Keith D. Boehm

Messenger RNAs for the multifunctional cytokines interleukin‐1α, interleukin‐1β and tumor necrosis factor‐α are present in adnexal tissues and in dermis of normal human skin

Abstract Interleukin‐1α (IL‐1α), interleukin‐1 β (IL‐1β) and tumor necrosis factor‐α (TNF‐α) are 3 cytokines that play a key rôle in cutaneous homeostasis and in the immunopathogenesis of a number of dermatologic diseases. Most studies have focussed on their production by keratino‐cytes and Langerhans cells. To determine whether there are non‐epidermal sites of cytokine transcription, biopsy specimens of normal human skin were probed for IL‐lα, IL‐lβ and TNF‐α messenger RNAs using the method of in situ hybridization. The results demonstrate that each cytokine mRNA is present at multiple sites within the skin, including epidermal appendages and adnexal structures (hair follicles, sebaceous glands), the dermal microvasculature, arrectores pilorum smooth muscle, and the dermal connective tissue. These data provide evidence that in vivo there are multiple sites other than the epidermis of constitutive IL‐lα, 1L‐Iβ, and TNF‐α gene transcription in normal human skin.

Transforming growth factor-beta1 in heart development

Abstract Defined biochemical stimuli regulating neonatal ventricular myocyte (cardiomyocyte) development have not been established. Since cardiomyocytes stop proliferating during the first 3–5 days of age in the rodent, locally generated ‘anti-proliferative’ and/or differentiation signals can be hypothesized. The transforming growth factor-beta (TGF-β) family of peptides are multifunctional regulators of proliferation and differentiation of many different cell types. We have determined in neonatal and maturing rat hearts that TGF- β 1 gene expression occurs in pups of both normotensive (Wistar Kyoto, WKY) and hypertrophy-prone rats (spontaneously hypertensive, SHR). TGF- β 1 transcript levels were readily apparent in total ventricular RNA from SHR pups within 1 day of age and elevated in 3–7 day old WKY and SHR hearts when cardiomyocyte proliferation indices are diminished. TGF- β 1 transcript levels remain at a ‘relatively’ high level throughout maturation and into adulthood in both strains. Further, TGF- β 1 transcripts were localized to cardiomyocytes of neonatal rat ventricular tissue sections by in situ hybridization. Immunoreactive TGF-β was co-localized to the intracellular compartment of neonatal cardiomyocytes at the light and electron microscopic level. In vitro analysis using primary cultures of fetal and neonatal cardiomyocytes indicated that TGF-βs inhibit mitogen stimulated DNA synthesis and thymidine incorporation. From these data, we propose that locally generated TGF-βs may act as autocrine and/or paracrine regulators of cardiomyocyte proliferation and differentiation as intrinsic components of a multifaceted biochemical regulatory process governing heart development.

Increased Basic Fibroblastic Growth Factor mRNA in the Brains of Rats Exposed to Hypobaric Hypoxia

Continued exposure of rats to hypobaric hypoxia results in both functional and structural changes in brain. A most striking structural change is the 50-80% increased capillary density in the cerebral cortex and other brain regions after 3 weeks of hypoxic exposure (LaManna et al., 1992; LaManna, 1992). The apparent increased density may be accompanied by a shift in the capillary segment length distribution towards longer capillary segments (LaManna et al., 1993). It is still not clear if the increased capillary density is due to new capillary branching or to elongation of existing capillaries, or both. Nevertheless, it seems likely that the microvascular adaptation to continued hypoxia is controlled by growth factors. The growth factors that control angiogenesis are not yet well understood, but basic fibroblast growth factor (bFGF) is known to activate endothelial cells resulting in capillary growth (de Juan et al., 1990), and this growth factor is increased following metabolic stress such as brain ischemia (Finkelstein et al., 1990; Lyons et al., 1991). In this study, we determined whether bFGF mRNA was increased in brains of rats exposed to 3 weeks of hypoxia.

MODULATION OF INTERFERON-GAMMA-INDUCED HLA-DR EXPRESSION ON THE HUMAN KERATINOCYTE CELL LINE SCC-13 BY ULTRAVIOLET RADIATION

Cell surface expression of major histocompatibility determinants on epidermal keratinocytes is a characteristic feature of a number of inflammatory dermatoses and in all likelihood is caused by diffusion of human leukocyte antigen (HLA)‐DR‐inducing cytokines from cells present in the dermal mononuclear cell infiltrate. Many of these same disorders respond to ultraviolet(UV) radiation phototherapy. Using the human SCC‐13 keratinocyte cell line as a model, UV radiation was found to inhibit interferon‐gamma‐induced HLA‐DR expression. Inhibition correlated closely with decreased steady‐state levels of HLA‐DR mRNA. These findings provide evidence that the therapeutic effect of UV radiation phototherapy may be mediated by its capacity to down‐regulate cytokine‐induced keratinocyte HLA‐DR expression.

Insulin-Like Growth Factors and Heart Development

Growth of the adult mammalian ventricular myocyte (cardiomyocyte) is the topic of considerable interest since heart muscle cells rapidly respond to increases in functional demands by an increase in cellular mass(l). Although the cardiomyocyte of the adult ventricle occupies up to 90% of the area of the left ventricle (LV) free wall, these cells comprise a unique population of a permanently post-mitotic, structurally and functionally delimited cell type that can only expand in width (primarily) and length to increasing functional demand on this vital organ. Therefore, the adult cardiomyocyte population is a static number of muscle cells that define the life-long structure and function of the ventricular portion of the heart. It is the function of the cardiomyocytes that can then be modulated by adjacent cell types (i.e., fibroblasts and endothelium), blood vessels (capillaries and arterioles) and neural/humoral stimuli in the mature organ.

C- Myc Proto-Oncogene Expression During Newt Limb Regeneration

Utilizing the method of in situ hybridization, myc-homologous RNA transcripts were detected in histological sections of the newt limb regenerate. A radiolabeled Xenopus myc-cDNA was used as probe. Autoradiographic grains representing myc-homologous RNAs were observed in cells of the thickened wound epidermis, irrespective of the layer examined. Further, mesenchymatous-like cells which form the blastema also contained multiple grains, indicating that these cells possess myc-like RNA molecules. The presence of RNAs, homologous to the myc proto-oncogene in cells of the regenerating newt limb indicate that a myc-related gene is expressed in these cells during the regenerative process and, therefore, may play an important regulatory role, as myc gene expression has been implicated in the control of cellular proliferation in other systems. Our results are discussed against the background of literature on c-myc proto-oncogene expression.