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Biomedical subjects

F Hofmann

Publications and source records attributed to F Hofmann.

At least 19 recordsLinked to original sources
PubMed2007

Analysis of calcium channels by conditional mutagenesis.

Ca2+ influx through various ion channels is an important determinant of the cytosolic Ca2+ concentration, which plays a pivotal role in countless cellular processes. The cardiac L-type Ca2+ channel, Ca(v)1.2, represents a major pathway for Ca2+ entry and is in many cells expressed together with other high- and low-voltage-activated Ca2+ channels. This article will focus on the use of conditional transgenic mouse models to clarify the roles of Ca2+ channels in several biological systems. The phenotypes of conditional Ca2+ channel transgenic mice have provided novel, and often unexpected, insights into the in vivo function of L-type and T-type Ca2+ channels as mediators of signaling between cell membrane and intracellular processes in blood pressure regulation, smooth muscle contractility, insulin secretion, cardiac function, sleep, learning, and memory.

Animals↗
PubMed2006

Inhibition of IGF-I receptor in anchorage-independence attenuates GSK-3beta constitutive phosphorylation and compromises growth and survival of medulloblastoma cell lines.

We have previously reported that insulin-like growth factor-I (IGF-I) supports growth and survival of mouse and human medulloblastoma cell lines, and that IGF-I receptor (IGF-IR) is constitutively phosphorylated in human medulloblastoma clinical samples. Here, we demonstrate that a specific inhibitor of insulin-like growth factor-I receptor (IGF-IR), NVP-AEW541, attenuated growth and survival of mouse (BsB8) and human (D384, Daoy) medulloblastoma cell lines. Cell cycle analysis demonstrated that G1 arrest and apoptosis contributed to the action of NVP-AEW54. Interestingly, very aggressive BsB8 cells, which derive from cerebellar tumors of transgenic mice expressing viral oncoprotein (large T-antigen from human polyomavirus JC) became much more sensitive to NVP-AEW541 when exposed to anchorage-independent culture conditions. This high sensitivity to NVP-AEW54 in suspension was accompanied by the loss of GSK-3beta constitutive phosphorylation and was independent from T-antigen-mediated cellular events (Supplementary Materials). BsB8 cells were partially rescued from NVP-AEW541 by GSK3beta inhibitor, lithium chloride and were sensitized by GSK3beta activator, sodium nitroprusside (SNP). Importantly, human medulloblastoma cells, D384, which demonstrated partial resistance to NVP-AEW541 in suspension cultures, become much more sensitive following SNP-mediated GSK3beta dephosphorylation (activation). Our results indicate that hypersensitivity of medulloblastoma cells in anchorage-independence is linked to GSK-3beta activity and suggest that pharmacological intervention against IGF-IR with simultaneous activation of GSK3beta could be highly effective against medulloblastomas, which have intrinsic ability of disseminating the CNS via cerebrospinal fluid.

Animals↗
PubMed2006

Mdm2, but not Mdm4, protects terminally differentiated smooth muscle cells from p53-mediated caspase-3-independent cell death.

p53 is a potent inhibitor of cell growth and an inducer of apoptosis. During embryonic development, Mdm2 and Mdm4 inhibit the growth suppressive activities of p53. However, whether tight surveillance of p53 activity is required in quiescent cells is unknown. To test this, conditional inactivation of mdm2 and mdm4 was carried out in smooth muscle cells (SMCs). Upon SMC-specific inactivation of mdm2, and not of mdm4, mice rapidly became ill and died. Necropsy showed small intestinal dilation, and histological analyses indicated a severe reduction in the number of intestinal SMCs. Increased p53 levels and activity were detected in the remaining SMCs, and the phenotype was completely rescued on a p53-null background. Interestingly, intestinal SMCs are caspase-3-negative and therefore did not undergo caspase-3-dependent apoptotic cell death. Together, Mdm2, but not Mdm4, prevents accumulation of active p53 in quiescent SMCs and thereby the induction of p53-mediated caspase-3-independent cell death.

Animals↗
PubMed2006

Influenza vaccination of healthcare workers: a literature review of attitudes and beliefs.

BACKGROUND: Influenza vaccination coverage among healthcare workers (HCW) is insufficient despite health authority recommendations in many countries. Numerous vaccination campaigns encouraging HCW to be vaccinated have met with resistance. We reviewed published influenza vaccination programs in healthcare settings to understand the reasons for their success and failure, as well as the attitudes and beliefs of HCW. METHODS: Relevant articles published up to June 2004 were identified in the MEDLINE/Pubmed database. RESULTS: Thirty-two studies performed between 1985 and 2002 reported vaccination rates of 2.1-82%. Vaccination campaigns including easy access to free vaccine and an educational program tended to obtain the highest uptake, particularly in the USA. Yet, even this type of campaign was not always successful. Two main barriers to satisfactory vaccine uptake were consistently reported: (1) misperception of influenza, its risks, the role of HCW in its transmission to patients, and the importance and risks of vaccination (2) lack of (or perceived lack of) conveniently available vaccine. CONCLUSION: To overcome these barriers and increase uptake, vaccination campaigns must be carefully designed and implemented taking account of the specific needs at each healthcare institution.

Attitude to Health↗
PubMed2006

Gating of the expressed T-type Cav3.1 calcium channels is modulated by Ca2+.

AIM: We have investigated the influence of Ca2+ ions on the basic biophysical properties of T-type calcium channels. METHODS: The Cav3.1 calcium channel was transiently expressed in HEK 293 cells. Current was measured using the whole cell patch clamp technique. Ca2+ or Na+ ions were used as charge carriers. The intracellular Ca2+ was either decreased by the addition of 10 mm ethyleneglycoltetraacetic acid (EGTA) or increased by the addition of 200 microm Ca2+ into the non-buffered intracellular solution. Various combinations of extra- and intracellular solutions yielded high, intermediate or low intracellular Ca2+ levels. RESULTS: The amplitude of the calcium current was independent of intracellular Ca2+ concentrations. High levels of intracellular Ca2+ accelerated significantly both the inactivation and the activation time constants of the current. The replacement of extracellular Ca2+ by Na+ as charge carrier did not affect the absolute value of the activation and inactivation time constants, but significantly enhanced the slope factor of the voltage dependence of the inactivation time constant. Slope factors of voltage dependencies of channel activation and inactivation were significantly enhanced. The recovery from inactivation was faster when Ca2+ was a charge carrier. The number of available channels saturated for membrane voltages more negative than -100 mV for the Ca2+ current, but did not reach steady state even at -150 mV for the Na+ current. CONCLUSIONS: Ca2+ ions facilitate transitions of Cav3.1 channel from open into closed and inactivated states as well as backwards transition from inactivated into closed state, possibly by interacting with its voltage sensor.

Barium↗
PubMed2006

Function of cGMP-dependent protein kinases as revealed by gene deletion.

Over the past few years, a wealth of biochemical and functional data have been gathered on mammalian cGMP-dependent protein kinases (cGKs). In mammals, three different kinases are encoded by two genes. Mutant and chimeric cGK proteins generated by molecular biology techniques yielded important biochemical knowledge, such as the function of the NH(2)-terminal domains of cGKI and cGKII, the identity of the cGMP-binding sites of cGKI, and the substrate specificity of the enzymes. Genetic approaches have proven especially useful for the analysis of the biological functions of cGKs. Recently, some of the in vivo targets and mechanisms leading to changes in neuronal adaptation, smooth muscle relaxation and growth, intestinal water secretion, bone growth, renin secretion, and other important functions have been identified. These data show that cGKs are signaling molecules involved in many biological functions.

Animals↗
PubMed2005

Distribution of cGMP-dependent protein kinase type I and its isoforms in the mouse brain and retina.

Nitric oxide (NO) modulates a variety of processes in the mammalian brain, but the mechanisms of neuronal NO signaling are poorly understood. In the periphery, many effects of NO are mediated via the generation of the second messenger cyclic guanosine-3',5'-monophosphate (cGMP) and activation of the cGMP-dependent protein kinase type I (cGKI). However, previous studies suggested that the expression of cGKI in the nervous system is rather restricted, thus, questioning the functional significance of the cGMP/cGKI pathway as a mediator of NO signaling in the brain. Here we have performed a detailed immunohistochemical study to elucidate the distribution of cGKI in the CNS and eye of the mouse. Expression of cGKI protein was detected not only in the previously described areas (cerebellum, hippocampus, dorsomedial hypothalamus) but also in a number of additional regions, such as medulla, subcommissural organ, cerebral cortex, amygdala, habenulae, various hypothalamic regions, olfactory bulb, pituitary gland, and retina. Immunoblotting with isoform-specific antibodies indicated that the cGKIalpha isoform is prominent in the cerebellum and medulla, whereas the cGKIbeta isoform is predominant in the cortex, hippocampus, hypothalamus, and olfactory bulb. Similar levels of the isoforms were detected in the pituitary gland and eye. Thus, it appears that distinct brain regions express distinct cGKI isoforms that signal via distinct pathways. Together, these results improve our understanding of the cellular and molecular mechanisms of NO/cGMP/cGKI signaling and indicate that the distribution and functional relevance of this pathway in the mammalian brain is broader than previously thought.

Animals↗
PubMed2005

Ca2+- and voltage-dependent inactivation of the expressed L-type Ca(v)1.2 calcium channel.

Ca2+-dependent regulation of the ion current through the alpha1Cbeta2aalpha2delta-1 (L-type) calcium channel transiently expressed in HEK 293 cells was investigated using whole cell patch clamp method. Ca2+ or Na+ ions were used as a charge carrier. Intracellular Ca2+ was either buffered by 10 mM EGTA or 200 microM Ca2+ was added into non-buffered intracellular solution. Free intracellular Ca2+ inactivated permanently about 80% of the L-type calcium current. The L-type calcium channel inactivated during a depolarizing pulse with two time constants, tau(fast) and tau(slow). Free intracellular calcium accelerated both time constants. Effect on the tau(slow) was more pronounced. About 80% of the channel inactivation during brief depolarizing pulse could be attributed to a Ca2+-dependent mechanism and 20% to a voltage-dependent mechanism. When Na+ ions were used as a charge carrier, the L-type current still inactivated with two time constants that were 10 times slower and were virtually voltage-independent. Ca2+ ions stabilized the inactivated state of the channel in a concentration-dependent manner.

Animals↗
PubMed2005

[Vaccinations in adults--who? when? why?].

Despite the success of childhood vaccinations in Europe, many infectious diseases pose a threat to adults, particularly because immunity induced by vaccination is not life long in some cases. This paper presents the rationale for adult boosters for diphtheria, hepatitis B, pertussis, poliomyelitis and tetanus. Moreover indication for adult-vaccinations against measles, mumps, German measles and varicella is discussed, as a significant part of the population in Germany is susceptible or without known immunity/vaccination history. Finally, immunisation of the elderly against infections with influenza-virus and S. pneumoniae will be described.

Adult↗
PubMed2005

A description of the standardized measurement procedures and recommended threshold limit values for biological hazards in Germany.

On the basis of EU directives 89/391/EEC (to encourage improvements in the safety and health of workers at work) and 2000/54/EC (on the protection of workers from risks related to exposure to biological agents at work), biological hazards at work have to be assessed and preventive measures have to be introduced in all member states of the EU. In Germany, national legislation (Biological Agents Ordinance - BioStoffV and Technical Rules on Biological Agents, TRBA) and recommendations of workers' compensation boards define standardized methods for the assessment of airborne mold, bacteria, and endotoxins. This article describes policies and practices in Germany for measurement of airborne bioaerosols and for interpretation of measurements relative to the standards. As an example, methods and results of measurements in agriculture are shown. The standardized measurement procedures proved suitable for use in livestock buildings. The results of the exploratory measurements in different livestock buildings confirmed the often high concentrations of airborne biological hazards in agriculture that are reported in the literature.

Agricultural Workers' Diseases↗
PubMed2004

Inhibition of L-type Cav1.2 Ca2+ channels by 2,(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) and 2-[1-(3-dimethyl-aminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl) maleimide (Go6983).

Phosphatidylinositol 3-kinase (PI3-K) is involved in physiological processes of cellular proliferation and inflammation and, as postulated recently, in the regulation of L-type Ca(2+) channels. The latter conclusion arose in part from the inhibitory action of the compound 2,(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), which has been established as a selective PI3-K inhibitor (IC(50) = 1.4 microM). Herein we show, however, that LY294002 and an inhibitor of protein kinase C (PKC), 2-[1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl) maleimide (Go6983), act as direct Ca(2+)-channel inhibitors, with IC(50) values of approximately 20 and 10 microM, respectively. Because both drugs are commonly used at concentrations of approximately 10 microM or higher, the interpretation of such experiments is questionable with respect to a regulatory action of PI3-K or PKC on L-type Ca(2+) channels.

Animals↗
PubMed2004

Distribution of IRAG and cGKI-isoforms in murine tissues.

cGMP kinase I (cGKI) signaling modulates multiple physiological processes including smooth muscle relaxation. The expression of cGKI and its substrate IRAG (Inositol 1,4,5-trisphosphate receptor associated cGMP kinase substrate) was studied. IRAG and cGKI were colocalized in the smooth muscle of aorta and colon. IRAG was present in the thalamus and in most of the myenteric plexus in the absence of cGKI. Coexpression of IRAG and cGKIbeta or cGKIalpha in COS-7 cells revealed that IRAG recruits cGKIbeta but not cGKIalpha to the endoplasmic reticulum. These results suggest that IRAG may be involved in cGKI-dependent and -independent pathways.

Animals↗
PubMed2004

Cerebellar ataxia and Purkinje cell dysfunction caused by Ca2+-activated K+ channel deficiency.

Malfunctions of potassium channels are increasingly implicated as causes of neurological disorders. However, the functional roles of the large-conductance voltage- and Ca(2+)-activated K(+) channel (BK channel), a unique calcium, and voltage-activated potassium channel type have remained elusive. Here we report that mice lacking BK channels (BK(-/-)) show cerebellar dysfunction in the form of abnormal conditioned eye-blink reflex, abnormal locomotion and pronounced deficiency in motor coordination, which are likely consequences of cerebellar learning deficiency. At the cellular level, the BK(-/-) mice showed a dramatic reduction in spontaneous activity of the BK(-/-) cerebellar Purkinje neurons, which generate the sole output of the cerebellar cortex and, in addition, enhanced short-term depression at the only output synapses of the cerebellar cortex, in the deep cerebellar nuclei. The impairing cellular effects caused by the lack of postsynaptic BK channels were found to be due to depolarization-induced inactivation of the action potential mechanism. These results identify previously unknown roles of potassium channels in mammalian cerebellar function and motor control. In addition, they provide a previously undescribed animal model of cerebellar ataxia.

Animals↗
PubMed2004

Effect of a diphtheria booster vaccination in adults with a documented history of an incomplete primary series vaccination.

BACKGROUND: An incomplete series of diphtheria vaccination is frequently found in the vaccination documents of adult patients. This paper investigates the effect of a booster vaccination in adults with an incomplete series of primary vaccination. MATERIALS AND METHODS: The effect of one diphtheria booster vaccination in adults with a documented history of only two childhood vaccinations has been investigated in 21 adults. Before the vaccination and 4 to 8 weeks thereafter, blood samples were taken and analyzed with an in vitro neutralization assay. RESULTS: None of the participants had prevaccinal full protective diphtheria antitoxin levels (AT) > or = 0.1 IU/ml and four (19%) had limited serological protection (AT 0.01 to 0.1 IU/ml). After the vaccination, 14 individuals (67%) had protective LeveLs and six (29%) had limited protective levels. The risk for post-booster non-protection (AT < 0.1 IU/ml) was 7.7 times higher in comparison with a group of 170 adults with a history of at least one booster vaccination. CONCLUSION: A specific immunologic memory exists in adults with a history of only two previous diphtheria vaccinations. However, our results also indicate the need for a second booster vaccination in this group if long-term protection is to be achieved.

Adult↗
PubMed2004

Differential effects of Rho GTPases on axonal and dendritic development in hippocampal neurones.

Formation of neurites and their differentiation into axons and dendrites requires precisely controlled changes in the cytoskeleton. While small GTPases of the Rho family appear to be involved in this regulation, it is still unclear how Rho function affects axonal and dendritic growth during development. Using hippocampal neurones at defined states of differentiation, we have dissected the function of RhoA in axonal and dendritic growth. Expression of a dominant negative RhoA variant inhibited axonal growth, whereas dendritic growth was promoted. The opposite phenotype was observed when a constitutively active RhoA variant was expressed. Inactivation of Rho by C3-catalysed ADP-ribosylation using C3 isoforms (Clostridium limosum, C3(lim) or Staphylococcus aureus, C3(stau2)), diminished axonal branching. By contrast, extracellularly applied nanomolar concentrations of C3 from C. botulinum (C3(bot)) or enzymatically dead C3(bot) significantly increased axon growth and axon branching. Taken together, axonal development requires activation of RhoA, whereas dendritic development benefits from its inactivation. However, extracellular application of enzymatically active or dead C3(bot) exclusively promotes axonal growth and branching suggesting a novel neurotrophic function of C3 that is independent from its enzymatic activity.

ADP Ribose Transferases↗
PubMed2003

Melanopsin and rod-cone photoreceptive systems account for all major accessory visual functions in mice.

In the mammalian retina, besides the conventional rod-cone system, a melanopsin-associated photoreceptive system exists that conveys photic information for accessory visual functions such as pupillary light reflex and circadian photo-entrainment. On ablation of the melanopsin gene, retinal ganglion cells that normally express melanopsin are no longer intrinsically photosensitive. Furthermore, pupil reflex, light-induced phase delays of the circadian clock and period lengthening of the circadian rhythm in constant light are all partially impaired. Here, we investigated whether additional photoreceptive systems participate in these responses. Using mice lacking rods and cones, we measured the action spectrum for phase-shifting the circadian rhythm of locomotor behaviour. This spectrum matches that for the pupillary light reflex in mice of the same genotype, and that for the intrinsic photosensitivity of the melanopsin-expressing retinal ganglion cells. We have also generated mice lacking melanopsin coupled with disabled rod and cone phototransduction mechanisms. These animals have an intact retina but fail to show any significant pupil reflex, to entrain to light/dark cycles, and to show any masking response to light. Thus, the rod-cone and melanopsin systems together seem to provide all of the photic input for these accessory visual functions.

Animals↗
PubMed2002

Gating of the expressed Cav3.1 calcium channel.

Intramembrane charge movement originating from Cav3.1 (T-type) channel expressed in HEK 293 cells was investigated. Ion current was blocked by 1 mM La3+. Charge movement was detectable for depolarizations above approximately -70 mV and saturated above +60 mV. The voltage dependence of charge movement followed a single Boltzmann function with half-maximal activation voltage +12.9 mV and +12.3 mV and with slopes of 22.4 mV and 18.1 mV for the ON- and OFF-charge movement, respectively. Inactivation of I(Ca) by prolonged depolarization pulse did not immobilize intramembrane charge movement in the Cav3.1 channel.

Calcium↗