Publications

APOBEC3G and APOBEC3F are human cytidine deaminases that serve as innate antiviral defense mechanisms primarily by introducing C-to-U changes in the minus strand DNA of retroviruses during replication (resulting in G-to-A mutations in the genomic sense strand sequence). The HIV-1 Vif protein counteracts this defense by promoting the proteolytic degradation of APOBEC3G and APOBEC3F in the host cell. In the absence of Vif expression, APOBEC3 is incorporated into HIV-1 virions and the viral genome undergoes extensive G-to-A mutation, or "hypermutation", typically rendering it non-viable within a single replicative cycle. Consequently, Vif is emerging as an attractive target for pharmacological intervention and therapeutic vaccination. Although a highly effective Vif inhibitor may result in mutational meltdown of the viral quasispecies, a partially effective Vif inhibitor may accelerate the evolution of drug resistance and immune escape due to the codon structure and recombinogenic nature of HIV-1. This hypothesis rests on two principal assumptions which are supported by experimental evidence: a) there is a dose response between intracellular APOBEC concentration and degree of viral hypermutation, and, b) HIV-1 can tolerate an elevated mutation rate, and a true error or extinction threshold is as yet undetermined. Rigorous testing of this hypothesis will have timely and critical implications for the therapeutic management of HIV/AIDS, and delve into the complexities underlying the induction of lethal mutagenesis in a viral pathogen.

Symptoms of T cell hyperactivation shape the course and outcome of HIV-1 infection, but the mechanism(s) underlying this chronic immune activation are not well understood. We find that the viral transactivator Tat promotes hyperactivation of T cells by blocking the nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase SIRT1. Tat directly interacts with the deacetylase domain of SIRT1 and blocks the ability of SIRT1 to deacetylate lysine 310 in the p65 subunit of NF-kappaB. Because acetylated p65 is more active as a transcription factor, Tat hyperactivates the expression of NF-kappaB-responsive genes, a function lost in SIRT1-/- cells. These results support a model where the normal function of SIRT1 as a negative regulator of T cell activation is suppressed by Tat during HIV infection. These events likely contribute to the state of immune cell hyperactivation found in HIV-infected individuals.

While psoriasis is one of the most common skin disorders in humans, effective, safe and inexpensive treatments are still largely unavailable. Chinese herbal medicine (CHM) has been used for centuries for treating psoriasis and several reports claim that systemic administration of one such CHM, Tuhuai, mainly composed of flos sophorae, smilax glabra roxb and licorice, is effective in psoriasis. However, the mechanisms by which this CHM improves psoriasis are not yet clear. Two universal features of psoriasis are epidermal hyperplasia and inflammation. Moreover, drugs that specifically inhibit epidermal hyperplasia and/or inflammation are widely used to treat psoriasis. Here, we investigated whether topical applications of Tuhuai extract exhibit anti-proliferative and anti-inflammatory activities in two murine models of inflammatory dermatoses. To assess Tuhuai's potential anti-proliferative effect, we disrupted epidermal barrier function twice-daily for 4 days in normal hairless mice followed by topical applications of either 1% Tuhuai extract or Vehicle to both flanks immediately after each barrier perturbation. Changes in epidermal proliferation and apoptosis were evaluated by immunohistochemistry and TUNEL staining. To assess the anti-inflammatory effects of Tuhuai, both irritant (phorbol ester) and acute allergic contact dermatitis (oxazolone) models were used. Whereas topical Tuhuai extract did not alter epidermal proliferation or induce irritation in normal skin, it both reduced epidermal hyperplasia in the epidermal hyperproliferative model, and reduced inflammation in both irritant and allergic contact dermatitis models. As topical Tuhuai extract exhibits anti-proliferative and anti-inflammatory properties in a variety of human models of inflammatory dermatoses, Tuhuai could provide an effective, relatively safe and inexpensive therapeutic alternative for the treatment of inflammatory dermatoses, including psoriasis.

Unintentional weight loss may occur spontaneously in older humans and animals. Further weight losses after surgery or illness in the older patients result in increased morbidity, mortality, and hospital readmission rate. A growing body of work has shown increased appetite and weight gain in response to administration of ghrelin, the "hunger hormone." We conducted two studies in senescent male Brown Norway rats to assess the ability of peripheral administration of ghrelin to increase body weight and food intake. One study assessed the effect of 2 wk of daily subcutaneous ghrelin administration (1 mg.kg(-1).day(-1)) to senescent rats in a baseline condition; a second study used the same administration protocol in an interventional experiment with aged rats subjected to a surgery with 10-15% blood loss as a model of elective surgery. In both studies, animals receiving ghrelin maintained their body weights, whereas control animals lost weight. Body weight stability was achieved in ghrelin-treated animals despite a lack of increase in daily or cumulative food intake in both experiments. Hormone and proinflammatory cytokine levels were measured before surgery and after 14 days of treatment. Ghrelin treatment appeared to blunt declining ghrelin levels and also to blunt cytokine increases seen in the surgical control group. The ability of peripheral ghrelin treatment to maintain body weights of senescent rats without concomitant increases in food intake may be due to its known ability to decrease sympathetic activity and metabolic rate, perhaps by limiting cytokine-driven inflammation.

AIMS

Sphingosine-1-phosphate (S1P) plays a vital role in cytoskeletal rearrangement, development, and apoptosis. Sphingosine kinase-1 (SphK1), the key enzyme catalyzing the formation of S1P, mediates ischaemic preconditioning. Ischaemic postconditioning (POST) has been shown to protect hearts against ischaemia/reperfusion injury (IR). To date, no studies have examined the role of SphK1 in POST.

METHODS AND RESULTS

Wild-type (WT) and SphK1 null (KO) mouse hearts were subjected to IR (45 min of global ischaemia and 45 min of reperfusion) in a Langendorff apparatus. Left ventricular developed pressure (LVDP), maximum velocity of increase or decrease of LV pressure (+/-dP/dtmax), and LV end-diastolic pressure (LVEDP) were recorded. Infarction size was measured by 1% triphenyltetrazolium chloride staining. POST, consisting of 5 s of ischaemia and 5 s of reperfusion for three cycles after the index ischaemia, protected hearts against IR: recovery of LVDP and +/-dP/dtmax were elevated; LVEDP was decreased; infarction size (% of risk area) was reduced from 40 +/- 2% in the control group to 29 +/- 2% of the risk area in the POST group (P < 0.05, n = 4 per group). Phosphorylation of Akt and extracellular signal-regulated kinases detected by Western blotting was increased at 10 min of reperfusion. The protection induced by POST was abolished in KO hearts. Infarction size in KO hearts (57 +/- 5%) was not different from the KO control group (53 +/- 5% of risk area, n = 4, P = NS).

CONCLUSIONS

A short period of ischaemic POST protected WT mouse hearts against IR. The cardiac protection induced by POST was abrogated in SphK1-KO mouse hearts. Thus, SphK1 is critical for successful ischaemic POST.