Short-term hyperglycaemia causes non-reversible changes in arterial gene expression in a fully 'switchable' in vivo mouse model of diabetes

AIMS/HYPOTHESIS

Irreversible arterial damage due to early effects of hypo- or hyperglycaemia could account for the limited success of glucose-lowering treatments in preventing cardiovascular disease (CVD) events. We hypothesised that even brief hypo- or hyperglycaemia could adversely affect arterial gene expression and that these changes, moreover, might not be fully reversible.

METHODS

By controlled activation of a 'switchable' c-Myc transgene in beta cells, adult pIns-c-MycER(TAM) mice were rendered transiently hypo- and then hyperglycaemic, after which they were allowed to recover for up to 3 months. Immediate and sequential changes in aortic global gene expression from normal glycaemia through hypo- and hyperglycaemia to recovery were assessed.

RESULTS

Gene expression was compared with that of normoglycaemic transgenic and tamoxifen-treated wild-type controls. Overall, expression of 95 genes was significantly affected by moderate hypoglycaemia (glucose down to 2.5 mmol/l), whereas over 769 genes were affected by hyperglycaemia. Genes and pathways activated included several involved in atherogenic processes, such as inflammation and arterial calcification. Although expression of many genes recovered to initial pre-exposure levels when hyperglycaemia was corrected (74.9%), in one in four genes this did not occur. Quantitative reverse transcriptase PCR and immunohistochemistry verified the gene expression patterns of key molecules, as shown by global gene arrays.

CONCLUSIONS/INTERPRETATION

Short-term exposure to hyperglycaemia can cause deleterious and persistent changes in arterial gene expression in vivo. Brief hypoglycaemia also adversely affects gene expression, although less substantially. Together, these results suggest that early correction of hyperglycaemia and avoidance of hypoglycaemia may both be necessary to avoid excess CVD risk in diabetes.

15-lipoxygenase-1 in colorectal cancer: a review

OBJECTIVE

Enzymes involved in the oxidative metabolism of n-6 polyunsaturated fatty acids, like lipoxygenase (LOX) and cyclooxygenase (COX), are significant in the pathogenesis of colorectal cancer. Of these enzymes, 15-LOX-1 is expressed in colon. Aim of this article is to describe the role and regulation of 15-LOX-1 in colorectal cancer and highlight its importance in cancer therapeutics.

METHODS

For our electronic literature research in PubMed and MEDLINE, key words related to 15-LOX-1 and colorectal cancer were used to find articles for this review.

RESULTS

From the evidences, we believe that 15-LOX-1 has anti-carcinogenic effects in colorectal cancer, dependent or independent of its metabolites, and is manifested through downstream pathways involving cGMP, PPAR, p53, p21 and NAG-1, increasing apoptosis and decreasing proliferation in cancer cells. Regulation of 15-LOX-1 expression is achieved at transcription level by global histone acetylation and may also be dependent on GATA-6, IL-4 and IL-13. Positive relationship exists between 15-LOX-1 and survival in colorectal cancer.

CONCLUSION

Evidences strongly support that therapeutic modulation of 15-LOX-1 may be a key to the treatment of colorectal cancer. However, it is still undecided whether the up-regulation of 15-LOX-1 alone can be sufficient to treat colorectal cancer and further studies are awaited.

Ectopic expression of c-Myc in the skin affects the hair growth cycle and causes an enlargement of the sebaceous gland

BACKGROUND

The hair follicle continually undergoes dynamic remodelling in a cyclical manner involving tightly coordinated patterns of cell proliferation, differentiation and apoptosis. The oncoprotein c-Myc is a key regulator of these events in epidermal keratinocytes, but its importance in the hair growth cycle has not previously been determined.

OBJECTIVES

To determine the role of c-Myc in the hair growth cycle.

METHODS

We characterized the hair follicle phenotype of transgenic mice that permit expression of a switchable form of c-Myc (c-Myc-ER) in the suprabasal epithelial layers of the epidermis and hair follicle.

RESULTS

c-Myc activation increased epithelial cell proliferation in the outer root sheath and distal hair follicle, without any substantial alteration in levels of apoptosis. Moreover, chronic c-Myc activation resulted in marked desynchronization of the murine hair growth cycle, uncoupling of hair cycle-related skin thickness and enlargement of the sebaceous gland.

CONCLUSIONS

These data implicate c-Myc in the control of hair growth cycling and hair cycle-related epidermal and sebaceous gland homeostasis. We suggest that c-Myc may be activating follicular stem cells either directly or indirectly and that this has important implications for control of the 'hair cycle clock', hair growth and epidermal maintenance.

Oncogenic co-operation in beta-cell tumorigenesis

Pancreatic islet neoplasms are rare endocrine tumours. The most common type is of beta-cell origin and is known as insulinoma, which can be either benign or malignant. The majority of insulinomas arise sporadically, but a small proportion develop as part of the hereditary multiple endocrine neoplasia type 1 (MEN1) syndrome. As for many human tumours, the genetic events that occur during the initiation and progression of insulinoma are poorly known. The men1 gene product, menin, is deficient in most hereditary cases, but is not obviously affected in the majority of sporadic tumours. Activation of the proto-oncogenes c-myc and ras has been observed during malignant progression, but their role in tumour initiation remains unproven. To address these questions, transgenic mouse models have been increasingly used to explore molecular and genetic events that might also precipitate human neoplasia. Transgenic mice expressing SV40 large T-antigen (Tag) oncogene in beta-cells develop tumours in a multi-stage progression from hyperplasia, angiogenesis, to solid encapsulated tumours. However, Tag, which inactivates the key tumour suppressors p53 and Rb, is not known to be involved in the pathogenesis of human insulinoma. The proto-oncogene, c-myc is implicated in beta-cell growth in both diabetes and tumorigenesis. Activation of Myc appears to be an early event in progression of human insulinoma. The effect of deregulated Myc expression on adult beta-cells in vivo has recently been investigated by developing transgenic mouse models in which the activity of Myc can be regulated ectopically. Although Myc activation initially promotes both proliferation and apoptosis in pancreatic beta-cells, apoptosis is the predominant outcome, giving rise to islet involution and diabetes. Importantly, inhibiting Myc-induced apoptosis (by co-expression of Bcl-x(L)) leads to significantly enlarged islets, many becoming highly vascularized, hyperplastic and invasive. These results suggest that, in the pancreatic beta-cells, early suppression of apoptosis is essential for the survival of Myc-activated beta-cells and islet neoplasia.

Action of Myc in vivo - proliferation and apoptosis

The protein products of many dominant oncogenes are capable of inducing both cell proliferation and apoptosis. Recent experiments employing transgenic mice that express an ectopically regulatable myc gene or protein have begun to elucidate the role of the balance between proliferation and apoptosis in Myc-induced carcinogenesis. An outstanding feature of these experiments is the demonstration that the balance between oncogene-induced proliferation and apoptosis in a given tissue can be a critical determinant in the initiation and maintenance of the tumor.

Reversible activation of c-Myc in skin: induction of a complex neoplastic phenotype by a single oncogenic lesion

The protooncogene c-myc regulates cell growth, differentiation, and apoptosis, and its aberrant expression is frequently observed in human cancer. However, the consequences of activating c-Myc in an adult tissue, in which these cellular processes are part of normal homeostasis, remain unknown. In order to achieve this, we have targeted expression of a switchable form of the c-Myc protein to the skin epidermis, a well characterized homeostatic tissue. We show that activation of c-MycER in adult suprabasal epidermis rapidly triggers proliferation and disrupts differentiation of postmitotic keratinocytes. Sustained activation of c-Myc is sufficient to induce papillomatosis together with angiogenesis--changes that resemble hyperplastic actinic keratosis, a commonly observed human precancerous epithelial lesion. All these premalignant changes spontaneously regress upon deactivation of c-MycER.