivo

We have previously shown that phosphatidylglycerol (PG) regulates the function of keratinocytes, the predominant cells that compose the epidermis, inhibiting the proliferation of rapidly dividing keratinocytes. In particular, soy PG, a PG mixture with a high proportion of polyunsaturated fatty acids, is efficacious at inhibiting these proliferating keratinocytes. Psoriasis is a skin disorder characterized by hyperproliferation of keratinocytes and inflammation. Data in the lung suggest that PG in pulmonary surfactant inhibits inflammation. To investigate the possibility of using PG containing polyunsaturated fatty acids for the treatment of psoriasis, we examined the effect of soy PG on inflammation induced by the application of 12-O-tetradecanoylphorbol 13-acetate (TPA), a contact irritant, to mouse ears in vivo. We monitored ear thickness and weight as a measure of ear edema, as well as CD45-positive immune cell infiltration. Our results indicate that soy PG when applied together with 1,25-dihydroxyvitamin D3 (vitamin D), an agent known to acutely disrupt the skin barrier, suppressed ear edema and inhibited the infiltration of CD45-positive immune cells. On the other hand, neither PG nor vitamin D alone was effective. The combination also decreased tumor necrosis factor-α (TNFα) levels. This result suggested the possibility that PG was not permeating the skin barrier efficiently. Therefore, in a further study we applied PG in a penetration-enhancing vehicle and found that it inhibited inflammation induced by the phorbol ester and decreased CD45-positive immune cell infiltration. Our results suggest the possibility of using soy PG as a topical treatment option for psoriasis.