Katsuma Tsuchihara

Altered lung surfactant system in a Rab38-deficient rat model of Hermansky-Pudlak syndrome

Several Long-Evans rat substrains carrying the phenotype of oculocutaneous albinism and bleeding diathesis are a rat model of Hermansky-Pudlak syndrome (HPS). The mutation responsible for the phenotype (Ruby) was identified as a point mutation in the initiation codon of Rab38 small GTPase that regulates intracellular vesicle transport. As patients with HPS often develop life-limiting interstitial pneumonia accompanied by abnormal morphology of alveolar type II cells, we investigated lung surfactant system in Long-Evans Cinnamon rats, one strain of the Ruby rats. The lungs showed conspicuous morphology of type II cells containing markedly enlarged lamellar bodies. Surfactant phosphatidylcholine and surfactant protein B were increased in lung tissues and lamellar bodies but not in alveolar lumen. Expression levels of mRNA for surfactant proteins A, B, C, and D were not altered. Isolated type II cells showed aberrant secretory pattern of newly synthesized [(3)H]phosphatidylcholine, i.e., decreased basal secretion and remarkably amplified agonist-induced secretion. [(3)H]phosphatidylcholine synthesis and uptake by type II cells were not altered. Thus Rab38-deficient type II cells appear to carry abnormality in lung surfactant secretion but not in synthesis or uptake. These results suggest that aberrant lung surfactant secretion may be involved in the pathogenesis of interstitial pneumonia in HPS.

A Mutation in Rab38 Small GTPase Causes Abnormal Lung Surfactant Homeostasis and Aberrant Alveolar Structure in Mice

The chocolate mutation, which is associated with oculocutaneous albinism in mice, has been attributed to a G146T transversion in the conserved GTP/GDP-interacting domain of Rab38, a small GTPase that regulates intracellular vesicular trafficking. Rab38 displays a unique tissue-specific expression pattern with highest levels present in the lung. The purpose of this study was to characterize the effects of Rab38-G146T on lung phenotype and to investigate the molecular basis of the mutant gene product (Rab38(cht) protein). Chocolate lungs exhibited a uniform enlargement of the distal airspaces with mild alveolar destruction as well as a slight increase in lung compliance. Alveolar type II cells were engorged with lamellar bodies of increased size and number. Hydrophobic surfactant constituents (ie, phosphatidylcholine and surfactant protein B) were increased in lung tissues but decreased in alveolar spaces, consistent with a malfunction in lamellar body secretion and the subsequent cellular accumulation of these organelles. In contrast to wild-type Rab38, native Rab38(cht) proteins were found to be hydrophilic and not bound to intracellular membranes. Unexpectedly, recombinant Rab38(cht) proteins retained GTP-binding activity but failed to undergo prenyl modification that is required for membrane-binding activity. These results suggest that the genetic abnormality of Rab38 affects multiple lysosome-related organelles, resulting in lung disease in addition to oculocutaneous albinism.

Myelolipoma of the lung: a case report and brief review.

Myelolipomas are rare tumours composed of mature adipose tissue and normal haematopoietic cells. They commonly occur in the adrenal glands, and involvement of the lung is extremely rare.1–6 We report a case of pulmonary myelolipoma presenting as an asymptomatic nodule unchanging in size for 10 years after being detected. A man in his 70s, a smoker, had a nodule in the left lower lobe (LLL) of the lung detected on a chest radiograph 10 years earlier. The nodule, 2 cm in maximal diameter, had not changed in size. The patient had never had haematological disorders including anaemia. He presented with intractable lumbago since 6 months, and MRI detected multiple bone tumours. CT of the chest indicated a large mass in the right lower lobe (RLL) and a small solitary nodule with rim-like calcification in the LLL of the lung (fig 1A). Sputum cytology showed carcinoma cells. He was clinically diagnosed as having lung cancer with multiple bone metastases. Chemotherapy and radiation therapy had no effect, and the patient died of respiratory failure. An autopsy was performed 7 h after death. Figure 1  (A) Chest CT shows a well-demarcated nodule (arrow) with a thin calcifying rim. (B) The cut surface of the left lower lobe of the lung shows a mixed yellow and red–brown nodule 2 cm in size. The grey–white portion (arrow) is a metastatic lung carcinoma component. Scale bar = 1 cm

Pulmonary surfactant transport in alveolar type II cells.

Abstract:  Pulmonary surfactant (PS) is a mixture of several lipids (mainly phosphatidylcholine; PC) and four apoproteins (A, B, C and D). The classical hypothesis of PS transport suggests that PS is synthesized in the endoplasmic reticulum and transported to the lamellar body (LB) via the Golgi apparatus. However, recent studies have raised questions regarding this single route. This study examined, independently, the intracellular trafficking route of three different components of PS, that is, PC, SP‐A and SP‐B. Alveolar type II cells were isolated from Sprague–Dawley rats or Japanese white rabbits. The cells were cultured with either [3H]choline or [35S]methionine/cysteine with or without brefeldin A, which disassembles the Golgi apparatus. LB was purified from disintegrated cells with sucrose density gradient centrifugation. [3H]PC was extracted from radiolabeled media, cells, and the LB fraction with Bligh–Dyers method. [35S]SP‐A or [35S]SP‐B was immunoprecipitated from each sample with a specific antibody. [3H]PC was transported and stored to the LB via a Golgi‐independent pathway. [35S]SP‐A was transported to the Golgi apparatus, underwent glycosylation, and was then constitutively secreted. The secreted [35S]SP‐A was re‐uptaken into the LB. [35S]SP‐B was transported and stored to the LB via the Golgi‐dependent pathway. These results indicate that, rather than a single route, surfactant components take different pathways to reside in the LB. These different pathways may reflect the different nature and role of each surfactant component such as surface tension‐lowering activity and innate host defense.

A three-microphone acoustic reflection technique using transmitted acoustic waves in the airway.

The acoustic reflection technique noninvasively measures airway cross-sectional area vs. distance functions and uses a wave tube with a constant cross-sectional area to separate incidental and reflected waves introduced into the mouth or nostril. The accuracy of estimated cross-sectional areas gets worse in the deeper distances due to the nature of marching algorithms, i.e., errors of the estimated areas in the closer distances accumulate to those in the further distances. Here we present a new technique of acoustic reflection from measuring transmitted acoustic waves in the airway with three microphones and without employing a wave tube. Using miniaturized microphones mounted on a catheter, we estimated reflection coefficients among the microphones and separated incidental and reflected waves. A model study showed that the estimated cross-sectional area vs. distance function was coincident with the conventional two-microphone method, and it did not change with altered cross-sectional areas at the microphone position, although the estimated cross-sectional areas are relative values to that at the microphone position. The pharyngeal cross-sectional areas including retropalatal and retroglossal regions and the closing site during sleep was visualized in patients with obstructive sleep apnea. The method can be applicable to larger or smaller bronchi to evaluate the airspace and function in these localized airways.